Robust optimization based harmonic mitigation method in islanded microgrids

Power quality issues in islanded microgrids comprising of various renewable energy sources have recently gained more attention. As the harmonic mitigation capability from distributed energy resources will vary for different network topologies, this paper introduces a unified single-end harmonic mitigation approach using a robust optimization model. In the proposed method, a central controller receives voltage harmonic distortion measurements of all buses in the microgrid, optimizes the global information, and then sends back the optimal voltage harmonic components to the local controller of each distributed generation units, which is added to the voltage reference generated by the respective droop controllers locally. The robustness lies in the design of the objective function in the central controller to solve a multi-attribute optimization problem in minimizing both the average total harmonic distortion (THD) and THD of the critical bus in the microgrid considering different coefficients for each term. It has been proved with a set of numerical simulations with different parameters that the search space is reduced around the global minima, which considerably reduces the search time and the number of iterations. The results show that the suggested controller is robust and effective with respect to the different coefficients of the modified objective function to mitigate voltage harmonic distortion in islanded microgrids.