A three-phase transformerless Boost inverter for the reduction of common-mode leakage current in photovoltaic applications

Abstract

Three-phase transformerless photovoltaic (PV) inverters with PV voltage step-up capability are widely used for integrating PV generation to the electric grid. A known issue with transformerless topologies is the generation of common-mode (CM) ground leakage currents. Several inverter topologies and modulation strategies have been proposed to suppress the CM currents below the limits set by relative standards. The proposed inverter topologies commonly have increased component count and lower efficiency than conventional three-phase inverters, while their modified modulation strategies commonly result in lower output voltage quality and DC-bus voltage utilization. This paper presents a new three-phase Boost PV inverter topology which achieves CM leakage current suppression by modifying the Boost converter instead of the three-phase inverter stage. The topology is formed simply with the addition of one diode in the Boost stage. The added diode losses have a minor effect on the overall conversion efficiency, while the inverter can be modulated with conventional modulation strategies, thus retaining a high output voltage/current quality. The structure and operating principle of the proposed topology are presented, and its effectiveness with respect to CM current suppression is demonstrated through simulation results in MATLAB/Simulink.