Battery Internal Resistance Estimation Using a Battery Balancing System Based on Switched Capacitors

Battery management systems (BMSs) are key components in battery storage systems in order to guarantee their safe operation and improve their performance, reliability, and efficiency. BMSs monitor critical parameters in the battery as state of charge (SOC), state of health (SOH), or temperature. Direct measure of SOC or SOH is not possible, while temperature, on the other hand, can be measured with different types of sensors. These sensors, although cost-effective, raise concerns regarding cabling, signal conditioning and acquisition systems, increasing cost, complexity, and decreasing reliability. The internal resistor of the battery has already been successfully used to estimate these parameters. BMS can also include the function of balancing (equalizing) cells of a battery pack. Among all available equalizing systems, those based on switched capacitors are interesting due to their simplicity and easy scalability. This article proposes an internal resistance (IR) estimation method for LiFePO
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batteries using signals naturally produced by a switched-capacitor equalizer (SCE). The IR will be used to estimate the battery temperature. It will be shown that the method can operate online and without interfering with the regular operation of the SCE.