Robust Virtual Inertia Control of a Low Inertia Microgrid Considering Frequency Measurement Effects

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.