A Novel DC Current Injection Suppression Method for Three-Phase Grid-Connected Inverter without the Isolation Transformer
Abstract-Grid-connected inverters without isolation transformer usually have certain amount of dc component injected to the ac grid due to current sensor error,tolerance of power switching device, asymmetry of PWM gating driving pulses etc. Many efforts, such as using blocking capacitor, current dc component feedback control and voltage dc component feedback control have been introduced to try to suppress the dc injection to the grid.This paper proposes a novel control strategy of suppressing dc current injection to the grid for three-phase inverter by accurately sensing the DC component of line voltages of three-phase inverter and adding a DC component control loop. DC suppression control scheme is presented. The suppression performance of the proposed DC rejection method is evaluated and compared with the traditional method. Finally, the control scheme is verified on a 20kW three-phase grid-connected inverter.
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