Design and Control for Three-phase Grid-connected Photovoltaic Inverter with LCL Filter

As the traditional resources have become rare, photovoltaic generation is developing quickly. The grid-connected issue is one of the most importance problem in this field. The voltage source inverter usually uses LC or LCL as the filter. LCL filter, which can reduce the required filtered inductance and save the cost, is adopted to connect the grid in this paper. However, reasonable design of LCL filter needs consideration in order to achieve optimal effect. Meanwhile, systems with LCL filter need more complex control strategies. 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.