This is the fourth article in a <a href="https://www.wevolver.com/article/how-to-select-the-right-reinforced-transformer-for-high-voltage-energy-storage-applications" rel="noopener noreferrer" target="_blank">5-part series</a> exploring power conversion. The series will provide insight into how the rapid electrification of vehicles and the switch to renewable energy is driving the demand for safe and reliable power conversion and electronic components.&nbsp;The articles were originally published in an&nbsp;<a href="https://www.mouser.com/news/bourns-power-ebook/mobile/index.html" rel="noopener noreferrer" target="_blank">e-magazine</a>, and have been substantially edited by Wevolver to update them and make them available on the Wevolver platform. This series is sponsored by&nbsp;<a href="https://www.wevolver.com/profile/mouser.electronics" rel="noopener noreferrer" target="_blank"></a><a href="https://www.wevolver.com/profile/mouser.electronics" rel="noopener noreferrer" target="_blank">Mouser Electronics</a>, an online distributor of electronic components. Through their sponsorship,&nbsp;Mouser Electronics&nbsp;supports engineers in designing sustainable and efficient applications for a greener future.&nbsp;<h2>Introduction</h2>The need to monitor the state of health of lithium-ion cells in battery packs during charging and discharging is a key requirement for Battery Management Systems (BMS) in high-energy applications such as hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs). Maintaining performance and safe operation is of paramount importance, as lithium-ion chemistries are prone to degradation and aging issues. A dangerous thermal runaway condition can occur if the ambient temperatures are out of specification or if the batteries are undercharged or overcharged, possibly causing cracks in the carbon and lithium plating.The three parameters measured by the BMS (Figure 1) to determine the state of a cell’s health are cell voltage, temperature, and current. The traditional solution employed to measure these parameters has been the use of shunt resistors. These passive components feature a relatively high absolute tolerance of 5 percent. However, the overall accuracy, when combined with a current sense module, can be reduced to as low as 0.01 percent. This article provides helpful BMS design information on the accuracy level that can be obtained using Bourns® Model CSM2F Series shunt resistors combined with a current-sense module designed for this purpose.<div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE2NTgwNjQ0Mjk4LUlNQUdFIDEtMDEuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 788px;" class="fr-fic fr-dib">Figure 1: Block Diagram of Battery Management System.<h2 class="fr-img-space-wrap2">Bourns® Shunt Resistors for Battery Current Measurement</h2></div>Bourns offers three shunt resistor models qualified by Bourns for harsh environment energy storage applications. The resistive element in all three models consists of large copper terminals as can be seen in the examples of the CSM Series on the left. Given that the resistivity of copper is 1.72 x 10-8 Ωm and that the resistance will increase by 0.393 % for every extra degree Celsius in temperature, the overall coefficient of resistance between the two points will be higher than the resistivity of the resistor alloy (max. 50 ppm/˚C or 0.05 %/˚C). If the distance between the two measurement points in copper is 3 mm in total as is the case with CSM2F-8515, the temperature coefficient of resistance, or TCR, will increase from 50 ppm/˚C (TCR of element) to 150 ppm/˚C (TCR of combined element plus copper terminal). The maximum current these shunts can carry is quite high. The Bourns® Model CSM2F-7036, for example, using Ohm's Law can carry 1000 A, DC/DC at a maximum power 50 watts. A typical battery pack for an HEV is 24 kWH. This is equivalent to 500 ampere hours in a 48 V vehicle. Therefore, the current can be very high, especially during periods of high power such as acceleration when moving or fast charging when stopped.&nbsp;<h3>Recommendations for Signal Processing</h3><div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE2NTc5ODcwNzQ3LUlNQUdFIDMtMDEuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 788px;" class="fr-fic fr-dib">Figure 2: Block Diagram of Signal Processing Circuit and Photo of Experiment.&nbsp;Bourns developed the typical current source module block diagram (Figure 2) to evaluate a shunt-based current measurement system’s accuracy. The module consists of an Analog Front End (AFE) with a current sense amplifier with analog buffer, 24-bit ADC and Serial Peripheral Interface (SPI). Several high-voltage bidirectional current-sense amplifiers from ADI, such as the model <a href="https://www.mouser.com/Analog-Devices-Inc/Current-Sense-Amplifiers/AD8210-Series/_/N-1yyh4l4Z6o48gZ1yyhna8" target="_blank">AD8210</a> or <a href="https://www.mouser.com/Analog-Devices-Inc/Semiconductors/Amplifier-ICs/Current-Sense-Amplifiers/AD8211-Series/_/N-6o48g?P=1yyhna6Z1yyh4l4&gclid=CjwKCAjw34n5BRA9EiwA2u9k3-Sp4U4oA9MaKwWJwe3JEK-By0AiM23RZUkK8CTQqzRjiXoNY98kHxoCTzsQAvD_BwE" target="_blank">AD8211</a>, have gains of 20 and common-mode voltages of up to 65V.</div>To evaluate the shunt, Bourns tested its Model <a href="https://www.mouser.com/new/bourns/bourns-csm2f-resistors/" target="_blank">CSM2F-8518</a> (100μohm nominal resistance), as shown in Figure 2. A single-board microcontroller kit is programmed to communicate with the module over an SPI connection. The current for the measurement was generated using a precision current source.The first measurement to be determined is the resistance of the shunt. This is done using the known current from the current source and a precision 4-wire voltmeter. Once the actual resistance of the shunt is measured, then the voltage across the shunt using the current sense module can be compared with the actual resistance value.The current sense amplifier has a common mode voltage of 80V maximum, allowing for the module to be placed at the high end in 48V battery systems. The module also contains a surface-mount temperature sensor with a PWM output proportional to the ambient temperature. Figure 3 shows the temperature sensor output at room temperature. The amplifier power is supplied by a DC supply of +5V. This experiment’s power comes from a Low Drop Out (LDO) regulator with the original supply coming from the USB interface. For an isolated 5V supply, a low-power micro converter using the <a href="https://www.mouser.com/new/linear-technology/adi-lt8301-lt8302-converters/" target="_blank">ADI LTC8301</a> (flyback or push-pull) can provide the necessary isolation with the required safety level.Figure 4&nbsp;shows the data points collected from the A/D input terminals with an average of 22.44364mV and peak-to-peak variation of 0.007mV over the sampling period.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE2NTgwMjA4NTY1LUlNQUdFIDQtMDEtMDEuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 788px;" class="fr-fic fr-dib">Figure 3: Data in Degrees Celsius Recorded by the Module.<h3 class="fr-img-space-wrap2">Determining Measurement Accuracy</h3>The accuracy of the measurements at room temperature can be calculated using the following formula.The accuracy:<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE1Mjg4MzgxMDk4LXRlc3QgNC5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 300px;" class="fr-fic fr-dib">The data at several DC currents ranging from 10mA up to 20A was recorded, and the accuracy calculated (Figure 5). The accuracy tends to degrade once the currents increase beyond 10 amperes, and the shunt starts to heat up. The resistance value used to calculate the current will drift as a result, which has a negative impact on the accuracy of the measurements. To further assist designers, Bourns has developed a look-up table that shows the normalized increase or decrease of the resistance with temperature. With this data, the original value used for the resistance can be modified by the factor shown in Figure 6 and correlated with the temperature sensor reading.<h3>Helping Ensure BMS Safety and Long Life</h3>Currents of several hundred amperes are measured by BMS in various e-mobility applications during battery charging and discharging. The ability to measure current accurately provides critical information for safety and ensures long battery pack life. Using an ultra-low resistance shunt resistor, and a precision AFE, can provide very accurate readings from very high to very low current levels with accuracy tolerances of less than 0.01 percent. Also, temperature sensing, and look-up tables from Bourns, can improve measurement accuracy as the temperature increases.&nbsp;<iframe id="652e6c7b12dae5c3c94c9375" width="250" class="specs-iframe" height="440" src="https://wevolver.com/iframe/specs/azoteq-iqs231bev02-s-evaluation-kit?iframe=true" frameborder="0" scrolling="no" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe>This article has provided a proven methodology to measure the cell voltage, temperature, and current to determine the state of health of a battery cell. Key in this process are Bourns® current-sense amplifiers featuring low offsets and high common mode voltages that enable high accuracy with the shunt being placed at the high end in 48V applications.Bourns® <a href="https://www.mouser.com/new/bourns/bourns-csm2f-resistors/" target="_blank">Model CSM2F Series</a> shunt resistors are manufactured in an International Automotive Task Force-approved facility certified to build components for harsh environment applications such as in high-energy BMS used in HEVs and BEVs.This article was originally written by Mouser and Bourns in an&nbsp;<a href="https://www.mouser.com/news/bourns-power-ebook/mobile/index.html" rel="nofollow" target="_blank">e-magazine&nbsp;</a>and substantially edited by the Wevolver team.&nbsp;It's the fourth article of a 5-part series exploring power conversion. Future articles will dive into power conversion solutions for critical applications such as automotive and renewable energy. &nbsp;Article 1 explored <a href="https://www.wevolver.com/article/how-to-select-the-right-reinforced-transformer-for-high-voltage-energy-storage-applications" rel="noopener noreferrer" target="_blank">how designers can make design decisions when working with high-voltage energy storage systems. &nbsp;</a>Article 2 <a href="https://www.wevolver.com/article/rechargeable-batteries-for-greener-solutions" rel="noopener noreferrer" target="_blank">discussed the potential of rechargeable batteries.&nbsp;</a>Article 3 <a href="https://www.wevolver.com/article/selecting-battery-management-systems-transformers-for-isolated-communications-in-high-voltage-energy-storage" rel="noopener noreferrer" target="_blank">examined the method for selecting transformers for Battery Management Systems (BMS).&nbsp;</a>Article 4 <a href="https://www.wevolver.com/article/accurate-measurements-using-shunt-resistors-and-current-sense-modules-in-high-energy-storage-applications" rel="noopener noreferrer" target="_blank">explained the necessity of shunt resistors to deliver accurate Battery Management Systems.&nbsp;</a>Article 5 <a href="https://www.wevolver.com/article/innovative-transformer-solution-addresses-traditional-challenges" rel="noopener noreferrer" target="_blank">provided an overview of innovative transformer solutions for power conversion.</a><hr><h2>About the sponsor: Mouser</h2><a href="https://eu.mouser.com/" rel="nofollow" target="_blank"></a><a href="https://eu.mouser.com/" rel="nofollow" target="_blank"></a><a href="https://eu.mouser.com/" rel="nofollow" target="_blank">Mouser Electronics</a>&nbsp; is a worldwide leading authorized distributor of semiconductors and electronic components for over 1,100 manufacturer brands. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE4NTY0Njg3ODM2LU1vdXNlciBiYW5uZXIgYXJ0aWNsZS5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 300px;" class="fr-fic fr-dib">

Article 4 of the Power Conversion Series. Shunt resistors combined with a current-sense module can deliver highly accurate battery management systems in high-energy applications.

Accurate Measurements using Shunt Resistors and Current Sense Modules in High-Energy Storage Applications

This is the third article in a<a href="https://www.wevolver.com/article/how-to-select-the-right-reinforced-transformer-for-high-voltage-energy-storage-applications" rel="noopener noreferrer" target="_blank">&nbsp;5-part series</a> exploring power conversion. The series will provide insight into how the rapid electrification of vehicles and the switch to renewable energy is driving the demand for safe and reliable power conversion and electronic components.&nbsp;The articles were originally published in an&nbsp;<a href="https://www.mouser.com/news/bourns-power-ebook/mobile/index.html" rel="noopener noreferrer" target="_blank">e-magazine</a>, and have been substantially edited by Wevolver to update them and make them available on the Wevolver platform. This series is sponsored by&nbsp;<a href="https://www.wevolver.com/profile/mouser.electronics" rel="noopener noreferrer" target="_blank"></a><a href="https://www.wevolver.com/profile/mouser.electronics" rel="noopener noreferrer" target="_blank">Mouser Electronics</a>, an online distributor of electronic components. Through their sponsorship,&nbsp;Mouser Electronics&nbsp;supports engineers in designing sustainable and efficient applications for a greener future.&nbsp;<h2 data-element-id="headingsMap-4-0">Introduction</h2>Battery Management Systems (BMS) connect to high-energy battery packs and manage the charging and discharging of the pack. They also monitor essential safety factors, including temperature, state of charge, and the pack’s state of health. Providing additional application protection, the BMS can connect the battery and disconnect it from the load or charging source, as required.This article provides an overview of the key features of battery monitoring Integrated Circuits (ICs) typically specified in BMS. It includes background information on battery-cell chemistries related to the requirements for communications in high-voltage BMS. An application example will explain the technology benefits that Bourns® transformers deliver to meet these specifications.<h2 data-element-id="headingsMap-5-0">Overview of Lithium-Ion Battery Chemistries</h2><div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE1MjI5NTI5MDc2LVBpY3R1cmUxLnBuZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 788px;" class="fr-fic fr-dib">Figure 1: Forecasted growth in lithium-ion sales.Consulting and market research firm Avicennes[1] has <a href="http://www.avicenne.com/reports_energy.php" target="_blank">predicted</a> that the usage of lithium-ion (Li-ion) battery cells for energy storage and automotive applications will continue to grow significantly through 2025 with compound annual growth rates up to 30 percent forecasted in China’s transport sector. As Li-ion usage grows and expands into new applications, it is important to understand the nature and use of various battery chemistries.</div>Table 1 summarizes the most popular chemistries by energy density, cell voltage, and charge rate for 48V and higher voltage battery packs. These next-generation packs match the power density required to drive new electronics and motor designs. The latest battery cell developments in different chemistries deliver the increased power energy over longer periods necessary for full-electric battery power.<div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE1MjI5NjE0NDQ4LVBpY3R1cmUyLnBuZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 788px;" class="fr-fic fr-dib">Table 1: Summary of most common Li-on chemistries for battery applications.&nbsp;There are several factors to consider when choosing the chemistry for a battery-powered application. &nbsp;As can be seen in Table 1, Lithium Nickel Manganese Cobalt (NMC) with Graphite has the highest energy density among the commonly used chemistries. This is advantageous for heavy loads such as consumer energy storage or plug-in electric vehicles. However, the disadvantage of this chemistry is that it creates a higher risk of lithium plating on the anodes, which can reduce battery life and lead to thermal runaway (fire or explosion). The potential for these harmful conditions can be exacerbated by today’s faster-charging connectors.</div>Lithium Titanate (LTO) has a lower energy density than NMC and does not suffer from the problem of cracking graphite, which together improves the estimated battery life. The lower internal resistance of LTO facilitates faster-charging rates making this battery chemistry beneficial for plug-in electric vehicles (EVs). The downside is the higher cost for heavier battery packs as more cells are needed to provide the necessary energy in kilowatt hours (kWh).Lithium chemistries have very narrow operating temperature ranges, typically from 20°C to 40°C. Operating outside these temperatures leads to a loss of capacity and a shorter lifespan. Elevated temperatures can also cause further degradation and a thermal runaway condition. <a data-lf-fd-inspected-kn9eq4roawkarlvp="true" href="https://www.nasa.gov/pdf/287383main_RP-08-75%2006-069-I%20NASA%20Aerospace%20Flight%20Battery%20Program%20_Part%20I-Volume%20II_FINAL_7-10-08_.pdf" target="_blank">A paper by NASA</a>, which studied the protection within 18,650 cells, found that the interrupt devices in all the cells connected in series and parallel were not as effective as single cells in preventing thermal runaway during fault conditions[2]. This study illustrates the strong need for a Battery Management System when multiple cells are interconnected.<div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE1MjM1MjE2MTcxLVBpY3R1cmUzLnBuZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 788px;" class="fr-fic fr-dib">Figure 2: Block diagram showing the battery management system in relation to the battery pack.&nbsp;&nbsp;A typical battery monitor IC (Figure 3) measures cell voltage and pack temperature and performs cell balancing. In some models, there is also a current sense input port for shunt-based current measurement. Including this feature makes sense in 48V systems that use a limited number of battery cells and do not experience hazardous voltage levels and, hence, monitoring ICs.</div>Conversely, it does not add a lot of value to integrate a current sense function into an IC for high-voltage battery packs. These packs require only one current sensing chip and several monitoring ICs to monitor the pack’s individual cells. For instance, the <a href="https://mynissanleaf.com/viewtopic.php?t=3498" target="_blank">2011 Nissan® Leaf®</a> has a working voltage of 360V and energy of 24kWh (NMC technology)[3]. The structure of the pack is 96S2P (192 cells). A simpler way to put it: If each monitoring IC can check 10 cells, then at least 20 monitoring ICs will be needed. Another consideration in high-voltage battery packs is that the BMS IC module or board must be located on top of the shunt resistor, which can pose a mechanical design challenge.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE1MjM1MjMzNTk3LVBpY3R1cmU0LnBuZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" class="fr-fic fr-dii">Figure 3: Block diagram of BMS IC.<h2 data-element-id="headingsMap-6-0">BMS High Voltage Communications</h2><h2 id="isPasted"> </h2>The BMS typically has two ports for isolated communications, allowing battery monitoring modules to be daisy-chained throughout the battery pack. The source and sink currents of the serial port drivers are balanced, enabling the IC to drive a transformer without saturating it. With a rated working voltage of several hundred volts, the transformer provides the necessary protection of the communications line from any hazardous voltage coming from the battery pack. &nbsp;Furthermore, the drivers on the IC encode a four-line serial peripheral protocol into the differential signal needed for isolated communication from board to board.Serial Peripheral Interface (SPI) is an interface bus commonly used to send data where one device or “master” transmits a clock pulse and control bit to a series of slaves. On each clock pulse, the slave either reads a command from the master, or transmits its data on the data line if the control bit is inverse. In this way, a central battery controller IC (master) can interrogate each monitoring IC (slave) in turn and retrieve necessary voltage and temperature information from the whole pack. In addition, the transformer and integrated common mode choke filter out common-mode noise from the daisy-chained network.<div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE2NTc5MzE0Mjc4LW1vdXNlciAzIG5ldy5wbmciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 788px;" class="fr-fic fr-dib">Figure 4: BMS transformer with Center Tap Capacitor and Resistor. Right: Image of SPU Signal.&nbsp;Although BMS ICs have balanced currents on their I/O pins, most manufacturers recommend a center-tapped transformer. These have been found to improve Common Mode Noise Rejection (CMNR) if a filter capacitor and termination resistor are used, Figure 4.</div><h2 data-element-id="headingsMap-8-0">Bourns® BMS Transformer Safety Features</h2>The windings inside the Bourns® Model <a href="https://www.mouser.com/new/bourns/bourns-bms-transformers/" target="_blank">SM91501AL</a> transformer use enameled fully insulated wire (FIW) that passes the dielectric strength (Hi-POT) test of 4.3kV (1mA, 60 seconds). Per Table 2N of IEC 60950[4], the minimum creepage distance for material group I, pollution degree 2 of functional insulation for a working voltage of 1600V is 8mm. The Bourns® Model SM91501AL transformer datasheet shows a minimum 10mm creepage distance. This is because the actual tracking distance over the transformer’s surface and chokes has been calculated at 10.4mm in the samples measured.The replacement test for IEC 60950 (IEC 62368-1)[5], which becomes mandatory in June 2019 for audio/video, information technology, and communication equipment will recognize FIW in the future. The use of FIW might qualify the device as having reinforced insulation with a lower working voltage (depending on the standard) of approximately 800V. This might allow the device to meet UL listing requirements and enable its use in additional applications such as consumer energy storage, which mandate reinforced insulation.Recommended Electrical CharacteristicsSome IC manufacturers’ recommended primary inductance values will depend on the voltage of the communication signals, the pulse widths, and the frequency. &nbsp;Bourns designed its Model SM91501AL transformer with a primary inductance span between 150µH and 450µH over an operating temperature range of -40°C to +125°C. &nbsp;The inductance is directly proportional to the permeability of the core. The permeability of the ferrite core of a transformer is temperature-dependent and tends to increase with temperature. Therefore, the Bourns® model’s primary inductance will drift up toward 450µH at the upper end of the temperature range. This is the reason for the large variation in the inductance value, as specified on the datasheet. <div class="fr-img-space-wrap"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE1MjM1NDQ5MjAyLVBpY3R1cmU2LmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 788px;" class="fr-fic fr-dib">Figure 5: Bourns Model SM91501AL Transformer on Bourns' BMS Demonstration Board.&nbsp;The BMS IC and transformer’s noise immunity can be evaluated using a bulk current injection (BCI) test. The BCI test injects current into the twisted pair lines at set levels over a frequency range of 1MHz to 400MHz with the bit error rate being measured. A 40mA BCI test level is sufficient for most industrial applications. The 200mA test level is typically used for automotive testing. The Bourns® Model SM91501AL and <a href="https://www.mouser.com/new/bourns/bourns-bms-transformers/" target="_blank">SM91502AL</a> have been evaluated by certain BMS IC manufacturers for select automotive applications and have successfully passed BCI requirements.</div><h2 data-element-id="headingsMap-9-0">Summary and Conclusions</h2>Li-ion battery power demand is predicted to grow at a CAGR of 20 percent to 30 percent over the next eight years. Battery Management Systems that integrate isolated communications are expected to be an important part of the battery system’s safety and security. An effective and reliable BMS will help increase Li-ion cells’ lifespan while also enhancing safe operation for end-users.Offering an optimal protection solution for isolated communications in industrial and consumer BMS applications, Bourns engineered its latest Model SM91501AL and SM91502AL BMS transformers with the higher working voltages of 1600V and 1000V, respectively. They feature an inductance value of 150µH and 450µH over an operating temperature range of -40˚C to + 125˚C, which meets higher voltage BMS requirements. Additionally, the transformer windings use fully insulated wire passing the dielectric strength (Hi-POT) test, further increasing electrical insulation protection for overvoltage transients.Bourns® Model SM91501AL and SM91502AL have been tested by several BMS IC companies in their test laboratories which found them to function well with their chipsets, passing the necessary BCI tests.This article was originally written by Mouser and Bourns in an&nbsp;<a href="https://www.mouser.com/news/bourns-power-ebook/mobile/index.html" rel="nofollow" target="_blank">e-magazine&nbsp;</a>and substantially edited by the Wevolver team.&nbsp;It's the third article of a 5-part series exploring power conversion. Future articles will dive into power conversion solutions for critical applications such as automotive and renewable energy. &nbsp; Article 1 explored <a href="https://www.wevolver.com/article/how-to-select-the-right-reinforced-transformer-for-high-voltage-energy-storage-applications" rel="noopener noreferrer" target="_blank">how designers can make design decisions when working with high-voltage energy storage systems. &nbsp;</a>Article 2 <a href="https://www.wevolver.com/article/rechargeable-batteries-for-greener-solutions" rel="noopener noreferrer" target="_blank">discussed the potential of rechargeable batteries.&nbsp;</a>Article 3 <a href="https://www.wevolver.com/article/selecting-battery-management-systems-transformers-for-isolated-communications-in-high-voltage-energy-storage" rel="noopener noreferrer" target="_blank">examined the method for selecting transformers for Battery Management Systems (BMS).&nbsp;</a>Article 4 <a href="https://www.wevolver.com/article/accurate-measurements-using-shunt-resistors-and-current-sense-modules-in-high-energy-storage-applications" rel="noopener noreferrer" target="_blank">explained the necessity of shunt resistors to deliver accurate Battery Management Systems.</a>Article 5 <a href="https://www.wevolver.com/article/innovative-transformer-solution-addresses-traditional-challenges" rel="noopener noreferrer" target="_blank">provided an overview of innovative transformer solutions for power conversion.</a><h2 data-element-id="headingsMap-10-0">References</h2>1. Avicennes, Christophe, Pillot, Rechargeable Battery Market 2017-2025 The Battery Show, Hannover, May 15, 2018&nbsp;2. &nbsp;NASA, Jeevarajan, Judith A., Safety Limitations Associated with Commercial 18650 Lithium-ion Cells presented at Lithium Mobile Power and Battery Safety 2010, Boston, MA&nbsp;3. &nbsp;Hayes, J. G., &amp; Goodarzi, G. A. (2018). Electric powertrain: Energy systems, power electronics and drives for hybrid, electric and fuel cell vehicles. Hoboken, NJ: John Wiley &amp; Sons.&nbsp;4. International Electrotechnical Commission, Information technology equipment – Safety – Part 1: General requirements IEC 60950-1 Edition 2, 2005&nbsp;5. International Electrotechnical Commission, Audio/Video, Information and Communication Technology Equipment- Part 1: Safety Requirements IEC 62368-1 Edition 2.0 2014-02&nbsp;<hr><h2 data-element-id="headingsMap-11-0">About the sponsor: Mouser</h2><a href="https://eu.mouser.com/" rel="nofollow" target="_blank"></a><a href="https://eu.mouser.com/" rel="nofollow" target="_blank"></a><a href="https://eu.mouser.com/" rel="nofollow" target="_blank">Mouser Electronics</a> is a worldwide leading authorized distributor of semiconductors and electronic components for over 800 industry-leading manufacturers. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.&nbsp;<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjE4NTY0Nzg3OTU5LU1vdXNlciBiYW5uZXIgYXJ0aWNsZS5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 300px;" class="fr-fic fr-dib">

Article 3 of the Power Conversion Series. Battery Management Systems (BMS) monitor essential safety factors in high-energy battery packs.

Selecting Battery Management Systems Transformers for Isolated Communications in High-Voltage Energy Storage

This is the fifth article in a <a href="https://www.wevolver.com/article/higher-reliability-and-longer-lifetimes-with-advanced-battery-management-in-healthcare-energy-storage-systems" rel="noopener noreferrer" target="_blank" style="border: 5px solid green;">5-part series (GOOD)</a> exploring Energy Storage Systems (ESS). The series will provide insight into emerging technologies, covering topics including battery manufacturing, testing, and application.The articles were originally published in an e-magazine, and have been substantially edited by Wevolver to update them and make them available on the Wevolver platform. This series is sponsored by Mouser, an online distributor of electronic components. Through their sponsorship,&nbsp;<a href="about%3Ablank" target="_blank" style="border: 5px solid green;">Mouser Electronics (GOOD)</a>&nbsp;supports the growth of a sustainable future fuelled by renewable and distributed generation technologies.<h2 data-element-id="headingsMap-4-0">Introduction</h2>Driven by tighter CO2 regulations and more eco-conscious consumers (BAD), the pace of migration to electric vehicles continues to accelerate. This is despite the high cost of the batteries, which stubbornly remain approximately half of the vehicle's overall cost.While many factors determine the cost of the battery, one area in which manufacturers can make significant headway in reducing cost is during the final stages of manufacturing. Specifically, during the battery formation and testing which can account for up to 20 percent of an EV’s battery cost.Battery formation and testing is a time-consuming process involving multiple charges and discharges that activate a battery’s chemistry. It can take up to two full days. This necessary procedure readies the battery for use and is critical to ensure its reliability and quality. Because of how slow the process is, it is a significant bottleneck that prevents battery manufacturing from achieving greater throughput, which would lower the overall cost to produce batteries. Partnerships between EV battery manufacturers and suppliers with formation and test systems expertise are allowing them to increase their attention to reducing the time and cost involved at this crucial stage of manufacturing while still maintaining the precision required for advanced battery chemistries.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzMTU0NTA3NTM3LW5pc3Nhbi1tZmctOTAwLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 788px;" class="fr-fic fr-dib"><h2 data-element-id="headingsMap-5-0">Faster Throughput Equals Lower Battery Cost</h2>To decrease the cost of batteries, manufacturers need to take a holistic approach that starts by leveraging suppliers’ system-level expertise to reduce the overall battery test circuit footprint while increasing the number of channels. It’s important to note that both must be done while maintaining the accuracy, precision, reliability, and speed of their battery formation and test measurements to ensure safety, performance, and reliability requirements are met.This is not easy to do. For the front end, the power supplies driving the battery charging circuits need to be tightly controlled. Going deeper, battery formation (BAD) and testing requires close monitoring of current and voltage profiles used during battery cycling to prevent overcharging and undercharging. This ensures safety during tests, while also maximizing battery longevity, which greatly lowers overall cost of ownership for the end user.For these critical battery measurements, very high-quality instrumentation amplifiers (in-amps) and associated shunt resistors are needed to measure battery charge/discharge current to better than ±0.05% accuracy, even under harsh factory conditions. The same level of accuracy applies to the difference amplifiers used to monitor the voltage over the entire thermal operational range.&nbsp;There are several ways to incorporate these components into a full solution, but it is a significant challenge to maximize performance and minimize the system footprint. ADI trys to combat this with the integration of the analog front end, power control, and monitoring circuits in a single IC, the <a href="about%3Ablank" target="_blank" style="border: 5px solid green;">AD8452 (GOOD)</a>. These ICs can include battery reversal prevention, overvoltage protection switches, and smart controls to prevent overcharge of batteries, and they can reduce the system footprint by 50 percent. This suite of capabilities allows battery manufacturers to incorporate more capabilities into test systems that will simultaneously make more efficient use of factory floor space. Moreover, they allow manufacturers to design systems with more functionality and more robust testing procedures.<iframe src="//players.brightcove.net/706011717001/HJgoScClQ_default/index.html?videoId=5815766383001" allowfullscreen="" frameborder="0" class="fr-draggable" style="width: 789px; height: 459px;" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe>Efficient power conversion is another opportunity to drive further system performance. By using advanced switching architectures, test systems can minimize power consumption by enabling bidirectional energy exchange with the grid. Efficient power conversion also reduces the need for heat management equipment, which can add to the system’s overall cost and power consumption. The net result is a reduction in wasted energy and manufacturing cost. Enabling these capabilities requires an appreciation of system features, such as isolated gate drivers, that support the faster switching needs of newer silicon carbide and gallium nitride power switching technologies.The benefits of working closely with suppliers who have system-level expertise and a broad portfolio of products goes beyond having access to more sophisticated components and building blocks. It also gives battery manufacturers access to reference designs for system architectures that can be more easily adopted, making time to market three to four times faster than if a battery manufacturer were to develop a formation and test system from scratch.<h2 data-element-id="headingsMap-7-0">Conclusion</h2>The global demand for EVs will&nbsp;increase at a Compound Annual Growth Rate of 21 percent out to 20211. The need for close partnerships between battery manufacturers and suppliers couldn’t be greater. Suppliers need to provide reliable, proven solutions that enable manufacturers’ systems to achieve new levels of efficiency. The best suppliers can help manufacturers bring these new capabilities to market even faster, and the results will allow battery and electric vehicle production to flourish.This article was originally written by Vikas Choudhary for Mouser and substantially edited by the Wevolver team. It's the final article of a 5-part series exploring Energy Storage Systems (ESS). Future articles will explore Communication Solutions for Essential Monitoring of Solar PV and Energy storage, electric vehicle production futures, and battery monitoring systems for lithium-ion solutions.&nbsp;<a href="https://www.wevolver.com/article/higher-reliability-and-longer-lifetimes-with-advanced-battery-management-in-healthcare-energy-storage-systems" rel="noopener noreferrer" target="_blank" style="border: 5px solid green;">Article one (GOOD)</a> outlined the Energy Storage Systems in healthcare applications. &nbsp;<a href="https://www.wevolver.com/article/icoupler-isolated-communication-solutions-for-essential-monitoring-of-solar-pv-and-energy-storage" rel="noopener noreferrer" target="_blank" style="border: 5px solid green;">Article two (GOOD)</a> explained communication systems for energy storage.&nbsp;&nbsp;<a href="https://www.wevolver.com/article/battery-stack-monitor-maximizes-performance-of-li-ion-batteries-in-hybrid-and-electric-vehicles" rel="noopener noreferrer" target="_blank" style="border: 5px solid green;">Article three (GOOD)</a>&nbsp;gave an overview of battery stack monitoring systems for li-on batteries.<a href="https://www.wevolver.com/article/critical-design-considerations-in-estimating-the-state-of-lithium-ion-batteries" rel="noopener noreferrer" target="_blank" style="border: 5px solid green;">Article four (GOOD)</a>&nbsp;provided a deep analysis of the critical design considerations in estimating the state of lithium-ion batteries.<hr><h2 data-element-id="headingsMap-8-0">About the sponsor: Mouser</h2>Mouser Electronics is a worldwide leading authorized distributor of semiconductors and electronic components for over 800 industry-leading manufacturers. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.<h2 data-element-id="headingsMap-9-0"><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzMTU0NjQzMDQ1LW1vdXNlciBsb2dvIGZvb3Rlci5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 788px;" class="fr-fic fr-dib"> References</h2>1 <a href="about%3Ablank" target="_blank" style="border: 5px solid green;">Electric Vehicle Market by Propulsion (BEV, PHEV, FCEV), Vehicle (PC,CV), Charging Station (Normal, Super, Inductive), Charging Infrastructure(Normal, Type-2-AC, CHAdeMO, CCS, Tesla SC), Power Output, Installation,and Region—Global Forecast to 2025. (GOOD)</a> MarketsandMarkets, June 2018

Article 5 of our Energy Storage Series: Reducing cost is during the final stages of battery manufacturing can assist the migration to electric vehicles.

Scaling Electric Vehicle Production Requires Advanced Battery Formation and Test Systems

This is the fourth article in a<a href="https://www.wevolver.com/article/higher-reliability-and-longer-lifetimes-with-advanced-battery-management-in-healthcare-energy-storage-systems" rel="noopener noreferrer" target="_blank">&nbsp;5-part series</a> exploring Energy Storage Systems (ESS). The series will provide insight into emerging technologies, covering topics including battery manufacturing, testing, and application.The articles were originally published in an e-magazine co-authored by Martin Murnane and Adel Ghazel and have been substantially edited by Wevolver to update them and make them available on the Wevolver platform. This series is sponsored by Mouser, an online distributor of electronic components. Through their sponsorship, <a href="about%3Ablank" target="_blank">Mouser Electronics</a> supports the growth of a sustainable future fuelled by renewable and distributed generation technologies.<h2 data-element-id="headingsMap-4-0">Introduction</h2>Lithium-ion batteries get employed in many vital applications, including energy storage (ESS), electric vehicles (EV), and EV chargers. In these applications, it is crucial to measure the state of charge (SOC) of the cells, which is defined as the available capacity (in Ah) and expressed as a percentage of its rated capacity. The SOC parameter can enable one to assess the potential energy of a battery. It is critically important to estimate the state of health (SOH) of a battery, which gives a measure of the battery’s lifetime, i.e. the battery’s ability to store and deliver electrical energy compared with a new battery. This article reviews the algorithms utilized for SOC and SOH estimation based on the coulomb counting method, the voltage method, and the Kalman filter method.<h2 data-element-id="headingsMap-5-0">Battery SOC Measurement Principle</h2>Accurate SOC estimation is one of the main tasks of battery management systems. It helps improve the system performance and reliability, and lengthen the lifetime of the battery (SOH). Precise SOC estimation of the battery can avoid unpredicted system interruption and prevent the batteries from being overcharged and over discharged, both of which can cause permanent damage to the battery's internal structure. &nbsp;However, since battery discharge and charge involve complex chemical and physical processes, accurate estimations of the SOC are not apparent under various operation conditions.The general approach for measuring SOC is to accurately measure both the coulombs and current flowing in and out of the cell stack under all operating conditions and the individual cell voltages of each cell in the stack. This data gets employed with previously loaded cell-pack data for the exact cells getting monitored to develop an accurate SOC estimate. The additional data required for such a calculation includes the cell temperature, whether the cell is charging or discharging when the measurements get made, the cell age, and other relevant cell data obtained from the cell manufacturer. Sometimes it is possible to get characterization data from the manufacturer of how their Li-ion cells perform under various operating conditions. Once a SOC has been determined, it is up to the system to keep the SOC updated during subsequent operation, essentially counting the coulombs that flow in and out of the cells. This approach's accuracy can be derailed by not knowing the initial SOC to an accurate enough state and by other factors, such as self-discharge of the cells and leakage effects.<h2 data-element-id="headingsMap-6-0">Technical Specifications</h2>This article encompasses the design and development of a coulomb counting evaluation platform to get utilized for SOC and SOH measurement for a typical energy storage module, which in this case is a 48V module, typically comprising 12 to 16 Li-ion cells. The Battery Management System (BMS) periodically measures each cell's voltage value and the battery pack’s current voltage, utilizing appropriate ADCs and sensors, and will run the SOC estimation algorithm in real-time. This algorithm &nbsp;uses measured voltage and current values and some other data collected by temperature sensors.<h2 data-element-id="headingsMap-7-0">SOC and SOH Estimation Methods Overview</h2>Regarding SOC and SOH estimation methods, three approaches mainly find employment: (1) a coulomb counting method, (2) voltage method, and (3) Kalman filter method.<h3 data-element-id="headingsMap-8-0">Coulomb Counting Method</h3>The coulomb counting method, also known as ampere-hour counting and current integration, is the most common technique for calculating the SOC. This method employs battery current readings mathematically integrated over the usage period to calculate SOC values given by:<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDY4MTU1MjU5LTEgbS5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 300px;" class="fr-fic fr-dib">Where SOC(t0) is the initial SOC, Crated is the rated capacity, Ib is the battery current, and Iloss is the current consumed by the loss reactions.The coulomb counting method then calculates the remaining capacity by merely accumulating the charge transferred in or out of the battery. This method's accuracy is linked &nbsp;primarily to a precise measurement of the battery current and accurate estimation of the initial SOC. With a previously known capacity, which might be memorized or initially estimated by the operating conditions, the SOC of a battery can be calculated by integrating the charging and discharging currents over the operating periods. However, the releasable charge is always less than the stored charge in the charging and discharging cycle. In other words, there are losses during charging and discharging. These losses, also with the self-discharging, cause accumulating errors. For more precise SOC estimation, these factors should get consideration. Additionally, the SOC should get recalibrated regularly, and the declination of the releasable capacity should get considered for a more precise estimate.<h3 data-element-id="headingsMap-9-0">Voltage Method</h3>The SOC of a battery, (its remaining capacity) can be determined using a discharge test under controlled conditions. The voltage method converts a reading of the battery voltage to the equivalent SOC value using the known discharge curve (voltage vs. SOC) of the battery. However, the voltage is more significantly affected by the battery current because of the battery’s electrochemical kinetics and temperature. It is possible to make this method more accurate by compensating the voltage reading by a correction term proportional to the battery current and by using a lookup.<h3 data-element-id="headingsMap-10-0">Kalman Filter Method</h3>The Kalman filter is an algorithm to estimate the inner states of any dynamic system—it can also &nbsp;determine the SOC of a battery. Kalman filters were introduced in 1960 to provide a recursive solution to optimal linear filtering for both state observation and prediction problems. Compared to other estimation approaches, the Kalman filter automatically provides dynamic error bounds on its state estimates. By modeling the battery system to include the wanted unknown quantities (such as SOC) in its state description, the Kalman filter estimates their values and gives error bounds on the estimates. It then becomes a model-based state estimation technique that employs an error correction mechanism to provide real-time predictions of the SOC. It can get extended to increase the capability of real-time SOH estimation using the extended Kalman filter. Notably, the extended Kalman filter is applied when the battery system is nonlinear, and a linearization step is needed. Kalman filtering is an online and a dynamic method, and it requires a suitable model for the battery and precise identification of its parameters. &nbsp;It also needs a large computing capacity and an accurate initialization.Other methods for SOC estimation include &nbsp;impedance spectroscopy, based upon cell impedance measurements, employing an impedance analyzer in real-time for both charge and discharge. Although this technique can get used for Li-ion cells SOC and SOH estimation, it was omitted in this article since it is based on external measurements utilizing instrumentation. The methods based on the electrolytes’ physical properties and artificial neural networks are not applicable for Li-ion batteries.<h2 data-element-id="headingsMap-11-0">Technical Principle</h2>Next, we’ll dive into the technical aspect of the topic, however for a more detailed description and equations, refer to the full article, <a href="about%3Ablank#TextLinks-12" target="_blank">A Closer Look at SOC\SOH Estimation Techniques</a>. The releasable capacity (Creleasable) of an operating battery is the released capacity when it gets completely discharged. Accordingly, the SOC is defined as the percentage of the releasable capacity relative to the battery rated capacity (Crated), given by the manufacturer.&nbsp;<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDY4MTY5MDY0LTJtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 788px;" class="fr-fic fr-dib">A fully charged battery has the maximal releasable capacity (Cmax), which can be different from the rated capacity. In general, Cmax is, to some extent, different from Crated for a newly used battery and will decline with the used time. It can get utilized for evaluating the SOH of a battery.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwMDQ1NDc5LTNtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">When a battery is discharging, the depth of discharge (DOD) can get expressed as the percentage of the capacity that has gotten discharged relative to Crated,<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwMDc0MzUzLTRtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">Where Creleased is the capacity discharged by any amount of current. With a measured charging and discharging current (Ib), the difference of the DOD in an operating period (Ʈ) can be calculated by<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwNDIyNDgyLTVtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">where Ib is positive for charging and negative for discharging. As time elapsed, the DOD is accumulated<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwMjM3Mzc4LTZtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">To improve the accuracy of estimation, the operating efficiency denoted as ŋ is considered and the DOD expression becomes,<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwNDUxNjYxLTdtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">With ŋ equal to ŋc during the charging stage and equal to ŋd during the discharging stage. Without considering the operating efficiency and the battery aging, the SOC can get expressed as<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwNDc0NjI1LThtLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">Considering the SOH, the SOC is estimated as<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzNDcwNDg1NDQ2LTltLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">The estimation process is based on monitoring the battery voltage (Vb) and Ib. The battery operation mode can be understood from the amount and the direction of the operating current. The DOD is adding up the drained charge in the discharging mode and counting down with the accumulated charge into the battery for the charging mode. After correction with the charging and discharging efficiency, a more accurate estimation can get realized. The SOC can then get estimated by subtracting the DOD quantity from the SOH one. When the battery is open-circuited with zero current, the SOC is directly obtained from the relationship between the OCV and SOC.Note that the SOH can get reevaluated when the battery is either exhausted or fully charged, and manufacturers specify the battery operating current and voltage. The battery may be considered drained when the loaded voltage (Vb) becomes less than the lower limit (Vmin) during the discharging. In this case, the battery can no longer be used and should get recharged. At the same time, a recalibration to the SOH can get made by reevaluating the SOH value by the accumulative DOD at the exhausted state. On the other hand, the used battery may be considered fully charged if (Vb) reaches the upper limit (Vmax), and (Ib) declines to the lower limit (Imin) during charging. A new SOH is obtained by accumulating the sum of the total charge put into the battery and is then equal to SOC. In practice, the fully charged and exhausted states occur occasionally. The accuracy of the SOH evaluation can be improved when the battery is frequently fully charged and discharged.Thanks to the simple calculation and the uncomplicated hardware requirements, the enhanced coulomb counting algorithm can be easily implemented in all portable devices, as well as electric vehicles. Additionally, the estimation error can be reduced to one percent (1%) at the operating cycle next to the reevaluation of the SOH.This article was originally written by Martin Murnane for Mouser and substantially edited by the Wevolver team. It's the fourth article of a 5-part series exploring Energy Storage Systems (ESS). Future articles will explore Communication Solutions for Essential Monitoring of Solar PV and Energy storage, electric vehicles production futures, and battery monitoring systems for lithium-ion solutions.&nbsp;<a href="https://www.wevolver.com/article/higher-reliability-and-longer-lifetimes-with-advanced-battery-management-in-healthcare-energy-storage-systems" rel="noopener noreferrer" target="_blank">Article one</a> outlined the Energy Storage Systems in healthcare applications. &nbsp;<a href="https://www.wevolver.com/article/icoupler-isolated-communication-solutions-for-essential-monitoring-of-solar-pv-and-energy-storage" rel="noopener noreferrer" target="_blank">Article two</a> explained communication systems for energy storage. &nbsp;<a href="https://www.wevolver.com/article/battery-stack-monitor-maximizes-performance-of-li-ion-batteries-in-hybrid-and-electric-vehicles" rel="noopener noreferrer" target="_blank">Article three</a>&nbsp;gave an overview of battery stack monitoring systems for li-on batteries.<a href="https://www.wevolver.com/article/critical-design-considerations-in-estimating-the-state-of-lithium-ion-batteries" rel="noopener noreferrer" target="_blank">Article four</a>&nbsp;provided a deep analysis of the critical design considerations in estimating the state of lithium-ion batteries.<a href="https://www.wevolver.com/article/scaling-electric-vehicle-production-requires-advanced-battery-formation-and-test-systems" rel="noopener noreferrer" target="_blank">Article five</a>&nbsp;looked at solutions for scaling electric vehicle production.&nbsp;<hr><h2 data-element-id="headingsMap-12-0">About the sponsor: Mouser</h2><a href="https://eu.mouser.com/" rel="noopener noreferrer" target="_blank">Mouser Electronics</a>&nbsp;is a worldwide leading authorized distributor of semiconductors and electronic components for over 800 industry-leading manufacturers. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjEzMTUxNjUzMzY1LW1vdXNlciBsb2dvIGZvb3Rlci5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 788px;" class="fr-fic fr-dib">

Article 4 of our Energy Storage Series: Accurate state of health and state of charge estimations is essential for safe and efficient battery use.

Critical Design Considerations in Estimating the State of Lithium-ion Batteries

Article 3 of our Energy Storage Solutions series: A state-of-the-art Battery Monitoring System allows you to extract the highest quantity of charge from your battery pack and  manage the charge and discharge cycles in a safer way extending battery life.

Battery Stack Monitor Maximizes Performance of Li-Ion Batteries in Hybrid and Electric Vehicles

<h2 dir="ltr" data-element-id="headingsMap-4-0">Introduction</h2>Once a luxury used primarily by early adopters, electric vehicles (EVs) are becoming increasingly commonplace due to rising awareness about carbon emissions and their impact on climate change, supportive government policies, volatile oil prices, and growing cultural acceptance of green energy use. Global EV stock is projected to reach 243 million by 2030 - over 30 times higher than today’s level [<a href="https://www.iea.org/reports/global-ev-outlook-2020" target="_blank">1</a>]. Most major car manufacturers are planning either a complete shift or a transition to EVs [<a href="https://www.nature.com/articles/d41586-018-07585-6?source=post_page-----e0f2661bf61----------------------" target="_blank">2</a>].As demand for electric vehicles increases, so does demand for improved performance, including decreased cost and charge time, increased range and battery life, and improved safety. The cost of EV batteries continues to fall and EV battery technology is advancing rapidly in the form of increasing capacity and energy density [<a href="https://www.iea.org/reports/global-ev-outlook-2020" target="_blank">1</a>,<a href="https://www.nature.com/articles/d41586-018-07585-6?source=post_page-----e0f2661bf61----------------------" target="_blank">&nbsp;2</a>]. However, increases in energy density are accompanied by a growing challenge - safety. In particular, lithium ion batteries - the power source of choice for EVs thanks in part to their high energy density - are susceptible to overheating, and even explosion, and safety incidents have been widely reported [<a href="https://www.mdpi.com/2076-3417/9/12/2483/htm" target="_blank">3</a>,<a href="https://link.springer.com/article/10.1007/s10694-019-00944-3" target="_blank">&nbsp;4</a>]. As EV batteries become more powerful and complex, ever more sophisticated battery management systems are needed to ensure the safe, reliable, and cost-efficient operation of electric vehicles.<h2 dir="ltr" data-element-id="headingsMap-5-0">What is a battery management system?&nbsp;</h2>Battery management systems (BMS) are electronic control circuits that closely and accurately monitor and regulate the charging and discharging of rechargeable batteries, serving as the “brains” of an EV battery system. The BMS maintains batteries within their safe operating area and ensures optimal use of the residual energy in batteries, thereby maximizing their safety, reliability, durability, and performance.<h3 dir="ltr" data-element-id="headingsMap-6-0">Functions of battery management systems</h3>Battery management systems are central to the safe and efficient operation of electric vehicles and perform a broad array of functions, including:Battery monitoring&nbsp;The BMS monitors the state of an EV battery system through a variety of direct and indirect measures. Current, voltage, and surface temperatures of battery cells are directly measured using sensors. These are in turn used to estimate the battery pack State of Charge (SOC), which indicates the charge level of the battery; the State of Health (SOH), which represents the remaining capacity of the battery pack and indicates when it should be replaced; the internal temperature of battery cells; and other parameters. Accurate voltage monitoring is of particular importance, since voltage deviations due to overcharging, over-discharging, or high power pulses can lead to significantly reduced battery life and safety issues.Battery protection&nbsp;The BMS is also equipped to prevent operations outside the safe operating area of and damage to the battery system, for example due to overcharging, over-discharging, or high temperatures. The action of the BMS can be physical (such as emergency shut down of the battery) or informational (by triggering an alarm or otherwise reporting trouble to the driver).For example, the BMS controls the charger to protect the battery from overheating as well as ensure optimal charge of the battery, thereby prolonging its life and improving capacity utilization. The BMS is also responsible for thermal management of the battery. Battery temperature has a significant impact on battery life and performance, and the BMS controls the pump, fans, coolant (where relevant), and heater to maintain the temperature of the battery pack within its optimum operating range.&nbsp;Battery optimization&nbsp;The BMS also optimizes battery performance via a process called cell balancing. Within an EV battery pack, no two cells are identical, due to manufacturing differences as well as variation in their on-vehicle environment. Weaker cells charge and discharge faster than other cells. Because charging and discharging stop as soon as any cell hits programmed upper and lower capacity limits, the weaker cells cause energy within the other cells to go unused while discharging and limit the capacity of the battery pack while charging. This also results in an increase in the number of battery charge and discharge cycles, which shortens the lifetime of the battery.Cell balancing helps resolve these issues and ensure optimum performance of the battery by equalizing the individual cells’ state of charge. Two types of cell balancing can be used – passive and active. In passive balancing a bleed resistor is used to dissipate energy from cells with excess charge until all cells have a similar state of charge. While this approach is lower cost, it is also less efficient since excess energy is lost as heat. Active cell balancing is a more complex technique that redistributes charge between cells during the charge and discharge cycles. While it is more efficient, since energy is transferred to where it is needed instead of being lost as heat, it also requires additional components at higher cost. Either method extends battery life and improves safety by preventing damage to battery cells due to overcharging or over-discharging.High precision cell voltage and temperature measurements and robust communication links between cells and to battery controllers can further contribute to optimizing battery performance. By collecting better measurements and communicating them faster, the BMS can be more responsive to battery conditions and enable more efficient use of the battery.<h2 dir="ltr" data-element-id="headingsMap-7-0">Communication</h2>The BMS also facilitates communication of information to the driver, for example by triggering an alarm or reporting the state of charge, as well as to other on-board equipment, for example to request changes in vehicle operation in response to monitored battery pack conditions.<h3 dir="ltr" data-element-id="headingsMap-8-0">Design of battery management systems</h3>Electric vehicles are powered by hundreds or even thousands of individual battery cells. These cells are connected in modules in series and parallel and placed inside a steel casing to form the battery pack. Battery packs are typically very large, occupying the entire floor area of an EV, and are connected to the BMS and thermal management system. The BMS transmits information from the battery pack to the controller, which converts the DC voltage produced by the battery pack and drives the motor, and the rotational energy from the motor is transferred to the wheels by the transmission system (Figure 1).<img src="https://images.wevolver.com/eyJidWNrZXQiOiAid2V2b2x2ZXItcHJvamVjdC1pbWFnZXMiLCAia2V5IjogImZyb2FsYS8xNTk3MjQzMjU3MTc1LUlMTFVTVFJBVElPTiAyMi0xLTAxICgxKS5qcGciLCAiZWRpdHMiOiB7InJlc2l6ZSI6IHsid2lkdGgiOiA5NTAsICJmaXQiOiAiY292ZXIifX19">Figure 1: Schematic showing layout of BMS, battery pack, controller, transmission, etc. within a car&nbsp;The BMS itself is a combination of hardware and software (Figure 2). Hardware includes sensing microchips, transceivers, power management microchips, and microcontrollers. The sensors measure battery voltage, current, and surface temperature to monitor the condition of individual cells. Transceivers relay information between components. Power management microchips allow the connection and isolation of the battery pack between the charger and load. Microcontrollers receive information from sensors and plug it into algorithms which model internal battery states, such as internal temperature, SOC, and SOH. Once these internal states have been defined, the microcontroller can make decisions, such as optimizing the charging and discharging of the battery or triggering alarm or safety modules.<img src="https://images.wevolver.com/eyJidWNrZXQiOiAid2V2b2x2ZXItcHJvamVjdC1pbWFnZXMiLCAia2V5IjogImZyb2FsYS8xNTk3MjQzMjk1MzYxLUlMTFVTVFJBVElPTiAyMS0wMSAoMSkuanBnIiwgImVkaXRzIjogeyJyZXNpemUiOiB7IndpZHRoIjogOTUwLCAiZml0IjogImNvdmVyIn19fQ==">&nbsp;Figure 2: Schematic showing layout and components of a simplified BMSBattery management systems can be implemented using a variety of architectures. The choice of architecture has a significant impact on the cost, development time, flexibility, and reliability of a BMS. Architectures can be broadly classified as centralized and decentralized (Figure 3). In centralized architectures, a single controller monitors, balances, and controls all battery cells and is connected to them through a large number of wires. This approach is relatively inexpensive but also challenging to expand. In decentralized architectures, which include distributed, master-slave, and modular architectures, the BMS functionality is not concentrated on a single circuit board. These approaches entail fewer wires and are more flexible, but also more expensive.<img src="https://images.wevolver.com/eyJidWNrZXQiOiAid2V2b2x2ZXItcHJvamVjdC1pbWFnZXMiLCAia2V5IjogImZyb2FsYS8xNTk3MjQzNDkzODAwLUlMTFVTVFJBVElPTiAyMi0wMSAoMSkuanBnIiwgImVkaXRzIjogeyJyZXNpemUiOiB7IndpZHRoIjogOTUwLCAiZml0IjogImNvdmVyIn19fQ==">&nbsp;Figure 3: Diagram comparing generic centralized BMS architecture to decentralized/distributed BMS architectureGenerally speaking, decentralized architectures are advantageous because they offer superior measurement precision, because shorter wires are less susceptible to noise; more reliable connections, because shorter wires are less prone to disconnection due to mechanical shocks and vibrations; scalability; and more robust communication between components.&nbsp;Achieving reliable, high performance communication is a key challenge faced by BMS designers. Besides opting for decentralized architectures, designers can improve communication between components (and therefore achieve more accurate, real-time measurements and control) by using microchips which consolidate a variety of functions and controllers with built-in diagnostic functions. Minimizing the number of components, as well as the size of the components which are used, offer the added benefit of giving designers more flexibility and allowing for optimal placement of components within the vehicle.Another challenge BMS can help designers tackle is security. Because EVs (including smart vehicles and autonomous vehicles) connect to the internet, these vehicles run the risk of cyberattacks. BMS security controllers can prevent unauthorized modification of the battery system, protecting the safety of the system as well as privacy and intellectual property.<h2 dir="ltr" data-element-id="headingsMap-9-0">What’s next for battery management systems?</h2>Demand for improved performance and societal changes are driving new developments in battery management systems. One trend which promises major improvements to the performance and cost of EVs is the advent of wireless BMS. In a typical BMS, components are connected by a large amount of wiring - up to several kilometers long - which adds weight to the EV and makes it less efficient. This wiring is also costly and prone to mechanical failure. Furthermore, the wiring can make it so complex and time consuming to replace an individual battery cell that it makes more sense to simply replace the entire pack. By eliminating the need for wiring and associated components, a wireless BMS helps decrease the weight and size of the BMS, thereby improving vehicle efficiency, extending driving range, and helping make vehicles easier and cheaper to produce and maintain. At the same time, wireless BMS could offer even more accurate and useful information about the condition of the battery cells.Another development is the increasing expectation that BMS components meet the most stringent safety standards. The safety of automotive components is assessed according to the ISO26262 standard, defined by the International Organization for Standardization (<a href="https://www.iso.org/standard/68383.html" target="_blank">5</a>). During the development of hardware and software components, all potential hazardous scenarios are evaluated for a particular component and classified based on the levels of severity, probability of occurrence, and driver controllability. The component is then assigned an Automotive Safety Integrity Level (ASIL), which indicates the level of safety required by the component to function normally without posing any threats to the vehicle. ISO 26262 defines four ASIL levels - A, B, C, and D - where ASIL D refers to the highest level of safety required. Vehicle manufacturers increasingly demand that BMS components are ASIL D compliant. At the same time vehicle designs are becoming increasingly complex, meaning that BMS suppliers need to be more rigorous than ever to meet safety requirements and ensure that EVs can operate safely.Finally, a rapidly evolving and urgently needed development for EVs is fast charging, especially for buses and shared mobility vehicles which need to operate continuously (<a href="https://www.annualreviews.org/doi/full/10.1146/annurev-control-053018-023643" target="_blank">6</a>). With the established AC charging, it can take several hours to fully charge an EV, whereas fast charging enables this within about 20 minutes. Batteries undergoing fast charging require more sophisticated battery management and much more accurate estimations of conditions inside battery cells to prevent overcharging and overheating.<h2 dir="ltr" data-element-id="headingsMap-10-0">Conclusion</h2>As electric vehicles become increasingly ubiquitous, so will demand for EVs to offer performance and cost which is comparable to that of traditional vehicles. By improving the safety and reliability of EVs, increasing the efficiency and range of EVs, and prolonging EV battery lifetimes, battery management systems will play a pivotal role in achieving comparable, affordable performance, thereby enabling society to reap the benefits of EVs on a large scale.<hr><h2 dir="ltr" data-element-id="headingsMap-11-0">About the sponsor: Infineon Technologies </h2>Infineon Technologies provides semiconductor products for use in a wide range of applications.&nbsp;Infineon Technologies is dedicated to developing integrated circuits and design resources for battery management systems that contribute to more efficient, longer-lasting, and reliable battery-powered applications. To learn more click&nbsp;<a href="https://www.infineon.com/" rel="noopener noreferrer" target="_blank">here.</a><img class="fr-fic fr-dib" src="https://images.wevolver.com/eyJidWNrZXQiOiAid2V2b2x2ZXItcHJvamVjdC1pbWFnZXMiLCAia2V5IjogImZyb2FsYS8xNTk3MjU2MTk0MzQyLUluZmluZW9uLWxvZ28tMDYucG5nIiwgImVkaXRzIjogeyJyZXNpemUiOiB7IndpZHRoIjogOTUwLCAiZml0IjogImNvdmVyIn19fQ==" style="width: 300px;"> <hr><h2 dir="ltr" data-element-id="headingsMap-12-0">References</h2><ol><li dir="ltr">Global EV Outlook 2020 – Analysis - IEA [Internet]. IEA. 2020. Available from: https://www.iea.org/reports/global-ev-outlook-2020</li><li dir="ltr">Figueres, C. Nature. [Online]. Available from: https://www.nature.com/articles/d41586-018-07585-6&nbsp;</li><li dir="ltr">Ouyang D, Chen M, Huang Q, Weng J, Wang Z, Wang J. A Review on the Thermal Hazards of the Lithium-Ion Battery and the Corresponding Countermeasures. Applied Sciences. 2019;9(12):2483. &nbsp;</li><li dir="ltr">A Review of Battery Fires in Electric Vehicles [Internet]. Springer. 2020. Available from: http://A Review of Battery Fires in Electric Vehicles &nbsp;</li><li dir="ltr">ISO 26262-1:2018 [Internet]. ISO. 2020. Available from: https://www.iso.org/standard/68383.html &nbsp;</li><li dir="ltr">Xinfan L. Modeling and Estimation for Advanced Battery Management [Internet]. Annual Reviews. 2020. Available from: https://www.annualreviews.org/doi/full/10.1146/annurev-control-053018-023643 &nbsp;</li></ol>

As EV batteries become more powerful and complex, ever more sophisticated battery management systems are needed to ensure the safe, reliable, and cost-efficient operation of electric vehicles.

battery management system (BMS)

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