Study on mathematical model and Lyapunov-based control for three-phase four-wire three-level NPC voltage-source rectifier

In this paper, the mathematical model of three-phase four-wire three-level neutral-point-clamped (NPC) voltage source rectifier (VSR) using switching functions is founded and its operating principle analyzed. Then a new nonlinear control law based on Lyapunov´s stability theory for the PWM rectifier is presented. With this control law, the converter can be stabilized globally for handling large-signal disturbances, and exhibit good transient response. Also, by designing new three-level sinusoidal PWM method, this paper solves effectively the problem that the neutral point potential of DC-link has triple-harmonic fluctuation resulting from existing three-level SPWM method. Computer simulations of the system confirm the validity of the mathematical model and the effectiveness of the proposed control strategy.