Injected Grid Current Quality Improvement for a Voltage-Controlled Grid-Connected Inverter

The injected grid current of the voltage-controlled grid-connected inverter has serious distortion due to the low frequency harmonic components in the output voltage, which is resulted by the dead time of the drive signals of the power switches, and the distortion cannot be eliminated even when an output voltage closed loop is incorporated. This paper introduces a virtual series impedance to increase the output impedance of the grid-connected inverter only at the dominated lower harmonic frequencies; thus, the injected grid current quality can be improved and the dynamic performance of the grid-connected inverter is not deteriorated. Experimental results from a 6-kW single-phase grid-connected inverter confirm the effectiveness of the proposed method.