SOC definition and estimation for EV Li-ion batteries

The main problems of existing SOC (state of charge) definition methods were analyzed, the concept of maximum available capacity was proposed based on the open circuit voltage (OCV) of a battery, and the battery SOC was redefined, thus the decoupling of a battery's charge/discharge capacity and work condition was realized. Through updating the maximum available capacity of a battery, the effect of aging on the SOC estimation accuracy was avoided. By converting the internal resistance voltage drop and the polarization voltage into the loss of discharge capacity, a method for calculating the actual available capacity of a battery or a battery pack was achieved, and its validity and feasibility were verified.