State of charge estimation for a Li-ion driving battery

For state of charge (SOC) estimation of a hybrid electric vehicle's (HEV) 8Ah Li-ion Battery, a Map model of the battery's stable state characteristics was built and then emulated. Significant parameters for the battery SOC estimation, including voltage, current, temperature, and so on, were chosen. Many tests, including high charge rate, discharge, and open circuit voltage (OCV)-SOC were systematically carried out. By using interpolation and fitting, any missing data was added in and then the battery's estimated stable-state SOC Map model was built. In view of temperature influences on the SOC, a temperature coefficient was advanced to modify the SOC. In order to effectively apply the algorithm, measures were taken to compress the data and accelerate the query rate. Emulations and modifications of the Li-ion battery were done, and the results indicate that estimations of SOC using this Map model yield SOC estimation errors within ± 4%.