Effects of open-circuit voltage tests and models on state-of-charge estimation for batteries in highly variable temperature environments: Study case nano-satellites

Nano-satellites are a rapidly developing field of the space industry. Their structure and environmental conditions impose requirements for their functioning and reliability. One of key systems to keep nano-satellites in operation is the energy storage, often in a form of batteries, which supplies power, when there is not enough generation from solar panels. Thus, it is desirable to monitor the battery states, such as the state-of-charge (SOC). This topic was investigated in connection to other applications as electric vehicles or stationary storage; however, their working conditions are different from nano-satellites’. We propose a SOC estimation method, which takes into account these conditions, especially wide and rapidly changing temperature. The SOC is estimated through an unscented Kalman filter (UKF), which uses open-circuit voltage as pseudo-measurement, obtained from an online parameter identification method. Furthermore, to achieve a high accuracy SOC estimation, various open-circuit voltage models and characterization test procedures were evaluated. Finally, the SOC root mean square error of 0.53% was reached for a rapid temperature varying nano-satellite mission profile with thermal gradient of 22.4°C/hour by using an extended Kalman filter for online parameter identification and UKF for SOC estimation, based on the analytical OCV model characterized from quasi open-circuit voltage test.