Control strategy of clustered micro‐grids for grid voltage unbalance compensation without communications
Baoquan Liu, Xuguang Zhao, Yan Liu, Yixin Zhu, Jingwen Chen
Abstract
Grid‐connected converters are expected to provide ancillary service utilising their spare capacities during operation. This study proposes a novel control strategy for clustered micro‐grids to compensate voltage‐unbalance of the power grid at the point of common coupling. Every micro‐grid are interfaced to the power grid through a micro‐grid inverter (MGI). All MGIs are designed independently with positive‐sequence (PS) and negative‐sequence (NS) control loops. Every micro‐grid autonomously performs grid synchronisation and mode switching. After grid‐connecting, a dynamic capacity allocation method is proposed for the MGIs to optimise its PS and NS capacity according to the grid voltage unbalance factor. Furthermore, a V–I droop control of the NS control loops is developed, with which each MGI can regulate its NS current according to the NS voltage in a droop manner. With the proposed method, all micro‐grids participate in grid voltage unbalance compensation according to their own potential capacities without communications. Finally, a micro‐grid cluster model with three micro‐grids is built on Matlab/Simulink to validate the proposed control strategy.