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Three-state three-phase Z-source inverter for transformerless photovoltaic systems

In this paper a modified Z-source inverter capable of reducing the leakage current in three-phase transformerless photovoltaic systems is proposed. The topology, based on the three-switch three-state single-phase Z-source inverter, only requires one additional switch when compared with the original three-phase Z-source inverter. In order to understand the operation principle of the proposed inverter, the three-switch three-state single-phase Z-source inverter is reviewed and its derivation to a three-phase system is carefully described. Furthermore, a guideline to design the switches, inductors and capacitors of the topology is presented. The main features of the proposed system are the low voltage stress across the switches and its dual grounding (the neutral point of the load and the negative point of the photovoltaic array are grounded), leading to higher efficiencies and lower leakage currents when compared with the conventional Z-source inverter. Simulation and efficiency results for the three-phase transformerless photovoltaic system are presented to validate the theoretical models.