Research on the SOC definition and measurement method of batteries used in EVs
MA Youliang, CHEN Quanshi, QI Zhanning(Department of Automotive Engineering, Tsinghua University, State Key Laboratory of Automotive Safety and Energy, Beijing 100084, China)
For the requirement of building up the battery management system of electric vehicles (EVs), the real time measurement and estimation of the state of charge (SOC) of the lead acid batteries are investigated, because the popular SOC definition is unsuitable under the condition of variable current discharge. The reasons of this kind of unsuitability are analyzed, and the characteristics and existing problems of different kinds of SOC measuring methods are compared. On the basis of what mentioned above, some corrections are given to the popular SOC definition, and the conceptions of "calibrated SOC" and "transient SOC" are introduced. The corrected definition of SOC can be suitable for the real time SOC estimation very well under the variable current condition of the batteries used in EVs. Based on the corrected SOC definition, the SOC's measuring method and the computational model are simple, convenient, practicable, and reliable.