Common Mode Voltage Reduction in a Single-Phase Quasi Z-Source Inverter for Transformerless Grid-Connected Solar PV Applications

The quasi-Z-source inverter (qZSI) is becoming a popular inverter topology that can buck or boost input voltage without a dc-dc converter and hence can be used in transformerless configuration. Due to its single-stage conversion, the qZSI can be used as an efficient transformerless grid-tie inverter. However, the common mode current is a major problem in transformerless topologies due to the absence of galvanic isolation. This paper proposes a modified pulsewidth modulation (PWM) technique to control the qZSI, along with two extra semiconductor switches, to reduce the common mode current. The proposed method offers an efficient solution for grid integration of solar photovoltaic systems. The proposed topology has the following features: 1) uses phase-leg shoot-through for boosting the dc voltage to the required level which eliminates the additional dc-dc converter; 2) eliminates the PWM deadtime and provides freewheeling through additionally connected switches; 3) minimizes the common mode current by modifying the PWM and adding additional switches at the output side of inverter; and 4) avoids the conduction of body diode of H-bridge which has poor reverse recovery characteristics. The proposed topology can efficiently control the reactive power, and the suitable PWM scheme is also reported. Simulation results have been performed with the Standard Test conditions of the photovoltaic panel. Experimental results for a single-phase 500-W prototype are presented to validate the proposed PWM scheme for the qZSI topology.