H-Bridge zero-voltage switch-controlled rectifier transformerless midpoint-clamped inverter for photovoltaic applications

A single-phase transformerless midpoint clamped H-bridge zero-voltage switch-controlled rectifier inverter topology is proposed in this article for photovoltaic (PV) systems to address the issue of common-mode (CM) voltage and leakage currents. Apart from the full H-bridge inverter, the proposed voltage clamping circuit consists of two switches and a full-bridge diode which clamps the ac terminal to the dc midpoint (consisting of two dc-link capacitors) during the freewheeling period. As a result, the CM voltage is held constant, which makes it suitable for the grid-connected PV system. The operating principle and CM effect of the proposed topology are analyzed and compared with the conventional topologies. This is followed by the thermal analysis and loss calculation, which shows that the proposed circuit is more efficient over the conventional topologies. Validation is carried out using MATLAB-Simulink using the PLECS toolbox followed by a scale down prototype of 1.5 kW. It is shown that the proposed inverter has the 98% ± 1% efficiency over a wide range of loads with a peak efficiency of 98.96%, and the total harmonic distortion of the output current relatively low (≤1.8%). The leakage current ( i {\mathrm {cm}} ) is measured for different values of parasitic capacitance that reaches a maximum of 16.65 mA for 330-nF capacitor under consideration, which is well below the limit set by different safety standards.