Robust Voltage Control for Harmonic Suppression in Islanded Microgrids Using Compensated Disturbance Observer

In low voltage (LV) islanded microgrids, practical issues such as nonlinear and unbalanced loads, unmodeled dynamics, and parameter uncertainties can cause high harmonic distortions, or even instability. To harness these problems, it is proposed in this paper to model the deviations of the voltage of the point of common coupling as an unmeasurable pseudo-disturbance. Based on this strategy, a compensated disturbance observer (CDOB) is then proposed to suppress harmonics. The CDOB enhances the merits of conventional disturbance observer in a novel structure. It improves the robustness, stability, and dynamical response. The controller is applied on an LV microgrid consisting of multiple distributed energy resources feeding local and common loads, through feeder lines with notable impedances. Comparative simulations and experiments are conducted to illustrate the performance of the presented approach.