Improvements to State of Charge Estimation Using Smooth Hysteresis Function for Battery Open Circuit Voltage
Michael Knauff, Steve Miller, and Tristan Wolfe (Naval Surface Warfare Center Philadelphia Division)
Many battery chemistries exhibit hysteresis in their open circuit voltage curves. Hysteresis can have a negative impact on state of charge estimation if it is unaccounted for in the estimator. Typically hysteresis is modeled using a discontinuous function that changes states after current reversal. An alternative approach explored in this paper uses a simple smooth dynamic equation to model the hysteresis. The advantage of using a smooth function is that it allows implementation in an extended Kalman filter, which utilizes the Jacobian of the dynamic model of the battery. This paper describes the smooth hysteresis function and its implementation in an extended Kalman filter based state of charge estimator, and presents modeling and simulation results demonstrating the effectiveness of the smooth hysteresis function.