Integrated On-line EIS Measurement Scheme Utilizing Flying Capacitor Equalizer for Series Battery String

In the electric vehicle and the battery energy storage systems, hundreds of battery cells are connected in series to reach the voltage requirement. Since the battery degradation can be assessed by the change in battery impedance, online impedance spectroscopy for individual cell are required. While conventional methods require an extra circuitry increasing the system cost, this paper proposes an online electro-chemical impedance spectroscopy (EIS) scheme that can be easily integrated into the switch-matrix flying capacitor equalizer. The real-time simulation shows that the measurement error within 5% is achieved for cell impedance by the measuring circuit seamlessly integrated into the series equalizer.