Evaluation of repetitive control for power quality improvement of distributed generation

Small-scale distributed generation (DG) is often not a natural 50 or 60 Hz AC source and so employs an inverter for the interface to the utility grid. Here, repetitive control is examined as a means of also using a DG inverter to improve the distortion of a local grid where a large proportion of the load is nonlinear. The proposed controller can offer better waveform quality in balanced and unbalanced conditions than PI controllers in either stationary or rotating reference frames. The inverter also requires a control loop to regulate the exported power. A decoupled P and Q controller is applied and compared to a traditional amplitude and angle controller. The controllers are tested for disturbance rejection of variations in grid voltage, DC-link voltage and load power.