A modular multilevel converter-based grid-tied battery-supercapacitor hybrid energy storage system with decoupled power control

This paper presents a modular multilevel converter (MMC)-based grid-tied batter-supercapacitor hybrid energy storage system (HESS), which can mitigate the active power fluctuation caused by intermittent renewable generation and also realize reactive power compensation as required by voltage regulation. The proposed HESS is novel in that batteries and supercapacitors are distributed into the upper arm and the low arm of the MMC, respectively, and it is therefore possible to design fully decoupled real power and reactive power control and simultaneously optimize the performances of batteries and supercapacitors. The system modeling and operational principles of the MMC are first presented in this paper. Based on these analysis, the power decoupling control between the upper arm and the lower arm is discussed in detail. Moreover, the state-of-charge balancing control strategy for batteries and the voltage balancing control strategy for supercapacitors are presented also, which are the vital elements for implementing the proposed decoupled active and reactive power control. Finally, the proposed HESS and its control strategies have been verified by MATLAB/Simulink simulations and experimental results.