A study on the inflence of two OCV tests on state of charge estimation of lithium ion battery

Lithium ion batteries have been widely applied in electric vehicles (EVs), thousands of batteries connected in series or parallel to drive the EVs, so, it is necessary to monitor the states of lithium ion batterie, especially the state of charge (SoC). The open circuit voltage (OCV) is essential for SoC estimation and often predetermined by offline OCV test data. In this paper, the incremental OCV test method and low-current OCV test method are introduced and compared at three temperatures. In addition, a joint estimation method is proposed to update the parameter and state in real-time. The experiments are conducted on LiFePO
₄
cells. The experimental results show that the incremental OCV test is reliable and suitable to determine the OCV-SoC relationship than the low-current OCV test.