Control of Grid - Connected Inverters with Nonlinear Inductors in Output LCL Filter

In grid-connected distributed energy resources (DERs), DC current of DERs is injected to a grid via a power processing unit. Function of this unit is to convert the input DC current to an AC current with acceptable specifications to the grid constraints. Performance of these systems is directly depended on their control systems methods. Recently introduced PR controllers are well suited for grid connected inverters due to their outstanding capability of tracking and disturbance rejection. In this paper, performance of these controllers on grid-connected inverters is studied, while the inductors of the output LCL filter have nonlinear behavior. By using a mixed feedback method, the apparent undesirable nonlinearity of inductors is used on the opposite direction to enhance the system performance. A 7kW inverter system performance is simulated and the results verify the designations.