An extended boost three-phase transformerless PV inverter for common-mode leakage current reduction

Abstract

A known issue with transformerless photovoltaic (PV) inverters is the generation of common-mode (CM) ground leakage currents. Single-phase transformerless topologies have been proposed that can achieve CM current suppression, but the relevant concepts do not perform equally well when applied to three-phase topologies. Existing three-phase transformerless topologies also have increased component count and losses, while their modified modulation strategies typically reduce output voltage quality and DC-bus voltage utilization. This article presents a new three-phase PV inverter topology which achieves CM current suppression by incorporating a modification, the addition of a diode, in the boost converter that precedes the three-phase inverter stage. The boost converter switching is coordinated with that of the inverter, which operates based on an adapted modulation strategy that practically eliminates the CM current when the PV array voltage is lower than a certain threshold. For higher PV array voltages, conventional modulation strategies can be applied, which are also shown to reduce the generated CM current by up to 90%. All the above strategies retain a high output voltage/current quality, while the added diode losses have a minor impact of approximately 0.3% on the converter efficiency. The effectiveness of the topology with respect to CM current suppression is demonstrated through simulations in MATLAB/Simulink and experimental results from a comprehensive laboratory setup.

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