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Virtual inertia control is considered as an important part of microgrids with high renewable penetration. Virtual inertia emulation based on the derivative of frequency is one of the effective methods for improving system inertia and maintaining frequency stability. However, in this method, the ability to provide virtual damping is usually neglected in its design, and hence, its performance might be insufficient in the system with low damping. Confronted with this issue, this paper proposes a novel design and analysis of virtual inertia control to imitate damping and inertia properties simultaneously to the microgrid, enhancing frequency performance and stability. The proposed virtual inertia control uses the derivative technique to calculate the derivative of frequency for virtual inertia emulation. Trajectory sensitivities have been performed to analyze the dynamic impacts of the virtual inertia and virtual damping variables over the system performance. Time-domain simulations are also presented to evaluate the efficiency of the virtual damping and virtual inertia in enhancing system frequency stability. Finally, the efficiency and robustness of the proposed control technique are compared with the conventional inertia control under a wide range of system operation, including the decrease in system damping and inertia and high integrations of load variation and renewable energy.INDEX TERMS Frequency stability, isolated microgrid, virtual inertia regulation, virtual synchronous machine.

Renewable energy sources (RESs), such as wind and solar generations, equip inverters to connect to the microgrids. These inverters do not have any rotating mass, thus lowering the overall system inertia. This low system inertia issue could affect the microgrid stability and resiliency in the situation of uncertainties. Today's microgrids will become unstable if the capacity of RESs become larger and larger, leading to the weakening of microgrid stability and resilience. This paper addresses a new concept of a microgrid control incorporating a virtual inertia system based on the model predictive control (MPC) to emulate virtual inertia into the microgrid control loop, thus stabilizing microgrid frequency during high penetration of RESs. The additional controller of virtual inertia is applied to the microgrid, employing MPC with virtual inertia response. System modeling and simulations are carried out using MATLAB/Simulink ® software. The simulation results confirm the superior robustness and frequency stabilization effect of the proposed MPC-based virtual inertia control in comparison to the fuzzy logic system and conventional virtual inertia control in a system with high integration of RESs. The proposed MPC-based virtual inertia control is able to improve the robustness and frequency stabilization of the microgrid effectively.

Virtual inertia emulation could be regarded as an inevitable component of microgrids with renewable energy, enhancing microgrid inertia and damping properties. In applying this control technique, a phase-locked loop (PLL) is necessary to obtain the estimation of the system frequency data. However, the employment of PLL could cause larger frequency oscillation to the microgrid due to its dynamics. This issue would be exacerbated in a low-inertia microgrid driven by high renewable penetration, severely deteriorating the frequency stability. Thus, the effect of PLL with measurement delay is a critical issue in utilizing the virtual inertia control. To overcome such problem, this paper proposes a robust virtual inertia control for a low-inertia microgrid to minimize the undesirable frequency measurement effects, improving the microgrid frequency stability. The robust H ∞ control design using a linear fractional transformation (LFT) technique is used to develop the virtual inertia control loop, considering the dynamics of PLL with measurement delay and the uncertainties of system inertia and damping. The efficacy of the proposed H ∞ control method is compared to the conventional and optimum proportional-integral (PI)based inertia control. The results show that the H ∞ -based robust virtual inertia control is superior to both conventional virtual inertia control and optimum PI-based virtual inertia control against a wide range of microgrid operating conditions, disturbances, and parametric uncertainties.INDEX TERMS Frequency stability, H ∞ control, inertia control, microgrid, renewable energy, virtual synchronous generator.