Electric vehicles Better battery management with wireless data transfer

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FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Battery management systems (BMS) are an essential component of electric vehicles (EVs). They are based on all cells in the battery pack monitoring and passing on their temperature, voltage and current data. The latter can be done via CAN (Controller Area Network), with the help of differential daisy chain communication or with a proprietary solution.

Battery management systems (BMS) are an essential component of electric vehicles (EVs). They are based on all cells in the battery pack monitoring and passing on their temperature, voltage and current data. The latter can be done via CAN (Controller Area Network), with the help of differential daisy chain communication or with a proprietary solution.

The BMS shown in Figure 1 consists of a microcontroller, an insulation barrier between the low-voltage and high-voltage sections and battery monitoring modules. The information from the battery cells is transmitted by cable.

Establishing the connections to the individual cells and the insulation are difficult and costly with wired solutions. If the cables are damaged in an accident, the entire battery pack has to be replaced. These and other problems have prompted car manufacturers and BMS solution providers to look for ways to transmit cell data wirelessly.

Transfer data from the BMS directly to the µC

The wireless transmission of battery cell data directly to the microcontroller of the BMS eliminates the problems of wired communication. In terms of performance, compromises compared to wired transmission are not acceptable. A critical performance parameter of a wireless BMS is the availability of the 2.4 GHz radio network. This must be guaranteed so that the BMS can function in real time once an EV has been started. This is where the reliability and performance of Texas Instruments' proprietary radio protocol comes into play. The basic idea behind it is that the network connects all the components involved in such a way that nothing stands in the way of the EV's journey.

The availability of a wireless BMS is measured by the extent to which the data from the wireless connectivity devices and the main radio node is available at any given time. In other words, it is the percentage of time that the wireless BMS network is collecting data or controlling the battery monitoring devices. Figure 2 illustrates this concept.

The network consists of a main controller, which is connected to the microcontroller of the battery pack, and eight wireless components. The evaluation module for the SimpleLink 2.4 GHz wireless microcontroller CC2662R-Q1 includes the radio part of the main node and the radio components. Each wireless component is connected to a battery monitor and balancer (in this case of type BQ79616-Q1), which measures the voltage and temperature of the battery cells in the BMS and reports the charge and health status of the cells to the microcontroller of the BMS via the main controller.

Data transmission in wireless BMS protocol

Data transmission must be fast and precise to avoid malfunctions or potentially dangerous situations. The wireless BMS protocol achieves a packet error rate of 10^-7 or better for a 10-node network. In other words, the data of a node is not available for 100 ms with an operating time of over 52,000 hours, which corresponds to an availability of over 99.999 %. The independence of the individual radio components also means that the availability of the entire BMS network is also greater than 99.999%.

These figures allow the use of a wireless BMS in challenging battery housings with limited space and significant attenuation and signal reflection phenomena. The wireless protocol, combined with the industry's best network availability, gives vehicle developers the ability to eliminate heavy, expensive and maintenance-prone wiring and improve the reliability and efficiency of electric vehicles. (kr)