Decentralised primary and secondary control strategies for islanded microgrids considering energy storage systems characteristics

Abstract

One of the main subjects of Microgrid (MG) islanded operation is its stability. Using the Energy Storage Systems (ESSs) in MGs, the stability can be improved. To ensure the proper operation of the ESSs, their State of Charge (SoC) should be monitored and controlled. In this paper, a new decentralized control method based on the conventional droop method is proposed which considers different types of ESSs used in islanded MG, i.e. ESSs with high power density and high energy density. In the proposed method, the ESS units are divided into two main categories. The master ESS is the main primary frequency control unit and the other ESSs respond to active and reactive power variations of the load and participate in the secondary control of frequency. For each of these categories, a new control method is proposed. The proposed method, including the primary and secondary control, is decentralized, and based on local measurements. Moreover, in the proposed method, a SoC equalization of ESSs is considered. To assess the stability of the MG, a small signal stability model is developed. Three scenarios are simulated to verify the effectiveness of the proposed method in MG frequency control and ESSs SoC balancing.