A voltage unbalance compensation strategy based on virtual impedance for DGs in island microgrid without sequence component separation

Abstract The increasing application of unbalanced loads may cause power quality issues in microgrid. In this paper, a voltage unbalance compensation strategy for distributed generators (DGs) in island microgrid is proposed to compensate the unbalanced bus voltage and improve the distribution effect of load current. The control system of the DGs mainly consists of active and reactive power droop controllers, a virtual impedance loop, voltage controllers. As the proposed voltage controller has two well decoupled control branches to independently control fundamental positive and negative sequence voltages, sequence component detection is not necessary for the implementation of virtual impedance. Then the positive sequence virtual impedance can be introduced to improve the power distribution effect of the DGs, and the negative sequence virtual impedance is introduced to compensate the voltage drop of the negative sequence current on the line impedance and to reduce the negative sequence circulating current. The design approach of the control system is discussed in detail. Finally, the validity and effectiveness of the proposed method are verified by simulation and experimental results.