I. Introduction
Conventional enormous synchronous generators (SGs) comprise rotating inertia due to their rotating parts. These generators are capable of injecting the kinetic potential energy preserved in their rotating parts to the power grid in the case of disturbances or sudden changes. Therefore, the system is robust against instability. On the other hand, penetration of distributed generating (DG) units in power systems is increasing rapidly. The most challenging issue with the inverter-based units is to synchronize the inverter with the grid and then to keep it in step with the grid even when disturbances or changes happen [1]–[3]. A power system with a big portion of inverter-based DGs is prone to instability due to the lack of adequate balancing energy injection within the proper time interval. The solution can be found in the control scheme of inverter-based DGs. By controlling the switching pattern of an inverter, it can emulate the behavior of a real synchronous machine. In the VSG concept, the power electronics interface of the DG unit is controlled in a way to exhibit a reaction similar to that of a synchronous machine to a change or disturbance. The VSG control generates amplitude, frequency, and phase angle for its terminal voltage based on its power command. Therefore, as a corollary, it can contribute to the regulation of grid voltage and frequency. In addition, synchronizing units, such as phase-locked loops, can be removed [4].