Modified Quasi-Z-Source Inverter with Model Predictive Control for Constant Common-Mode Voltage

The common-mode voltage (CMV) of transformerless inverters in photovoltaic system should be properly addressed. The conventional CMV reduction methods for voltage source inverters should be modified when applied to the quasi-Z-source inverters with shoot-through states. The shoot-through states in a quasi-Z-source inverter may lead to high-frequency harmonics in the CMV, thus inducing severe leakage currents. Hence, this paper analyzes the CMV in the quasi-Z-source inverter. More importantly, a modified quasi-Z-source inverter that can achieve a constant CMV through model predictive control is discussed. Furthermore, redundant switching vectors are added to reduce the computation burden when the model predictive control is adopted. Simulations are presented to validate the CMV reduction methods.