Battery Stack Monitor Maximizes Performance of Li-Ion Batteries in Hybrid and Electric Vehicles: Page 4 of 8

April 29, 2020 //By Cosimo Carriero, Analog Devices
Battery Stack Monitor Maximizes Performance of Li-Ion Batteries in Hybrid and Electric Vehicles
Lithium-ion (Li-Ion) batteries offer a high energy density, but to maximize performance, a battery monitoring system (BMS) is mandatory. A state-of-the-art BMS not only allows you to extract the highest quantity of charge from your battery pack, but also lets you manage the charge and discharge cycles in a safer way, which results in an extended life.

ADI is demonstrating the industry’s first wireless automotive BMS concept car, combining the LTC6811 battery stack monitor with ADI’s SmartMesh network technology in a BMW i3.2 This is a significant breakthrough that has the potential to improve reliability and reduce cost, weight, and wiring complexity for large multicell battery stacks for EV/HEV.

Figure 2. Parallel independent CAN modules.

Figure 3. Series modules with CAN gateway.

The Importance of an Accurate Measurement

Accuracy is an important feature for a BMS and it is critical for LiFePO4 batteries.3,4 To understand the importance of this feature, let’s consider the example in Figure 5. To prevent overcharge and discharge, the cells of the battery are kept between 10% and 90% of full capacity. In a 85 kWh battery, only 67.4 kWh are available for normal driving. If there is a measurement error of 5%, to continue to operate the battery safely, the cells must be kept between 15% and 85% of their capacity. The total available capacity has been reduced from 80% to 70%. If accuracy is improved to 1% (for LiFePO4 batteries 1 mV measurement error translates into 1% SOC error), the battery can be operated now between 11% and 89% of full capacity, with a gain of 8%. With the same battery and a more accurate BMS, automobile mileage per charge is increased.

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