Accurate and robust real-time state estimation is essential to the reliable and safe operation of the hybrid energy storage system. This paper handles a closed-loop method for state-of-charge estimation of lithium-ion battery and ultracapacitor hybrid system. In this work, a fractional-order model is developed to approximate the dynamic behavior of the lithium-ion battery and ultracapacitor. Then, a closed-loop method is proposed for model parameter and state-of-charge estimation. Experiments under dynamic load profiles are used to verify the proposed method. The experimental results indicate that the proposed method can obtain robust estimation results for the hybrid energy storage system, and is appropriate for real-time systems.
Keywords lithium-ion battery, ultracapacitor, fractional order model, state estimation