Comparative Assessment of Three-Phase Transformerless Grid-Connected Solar Inverters

Solar energy is a promising alternative energy source for a sustainable pollution-free future. Due to the requirements of high efficiency, reliability, power density and low cost, transformerless PV inverters can be utilized in a grid-connected solar energy system. However, this suffers from no galvanic isolation and leakage currents through the stray capacitances between the PV array and the ground which results in some degradation of the system's performance as well as safety issues. This paper performs a comprehensive review and comparison of the performance of different 3-phase inverter topologies combined with different pulse width modulation (PWM) schemes in transformerless PV systems. Moreover, a modified discontinuous PWM technique was proposed for an H8 inverter to reduce leakage currents in this paper. The analysis was carried out for 50 kW PV inverters. The key performance of each inverter topology such as common mode voltages (CMVs), leakage currents, current harmonics and efficiency are holistically evaluated by using simulation results. Also, the merits and demerits of each system are highlighted.