Adaptive repetitive control with feedforward scheme for grid-connected inverters

This study is concerned with control of grid connected inverters using odd-harmonic repetitive scheme. Owing to the inherent long convergence period of repetitive control, a feedforward loop of the fundamental component of the grid voltage is used to make sure that the inverter´s output current is bounded during the convergence period. The well-known deficiency of repetitive control in rejecting harmonics when used with varying grid frequency has been solved by using an adaptive scheme in which the switching and sampling frequencies vary with respect to the grid frequency. The main qualities of the proposed controller are its effectiveness, simplicity and straightforwardness of implementation using a digital signal processor. Simulation and practical results are presented to demonstrate the controller capabilities.