A Novel Three-Phase Transformerless H-8 Topology With Reduced Leakage Current for Grid-Tied Solar PV Applications

In this paper, a novel transformerless topology is proposed for three-phase grid-connected applications. The proposed topology has eight switches, and it combines the advantages of both dc-bypass and ac-bypass circuit configurations. The modulation strategy for the proposed topology is based on sinusoidal pulsewidth modulation followed by dedicated logic functions enabling control over the full range of modulation index. Logic functions are responsible for producing gate pulses for the eight switches, which are controlled in such a way that the variation in common-mode voltage (CMV) during inverter operation is low. Low variation in CMV throughout the operation results in reduced leakage current. The topology is capable of limiting the leakage current as per the German standard DIN VDE 0126-1-1. The output voltage of the proposed topology is unipolar, which results in low stress on the output filter inductors and low THD. There are two additional switches in the proposed topology compared to the conventional three-phase topology, but due to the special modulation strategy used, the drop in efficiency is insignificant. Theoretical analysis, simulation, and experimental results are presented to validate the concept of the proposed topology. Results show low variation in CMV and low THD in the output grid current.