Recently, due to emerging high frequency and wide band gap switches like GaN and SiC, miniaturizing the converter is one of the most important criteria for power electronics engineers. In power electronic converters, magnetic components, like high power inductors, are the key components and correctly designing them has considerable effect on the net efficiency and size of the power converter.

Among high power inductors, there are a wide range of applications where the inductor current has high frequency and very low frequency, or DC components like DC-DC inductors, power factor correction (PFC) inductors, output filter inductors and chokes. In such applications, designing the winding and selecting the wire type is the most challenging part of the design, to comprise and control both low frequency and high frequency conduction losses.

To solve the problem, one solution is using litz wire, however, it has poor porosity or filling-factor of about 40 – 50% for high frequency applications. Hence, compared to solid copper wire, litz wire makes the power inductors bulky with higher direct current resistance (DCR), which adversely affects the power losses for low frequency or DC currents. Due to this fact, in recent power converter applications, new inductor winding structures are proposed based on solid wire and companies like Bourns are manufacturing flat wire inductors for renewable energy applications. However, improper designing of solid wire increases ESR for high frequency applications.

To make an optimal compromise between DCR and ESR at high frequencies, several solutions based on solid copper wire have been proposed in the literature. For example, in, a design procedure for round wire is presented with a single layer winding structure to reduce ESR for high frequencies. However, this winding structure is suitable for toroid shapes, while for the other core geometries such as a P-core geometry, the inductor will become bulky and a major part of the core’s window area remains empty. Another alternative is multi-layer foil windings; however, this wire type is suitable for medium frequency transformers with interleaved windings. For inductors and other multi-layer windings, foil wire presents higher losses due to the proximity effect between the layers.

Among different solid wire types, flat spiral and helix shapes present superior performance, while they have better manufacturability in printed circuit boards (PCBs) and a reduced size of magnetic components. Spiral shapes have proximity effect issues and are more suitable for high frequency planar transformers. Solid flat wire winding presents better thermal conductivity and DCR; however, more work is needed to have accurate and simple models suitable for design optimization algorithms. Fig. 1 shows a power inductor based on a helical flat wire coil.

This study accurately models and formulates inductor DCR and ESR based on solid flat wire. Then, the performance of this structure is compared to solid round wire with equivalent wire gauge and window size, using 2D FEM simulations. In this research, the formulation and simulations are considered for inductors with cylindrical geometries such as PQ and P-core types, which are considered the most frequently used core geometries with higher power density and fewer leakage flux problems.

The main parameters of the solid flat wire inductor are defined based on equivalent winding parameters with multi-filar solid round wire. Then, the solid flat wire formulations for DCR and ESR are derived. Next, 2D FEM simulations are presented and the two winding structures are compared. Based on FEM simulations, the ESR formula is further modified, and conduction losses of the inductor are formulated for DC-DC converters. Finally, experimental results for a laboratory sample with flat wire are presented.

Modeling of the Flat Wire Inductor

Without loss of generality, the main parameters of the flat wire coil are formulated based on an equivalent inductor with solid round wire, which has a similar winding area, i.e., equal winding internal radius, r_w, radial thickness, D_w and height, H_w, as shown in Fig. 2. Furthermore, it is assumed that round solid wire has a non-twisted bundle containing m strands, or m-filar, with diameter of d_s. In this paper, it is assumed that solid round wire has few non-twisted strands. Obviously, a higher number of twisted strands improves ESR, however, in this case the wire is classified as litz wire and not solid wire.

Regarding Fig. 2 and the round wire parameters, the flat wire thickness, t_w, can be calculated by:

Assuming a unit porosity factor for the round wire inductor, i.e., negligible space between round wires, the filling-factor of copper cross section area would be equal to π/4. Then, assuming a similar copper filling-factor for the flat wire winding, the space between turns, s, is derived by:

Considering the cylindrical symmetry shown in Fig. 2, the conductance of a differential ring, dG, with a distance of r from the z-axis and differential cross section area of t_wdr is:

Here, σ = 5.8 × 10⁷ S/m is the conductivity of copper. Each turn can be considered as an equipotential surface and the total conductance of one turn, G, can be derived by:

Using (4), the DCR of the flat wire winding, R_dc, with N number of turns, is derived from:

It is worth noting that the helical effect on the length of the winding is neglected in (5), since the pitch of the coil is much lower than the coil’s mean diameter, i.e. (t_w+s) << (2 r_w+D_w).

To calculate ESR, R_ac, under sinusoidal alternating currents (AC), several analytical solutions have been developed in literature. However, they are mainly developed for solid round wire. For rectangular conductors, recent analytical formulations are developed only for a single solid flat wire in 2D x-y plane. Furthermore, according to the analytical solutions, the formulas are accurate when the thickness of the conductor is less than double the skin depth, δ, which is defined by (6).

Here, μ0 and f are the vacuum permeability and frequency of the sinusoidal current, respectively. For high power inductors, the flat wire thickness, t_w, is typically selected high enough to carry high currents and for high frequency DC-DC converters, typically t_w ≥ 2δ. Hence, in this study, analytical formulations will not be accurate enough.

Neglecting the fringing effects of the distributed air gaps, shown in Fig. 2(b), to calculate R_ac, first it is assumed that the inductor current effectively passes through rings with radius of r_w and thickness of skin depth,δ, by assuming t_w << D_w. Hence, the ESR, R_ac, as a function of f, is calculated in (7), by assuming that δ is much smaller than D_w and t_w ≥ δ.

However, rings-model is affected by edge-effects of the first and last turns and the space between turns, s. Using FEM simulations, it is shown that for a specific N and t_w, this model can be corrected by a fix correction factor of k_w, as included in (7) and the presented formulation accurately derives R_ac in a wide range of operating frequencies defined by:

Here, f_min is the minimum frequency at which the model is accurate and is defined by t_w ≥ δ criterion using (6). Next, FEM simulations are presented to compare the two different solid wires and Rac model assumed in (7).

2D FEM Simulations and Modified ESR Formula

To calculate Rac, 2D Poisson equation for the magnetic potential, A, under steady-state condition, is solved in (9), neglecting the displacement currents:

Where, J_s, J_ind and J_t are the peak density values of source current, induced current and total current, respectively. For operating frequency of f, J_ind relates to A, as presented in (10), and the relation between the inductor’s peak current, I_L, and J_s are obtained by (11), as follows:

In (11), the integral is calculated on a surface area of one turn. By solving A, R_ac can be achieved by calculating ohmic loss in all cylindrical coordinate and dividing the calculated loss by the squared value of the inductor current, as follows:

To compare the two solid copper wires, first it is assumed that the power inductor is implemented with solid round wire with N = 8, r_w = 12.5 mm, and m = 4 with d_s = 1.50 mm. In this design, 20 μm is considered as the insulator thickness between conductors, which has negligible effect on the final dimensions and DCR.

Hence, D_w and H_w are calculated at approximately 6 and 12 mm, respectively. On the other side, according to Fig. 2 and using (1) and (2), t_w and s are calculated at 1.178 and 0.322 mm, respectively. The two inductors are implemented by a PQ50 core with a height of 33.0 mm. For the sake of simplicity, in the following simulations, the core is considered linear and lossless with a relative permeability, μr, of 2400. To have a negligible fringing effect, three 0.25 mm gaps are considered at the center leg of the core.

To calculate the DCR of the two inductors, two FEM magnetostatic simulations have been done for the two inductors. The DCR for the flat wire and round wire inductors are derived as 1.8766 and 1.9590 mΩ, respectively, meaning that the inductor with solid flat wire has a 4.2% lower DCR. On the other side and using (5), the DCR is calculated at 1.8770 mΩ, which is very close to the magnetostatic simulation result, at approximately a 0.02% margin of error.

Fig. 3 shows a 2D Eddy-current FEM simulation and the mesh plot for the solid flat wire inductor model with f = 100 kHz and an AC peak current of I_L = 5 A. Based on 2D eddy-current FEM simulations, the inductor value is calculated at approximately 34.8 μH. By using (12) and post-processing the magnetic vector potential, A, R_ac is derived at approximately 33.3 mΩ. As seen in Fig. 3(b), except for the edge effects, the current mainly passes through rings.

Using similar FEM simulations, ESR for the solid round wire inductor is calculated at 49.0 mΩ, i.e., 47.1% higher than the flat wire inductor. For the round wire design, there are two main reasons behind its higher ESR. The first reason is that the coil has two layers and the number of layers adversely affects the winding’s ESR. The second reason is the fact that here the bundle is not twisted, and the current is not uniformly distributed between the four strands.

Fig. 4 compares the ESR of the two designs for different frequencies up to 1 MHz and shows that the solid flat wire is significantly better, especially at higher frequencies, while the proximity effect between the two layers of the round wire design increases significantly. It is worth noting that for solid wire design with fewer parallel branches, m < 4, the ESR will be even higher which confirms the superiority of solid flat wire.

To show the proposed assumptions described in (7), FEM simulations under different operating frequencies are done for two inductors manufactured with solid flat wires. Table 1 presents the calculated R_ac for the two inductors with N = 4 and 8, and similar t_w = 1.178 mm and s = 0.322 mm. Using (8), f_min is calculated at approximately 3 kHz, hence Table 1 presents the results for frequencies from 3 kHz up to 1 MHz. To calculate k_w, first, R_ac is calculated by (12) using FEM simulations. Then, using (7), the physical parameters of the winding and the known Rac, kw can be calculated for each FEM simulation, as included in Table 1.

According to Table 1, kw for the two designs is almost constant with less than a 4.2% variation from 3 kHz up to 1 MHz. Similar FEM simulations have been done for D_w = 9.0 mm and f = 100 kHz, and k_w values for N = 4 and 8 are derived at approximately 0.4768 and 0.7510, respectively which are very close to the results presented in Table 1. This means that for t_w << D_w, which typically occurs for high power inductors, k_w is approximately independent of D_w. Hence, assuming the constant filling-factor of π/4 defined in (2), k_w only depends on the number of turns and wire thickness. Typically, inductors based on flat wire are made with few turns, and it is feasible to calculate a table-function of k_w (N, t_w) for calculating ESR in a wide range of operating frequencies, which is suitable for design optimization algorithms.

As concluded from the above-mentioned analysis and simulations, equation (7) can model R_ac in a wide range of operating frequencies. Hence, it is possible to formulate the conduction losses of flat wire inductors for DC-DC converters as follows. As an example, for a buck converter with a regulated output voltage of VO and load current of IO, the maximum current ripple occurs at a duty cycle of 50%.

In this condition, the voltage of the inductor, L, is like a square wave voltage source with an amplitude of V_O and switching frequency of f_s. Using the Fourier series, the inductor voltage, v_L(t), and its hth current harmonic amplitude, I_h, can be formulated by:

Hence, using (7) and (14), the maximum AC conduction losses, P_ac, are derived by:

Here R_ac^h calculates the ESR for hth harmonics, i.e., for f = hf_s, by using (7). In (14), the current amplitude significantly reduces for high order harmonics, hence, the AC conduction losses can be well approximated up to the 9th harmonic, as follows:

Moreover, it is assumed that the self-resonant frequency of the inductor is higher than the 9th harmonic and the inductance value of L can be considered constant in the above-mentioned analysis. DC conduction loss, P_dc, is calculated by (17), where R_dc is the DCR of the inductor calculated by (5):

Finally, a simulation has been done for a buck converter with f_s = 100 kHz, V_O = 100 V and I_O = 30 A based on the flat wire inductor the number of turns = 8 and L ≈ 34.8 μH, as presented in Table 1. It is assumed that the output voltage has negligible ripple, and the duty cycle of the buck converter is 50%. Using (16) and (17), P_ac and P_dc are calculated at approximately 0.558 W and 1.689 W, respectively. The calculated values have been verified by doing a transient FEM simulation with a time step of 50 ns. According to the FEM results, the total conduction loss, P_ac plus P_dc, are calculated at approximately 2.402 W which has at approximately 5.5% deviation from analytical calculations.

Experimental Results

To verify the analytical formulations, a 5.6 μH, 80 A power inductor is implemented with N = 4, t_w = 2.0 mm, D_w = 9.5 mm, s ≈ 0.6 mm and r_w = 11.0 mm, as shown in Fig. 5(a).

To have 5.6 μH inductance, three 0.4 mm air gaps are required at the middle leg of the core, to reduce the fringing effects. However, for the sake of simplicity, only one 0.4 mm gap is considered for ESR measurements. The core is PQ50 with N95 ferrite material and a height of 33 mm. According to (5), DCR is calculated at approximately 387 μΩ for this inductor, including 4.5 cm extra length of wire for the end terminals. To measure DCR of the inductor, a 25 A DC current was applied to the inductor and voltage of approximately 10.0 mV was measured at room temperature, which means that the DCR is measured at approximately 400 μΩ, i.e., a 3.35% margin of error from theoretical calculations.

For this inductor and using FEM simulations, the correction factor, k_w, for the mentioned N and t_w is calculated at approximately 0.9764, with less than 4.0% deviation from f_min ≈ 1 kHz, defined by (8), up to 1.0 MHz. To measure the ESR, it is worth noting that the core also reflects extra ESR in the inductor coil, due to the eddy-current and hysteresis losses in the core.

To exclude the reflected resistance from the core, the ESR of an inductor made by 1050×0.05 mm litz wire, N = 4 and the same core is measured as the reference measurement. Regarding FEM simulations, AC and DC resistances of the litz wire are very close to each other for operating frequencies under 100 kHz, with less than a 2% change. Hence the measured ESR of the reference inductor with the litz wire is approximately equal to its DCR plus the extra ESR reflected from the core. Using a WYNE KERR 6500B impedance analyzer and f = 100 kHz, the total ESR, including the core effects, for the flat wire inductor and the reference inductor with litz wire are measured about 14.6 and 6.4 mΩ, respectively. Moreover, the DCR of the reference inductor is measured at approximately 4.2 mΩ. Hence, the ESR of the flat wire winding at 100 kHz is measured at approximately 12.4 mΩ, which has about a 12 % error from (7) with the mentioned kw.

Conclusion

This article presents modeling and analysis for high power inductors manufactured with solid flat wire and develops formulations to accurately calculate their AC and DC resistances. The simulations and experimental results show that the flat wire type presents superior DCR and ESR, compared to a non-twisted solid round wire, using an equivalent wire gauge and window area. Furthermore, by using FEM simulations, a correction factor has been defined to accurately calculate ESR for different turn numbers and wire thicknesses, with less than a 5% error, which is suitable for design algorithms. The model has been verified by experimental results and further FEM simulations using different wire sizes and number of turns in a wide range of operating frequencies. Furthermore, based on the ESR formula, the maximum AC conduction loss of a flat wire inductor has been formulated for buck converters.

To learn more, visit TTI Inc.

The post Modeling of High Power Inductors Based on Solid Flat Wires for Compact DC-DC Converters appeared first on Engineering.com.

The growth and evolution of photodetectors started with military investments and defense needs. During the Cold War, significant advancements in low-light detection technologies were driven by military needs, particularly for heightened surveillance and communication systems. Technologies such as the avalanche photodiode (APD), first patented by Jun-ichi Nishizawa in 1952, were heavily researched in the 1960s and 1970s and were pivotal in advancing photodetector capabilities. Post-Cold War, these technologies transitioned into civilian applications, leading to widespread industrial and consumer adoption.

Best practices for innovating with photodetector technologies

The types of photodetectors vary based on the material used, the operational mechanism, and their application-specific properties. These devices range from basic PN junction photodiodes to advanced technologies like avalanche photodiodes (APDs) and quantum dot photodetectors. Other types include photomultiplier tubes (PMTs), charge-coupled devices (CCDs), metal-semiconductor-metal (MSM) photodetectors, and emerging materials like graphene-based photodetectors. Each type has distinct characteristics, making them suitable for a variety of applications, including telecommunications, autonomous systems, medical imaging, environmental monitoring, industrial scanners and consumer electronics. It’s imperative to begin any design and engineering process by understanding what the application needs and asking all the questions upfront during the planning stage.

Some key considerations are:

• Spectral range and materials: Spectral range is the range of wavelengths over which the photodetector is sensitive, typically measured in nanometers (nm). The below image shows some of the photodetector materials that are used to detect signals ranging from UV wavelengths to Long Wave Infrared (LWIR) wavelengths. With the longstanding evolution of photodetector technologies, many materials for components currently in use may be outdated compared to new advancements. Development of compounds like Silicon carbide (SiC), Gallium nitride (GaN), indium gallium arsenide (InGaAs), and other semiconductor materials like InGaAsSb have enhanced photodetectors’ sensitivity and spectral range. These materials detect short-wave infrared (SWIR) and middle-wave infrared (MWIR), increasing their versatility. Organic, graphene-based and flexible photodetectors expand possibilities for wearable technology and biomedical applications.

• Quantum efficiency (QE): Quantum efficiency is the ratio of the number of charge carriers generated to the number of incident photons, often expressed as a percentage.
• Detectivity (D*): Detectivity is a normalized measure of a photodetector’s sensitivity, expressed in Jones (cm·Hz^1/2/W). It combines responsivity and noise characteristics. Responsivity measures the electrical output per unit of optical input power, typically expressed in amperes per watt (A/W) or volts per watt (V/W).
• Noise: A constant consideration with sensitive components is its bulk noise, which is a combination of the shot and Johnson noise of the detector and often is derived from the dark current of the detector. Noise equivalent power (NEP) is the amount of optical power required to generate a signal equal to the noise level of the photodetector, typically measured in watts per root hertz (W/√Hz).
• Device architecture: A photodetector’s architecture, including the active area, the device thickness, and the composition of each layer impacts its efficiency, capacitance and response time. Advanced designs that incorporate specialized epitaxial layering, such as heterostructures and quantum wells, can enhance performance. Pixel configuration for imaging applications is critical. Higher pixel density can improve resolution, while larger pixels may enhance sensitivity.
• Speed and response time: Response time is the time it takes for a photodetector to respond to an optical signal, typically measured in nanoseconds (ns) or picoseconds (ps). This impacts the detectivity of photodetectors. Innovations in materials with high electron mobility have lowered capacitance, increasing the bandwidth (Hz) of photodetectors.
• Integration: Close collaboration with end-users and industry partners helps to develop photodetectors that meet the precise needs of various applications. Hybrid integration of photodetectors with other components, like receiver systems, leads to more efficient and scalable solutions, improving performance while broadening their application scope.
• Reliability, durability and robustness: Developing photodetectors that can withstand extreme conditions, such as extreme temperatures, mechanical stress and radiation, has expanded their use in military, aerospace and industrial applications. This goes hand in hand with thermal management and packaging. Advances in coatings and packaging techniques have demonstrated improved photodetector reliability.
• Costs and resource: Costs and resources naturally impact all decision-making and capabilities for investing in growing photodetector technologies. Photonic integrated circuits allow for compact, high-performance systems that are cost-effective. Advances in nanofabrication have allowed for the creation of smaller, more efficient photodetectors. Developing photodetectors compatible with other high-volume semiconductor manufacturing process technologies like complementary metal-oxide-semiconductor (CMOS) facilitates the production of affordable, high-performance sensors.  

Photodetector engineers can balance heightened specialization with optimized approaches for success, scalability and future growth by having these conversations on the front end. It’s important to balance overall best practices with the application’s specific standards and certifications, especially for consumer, automotive, aerospace, defense and medical industries.

Photodetector technology supplements and revolutionizes many applications

Today, photodetector technology is a vital component that underpins countless technologies, including gas sensing, motion sensors and consumer electronics. In telecommunications, it enables high-speed data transmission in fiber optic networks. In aerospace and defense, they’re used for target recognition and range finding; in R&D, there’s a wide range of spectroscopy applications. Their 3D scanning applications are essential in architecture, construction, autonomous vehicles and industrial controls. Photodetectors also enable environmental monitoring to detect pollutants and monitor environmental changes.  Photodetectors are also pivotal in medical imaging and are used in devices like CT scanners and MRI machines for precise imaging and remote patient monitoring technologies.

Photodetector evolution comes with growth challenges

Acknowledging common industry pain points from the beginning positions engineers and organizations with the information they need to address and mitigate challenges. The photonics industry is small, requiring talent to collaborate frequently within and across disciplines. Having dedicated foundries for photodetectors may not be financially viable. As a result, partnership is vital for meeting the technical demands of development. Universities and research entities stand at the forefront of evolution.

Systems integration presents another challenge, given unique applications and the need for collaboration within photonics technologies. This demands a clear understanding of the product, environment and objectives which is especially critical for custom, application-specific developments.

Optimizing size, weight, power and cost (SWaP-C) is a paramount concern for the design and development of photodetector technology. Investments and specially dedicated resources are essential to future-proof designs for growth and innovation while offering a competitive edge for organizations in nearly every industry.

The future of photodetector technology is bright

Growth and innovation in applying photodetector technology will undoubtedly continue over time. As this technology becomes more widespread, its success is showcased by how little individuals notice the impact on their everyday lives. The seamless integration of photodetectors into various applications is a testament to their efficiency and effectiveness. Knowing what to expect is essential to harnessing the benefits and opportunities of this next wave of innovation. Advancements in materials, quantum photonics, AI integration and sustainable technologies promise to enhance performance, efficiency and cost-effectiveness, driving innovation in autonomous systems, security, medical diagnostics, environmental monitoring, consumer electronics and beyond. As organizations continue to develop and integrate these technologies, there’s no denying the widespread potential for photodetectors to address complex global challenges and improve everyday life. The future holds exciting possibilities, with these advancements seamlessly blending into the fabric of our daily experiences.

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Recent growth in renewable energy generation has triggered a corresponding demand for battery energy storage systems (BESSs). The energy storage industry is poised to expand dramatically, with the G7 recently setting a 1500GW global energy storage target for 2030. Meanwhile, BloombergNF estimates that investments in energy storage will grow to $103 billion over that period. At the same time, the cost per kilowatt-hour of utility-scale battery systems is likely to drop significantly, making controlling system costs critical.

Battery systems aren’t just designed to serve as local power backups, such as the systems used to power critical facilities (including hospitals and data centers) when the normal power source fails. BESSs also offer other benefits and ancillary services, including load-leveling, spinning and regulation reserves, frequency regulation, transmission and distribution deferral. These features maximize BESSs as a valued asset to utilities.

Today’s BESSs are increasingly designed to feed local micro-grids to supply power to small areas when demand rises. They store electrical energy produced by solar or wind power generators, then inject that energy back into the grid when needed.

As the power density of modern lithium-ion batteries grows, BESS integrators are striving to offer their customers more power in a smaller footprint. However, with higher power levels, circuit protection becomes increasingly important.

BESS circuit protection

Renewable energy providers are incorporating new generations of high-efficiency power semiconductor devices into their systems to control power in inverters and converters. Because these are sensitive electronic devices, they require robust protection against energy surges. The design of BESSs can still be considered to be in its infancy, given that the technologies that go into them are evolving rapidly. As a result, many of the electrical engineers integrating those solutions are seeking guidance in selecting and implementing appropriate circuit protection strategies.

A comprehensive circuit protection strategy is crucial to meeting BESS integrators’ most critical objectives:

• To prevent costly service interruptions to end-users with critical uptime requirements, such as hospitals, industrial processing plants and data centers. For example, the cost of data center downtime is in the range of $8,000 per minute.
• To prevent revenue losses for renewable energy suppliers.
• To prevent power disruptions to the local area.
• To protect the workers who will install and maintain the BESSs that integrators design.
• To prevent damage to the BESS equipment itself, which would jeopardize the sizable investment that the end-users or renewable energy suppliers have made.
• To provide grid stability via power generation from renewable sources.

Electrical faults within a BESS can pose significant hazards to workers, including the risk of electric shocks, chemical/electrolyte burns, and the release of toxic or explosive gas. The three main areas of concern are protection against electrical overcurrents, ground faults and arc-flash hazards.

Overcurrent protection

Inverter protection is one of the most important facets of BESS circuit protection. Inverters are typically — although not always — located outside of the trailer or other enclosure in which the banks of batteries are housed. A DC/AC inverter converts direct current (DC) output from batteries into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid. However, a BESS also allows storing the DC current generated by renewable energy sources to a bank of batteries. Later, when there’s a demand for that stored power, a DC/AC inverter converts the DC battery power into AC power that can then be exported to the grid.

In order to provide the longest possible battery discharge times, BESS designers are building in large battery banks. Each of those batteries represents an energy source. Any fault in the system can lead to dumping a massive amount of energy all at once — with all the dangers to people and equipment that could pose.

In the 2017 edition of the National Electrical Code (NEC) Article 706 spells out the overcurrent protection requirements for Battery Energy Storage Systems. The code says:

• Disconnecting Means: “A disconnecting means shall be provided at the energy storage system end of the circuit. Fuse disconnecting means or circuit breaker shall be permitted to be used.”
• Direct Current (DC) Rating: “Overcurrent protective devices, either fuse or circuit breakers, used in any DC portion of an ESS shall be listed and for DC and shall have the appropriate voltage, current, and interrupting ratings for the application.” Exception: Where current-limiting overcurrent protection is provided for the DC output circuits of a listed ESS, additional current-limiting overcurrent device shall not be required.
• Location: “Where energy storage system input and output terminals are more than 1.5m (5 ft) from connected equipment, or where the circuits from these terminals pass through a wall or partition, overcurrent protection shall be provided at the ESS.”
• Sizing: “Overcurrent Device Ampere Rating… provided on systems serving the ESS and shall be not less than 125 percent of the maximum current calculated.”

The existence of these Code requirements helps validate the importance of selecting the proper overcurrent protection in the ever-growing market of BESSs.

A wide range of fuses are available to handle a variety of current overload applications. High-speed fuses are the usual choice for these DC ESS applications because they are much smaller, faster and less expensive than DC circuit breakers. The maximum interrupting rating for circuit breakers tops out at about 200,000 to 300,000 amps. In contrast, the latest generation of high-speed fuses (such as Littelfuse PSR Series High-Speed Square-Body Fuses) (Figure 1) can interrupt up to 150 kA of DC current (or 200 kA AC) in a much smaller footprint than a DC circuit breaker.

High-speed fuses are designed to operate about 24 times faster than conventional fuses in order to protect sensitive power semiconductor devices (such as diodes, triacs, IGBTs, SCRs, MOSFETs and other solid-state devices) that are built into inverters, UPSs, battery management devices and other systems, by reducing peak let-through current and let-through energy (I²t).

These fuses are also invaluable for protecting a BESS’s DC batteries. Each battery is protected by DC fuses at the positive and negative terminals to isolate the battery during any internal short-circuit condition. DC combiners, where the outputs from multiple battery racks are combined to feed the inverter, are critical locations that are susceptible to high DC overcurrent faults. Typically, at this location, output strings from batteries are protected by DC fuses with the highest possible DC interrupting rating.

Ground faults

A variety of factors can contribute to the development of ground faults. These factors include insulation or component degradation (often as a result of overvoltage or overtemperature), humidity/moisture, rodents, dust accumulation between live parts of the system and human error. Unless an appropriate ground-fault device is used, low-current ground faults can often go unrecognized.

BESSs are typically ungrounded systems. The system may remain in operation after the first ground fault, resulting in higher voltage on the unfaulted bus, with reference to ground, but with no current flow. However, subsequent ground fault on the opposite bus can have catastrophic consequences from both an equipment-protection and worker-safety perspective. A second ground fault on an ungrounded system may constitute a phase-to-phase fault that can result in arcing, fires and severe damage or injuries. Most electrical faults, including arc flashes, begin as ground faults and so detecting these faults early is essential so they can be addressed before serious damage or injury occurs.

For ungrounded BESS systems, designers can choose from three options for ground-fault detection for the DC side:

1. Active insulation monitoring. This approach involves injecting a low-level signal that seeks the lowest-resistance path back to the relay through ground. The leakage current returning to the relay is directly proportional to the insulation of the system to ground. This method is attractive, but has some significant challenges, including difficulty in locating the exact fault location, susceptibility to system capacitance and interference of the active signal with other components of the electrical system.
2. Passive voltage monitoring with respect to ground. This method does not inject an active signal; instead, it monitors the voltage of each side of the DC bus (or each phase of the AC bus) with respect to ground. The advantage is that there is no active signal to cause any interference, but fault location is a challenge with this method as well.
3. Passive current monitoring through use of a ground neutral ground reference. The Littelfuse SE-601 Series DC Ground-Fault Monitor (Figure 2) can provide such a reference. This approach creates a neutral ground point in between the DC bus voltages and looks for leakage current to or from ground. The advantages of this system are that the fault location (positive or negative DC bus) can be determined, there are no active signals to cause interference, and the reference module usually serves to limit fault currents to a safe value. The disadvantage of this method is that a symmetrical fault (a fault of equal resistance to ground on both buses simultaneously) might not be detected.

Any current running through to ground requires attention. Sensitive ground fault-relays will pick up leakage currents at 10 mA or even lower. The latest ground-fault relays can pick up levels of fault current as low as 30 milliamps. Typically, a ground reference module is installed between the negative and positive portions of a DC system, the reference model is connected to the relay, and the relay is connected to the ground.

Although most BESSs are ungrounded, grounded BESSs do exist but require different methods of ground-fault detection. Designers need to weigh the relative merits of an AC ground-fault relay vs. an AC insulation monitor. An AC ground-fault relay, such as the SE-704 Earth-Leakage Relay (Figure 3), offers very sensitive ground-fault detection and can be used on systems with significant harmonic content. The output contacts can be connected for use in protective tripping circuits or in alarm indication circuits. The analog output can be used with a PLC or a meter.

In contrast, an AC insulation monitor such as the PGR-3200 Series Insulation Monitor (Figure 4) which operates on one- or three-phase ungrounded systems up to 6 kV, can also be used on grounded systems to monitor the insulation for damage when the system is de-energized.

Many designers choose to use a breaker between each battery bank and the combiner box to simplify performing inspection or maintenance on each bank individually. An ungrounded DC ground-fault monitor, such as the Littelfuse SE-601 Series, can be used to monitor the status of the battery banks. It can be used in combination with the EL3100 Ground-Fault and Phase-Voltage Indicator (Figure 5) for 3-phase systems. It meets both the NEC and CE Code requirements for ground detectors for ungrounded AC systems.

Arc-flash protection

According to OSHA, arc-flash events are responsible for approximately 80 percent of electrically related accidents and fatalities among qualified electrical workers. Even when there are no injuries to workers, an arc flash can destroy equipment, requiring costly replacement and system downtime.

The high levels of DC power that feed into inverters from the combined output of the banks of DC batteries creates the potential for arc-flash incidents. When the outputs of multiple daisy-chained batteries are brought together in a combiner box, they can also produce sufficient DC voltage to initiate an arc. Unlike with sinusoidal AC power, where the zero crossing helps AC arcs extinguish themselves, there’s less chance that DC arcs from batteries will be self-extinguishing,

Arc flashes present a number of hazards. The heat can be more intense than the temperature on the surface of the sun, and the accompanying explosion may hurl debris at the speed of a bullet. The threat to both maintenance personnel and nearby equipment is obvious. To mitigate these hazards, arc-flash relays are designed to detect the light from an emerging arc flash and trip an upstream circuit breaker as quickly as possible. For example, the PGR-8800 Series Arc-Flash Relay (Figure 6a) can detect and send a trip signal in less than 1 millisecond, preventing an arc from growing into a potentially catastrophic incident. The trip time for a typical AF0100 Series Arc-Flash Relay (Figure 6b) configuration is less than 5 milliseconds.

Installing an arc-flash relay system involves placing light sensors around the interior of the enclosure that houses the inverter and the associated bus bars most likely to be the origin of an arc. The power semiconductor device inside the inverter usually fails safe, but it is possible that it or its connectors could fail to ground and cause an arc flash.

Arc-flash considerations for DC and energy storage applications

Allow calculating the arc flash potential for to develop the calculations for arc-flash incident energy on, particularly the development of IEEE 1584 (Guide for Performing Arc-Flash Hazard Calculations). A revision is forthcoming based on further testing with AC systems. However, DC arc flash has been less studied and is less understood. The DC fault currents can be released rapidly on almost all types of BESSs, but those employing lithium-ion batteries can release very large amounts of current very rapidly.

The purpose of arc-flash calculations is to determine the largest possible incident energy. However, a few factors that may not be intuitively obvious can result in higher incident energy levels than would be anticipated if only an overcurrent protective device were used. These factors include:

• Battery age: As batteries age, their internal impedance increases. This can result in lower arc-flash current, which can in fact lead to higher energy because the overcurrent protection device takes longer to operate.
• State of charge: A partially depleted battery bank may not produce full arcing or short-circuit current. Using an arc-flash relay instead of relying on overcurrent protection devices alone for arc-flash protection can help designers realize a consistently low incident energy throughout the lifetime of the BESS.

It’s also important to keep in mind, for incident energy calculations, that battery cabinets tend to direct the energy out of the cabinet door. Large-scale BESS enclosures can expose personnel to even more energy during an arc flash, both by containing the fault and by making it more difficult for workers to self-rescue within a typical two-second window.

The battery banks themselves represent an arc-flash protection challenge in a BESS. An arc flash on one battery bank will be fed from other parallel battery banks. This can be resolved by monitoring the battery bank and disconnecting them from the bus on a fault. At this point, the arc fault is only fed from the faulted bank, reducing its total energy by a factor proportional to the total number of parallel battery banks. The remaining battery banks will continue supplying, or being supplied with, energy. Although disconnecting a faulted bank has a significant impact on operations and reducing incident energy, a fault local to the battery bank is more difficult to address. One option is to provide the means to disconnect/ de-couple sections of the battery bank physically, further reducing the voltage of each remaining section and reducing the hazard and available incident energy while maintenance is being performed.

How Littelfuse can help

Littelfuse is committed to helping BESS integrators ensure that their circuit protection strategy is complete. In some cases, Littelfuse can modify standard circuit protection products to fit an application’s unique requirements. Littelfuse personnel also work with BESS integrators to review their circuit protection plan and ensure it makes sense for the specific application and provides adequate protection for both equipment and workers. By walking integrators through the advantages and costs of the various options available, Littelfuse can help them make informed, cost-effective choices for specific products and locations.

To support the growing BESS market, Littelfuse will provide this expert design assistance at no cost to the system integrator. To request Littelfuse help in creating a comprehensive circuit protection strategy, integrators need only supply some basic information: all voltage levels each circuit will see, the nominal currents each circuit will see in steady state, the available short-circuit current, and the time constants of the application (based on the inductance to resistance ratio).

Visit TTI to learn more about how Littelfuse can help you develop a BESS circuit protection strategy.

The post Battery energy storage systems demand a comprehensive circuit protection strategy appeared first on Engineering.com.

Written by: Ryan Smart, Vice President of Product, Harwin

Electrically powered vertical take-off and landing (eVTOL) aircraft are shaking up the aerospace industry. The trend is similar to the effect that electric vehicles (EVs) have had on the automotive market. This article explores the requirements of eVTOL applications, focusing on battery management and power and signal connectivity. The area is of vital importance, as the aircraft need detailed data about the onboard battery/powertrain system to run safely.

According to McKinsey, eVTOL has attracted $12.8 billion in investment over the last 12 years. Currently, around 200 companies worldwide have development projects in the sector.

eVTOL is suitable for various applications, but the most popular one is urban transportation. Aerial taxis will offer faster, greener and more efficient transfers from city locations, such as financial quarters, to airports. eVTOLs could replace the helicopter services currently used for this purpose.

eVTOL-based transportation will also be more cost-effective. Aviation fuel costs are constantly increasing, but most eVTOL aircraft don’t require any fuel. There are also other commercial and logistical benefits. The first of these is noise: eVTOL will help reduce noise pollution. At the moment, this is the main factor restricting helicopter operation at nighttime. With eVTOLs, however, commercial flights could potentially run 24/7. Replacing helicopters could also improve air quality in city centers, as eVTOLs don’t generate air pollution.

Key engineering design considerations

Unlike conventional aircraft, eVTOL must deliver vertical and horizontal propulsion. The movement can be achieved with fixed vertical rotors for take-off/landing and horizontal ones for moving forward. Alternatively, the rotors can use actuators to move between vertical and horizontal flight configurations.

Powering the constituent electrical actuators is another critical function. These actuators control the aircraft roll moment by deflecting aileron surfaces and pitch moment by deflecting the elevator. Yaw moment is managed through rudder deflection and thrust force by changing the propeller speed. The aircraft designs must also incorporate the infrastructure for distributing power to electric-propulsion motors, positioning systems, tele-networking and cockpit/mission systems.

As eVTOLs are smaller and lighter than conventional aircraft, they are also less stable. While traditional aircraft become lighter during flight as they burn fuel, eVTOLs don’t. They remain the same weight throughout the flight, which puts more stress on the structure during landing. These requirements need to be built into the design. This means using robust materials in the airframes as well as electrical components.

Importance of battery monitoring in eVTOL designs

eVTOL aircraft are powered by large Li-ion batteries. Therefore, an effective battery management system (BMS) is essential. Data relating to current, voltage, temperature and other parameters must be continuously available to ensure optimal performance and safety of the passengers. If a battery fault that should have been detected leads to an accident, the aircraft manufacturer or operator could damage their reputation beyond repair.

In an electric road vehicle, managing risks is more straightforward. The EV can automatically stop and alert the occupants if there is a risk of thermal runaway within the battery. For eVTOLs, it is not as simple. When a fault occurs, the aircraft could be thousands of meters up in the air. Likewise, if a cell malfunctions and goes offline, the effect might be severe. In a ground vehicle, it will mean a loss of traction. But for an eVTOL, a power failure could result in a sudden drop in altitude. That’s why BMS monitoring of the cells needs increased scrutiny to identify and mitigate potential problems as quickly as possible.

What to look for in a connector

The connectors used in eVTOL BMS implementations need to be chosen carefully. Here is a summary of what engineers should consider:

Compactness: eVTOLs are dependent on electrical propulsion, so the components need to be small. They must take up minimal board space and have low profiles.

Contact density: eVTOLs’ battery packs feature many Li-ion cells. Compact connectors with dense contact arrangements help achieve data acquisition more easily.

Weight: eVTOL designs have strict weight constraints, so the fuselage and hardware must be as light as possible. The same goes for the components used. Light construction helps maximize the number of passengers or the amount of cargo the aircraft can carry.

Reliability: To guarantee passenger safety, the connectors must function over a prolonged operational life without failure.

Robustness: The connectors must maintain continued operation in harsh working conditions. They will have to withstand shocks, vibrations and extreme temperatures.

EMI susceptibility: Due to proximity to electrical sources, the designs must consider electromagnetic interference (EMI). Overlooking the issue can result in poor data quality, which can affect the decisions made by the BMS.

Component expense: As the eVTOL sector is very cost-sensitive, keeping the bill-of-materials (BoM) down is vital. This, combined with the low volume levels, means that custom-built components are not an option. Instead, companies must have access to off-the-shelf products to optimize their budgets.

Quality: Complete output repeatability in the production process is paramount when supplying parts to the aerospace market. Any variation could have dire consequences. That’s why it’s essential to work with connector suppliers that conform to globally recognized quality standards.

Picking the most applicable products

Harwin has a long history of providing aerospace OEMs with high-reliability (Hi-Rel) connectors. Committed to quality engineering, its manufacturing facility is certified per EN9100D/AS9100D quality standards. When working with the eVTOL sector, the Harwin team benefits from experience with unmanned aerial vehicle (UAV) projects. Regarding size, weight and robustness, the connectors used in UAVs have similar requirements to those used in eVTOLs.

Optimized for use in various eVTOL systems, the 1.25mm-pitch Gecko connectors deliver powerful performance and reliability. The lightweight and compact components have 2A-rated contacts made from a durable Beryllium-Copper. The patented 4-finger design means that interconnections remain unaffected by even the most intense shocks and vibrations.

Some applications, such as eVTOL BMS installation, require a larger number of contacts and large signal currents. Here, Harwin’s Datamate 2mm-pitch Hi-Rel connectors offer significant advantages. They are available in single, dual and triple-row configurations. Like the Gecko series, they provide industry-leading resilience to harsh environments. This means withstanding shocks of up to 100G. Their contacts can carry 3A of current (3.3A on an individual contact). A choice of latching mechanisms makes it easy to find the best match for the available space or the operating conditions.

Gecko and Datamate connectors can come with integrated back shells to combat EMI issues. Cable assemblies are also available to accompany them. They are available in any length and configuration, even for small quantities. Harwin also offers Mix-Tek versions of both connector series. These devices make it possible to address power and data signals with just one component, saving space and simplifying design layouts.

Conclusion

eVTOL will offer an environmentally friendly and more economical way of providing short-hop flights. The lower costs and 24/7 operation could make it accessible to more people. Battery reserve and performance will be central to eVTOL services, and will also provide manufacturers with a way to differentiate their models in a competitive market. Recharging speed and the distance the aircraft can travel before recharging will be key differentiators. These requirements highlight the role of the BMS function in boosting battery performance and extending its longevity. Finally, having superior BMS interconnects means that accurate data is always available. This helps maintain optimal safety in eVTOL aircraft.

To learn more, visit TTI and Harwin.

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Radar systems are continuously evolving as threats become more diverse. These systems are expected to register anything from drones to hypersonic missiles. As a result, modern radars are becoming more agile. Increasingly, that means they rely on a multifunction array (MFA), where one array can be used for search, track and targeting as well as electronic warfare and communications functions.

The need for a single-array configuration, paired with the desire to improve signal-to-noise ratio (SNR) with an analog-to-digital converter (ADC) on every antenna element, was a catalyst for the adoption of fully digital beamforming.

With fully digital beamforming, shown below, each antenna element can transmit and receive multiple beams or split them in different directions simultaneously without interference. In addition, each element is software-defined, so control and tuning can occur on an application-specific basis. Designs that leverage fully digital beamforming use space more efficiently while achieving more comprehensive radar coverage.

Radar systems and other military applications have always been restricted by size, weight and power (SWaP) requirements. Now, engineers are up against additional size constraints to support electronics with fully digital beamforming. In addition to managing higher power consumption, integrated devices must fit in a denser phased array with an antenna pitch measuring half the wavelength (i.e., λ/2) or less for optimal array performance. Wavelength decreases as frequency increases, so size requirements only become more restrictive in high-frequency applications.

Under these conditions, there’s a variety of components that must fit into a smaller amount of board space. Here are some component selections that deserve special consideration:

Energy storage capacitors

Energy storage capacitors in radar T/R modules support pulsed operation in power amplifiers, and with high-performance expectations and little space, these passive devices are especially SWaP-challenged. Low-profile aluminum electrolytic capacitors like the MLPS Flatpack series, designed and manufactured by Knowles Precision Devices’ subsidiary Cornell Dubilier, offer high capacitance density in a flat configuration for space-saving. These military-grade capacitors are optimized for 10,000 hours at 105 °C, making them ideal for T/R modules and other system electronics that maintain high performance and reliability in a small footprint.

Wideband filters

Wideband filters with high rejection are similarly challenged by strict SWaP requirements. To protect the receiver, these filters must be positioned at every element, and as mentioned above, they must be sized at λ/2 or less to fit in the phased array antenna pitch.

Knowles Precision Devices’ 10 GHz surface mount bandpass filters support direct sampling receivers enabled by high-speed RF-ADCs. With deep expertise in high-reliability ceramic devices, Knowles Precision Devices fabricates its DLI brand filters on high-k ceramic substrate materials to achieve high performance in a footprint smaller than λ/2.

Bypass capacitors

Fully digital beamformers often include devices, like low-noise amplifiers, that can be implemented as high-frequency monolithic microwave integrated circuit (MMIC) dies. MMIC amplifiers with broadband gain need protection from RF noise on the supply line. Bypass capacitors offer an efficient path for RF energy to ground before it enters a gain stage. Look for wire-bondable microwave capacitors (rather than surface-mount) that can provide the right amount of capacitance at a high operating voltage for MMICs in high-frequency applications like radar.

High Q capacitors

Q factor, or quality factor, is a figure used to rate and compare multi-layer ceramic capacitors (MLCCs) based on merit. It’s expressed as the ratio between stored energy and lost energy per oscillation cycle. In resonant circuits, power loss is accounted for via the equivalent series resistance (ESR). Higher ESR indicates higher losses in the capacitor. In high-frequency applications, maintaining efficiency and reliability at the component level is an important contribution to performance optimization. MLCCs built with high Q material are specifically designed to overcome this design challenge.

High Q MLCCs will have a low εr value, and they’re generally built in the pF range to mitigate power loss and minimize the likelihood of overheating. High frequency and low power loss are critical parameters for radar systems. Consider MLCCs based on high Q dielectrics to ensure high performance. Knowles Precision Devices offers ultra-low ESR, high temperature, high power, ultra stable and leaded options.

High-reliability capacitors

Radar systems subject components to intense operating conditions. To ensure quality and performance over time, they must face testing at elevated conditions. Manufacturers perform accelerated life cycle testing to better inform you of a component’s limitations. For example, chip capacitors and dielectric formulations undergo burn-in or voltage conditioning to assess their reliability at a specific voltage and temperature level for a duration of time. Capacitors that fail this test usually lose resistivity under these conditions early in the test cycle.

Common high-reliability military specifications, including MIL-C-55681, MIL-C-123 and MIL-C-49467, each have their own applicable specifications for reliability testing. Work with a manufacturer that has the experience and capacity to run and document these tests. Knowles Precision Devices typically uses a test voltage that is twice the working voltage rating of the device, at 85°C or 125°C for a duration of 96, 100, or 168 hours of test time, and maintains the capacity to process approximately four million parts per month to uphold strict screening criteria.

Supporting innovation in radar systems

While many manufacturers can accommodate MIL-level screening and high-reliability applications, Knowles Precision Devices has designed and tested to these standards for decades with no field failures. The support of an experienced component design and manufacturing company with custom capabilities and extensive testing equipment is key to the continued success and advancement of radar technologies. Whether you’re working with a cutting-edge system or legacy equipment, every component selection makes a difference, so leverage a component manufacturer’s expertise. Knowles Precision Devices’ engineering team monitors current trends that impact your design needs and adapts accordingly, so your team can focus on the core research and development efforts at hand.

For more information on off-the-shelf or custom components for radar or other high-reliability systems, contact Knowles Precision Devices to connect with our engineering team.

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Executives and decision makers know it’s not easy to automate industrial processes, but what they may not understand is why. The challenges arise from the fact that most facilities are made up of bespoke machines used to make specific parts, products or assemblies. Hence, there is rarely a one-size-fits-all solution.

Obvious examples of this phenomena can be seen with grippers, effectors and tools that physically interact with products or parts. This equipment must be tailored to hold, move and manipulate an object with specific geometry. But specialization doesn’t end there. An often-overlooked piece of customized equipment are industrial automation control panels. Afterall, if the control panel operates custom machinery, it makes sense that it also needs to be customized.

But these modifications aren’t easy. A search of Jameco, a supplier of industrial automation parts, for products only from MEAN WELL, which is just one of their manufacturing partners, comes up with almost 6,400 results. So, how does anyone make sense of it all?

To understand control panels and how one would go about customizing them for a particular application, engineering.com sat down with Gil Orozco, vice president of Product Management at Jameco and Harland Chen, field application engineer at MEAN WELL.

What is an industrial automation control panel?

Industrial automation control panels act as a central hub for all the components and tools used to monitor, instruct and integrate machinery. “Industrial automation control panels are the backbone of automation,” says Chen. “Panels enhance the efficiency, productivity, safety and quality of the system.”

Just like the machines they operate; panel parts need to be uniquely selected to meet particular needs. “The specific components used will depend on the intended function and complexity of the control panel,” confirms Orozco. “Customer applications are endless. [Selecting the right components] depends on what the customer requires.”

Even though contents can vary, control panels typically consist of:

• Circuit breakers and fuses, which cut the power supply in the event of excess current or faults in the system. This is done to protect other circuitry.
• Switches and/or buttons, which make up parts of the human machine interface (HMI) that enables human operators to manually control or preset operations.
• Indicators, which contain LED lights, computer monitors and gauges. These HMI parts are used to keep human operators informed of the status of the facility’s equipment.
• Power supplies, which includes the electrical batteries, generators and/or grid connections needed to ensure components operate.
• Control relays, which help control high-power devices or circuits with low power signals.
• Terminal blocks, which provide access points to connect and secure wires and cables.
• Programmable logic controllers (PLCs), which are advanced automation and control circuits used to manage equipment and systems based on measured inputs and code.

With the rise of Industry 4.0, many of these control panel components have become smarter. They can communicate with digital systems, connect to the Industrial Internet of Things (IIoT) and even digest data, predict performance or make decisions on how to operate. “The components are really in some respect endless,” says Orozco. “In some [instances], you have very smart components [and others] where you have some very basic analog components. So, it really starts with the customer’s application. How we make sense of all that depends on what the customer needs and how can we support them.”

In other words, each of the above parts must be optimized to the task being controlled by the panel. And since there are hundreds, maybe thousands of options for each part, engineering expertise is needed to ensure the panel is optimized to its needs.

What role do control panels play in industrial automation?

Control panels act as the brain and central nervous system of an automated facility. They regulate and manage systems using hardware, software and input data from HMIs, sensors, cameras and more. A control panel need not be fully automated. Some require human interactions, others can be autonomous, and many fall somewhere in between.

Chen explains, “By integrating the programming logic controls, the human machine interface … and various sensors and alternators, the control panels enable the real-time data acquisition and a precise control of the industrial operation.”

So, the benefits of the fully automated systems are that they offer consistent, precise and accurate control. In contrast, systems with human interactions may involve industrial operations that can be more unpredictable, requiring the oversight of human operators who can quickly adapt to a situation.

Automation control panel safety, compliance and regulations

Strict safety, compliance and regulation standards exist to prevent control panels from causing electrical shocks, fires and damage to people or property. “The control panel must adhere to this compliance and regulation to ensure safe operations,” Chen explains. Control panels require “electrical safety, proper grounding and protection against flash cases. Compliance with standards like UL 508A in the U.S., or ‘CE markings’ in Europe and the CSA certification in Canada are essential.”

He also notes the importance of ensuring the electronics operate at safe temperatures, meet environmental safety requirements and have ingress protection (IP) ratings — which measures how well an electrical device is protected from water or dust.

Since so much customization comes into play when finding the right automation control panel, ensuring that it meets safety, compliance and regulation standards is not easy. So once again, engineering expertise is required to guarantee success.

Engineering expertise for industrial control panels

Jameco offers almost 60 different DIN rail terminal blocks from MEAN WELL alone. When other manufacturing partners are included in the search, the number increases by a factor of three.  So, how does anyone know which control panel parts are needed for their particular setup?

Chen and Orozco suggest contacting Jameco and MEAN WELL directly. “It boils down to the customer’s needs,” says Orozco. “Applications and components are endless and there are many different brands and options … We need to understand the [given] application to provide a solution to the customer. And that’s where Jameco and MEAN WELL come in … We take an approach to understanding the customer’s requirements to show what total solutions we can offer them.”

Chen used the example of sizing a power supply. “The power supply we evaluate is based on the necessary functionalities of the [given] control panel. We consider the components, space [and] installation of the power supply.”

With the help of Jameco and MEAN WELL, manufacturers can make sense of all the available options, components and customizations they can add to their control panels. Instead of being lost in a forest of part numbers and compliance documentation, they will see a path to the right solution for a given situation.

“We evaluate based on the region, power and customer,” adds Chen. “If the customer needs to meet a specialized safety standard, our factories in China and Taiwan offer the certification needed for the specific safety and power supply standard.”

For more information on automation control panels solutions, read more about industrial power components.

The post Customizing automation control panels is challenging, but skipping it is worse appeared first on Engineering.com.

Electrification has a profound impact on a wide range of industries. In the past, current sensing technology was mainly used in industrial sectors, but with the introduction of the Paris agreement and the push to pursue clean energy along with the launch of rechargeable lithium-ion batteries, there are now many applications expanding current sensor use. In addition, this movement has created the need to move to a much higher range of current than ever before. Lithium-ion batteries used in automotive applications have a very high energy density; therefore, the need for high power current sensors has become paramount.

Here’s what engineers need to know about current sensor technology and how to use it in electric vehicles.

What are current sensors and where are they used?

As platforms become more electrified, current sensing is required in applications such as power conversion, battery charging in electrical vehicles, and industrial equipment and processes. To monitor electrical current flow and measurements in applications, high power current sensors can help satisfy the needs.

Current sensors are designed to detect and measure the current passing through a wire or conductor. They generate a signal that is proportional to the current, which can take the form of analog voltage, current, or a digital output.

This output signal serves various purposes:

• It can display the measured current
• It can be stored for further analysis in a data acquisition system
• It can be used for control purposes to limit or stop the flow of current

Current sensors play a critical role in maintaining the safety of battery systems. In modern battery systems, they monitor two key parameters of the battery: state of charge (SoC) and state of health (SoH). To do so, they must accurately track the power consumption of electric vehicles and estimate the remaining charge in the battery.

Current sensors are designed to measure current. Shunt sensors, for example, use Ohm’s law and manipulate Ohm’s law depending on what factor is being solved. For example, if voltage is being calculated, then Ohm’s law can be rewritten as V= I*R.

Types of current sensors

There are different current sensor technologies: Shunt current sensors (or direct in-line), open-loop current sensors, close-loop current sensors and flux gate current sensors. Each has certain advantages and disadvantages.

In a shunt current sensor, a precisely calibrated shunt resistor is placed in series with the load (the part of the circuit where current needs to be measured). As the current flows through the shunt resistor (often referred to as the bus bar), a specific resistance value can be obtained along with an accompanying voltage. The resultant current can then be accurately calculated. Shunt current sensors contain a conductive copper alloy bar that is placed in series with the current source to be measured.

Shunt sensors have some advantages. They are very robust, and are also typically lower in cost due to a very simplified design. However, they also have several distinct disadvantages: excessive heat, zero off-set, poor accuracy, required compensation, susceptibility to corrosion, and creepage. Some end users prefer shunt-based solutions for low-current (50 amp) measurements. However, due to the increasing needs of current measurement range and accuracy requirements, EV suppliers are migrating away from shunt-based current sensors and changing to magnetic flux-based current sensors, especially in high-current environments above ±500 amps to ±1500 amps and beyond to further improve measurement accuracy.

Honeywell offers a variety of magnetic-based current sensors with different configurations to satisfy customers’ high current application needs and requirements. These sensors fall into three types: Open-loop Hall-effect current sensors, close-loop Hall-effect current sensors, and flux gate and advanced flux gate current sensors.

The open-loop Hall-Effect current sensor comprises a few key components: a Hall element, ferromagnetic magnetic core and an amplifier. Functioning as a transducer, the Hall element detects the presence and intensity of a magnetic field, generating a voltage value aligned with the current in the targeted conductor.

Open-loop current sensors have both benefits and drawbacks. On the positive, they offer a simpler design, reduced cost compared to closed-loop Hall technology and a notable advantage in response time. These features make them particularly suitable for applications in motor control. Additionally, open-loop current sensors exhibit higher current measurement capability and are well-suited for operation in a wide temperature range. Even though open-loop sensors can be very accurate, they are not as accurate as a closed-loop Hall-effect design. Also, if the internal circuitry is not designed correctly, temperature drifts can pose a challenge.

Open-Loop Hall-effect current sensors offer low cost, simpler design, compact size, light weight, high bandwidth and fast response time.

The closed-loop Hall-effect current sensor is designed with several key components: a ferromagnetic magnetic core, a Hall-effect sensor, a secondary conductor and a feedback amplifier. The magnetic core concentrates the magnetic field. As primary current (IP) flows through the core’s conductor wire, it generates and concentrates a magnetic field within the core. The Hall-effect sensor detects this magnetic field, producing a proportional voltage corresponding to the primary current. Subsequently, the feedback amplifier amplifies this voltage and directs it back to the secondary coil, generating a magnetic field in the opposite direction.

Closed-loop current sensors can be designed to measure ac and dc currents and offer high accuracy and low temperature drift.

Closed-loop current sensors offer high accuracy, high sensitivity and linearity, lower offset error, temperature stability and immunity to magnetic field drift.

Flux gate current sensors operate in a similar manner as Hall-effect based closed-loop current sensors. However, the sensing technology used to monitor the magnetic field in the sensor’s magnetic core is different. In the case of a Flux gate sensor, the primary conductor carrying the current to be measured passes through the center of a magnetic core loop. The current flow in the conductor tends to generate a magnetic flux in the core.

Flux gate current sensors are versatile, accurate, and have excellent linearity and wide frequency response. These sensors are used in a wide range of applications, including electric vehicles, EV charging stations, renewable energy systems, power and industrial automation.

Current sensors in EVs

In electric vehicle applications, a battery management system (BMS) is a crucial and sophisticated subsystem designed to monitor, control and optimize the performance of the rechargeable batteries within the vehicle’s battery pack. The BMS continuously monitors various parameters and the health of batteries within the battery pack. This includes parameters such as voltage, current and temperature. Real-time monitoring with a current sensor allows the BMS to detect any abnormalities or deviations which stray away from optimal operating conditions.

Current sensors also play a pivotal role in motor control applications. They facilitate real-time monitoring of the current flow through the motor. They also provide robust protection for the motor and prevent potential damage caused by excessive current flowing into the motor’s windings. These sensors can initiate protective measures such as motor shutdown or alarm activation when the current exceeds predefined thresholds.

Honeywell offers an extensive portfolio of advanced current sensors. Through continuous innovation and refinement, Honeywell develops new products that offer differentiation from our competition. To learn more, visit Honeywell at TTI.

The post The 4 types of EV current sensors appeared first on Engineering.com.

Ever since internal combustion engines dominated the automotive industry, vehicles have been mechanical systems — with electrical add-ons here and there. This perception is changing with the rise of electric powered vehicles and features. Consequently, the engineers tasked with making this shift a reality must overcome a challenge: modern 12-volt electrical systems can’t keep up.

The shift to more electric vehicles is pushing the automotive industry to a 48-volt standard. (Image: Bigstock.)

Go back far enough and engineers only needed a six-volt battery to run headlights, turn signals and other essential features. But as more electrical systems (such as power windows, locks and stereos) became standard, the six-volt system could no longer keep everything running. As a result, the industry switched to a 12-volt standard in the 1950’s.

Modern day vehicles are mirroring this history. Engineers designing vehicles — be it cars, snowmobiles, electric scooters, jet skis and even forklifts — must now consider numerous complex, power-hungry systems and features. In automotive, for example, advanced driver assistance systems (ADAS), autonomous driving systems, sensors, infotainment modules and on-board computers are becoming standard. These electronics put too much strain on a 12-volt battery — thus 48-volt batteries are predicted to become the new standard architecture in transportation. To help smooth this transition towards a 48-volt future, Molex offers its MX-150 mid-voltage interconnect technologies.

The shift to 48-volts is inevitable

Ironically, the transfer to 48-volt systems is stymied by the sheer number of electronics within modern vehicles. According to Kirk Ulery, distribution business development manager at Molex, though the need to move to 48-volts is apparent, most standard parts available to automotive manufacturers are designed for 12-volt architectures. This makes it expensive and complex to jump to 48-volt systems.

The shift towards 48-volts is less a question of if, and more a question of when. (Image: Bigstock.)

Nonetheless, Ulery sees the writing on the wall. “We’re getting to a point where the wire size must increase in a 12-volt system to handle the amount of power you need for all the new features. That’s where the 48-volt system comes in. It goes back to Ohm’s law. When you increase your voltage by a factor of four, you increase the power by a factor of four. So, you have four times the wattage to power these devices.”

We can see the shift to 48-volts today with electric and mild-hybrid vehicles. In mild hybrids, the vehicle will stop the internal combustion engine and run on electrical power when able. It will then start the engine as required. Meanwhile, fully electric vehicles run completely on electrical motors.

“The common thing is that they are moving traditional mechanical functions off a serpentine belt to a series of electric motors,” points out Ulery. He gives an example of a heavy-duty pickup truck using mechanical energy for its power steering. In many vehicles this function is becoming electrified. “The amount of time you need the power steering was robbing some of the engine’s horsepower. By moving it to a separate electrical system, you can control that and maintain more power through the drivetrain … It makes a significant difference in the amount of power you have for the vehicle.”

This demonstrates how even heavy-duty applications are becoming electric in mechanical vehicle systems, and how much the number of power-hungry systems operating electrically is increasing. As a result, 12-volt batteries will not be able to handle the increased load. Therefore, the shift to 48-volt architectures is less a question of if, and more a question of when.

The benefits and challenges of transitioning vehicles to 48-volts

For engineers, one of the primary benefits of 48-volt architecture is its ability to operate at similar wattages using smaller gauge wires. In other words, the larger the voltage, the lower the current needs to be to maintain the power. Thus, smaller, lighter and less expensive wiring harnesses can be used to improve a vehicle’s range, price and ecological footprint.

Ulery sees this as a primary incentive for the change. “The current drive to 48-volts has to do with smaller wires. They cost less, weigh less and are easier to maneuver [around other internal systems under the hood] … Generally, smaller wires with the same amount of wattage [produce] a significant reduction in weight and costs.”

The higher voltage also creates the ability to design a wiring harness with lower resistive losses. “There are some requirements you have to look at when you get to smaller wires. They tend to have slightly higher resistance,” says Ulery. “When you design a wiring harness you know the bulk resistance. [It] is a significant factor in determining the size of the wires.” This means engineers can optimize the wire harness for weight and resistance loss by adjusting the size of the wires. Generally, 48-volt systems can result in a lighter harness that also has lower resistance losses when compared to 12-guage architectures.

Like weight, temperature is another limiting factor when designing the wiring harness of a vehicle. Electric and hybrid vehicles need to stay cool, as heat increases the rate of mechanical deterioration and can cause catastrophic battery failure. Since the shift towards a 48-volt architecture can result in a wiring harness with lower resistive losses, it will also lose less energy to heat. As a result, the higher voltage could translate into a vehicle that operates at a lower temperature.

“Temperature is an issue we calculate for whenever we’re designing automotive wiring,” Ulery explains. “We typically use a current rating that’s based on a specific temperature rise when fully energized.” He adds that a fully energized system is an extreme case, and the calculation would result in an over-engineered wire — which would produce a cooler vehicle anyway. He says, “the duty cycles are such that temperature rise is not usually an issue.”

So why not take the plunge and shift to 48-volts now? Costs, part availability and legacy systems within the automotive industry makes the transition difficult. “It’s a challenge to find components that work with 48-volts,” says Ulery. He then used the Tesla Cybertruck as an example. Though the new vehicle is primarily a 48-volt architecture, the company stepped down voltages in some locations to ensure available parts were compatible.

“No vehicle OEM builds everything,” says Ulery. “The only thing they tend to make are the engines and body panels. Everything else in the car is purchased. Back-up sensors, digital cameras, radios are all purchased. So, to change the industry will take time as suppliers need to change parts to the 48-volt architecture.”

In other words, shifting to 48-volts too soon comes with part availability, compatibility and format adoption risks. In addition, the manufacturer would need to increase development costs to design parts that work at the new voltage. So, much like the Cybertruck, as more vehicles move to 48-volts, many of their sub-systems will likely still operate at 12-volts.

MX-150 mid-voltage connector provides new options for transportation

One part that is widely available for 48-volt automotive and transportation applications are the MX-150 mid-voltage connector provided by Molex. This connector is an expansion of the MX-150 product line which is standard to the automotive industry. So, selecting this connector helps to minimize format adoption and compatibility risks.

MX-150 mid-voltage connectors. (Image: Molex.)

“MX-150 is one of the largest global Molex product lines,” says Ulery. “With the mid-voltage [version], we have it certified up to 60-volts. We made some slight changes to our housing to make sure that we meet all IEC requirements for creepage and clearance. … So, customers are assured that when they use it for 48-volts, or even 60-volts, that the connectors will pass any type of regulatory requirements that they might be subjected to.”

In fact, the connector is already in use for 48-volt applications. And since it’s compatible with legacy MX-150 connectors, customers shifting to a 48-volt architecture spent less time and money on engineering. For example, the connector position assurance (CPA) key ensures all connections are properly mated and safe from accidental disconnections. So, the engineering to connect legacy MX-150 connectors is already done.

“You can both feel and hear the latch click,” says Ulery. “Then the CPA slides under the latch to make sure that it cannot come apart unless you physically move the key. If anyone’s ever tried to do work on even simple electronics on a vehicle, you learn very quickly how hard these things are to get apart.”

MX-150 mid-voltage connectors also have applications for other vehicles. “We’re seeing so much electrification today,” says Ulery. “Electric bicycles, scooters, even electric snowmobiles, personal watercraft and marine applications. Every one of those that’s set up to be fully electrified can benefit from a 48-volt system.”

Various electric vehicles can benefit from a 48-volt architecture. (Image: Bigstock).

Engineers testing parts in physical prototypes running on 48-volts must still overcome one hurdle: sourcing the parts to test. Vehicle parts tend to be available in bulk to reduce their costs for manufacturers. In other words, getting access to a few dozen connectors for the sake of testing can be difficult.

Ulery says for Molex customers this problem is solved by their partner TTI. “TTI has our reliable interconnect technologies in stock, and local contacts so [customers] can call immediately and get the parts they need. I work closely with TTI to get them to understand where connectors can be used and the value proposition to add them into designs. They have the engineering expertise to help [TTI and Molex] customers get their products out faster.”

To get access to MX-150 mid-voltage connectors and other Molex connectors via TTI, visit Molex at TTI.

The post Preparing for the 48-volt shift in automotive systems appeared first on Engineering.com.

Today’s lithium-ion batteries are a good start, offering favorable energy density, cell voltage and lifespan. But the price, material availability and risk of thermal runaway of Li-ion batteries are downsides driving research into better alternatives.

Aqueous batteries are one such option. They’re safe, low cost, eco-friendly and have high ionic conductivity. However, their energy density and specific capacity are relatively low, limiting their practical use to large stationary energy storage where size is not an important factor.

What is an aqueous battery, and how do they differ from non-aqueous lithium-ion? Here’s everything you need to know about this promising energy technology.

Aqueous versus non-aqueous electrolytes

Aqueous batteries use water as the solvent for electrolytes. Traditional Li-ion batteries, in contrast, use non-aqueous carbonate and highly flammable organic solvent electrolytes. These electrolytes come with the risk of many serious hazards, such as harmful leakage, fire and explosion.

It is safer to replace these organic electrolytes with a non-volatile aqueous electrolyte with high thermal resistance. This would also lower the cost of the battery, as the separators and salts used for aqueous electrolytes are less expensive than for non-aqueous electrolytes.

However, because of their limited solubility and low cell voltage, aqueous batteries have a lower energy density than non-aqueous batteries. Aqueous electrolytes have high ionic conductivity, approximately 10^-1 S/cm higher than the other types of electrolytes: organic electrolytes (10^-3 – 10^-2 S/cm), polymer electrolytes (10^-7 – 10^-3 S/cm) and inorganic solid electrolytes (10^-7 – 10^-2 S/cm).

How to commercialize aqueous batteries

There are still challenges hampering the full commercialization of aqueous batteries. Aqueous electrolytes have a narrow electrochemical stability window, only 1.23 V, which is the main culprit for the decomposition of electrode materials. Researchers are looking for a suitable electrode material that can stay stable while operating in this condition.

An additional issue with aqueous batteries is their high self-discharging rate, where the battery loses its charge even while not in operation. This battery self-discharging is caused by the diffusion of ions through the electrolyte and the electrode materials’ reaction with water. With higher temperatures it becomes worse, causing corrosion of the electrodes and resulting in decreased battery performance and lifespan.

To enable aqueous batteries for demanding applications such as EVs or battery energy storage systems, the three most important parameters that must be improved are: higher cell voltage (which requires cathode improvements), a more stable metal anode interface and a larger electrolyte electrochemical window.

Challenges and potential solutions for each essential segment of aqueous batteries: anode, separator/electrolyte and cathode. (Image: Challenges and possibilities for aqueous battery systems, Communications Materials, Ahn et al.)

The electrochemical window of electrolytes is an important parameter for designing higher cell voltage batteries. At higher voltages, electrolytes decompose and interfere with the oxidation/reduction of the cathode/anode materials. The electrochemical window (EW) represents the range of the electrode’s electric potential between which the substance is neither oxidized nor reduced. The electrolytes should have a wider range of electrochemical windows that is greater than the range of the battery’s operating cell voltage. Electrolytes with narrow electrochemical windows are prone to irreversible decomposition, which deteriorates battery capacity. This affects the electrodes’ efficiency, since they react with the electrolyte instead of driving the electrochemical reaction.

Electrodes and electrolyte improvements for aqueous batteries

Researchers are exploring strategies to improve both electrodes and electrolytes to develop better aqueous batteries. To do so, they must find the proper electrode material and adapt the electrode’s structure to accelerate ion transport, improving interfacial stability and limiting the corrosion of current collectors.

Today’s commonly used Li-ion battery types are NMC (nickel manganese cobalt) and LFP (lithium iron phosphate). The LFP cathode is considered the most promising in organic electrolyte batteries. This is because of the wide availability of iron and the robustness of the phosphate anion, which make them safe for high-energy density and provide good performance of the battery. Unfortunately, well-performing cathodes that are proven in organic electrolytes may not provide the same performance in aqueous batteries. LFP cathodes cannot be used in aqueous electrolytes because of their surface instability that makes them electrochemically vulnerable.

Currently, the cathodes commonly used for aqueous batteries have a spinel structure (such as LMO, lithium-ion manganese oxide). The average cell voltage of spinel LMO is about 1.04 V, which is much lower than the LFP cell voltage of 3.2 V.

Researchers are looking to improve electrolytes by adjusting the composition of the solid electrolyte interphase (SEI) layer, extending the EW range and limiting water-based side reactions. The SEI is a passivation layer formed on the anode’s surface by electrolyte decomposition. The quality of the SEI plays a critical role in the long term cyclability and capacity of the battery.

The latest research in aqueous batteries

Researchers from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences recently developed an aqueous battery with significantly improved energy density. Published in Nature Energy, “Reversible multielectron transfer I⁻/IO₃⁻ cathode enabled by a hetero-halogen electrolyte for high-energy-density aqueous batteries,” documents the development of a multi-electron transfer battery that significantly improves energy density. The battery uses concentrated hetero-halogen electrolytes that contain ions from iodide (I^–) and bromine (Br^–) which enabled the multi-electron transfer. The battery used a metallic cadmium anode that provided a high energy density of over 1,200 Wh/L and a high current density of 120 mA/cm².

The DICP researchers successfully demonstrated a safe and high energy density aqueous battery, an important step towards their use in demanding applications such as energy storage systems and possibly even EVs.

The post What’s an aqueous battery, and how do they compare to current EV batteries? appeared first on Engineering.com.

Batteries store more than just electricity. In a world desperate to transition to renewable energy, batteries store the promise of a greener future. And to fulfill that promise, they need the help of a battery management system, or BMS.

“Any place where there are batteries, there has to be a battery management system,” Mohammad Mohiuddin, field applications engineer at Eaton, told engineering.com.

Mohiuddin and his team help engineers design and build battery management systems that can handle the unique requirements of their applications. While there are some off-the-shelf BMSs, most of the time these crucial systems need a designer’s touch. Here’s what you need to know about how they work and why they’re so important for the energy transition.

What is a battery management system?

Today’s battery-powered applications are significantly more complex than a pair of classic AAs. Electric vehicles (EVs), for instance, involve massive lithium-ion battery packs with multiple cells connected in series and parallel. It’s essential to ensure that these cells charge and discharge at a equal rate, which enables the system as a whole to perform at its best for the longest possible lifetime. Even more importantly, it’s crucial to ensure that these batteries work safely within their operating limits, as thermal runaway is a real hazard in lithium-ion battery systems.

Primary functions of a BMS. (Image: Eaton.)

And EVs are easy compared to today’s energy storage systems. These are room-sized banks of batteries that store energy from renewable sources, such as solar and wind, and distribute it as needed. As with EVs, all the cells of an energy storage system must be put to optimal use and protected from adverse conditions. But while EV batteries have a capacity measured in tens of kilowatt-hours, energy storage systems can reach into the gigawatt-hour range, with significantly higher power outputs.

Complicating the matter even further is the addition of supercapacitors into the mix, an increasingly common technique for large-scale energy storage. While batteries have been a well-understood technology for many years, supercapacitors are on the frontier of energy storage. Combining the two technologies is a challenge for many of Mohiuddin’s clients. “They want to know the conditions that a supercapacitor has to be operated along with the batteries so that the two can go together,” he said.

Despite their differences, EVs and energy storage systems both solve these challenges in the same way: the battery management system. The BMS is the brain of any battery system. It’s responsible for monitoring the condition of every cell in the battery pack and distributing the load accordingly, keeping track of important parameters including state-of-charge (SoC) and state-of-health (SoH). The BMS is also responsible for optimizing the life of the battery system by performing charging and discharging in a safe and sustainable way. If something should go wrong, it’s the BMS’s job to safely bring the battery under control or shut it down if necessary.

Key components of a battery management system

Any complex battery-powered application requires a BMS customized for its requirements. But while the details will be different, there are several components common to every BMS. The below diagram shows these BMS building blocks.

The building blocks of a BMS. (Image: Eaton.)

If the BMS is the brain of the battery, the controller is the brain of the BMS. This chip coordinates the functions of the BMS, monitoring the state of each cell and balancing the load amongst them. The controller also maintains communication with other systems, such as an EV’s main computer. This communication can be either wired or wireless. If wired, the signal will be filtered through a common-mode chip inductor before passing through to the connector. If wireless, the controller will be connected to an RF module, typically for Wi-Fi or Bluetooth Low Energy (BLE). A power module brings down the high voltages at the BMS input to smaller values suitable for the electronics in the controller.

Closeup of the Eaton EPM12V1 power module, a non-isolated DC-DC converter suitable for battery management systems, connected to an Eaton common-mode choke and terminal block. (Image: Eaton.)

One of the most important components in the BMS is the primary fuse, which provides overcurrent protection to the whole battery pack. The BMS also includes a self-control fuse further down the circuit, attached to the BMS controller, that provides an additional layer of protection. “If an anomaly occurs, if the current is flowing and it is not being controlled for some reason, the controller can actually blow the self-control fuse open,” Mohiuddin said. Finally, there are additional fuses on each cell that can act quickly to shut down problematic cells without having to shut down the entire battery pack.

Another fundamental BMS component is the current sense resistor, which monitors the current coming in and out of the battery pack and feeds that data to the BMS controller. This is no ordinary resistor. It must have both an extremely small resistance, on the order of a few milliohms, as well as an extremely tight tolerance, on the order of 1% or less. It must also be able to handle high levels of power, as much as 20 watts, without breaking down. To meet these requirements, Mohiuddin explained that Eaton’s current sense resistors are designed with specialized materials.

There’s more. “These resistors are available not only in two terminals, but four terminals,” Mohiuddin said, describing a measurement scheme called the Kelvin, or 4-wire, method. “The two additional connection points allow precise monitoring of the current going through it and the voltage drop across it.”

Finally, the BMS monitors the temperature of the batteries using negative temperature coefficient (NTC) thermistors. If the temperature gets too high, the controller can adjust the current to prevent dangerous overheating.

Sourcing the right components for your BMS

With the BMS serving such an important role in today’s advanced battery-powered applications, it’s crucial for engineers to design these systems to the highest possible standards. While the specific components necessary for each BMS will differ, look for components that have been designed and tested for battery management applications. These will provide the temperature, power and durability requirements that are so often necessary in BMS design.

Eaton offers battery management system components in each of the building block categories described above. For example, Eaton’s Bussmann series CC06FA fuses are designed for automotive BMS applications, and so are Eaton’s Bussman series CSKA current sense resistors, which use the 4-wire Kelvin method for increased measurement accuracy. If you need help designing your BMS, Eaton application engineers like Mohiuddin can share their expertise.

“We advise customers on what is needed and what is going on with harvested energy from different sources,” he said.

To learn more about components for battery management systems, visit Eaton at TTI.

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