Modeling and analysis of battery hysteresis effects

Battery state estimation is an essential step in providing an optimal management system for the battery. With an accurate relaxation-effect model, the battery's open circuit voltage (VOC) can be obtained from direct measurements of the terminal voltage and load current. The battery's state-of-charge (SOC), thereby, can be accurately estimated if a precise model for the VOC-SOC relationship with hysteresis effect is considered. This paper proposes a novel battery hysteresis effect dynamics model that provides a compact and accurate description of a family of the battery VOC-SOC trajectories over a large operating range and charging/discharging control strategies such as those used in Plug-in Hybrid Electric Vehicles (PHEVs). The battery hysteresis loops are modeled as responses to a Linear Time-Invariant (LTI) four-state system with various initial conditions. Experimental validations demonstrate that the proposed model can provide accurate descriptions of the battery hysteresis loops. The proposed hysteresis effect modeling method can be used as the basis for the VOC-based battery SOC estimation.