A modified Z-source inverter topology for stable operation of transformerless photovoltaic systems with reduced leakage currents

Three-phase Z-source inverters are an interesting solution for connecting transformerless photovoltaic systems to the grid, due to its boost characteristic. Nevertheless, the traditional topology and its pulse-width modulation techniques generate undesired leakage currents in transformerless systems. Moreover, a recent study showed that, under certain conditions, the Z-source inverter presents stability issues. Therefore, this paper proposes a modified Z-source inverter topology and a particular pulse-width modulation that allow the three-phase Z-source inverter transformerless photovoltaic system to operate always in the stability range with very low leakage currents. A comparative study between the proposed system and the traditional dc-dc boost converter cascaded with a voltage source inverter is carried out, in order to highlight the major features of both solutions. Furthermore, simulation results of the three-phase proposed Z-source inverter topology connected to a RL load are obtained to validate the theoretical models.