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A Low-Loss Grid Decoupling Mechanism in a Transformerless Single-Phase Interfacing Inverter

To alleviate harmonic interaction between the interfacing inverter and the grid, the impedance reshaping of the inverter or the equivalent grid impedance is preferred. This paper proposes a grid decoupling mechanism to meet the Nyquist stability criterion in a transformerless photovoltaic (PV) single-phase grid-connected voltage source inverter. The decoupling mechanism is composed of dual unit point-of-common-coupling (PCC) voltage feedforwards, in which one is inserted into the inverter control, and the other generates voltage regulation of an additional bidirectional voltage-source converter (B-VSC) in series with the capacitors of LCL filter. To avoid leakage current due to stray capacitances between PV panels and the earth, the input of the B-VSC is connected to the dc bus of the inverter and supplied with lower voltage than 50V. As the volt-ampere (VA) rating of the B-VSC is minor, the system efficiency is not sacrificed. Simulation and experimental results show the effectiveness of the proposed system. The proposed inverter prototype has been built to validate the effectiveness of the proposed method.