Active Recovery Control Strategy Under Nonlinear Unbalanced Load with Multiple Micro-source Islanding

Multi-micro-source islanding active restoration is an important measure to protect critical loads and regional power supply under extreme conditions. Load self-organization will cause bus voltage unbalance and frequency fluctuation, in which the nonlinear and unbalanced loads will further aggravate the situation, affecting the safe and stable operation of islanded microgrid active recovery. To address this problem, an unbalanced voltage and frequency fluctuation suppression strategy based on model-free predictive control algorithm is proposed. The strategy outputs the optimal reference power to the sag control in real time according to the load demand. By adjusting the optimal power output, the traditional negative sequence compensation algorithm solves the problem of voltage imbalance and voltage and frequency fluctuation when nonlinear unbalanced loads exist simultaneously at multiple PCC points of islanding active recovery. Finally, the parallel restoration strategy based on the black-start principle is formulated, and the effectiveness of the proposed method is verified by building simulation models under different control modes using simulation software.