A high performance grid interfacing power conversion system for renewable power generation applications

Grid interfacing power conversion unit, connecting the renewable energy and utility grid, is a key section of the renewable power generation system, and quality of the generated power passed on to the utility grid greatly relies on the performance of the interfacing unit. In order to suppress the interfacing unit output current harmonics around integral multiple switching frequency more effectively, LCL filter is introduced to substitute the traditional L filter. However, LCL filter, a third-order system, may cause the control system unstable. For this, in the grid interfacing power conversion system, an additional capacitor current closed-loop is added to the conventional dual closed-loop scheme, where the capacitor current feedback signal is obtained through estimation. The system stability is ensured with no more additional sensors, at the same time both the filtering performance and system efficiency are increased compared with the traditional passive damping method. In addition, the design procedure of the output filter and the grid synchronization are specified. Effectiveness and feasibility of the grid interfacing power conversion system are verified by both the simulation and experimental results.