Controls of hybrid energy storage systems in microgrids: Critical review, case study and future trends

Abstract

In a microgrid, a hybrid energy storage system (HESS) consisting of a high energy density energy storage and high power density energy storage is employed to suppress the power fluctuation, ensure power balance and improve power quality. Since the HESS integrates energy storage with slow and fast dynamic characteristics, the control system design is a challenge. The objective of this article is to critically analyze and compare the control methods of the HESS in microgrid as well as to identify the shortcomings of the existing control methods. The control strategies in the HESS can be divided into three types: centralized, decentralized and distributed. In each type, a variety of the latest control systems are discussed and studied. In addition, this article investigates the impact of time delay caused by communication system on centralized and distributed controllers in the HESS. This article also presents a novel droop coordinated control method in a case study, which is used to verify the feasibility of the simplification and multi-function of the controller. Based on the literature reviews and case study, the insights on the future development trend of the control strategy in the HESS, including the simplification of the comprehensive multi-function controller, compensation of the time delay, improvement of the control accuracy, automatic tracking of the dynamic performance of the load and the combination of the multiple energy storage, are elaborated.