Battery internal resistance estimation using a battery balancing system based on switched capacitors

Battery Management Systems (BMS) are key components in battery storage systems in order to guarantee their safe operation and improve their performance, reliability and efficiency. BMS monitor critical parameters in the battery as state-of-charge (SOC), state-of-health (SOH) or temperature. Direct measurement of these parameters is either impossible (e.g. SOC or SOH) or costly and unreliable (e.g. temperature), so they are often estimated. 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, making them a research focus for several years. This paper proposes an internal resistance (IR) estimation method for LiFePO4 batteries using signals naturally produced by a switched capacitor equalizer (SCE). The method operates online and without interfering with the regular operation of the equalizer.¹