Self-Disciplined Large Signal Stabilizer Design for Hybrid Energy Storage System in Renewable DC Power Systems

Due to the different characteristics of energy storages (ESs), proper dynamic power allocation to ESs in a hybrid energy storage system (HESS) is of high significance. To this end, integral droop (ID) controllers have been applied to a class of ESs (denoted as ES_Hs) with high ramp rates but low energy density. Conventional V-P droops have been adopted to regulate a class of ESs (referred to as ES_Ls) with high energy density but limited response speeds. Based on the cooperation of IDs and V-P droops, high/low frequency components of the load change can be autonomously responded to by ES_Hs/ES_Ls, thus possibly prolonging the HESS lifetime. However, existing works only focus on the small signal stabilization of HESSs, whose validity may only hold under certain equilibria. To address this issue, an original self-disciplined large signal stabilizing scheme is presented in this paper. Under this scheme, a compound stabilizer comprising disturbance observers and a backstepping controller is delicately designed for an ES-interfaced converter. The observers estimate the possible disturbances induced in the converter. Those estimations would be further neutralized by the backstepping controller, which simultaneously guarantees converter system stability in the large signal sense and drives the converter terminal voltage tracking the reference given by either the ID or V-P droop. Because of the proposed stabilizer, no communication happens in HESS, and the large signal stability of overall system can be spontaneously realized with rigorous mathematical proofs by Lyapunov techniques. This stabilizing scheme for HESS application is arguably reported for the first time in this article. A detailed parameter selection guideline is also provided. The effectiveness and feasibility of the compound stabilizer are verified by both simulations and hardware experiments.