DC voltage control of grid-connected inverters under imbalanced voltage

In the environment of imbalanced grid voltage the second order harmonic component in the power of the grid-connected inverter makes the DC voltage fluctuated and affects both the stability of DC voltage and the grid-connected power quality. Under the imbalanced grid voltage the dynamic process of the DC voltage of the inverter and the impact of the dynamic process on output DC voltage are analyzed. Under the balanced grid voltage, based on the PQ control model of the inverter a negative sequence control loop is led in, and the superimposed fundamental positive- and negative-sequence voltage control with the DC voltage control improve the control effect of the inverter and make the fluctuation of both DC voltage and grid-connected power smaller, meanwhile the decrease of the capacitor voltage fluctuation at the DC side reduces the third-order harmonic component in the grid-connected current of the inverter. The effectiveness and superiority of the proposed control strategy for grid-connected inverter are validated by simulation results. Using the proposed method, the capability of stable operation of the grid-connected inverter under imbalanced grid voltage can be improved. ©, 2015, Power System Technology Press. All right reserved.