Battery Management System (BMS) Implementation Form and Chip Performance Analysis

The battery is the most important component in electric vehicles, and its performance directly influences charging speed, vehicle battery life, and safety concerns. Carmakers have introduced BMS  technology to electric vehicles to monitor battery data in real time in order to alleviate these difficulties, enhance battery efficiency, and extend battery life.

Ⅰ.  What role does BMS  play in electric vehicles and its realization form?

In electric vehicles, the BMS  system is primarily responsible for managing battery charging and discharging. Battery state analysis, power management, battery information management, battery status monitoring, and battery protection are all possible with the BMS  system. Battery overcharge, overdischarge, and high temperature can all be avoided with proper management, and battery performance and service life can be improved.

Figure. 1

The BMS  system is generally built in one of two ways: centralized or distributed. The data from the battery pack is collected and monitored by the centralized BMS  through a bus. A high-voltage area and a low-voltage area are separated in the centralized BMS,  The data from a single battery is collected in the high-voltage area, while the low-voltage area primarily integrates power supply, communication, and other lines. The centralized BMS  system is commonly used in low-voltage and small-capacity batteries, such as robots and small two-wheeled electric vehicles, because of its low cost and simple topology.

Figure. 2

Modular and hierarchical management is used to run the distributed  BMS,  The LECU will be linked to each group of batteries, and data such as voltage and temperature of the battery cells will be collected to determine the battery's status. The entire battery voltage, total bus voltage, and insulation resistance are all monitored by the high-voltage area. The LECU and high-voltage area data is processed and entered into the BMU, which is then aggregated and forwarded to the BSE. The BSE makes the final decision.

Under the tuyere, competition is unavoidable, and electric vehicles are rapidly evolving. To provide vehicle companies with more options, many chip vendors have launched BMS  chips one after the other.

Ⅱ.  TI high precision battery monitoring, balancing, protector

Automobile electrification is accelerating and irreversibly, and the  BMS system has emerged as the central issue. TI has achieved significant progress in the field of electric vehicle BMS.  releasing wired and wireless  BMS solutions that meet the ASIL D standard, setting the industry standard.

Figure. 3

The BQ79614-Q1 is a high-precision battery monitor, balancer, and protector for hybrid and pure electric car  BMS modules. It can track the temperature of the battery in real time and automatically halt and restart to prevent overheating. operate. The chip's operating voltage is 12V, and it can accurately monitor the voltage of 14 batteries in 128μS. The front-end filter and the post-ADC low-pass filter are both integrated into the BQ79614-Q1 chip. The front-end filter is meant to save money by allowing the battery input circuit to employ a basic, low-voltage differential RC filter. The ADC low-pass filter is used to monitor the filtered DC voltage, which makes calculating the battery's level of charge simple. It can be used to measure an external thermistor in this chip. The BQ79614-Q1 may communicate with the BQ7600 device or directly with the MCU using the  UART  interface. The MCU can interact directly with the battery pack using an isolated differential daisy chain in the event of aberrant communication lines.

Ⅲ.  ST 14S high-precision, fast-speed battery monitoring and protection chip

STMicroelectronics (ST Microelectronics, or ST) has dominated the semiconductor market for many years, and its chip applications span a wide range of industries. It has also grown into a key producer of automotive chips. It has launched a high-performance, high-efficiency 32-bit automotive-grade MC, a high-precision, low-energy-consumption VIPower smart switch, a multi-channel, high-precision  BMS IC, and different protective devices in the automotive area to suit market and design needs. In the realm of automotive electronics, ST can provide a broad variety of application products, technical support, and solutions.

Figure. 4

ST has released the L9963 automotive BMS IC. High precision and measurement speed are two of the chip's features. Its accuracy error is only 2mV, and it can read 96 units of data in 4 milliseconds, earning it high praise in the industry. The accuracy and measurement speed of the IC are the most important aspects of BMS,  The state of each unit can be read more precisely with high precision. The increased measurement speed primarily addresses the aging issue, enhances detection accuracy, and provides real-time feedback on battery health.

The L9963 can monitor 4 to 14 battery cells in series as well as 7 external NTCs in 48V or higher voltage grids.  SPI  and isolated interfaces are used for data transmission. Daisy-chaining, on the other hand, allows 1 to 31 devices to be connected, with a total data conversion delay of fewer than 4 microseconds. The L9963 daisy chain's communication serial bus bandwidth is 2.66Mbps, which considerably minimizes data sampling delay. The data reading of 434 units can be completed in 16 milliseconds using a daisy chain connection of 31 L9963s. External communication and monitoring are also possible thanks to the chip's 9  GPIO  external communication port. This chip's feature is its redundant circuit function, which also serves as a form of driving safety precaution. On the internal ADCs, the L9963's redundancy function can do cross detection. To avoid driving accidents, if one of the ADCs fails, the ADC closest to it will take over the failed ADC.

ST also released three evaluation boards based on the L9963 for use with the  SPC58 Chorus MCU, bringing the evaluation board closer to the final research product and speeding up developers' research.

Ⅳ.  ADI 12-way battery monitor

The first integrated high-voltage battery stack monitor was introduced in 2008, according to ADI's official website, and it has since been iteratively upgraded to the fourth generation, with the fifth generation still in the research and development stage.

Figure. 5

ADI's fourth-generation  BMS IC is the LTC6811-1. It's a monitor for battery packs. It can detect the voltage of up to 12 batteries connected in series. The measurement precision is superior than that of ST L9963. The measurement error is less than 1.2 mV in total. It just takes 290 seconds to detect the battery. The LTC6811-1 can connect numerous batteries in series, allowing it to monitor battery status in high-voltage battery strings in real time. An ISOSPI interface on the chip allows for high-speed long-distance communication with the device. The LTC6811-1 can connect 12 sets of batteries in a daisy chain to achieve multi-channel communication, monitor battery state, and perform suspend and start operations based on the battery's current status. A separate power supply powers the chip.

Ⅴ. Summary

The BMS system in a car serves as a link between the vehicle and the kinetic energy management system. The BMS IC's performance has an impact on the electric vehicle's safety, battery life, and mileage. A BMS system with improved sampling accuracy and faster speed will help you get the most out of your batteries while also increasing stability and reliability.