Selective frequency synchronization technique for fast grid connection of islanded microgrid using prediction method

Abstract

In this paper, a novel frequency synchronization method is proposed for fast connection the islanded microgrid to the existing grid. In the conventional frequency synchronization method, the output of the synchronization controller is limited to maintain the voltage quality of the islanded microgrid. Due to this limitation of the output, the micro grid voltage has a nonlinear characteristic during the synchronization process. Conventional methods that do not consider the nonlinear characteristic have a drawback in that the synchronization speed can be slowed depending on the convergence direction of the frequency. To overcome the drawback, the nonlinear characteristic of the conventional method is analysed during the synchronization process. Based on the analysis, the synchronization speed is predicted according to the synchronization direction of the microgrid voltage. Using this prediction, a novel synchronization technique that finds a relatively fast synchronization direction is proposed. A 2MVA microgrid system is constructed using a real-time hardware-in-loop system and experimental results are presented to verify the validity of the proposed method. From experimental results, it is confirmed that the proposed method guarantees a faster synchronization speed than the conventional method.