Robust Optimal Virtual Inertia Control for Microgrid Frequency Regulation Considering High Renewable Energy Penetration

The rapid increase in penetration of wind and solar power into power systems reduces the rotational inertia of the systems. The low inertia results in high-frequency perturbation and rate of change of frequency (RoCoF), which could lead to frequency instability during contingencies. This problem can be tackled by developing virtual inertia (VI) control scheme in the microgrid (MG). The VI control injects active power via an energy storage system (ESS) to the MG during periods of frequency deviations. In this way, the VI control imitates the inertia characteristic and adds to the total inertia of the MG. Therefore, this paper proposes a robust linear quadratic integral regulator (LQRI) to regulate the frequency deviation and enhance the MG frequency stability. The control problem is formulated in terms of linear matrix inequalities (LMI) in the discrete-time domain. The optimal controller gains are obtained by solving the LMI using convex optimization. The correctness and efficiency of the proposed scheme are demonstrated via discrete time-domain simulation under varying renewable energy sources and loads. The results show that the proposed controller can suppress the frequency deviation at a very fast rate. Finally, a comparative examination of the proposed scheme with an existing VI controller is provided to highlight the improvement in the frequency response of the MG under contingencies.