A Novel Transformerless Inverter Topology Without Zero-Crossing Distortion

Abstract

The elimination of the transformer in solar photovoltaic inverters has reduced the size, the weight and the losses in the system.  On the other hand, the galvanic connection between the DC source and the grid generates leakage current through the earth parasitic capacitance. The leakage current depends on both the inverter topology and the control strategy. Among the existing inverters is the Highly Efficient and Reliable Inverter Concept (HERIC) topology that has low leakage current level and high efficiency. However, this topology suffers from low frequency harmonics and current zero crossings distortions. To eliminate these harmonics and distortions, a new transformerless inverter is proposed.   The design is a conventional full bridge inverter with an extra AC bypass.  The bypass branch disconnects the inverter from the grid during the freewheeling period.  Simulation results indicate that the zero crossings distortions are totally eliminated and that the low frequency harmonics are significantly reduced as a result of the appropriate applied control.  Moreover, losses analysis of the proposed design yields an efficiency of up to 94.14% and shows that the topology meets relevant standards.