Voltage Control Strategy of Islanded Three-Phase Voltage Source Converter Under Unbalanced Loads Based on Disturbance Observer

Ensuring symmetrical of three-phase inverter output voltage is one of the most vital user requirements. However, the unbalanced loads will lead to the inverter output voltage imbalance using traditional PI control. The mechanism of three-phase output voltage distortion under unbalanced loads is analyzed based on the symmetrical component method first. Then a disturbance observer has been built to obtain the residual signal of the system. To compensate the effect of distortion caused by unbalanced loads, it is proposed to add compensation voltage signal and compensation current signal respectively to traditional voltage and current dual closed-loop control. The feedforward voltage control strategy is proposed which can eliminate the influence of unbalanced loads by removing 2 times power frequency fluctuation in dq coordinate. Simulink results demonstrate the effectiveness of the proposed control strategy using Matlab/Simulink.