To meet the rising energy needs of the world, the participation of renewable energy sources (RESs) in the power system has been boosted exponentially, primarily due to environmental issues. Islanded operation of power grids as microgrids (MGs) is more common now. Although this has several advantages, the diminished inertia constant has emerged as one of the serious consequences of high penetration level of RESs and islanded operations, which worsens the frequency stability with a higher value of rate of change of frequency (RoCoF). To address this issue, this article proposes a modified form of internal model control (IMC)-based virtual inertia (VI) control, which provides the necessary VI power in low inertia MG, regulates the system's frequency deviation and prevents system instability. The proposed controller has been optimally designed through the grey wolf optimizer (GWO) algorithm with integral time absolute error (ITAE) as the cost function. To demonstrate the effectiveness of the proposed controller, a comparative analysis with existing methods, such as a conventional VI controller, VI emulator based on model-predictive controller, MATLAB-based IMC tuning algorithm for proportional-integral (PI) and proportional-integral-derivative (PID) controller is given under different disturbance and operating conditions. Compared with the conventional VI control method, the frequency deviation has been reduced by almost 80.91% when using the proposed method, for normal operating conditions of system inertia and load damping. Similarly, 79.13% and 73.93% have been reduced in frequency deviation for medium and low operating conditions of system inertia and load damping, respectively. The outcomes from MATLAB simulation show that the given controller offers better frequency responses with improved transient response in comparison with other controllers.
