Improvements to the H5 inverter topology for transformer‐less grid‐photovoltaic interface applications

Abstract

Incorporation of transformer in grid-photovoltaic (PV) interfaces makes the systems bulky and expensive, and reduces the system efficiency. Consequently, in recent years, researchers have proposed many transformers-less inverter topologies for grid-PV interface applications. Among them, the H5 topology is one with the simplest structure, least switches, and higher efficiency. However, its ground-leakage current repression property is unsatisfactory due to its asymmetry structure and switch-junction capacitance effects. From the aspect of single-phase transformer-less grid-PV interface applications, this study proposes an improved H5 topology, namely 2D-H5 topology, by incorporating a capacitor divider with a clamp branch consisting of two blocking diodes in the basic H5 structure in order to maintain constant common-mode (CM) voltage. The constant CM voltage will cause no CM (i.e. ground-leakage) current through the stray capacitance between the PV array and the ground. Besides, the proposed topology provides the same differential-mode characteristic as good as in a unipolar modulation full-bridge (H4) inverter for ensuring quality of grid injected power. The proposed topology has been analysed in detail, and verified with satisfactory simulation and experimental results in comparison to the existing transformer-less H5 topology. The proposed improvement enables a reduction in the ground-leakage current in conformity with PV interface standards.