Enhancing Dynamic Performance of Islanded Microgrids by Fractional-Order Derivative Droop

Islanded operation of microgrids (MGs) with parallel-operated inverters imposes many control challenges in terms of stability and dynamic behavior, especially at contingency events. Hence, improving the dynamic performance and the stability margin is essential for robust MG operation. Therefore, the fractional-order derivative (FOD) droop controller is proposed to achieve these goals. A detailed small signal model is developed for the entire MG with the proposed controller and then used to assess the stability of the MG. The FOD and the integer-order derivative (IOD) droop controllers are applied to a benchmark MG and tuned via an optimization procedure under multiple loading conditions. The results show that the extra degrees of freedom introduced by the FOD droop facilitate pushing the dominant modes toward the required stability region. The proposed FOD droop is compared to the IOD droop, conventional droop, VOC, and virtual synchronous generator controllers under several contingency events and a reconfiguration scenario using MATLAB/SIMULINK, where the proposed controller shows superior performance. The experimental validations demonstrate the improved power-sharing performance of the proposed FOD droop controller.