A Real-time Circuit Topology for Battery Impedance Monitoring

All batteries suffer from irreversible electrochemical changes as a result of their continuous operation. Deep depths of discharge and/or high discharge currents will inherently result in a reduction of performance over time. To track a battery lifetime, or state of health (SoH) requires an extension from the common internal resistance model and must be regularly assessed. To track SoH, an intelligent battery management system can be deployed to track the drift in usable capacity, but without a minimal impedance model, the impulse response and runtime cannot be accurately depicted. Electrochemical impedance spectroscopy (EIS) has proved to be an effective tool to extract the signature equivalent circuit associated with a single battery module or cell. Unfortunately, implementation at low cost has remained a challenge. In this paper, the circuit topology for a stand-alone EIS measurement board is proposed in an effort to reduce cost and complexity. The challenges and design considerations in developing a real-time EIS board is discussed. The circuit topology is then verified through a simulation environment under low (1 Hz), medium (1 kHz), and high frequency (100 kHz) test cases.