How to Find the Right High Voltage BMS Solution

Last time we talked about Battery Management Systems for EVs, so next we'll talk about how to find a more suitable high-voltage BMS solution?

It is vital to select the right BMS components to ensure the safety and high performance of the entire battery system in an electric vehicle over its lifetime. It can dramatically increase the range and lifetime of lithium-ion batteries, allowing automakers to differentiate themselves in a highly competitive market.

In practical applications, it is difficult to say which HVBMS architecture or reference design will be suitable for all applications and meet the needs of all automakers. However, one thing that should be considered as a priority in the solution selection process is that any reference design must be flexible enough to accommodate all possible future architectures. For example, different system voltages ranging from 400V to 1,000+V need to be addressed, as well as upcoming 2 x 400V hybrid configurations for switchable 800V charging and 400V driving, among others.

The BMS consists of three modules, the Battery Management Unit (BMU), the Battery Monitoring Unit (CMU) and the Battery Junction Box (BJB). How to establish internal BMS communications between the BMU, CMU and BJB subsystems, which act as the brain of the system, will also require designers to make a careful evaluation when selecting a solution.

NXP's scalable high-voltage battery management system (HVBMS) reference design contains all three modules of the BMU, CMU and BJB.

BMU

The BMU utilizes the ASIL D safety-compliant S32K3 microcontroller (MCU) family. the MCU and other components in the BMU are powered by FS26 SBCs to enable robust power management at the system level.    The RD-K344 BMU development board contains several NXP components such as S32K344, FS26, MC33665A, HB2000, TJA1145A, PCA2131, NBP8, and MC40XS6500, which helps in the rapid prototyping of the HVBMS hardware and software; for the intra-cell communication, the reference design provides two possible architectures : Isolated Electrical Transfer Protocol Link (ETPL) or CAN/CAN FD.

CMU

The CMU's reference design board features four new ASIL D-compliant battery controllers (BCCs) that can collectively monitor and balance up to 56 cells. Because capacitive coupling is used to isolate on-board communications, multiple boards can be daisy-chained to extend the number of battery cells to systems up to 800V, providing extreme scalability.

The RD33775ACNTEVB is a centralized CMU reference design with ETPL communications, and this evaluation board also contains four MC33775A analog front ends (AFEs) connected in a daisy chain.

BJB

BJB's design utilizes two new MC33772C ICs, a 6-channel lithium-ion battery controller IC for electric vehicle applications that redundantly measures battery pack current and several high voltages. The BJB can also perform Coulomb counting without MCU interaction for highly accurate state-of-charge and function-state calculations.

Figure 1: Block Diagram of HVBMS 400V ETPL Architecture

While the majority of all-electric vehicles on the road today utilize 400V batteries, the overall trend will gradually shift to 800V battery architectures. Pure electric vehicles operating at the high 800V voltage have much shorter charging times and are more responsive to consumer demand. More and more automakers will introduce 800V architecture models in the next five years.

NXP's RD-HVBMSCT800BUN is a reference design kit for 800V high-voltage battery management systems (HVBMS). It provides a complete hardware solution including the RD-K358 BMU, the RD33774CNT3EVB Cell Monitoring Unit (CMU) and the RD772BJBTPL8EVB Battery Junction Box (BJB) as well as software drivers and scalable functional safety documentation. Automakers, suppliers and software ecosystem partners can use the kit directly for development, testing and demonstration.

Figure 2: 800V High Voltage Battery Management System RD-HVBMSCT800BUN Design Kit Contains All Three Submodules of BMU, CMU and BJB.

The Texas Instruments (TI) ADS131B24-Q1 is a highly integrated voltage, current, and temperature sensor product for electric vehicle HVBMS. It features a high level of integration, including:
Two synchronized-sampling, high-precision 24-bit ADC channels (ADC1A, ADC1B) for high-resolution and high-accuracy battery current measurement using an external shunt resistor.
Two independent digital comparators per ADC with programmable thresholds for fast overcurrent detection.
Two multiplexed 16-bit ADC channels (ADC2A, ADC2B) for voltage and temperature measurements using external high-voltage resistor dividers. Shunt temperature is measured using an external temperature sensor, such as a thermistor or an analog output temperature sensor.

In addition, each ADC is equipped with a channel sequence generator, which automatically steps through the multiplexer inputs of the debug configuration to minimize communication on the serial peripheral interface (SPI).   The multiple monitoring and diagnostic functions integrated in the ADS131B24-Q1 mitigate and detect random hardware failures, and are very helpful in developing a safe and efficient EV BMS.

Figure 3: Block Diagram of Electric Vehicle Battery Pack Monitoring System based on ADS131B24-Q1.

Looking to the Future of HVBMS

Globally, the trend toward vehicle electrification continues to accelerate. By 2028, the global light-duty vehicle market is expected to reach 93 million units, with xEVs holding 53.5% of the market share. Pure electric vehicles are leading market growth, with a CAGR of 22.1% from 2022 to 2028, compared to the overall 16.7% CAGR for xEVs over the same period.

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