Research on design and control of a grid-connected photovoltaic inverter

The grid-connected issue is one of the most importance problem in the photovoltaic generation field. The filter used to connect the grid can be L, CL, LC or LCL four forms according to the different conditions. LCL filter, which can reduce the required filtered inductance and save the cost, is adopted to connect the grid in this paper. This paper firstly introduces a whole scheme of LCL filter design, then analyzes a two-loop control method in detail which uses the capacitor current and grid current as the inner and outer control variable respectively. Detailed discussion about the role of the loops and the influence on the system caused by every parameter of the controller are given out. Finally experimental results verify the correctness of the analysis and availability of the control strategy.