Optimal Frequency Regulation Scheme in a Wind Power Integrated AC Microgrid

The microgrids have a mixed structure with synchronous machine equivalence and multiple DGs connected via inverters. The presence of inverters is reflected in terms of deficiency in AC microgrid inertia. As a result, deficiency in grid inertia reflects in terms of large change in frequency. However, due to simple design process, self-adaptive nature, and faster response, the linear quadratic regulator (LQR) based optimal control law is designed to maintain nominal grid frequency at lowest level even against high wind power penetrations and grid uncertainties. To reduce frequency sensitivity towards inertia variations, the LQR gains are optimized through linear matrix inequality (LMI) approach. The asymptotic convergence and improved stability against disturbance rejection sensitivity of the LQR-LMI approach are validated using the Lyapunov's theorem and the Nyquist contour, in comparison to the conventional LQR through MATLAB simulations. The presented LQR-LMI reduces the deviations in microgrid frequency with improved stability under varying conditions such as random load demands, high wind power penetrations, unwanted sudden wind power outage and microgrid inertia uncertainties. The responses of the proposed LQR-LMI method are also compared with the conventional LQR and the nonlinear sliding mode controller (SMC). The results demonstrate improved stability, reduced frequency deviations, minimized oscillations, lower control energy consumption, reduced overshoots and undershoots, and faster response times compared to both the conventional LQR and SMC. The simulated trajectories showcase the robustness of the presented optimal control scheme in reducing the frequency deviations with minimum time characteristics.