Robust LQG/LTR-based Coordinated Control for a High-Fidelity Model of the Single-Machine Infinite-Bus System

This paper presents a robust linear-quadratic-Gaussian/loop transfer recovery (LQG/LTR)-based coordinated controller for excitation and turbine-governor control in a single-machine infinite-bus (SMIB) system. The main goal of the controller is to enhance the transient stability and robustness of the SMIB system under large disturbances. The novelty of the proposed approach lies in its systematic progression from developing a physics-based, high-fidelity SMIB plant model that incorporates a synchronous generator, transient and sub-transient flux linkages, and turbine-governor dynamics for system validation to designing a reduced-order control-design model of the SMIB system for controller synthesis and stability analysis. The LQG/LTR approach utilizes Jacobian linearization, optimal control theory, and an enhanced Kalman filter, designed using the LTR procedure and a detailed frequency-domain loop-shaping analysis, alongside an iterative tuning and validation process across reduced-order and high-fidelity models, to achieve a reasonable balance between noise/disturbance rejection, robustness recovery, nominal system performance, and stability margins for the SMIB system. Rigorous simulations and comparative studies of the LQG/LTR and three nonlinear controllers are performed under different real-world operating scenarios, such as a three-phase short-circuit fault at the generator terminal and load variations. The simulation results for the high-fidelity SMIB plant model show that the proposed LQG/LTR strategy exhibits superior control performance compared to the three nonlinear controllers in terms of transient stability, convergence rate, rotor angle and frequency control, voltage regulation, and robustness under process and measurement noises, model uncertainties, severe faults, and load fluctuations.