Research On Control Strategy For Double-mode Inverter

The utility interface inverter with the function of grid-connected mode and stand-alone mode is needed in renewable energy and distributed generation system. Characteristics and control strategies of the double-mode inverter have been researched in the paper, including the injection current control and mode transfer control.Firstly, the direct current control strategy for grid-connected mode is studied. Grid voltage feedback control is used to prevent high DC voltage of the input when the inverter is starting. A 1kVA single phase full bridge has been implemented to verify the analysis. In order to improve the high order harmonics, LCL filter is discussed in the paper, design guideline of the filter is also given.Secondly, in order to keep a smooth voltage profile across the critical load for the transition between grid-connected mode and stand-alone mode, a control strategy comprising the islanding detection algorithm and the seamless transition algorithm is proposed.Thirdly, a novel indirect current control algorithm for double-mode inverter has been proposed to improve the seamless transition algorithm, which can control the output voltage of the inverter both in grid-connected mode and stand-alone mode. Simulation results and experiment results are provided to validate the algorithm.