Identification and Fast Measurement Method of Open-circuit Voltage

Abstract

Accurate measurement of the open-circuit voltage (OCV) promotes state of charge (SOC) accuracy. In this study, three transformation methods are employed to make the OCV identifiable, and factors affecting the accuracy of OCV identification are investigated. Furthermore, a fast OCV measurement method is proposed. The results show that the forward difference transformation and the adaptive differential evolution algorithm are more suitable for OCV identification. The accuracy of OCV identification is affected by pulse characteristics, sampling frequency, C-rate, and resting time between pulses. Positive-negative (PN) pulses of equal amplitude are more suitable for OCV identification than hybrid pulse power characteristics. A method for fast OCV measurement is developed based on the relationship between the identification error of the OCV and the number of PN pulses. A total of 57 PN pulses with an amplitude of 2 C are used to realize accurate OCV identification at various charge/discharge states, C-rate, and SOC, with an average error of −0.03% (about 1 mV). The proposed method only needs to obtain the battery voltage and current to achieve a fast measurement of OCV, which also serves as a foundation for an accurate estimation of the battery state.