A battery model including hysteresis for State-of-Charge estimation in Ni-MH battery

According to the measurement of the Ni-MH battery electrochemical impedance spectroscopy (EIS) and the relationship of the OCV-SOC , one basic equivalent-circuit model structure including hysteresis voltage for Ni-MH battery is presented, which can be applied for the estimation of battery state of charge (SOC). The model approach is evaluated by comparing the measured and the simulated battery voltage corresponding to several current profiles. Voltage hysteresis is shown to play a critical role in the Ni-MH battery model. Then the relationships among different physic variables and states variables of this model are expressed by the discrete-time state-space functions. Based on the Extended Kalman Filter, the Stare of Charge (SOC) for the Ni-MH battery model is estimated by using the date such as current and voltage which are real-time tested by the battery test instrument. Finally, the behavior of the algorithm in terms of accuracy is examined. Voltage hysteresis is shown to play a critical role, and this effect makes determining the SOC particularly difficult for Ni-MH batteries relative to other battery systems.