A Comparative Analysis of Space-Vector PWM Techniques for Transformerless Three-Phase Voltage Source Inverters

Transformerless inverters have become of special interest of the international scientific community, because of their importance in the energy conversion stage of a photovoltaic (PV) plant. The popularity of this type of inverters, comes from their excellent characteristics like high efficiency, small size, low cost and the reduced weight. However the Common Mode Voltage (CMV) variations arise as an important issue to be solve when the inverter is directly connected to the grid. Those CMV variations can generate high frequency currents through the parasitic capacitance and the ground path, also called Leakage Ground Currents (LGC). These LGC can be an important safety risk for humans in contact with the PV instalation, therefore they should be avoided. In this paper a comparative analysis of Reduced Common Mode Voltage PWM (RCMV-PWM) methods for common mode current reduction in three-phase transformerless PV systems is presented, the RCMVPWM methods considered in this paper are: the Near State PWM (NSPWM), Active Zero State PWM (AZSPWM) and Remote State PWM (RSPWM). Numerical results are given in order to provide information about the main advantages and drawbacks of the analyzed methods.