Nonlinear Optimal Control of Three-Phase Inverter Based on State Feedback Exact Linearization Theory

Due to the nonlinear and strongly coupled mathematical model of the three-phase inverter in the synchronously rotating dq coordinate system, it is difficult to deal with the design of controller. Herein, the precise linearization theory of state feedback is applied to construct an affine nonlinear model of the three-phase inverter. Although the dynamic response of the inverter can be improved by the state feedback control, the steady-state characteristics are not as satisfactory as expected. To solve this problem, an integral control plus state feedback scheme is proposed to build an augmented control system for the three-phase inverter. As for control parameter tuning, the linear quadratic regulator (LQR) method is usually not considered as the effective solution to voltage source inverter (VSI) systems because of its inability to ensure reference voltage command tracking. Although the linear quadratic tracker (LQT) method performs well in tracking, its control effect may be compromised by the nonlinear behavior of the system. The three-phase inverter augmented control system proposed in this paper not only addresses the disadvantages of the LQR method in command tracking, but also eliminates the steady-state error, which enables it to perform as well in tracking as the LQT method.