Adaptive state of energy evaluation for supercapacitor in emergency power system of more-electric aircraft

This paper presents an adaptive state of energy (SOE) evaluation method for a supercapacitor in the emergency power system of a more-electric aircraft. The adaptive SOE evaluation is realized based on a dynamic first-order RC equivalent circuit and its self-adaptive updated parameters. First, a dynamic first-order RC equivalent circuit with three parameters (i.e., the charge/discharge resistance R0, the dynamic self-discharge resistance R1, and the dynamic capacity C1) and a state-space model are introduced for modeling the supercapacitor. Then, an adaptive sliding mode observer is designed for tracking the dynamic change of the three state-space model parameters (i.e., R0, (R0+R1)/R1C1, and 1/R1C1). With this design, the three parameters of the dynamic first-order RC equivalent circuit can be updated adaptively along with the derivation of the three state-space model parameters. Moreover, the adaptive sliding mode observer is redesigned with a sign function, which can enhance the convergence rate of the three self-adaptive updated parameters. Finally, the accurate SOE evaluation would be achieved based on the three self-adaptive updated parameters. Various simulations and experiments are conducted to validate the adaptive SOE evaluation method. It is shown that the adaptive SOE evaluation method can achieve 0.5% of the maximum relative error of the estimated SOE. Compared with the commonly used method, the adaptive SOE evaluation method has over 1% improvement for the SOE estimation accuracy.