An Optimal Nonlinear Fractional Order Virtual Inertia Control Strategy for Islanded Microgrids with Renewables

The large-scale integration of renewable generation into microgrids can lead to decreased inertia, resulting in high rates of change of frequency and frequency instability. This issue is even more complex in islanded MGs that incorporate a high proportion of RGs and need to deliver power to loads in islanded mode. To address this problem, a virtual inertia control scheme can be employed to enhance system inertia and maintain frequency stability. In this article, we propose a novel control strategy named the optimal nonlinear fractional-order PI-based virtual inertia controller, which integrates a nonlinear fractional-order PI controller into the conventional VIC loop. The designed ONFOPI+VI controller, which considers both inertia and damping properties, is optimized using the Coot optimization algorithm. Furthermore, an alternative control methodology, denoted as OFOPI+VI, has been developed to analyze and evaluate the outcomes obtained from the proposed ONFOPI+VI control structure. This paper compares the performance of the proposed ONFOPI+VI strategy to that of the OFOPI+VI and other VIC techniques for different RG and load variations under various scenarios. Simulation results and detailed analyses confirmed that the ONFOPI+VI controller significantly outperformed conventional methods, yielding at least a 30% improvement in IAE and a 20% improvement in ITAE compared to other control techniques.