State of charge estimate for super-capacitor based on sliding mode observer

Abstract

Super-capacitor with the features of high power density and long life is used as a new kind of energy storage methods for electric bus. State of charge (SOC) indicates the remaining power, which is very important for super-capacitor bus. In this paper, a SOC estimate method based on sliding mode observer is studied. The design of sliding mode observer is based on the “two-branch” equivalent circuit super-capacitor model. The parameter identification of the “two-branch” super- capacitor model is also studied. The charge and discharge experiment is implemented on a super-capacitor test instrument. The sliding mode observer method is compared with ampere hour method; the result shows that the precision of the sliding mode observer method is almost the same with ampere hour method so as to complete the super capacitor SOC estimation with high accuracy.