Performance Improvement of the Unbalanced Voltage Compensation in Islanded Microgrid Based on Small-Signal Analysis

A low-voltage microgrid is naturally three-phase unbalance due to the connection of unbalanced loads. Voltage unbalance compensation (VUC) strategies of inverters have been proposed to compensate the voltage unbalance on the point of common coupling. However, the small-signal analysis of these VUC strategies has not been investigated in a microgrid with multiple inverters, which is due to the difficulty of the state-space modeling for unbalanced microgrids. This lack of discussion may result in a poor performance of the microgrid when the parameters of VUCs are not well designed. To investigate the dynamic behavior of the unbalanced microgrid with VUC strategies, this article develops a detailed state-space model for an unbalanced microgrid using the dynamic phasor method. Then, based on the developed model, small-signal analysis is carried out to investigate the effect of the VUC control on the dynamic behavior of a microgrid. It is found that a poor design of the VUC controllers may result in the instability of the microgrid. Finally, an improved compensation method with better compensation performance is proposed. Experimental results are used to validate the effectiveness of the proposed method.