Performance enhancement & control of renewable energy sources inverters

Over the last few years, load growth, environmental issues and the increasing importance of declining energy costs have brought about a vast change in the focus of more and efficient use of renewable energy resources. In grid-connected renewable energy sources (RESs), the DC current of RES is injected to the grid by power processing interfaces after it has been converted to the AC current acceptable by the grid constraints. The functionality of these systems is directly related to their controlling structure. In this paper, the performance of proportional resonant controllers on grid-connected inverters is studied while the inductors of the output LCL filter show nonlinear behavior. By using a combinational feedback method, the apparent undesirable nonlinearity of inductors is used in the opposite direction to enhance the system performance, which not only leads to better technical characteristics but also improves the efficiency. Using a Luenberger observer also helps to reduce one of the current sensors per phase, needed for the proposed controlling structure. A 7kW inverter system performance is simulated and the results verify the designations.