Study of the Control System of Three-Level PWM Rectifier Based on Virtual Flux Oriented

This paper presents a novel decoupling control strategy for three-level NPC PWM rectifier without line voltage sensors, combining virtual flux oriented control (VOFC) with traditional direct current control based on the decoupled d-q frame. A virtual flux linkage vector can be constructed similarly to the observation of AC motor flux linkage, which may serve as the oriented vector in the vector control of the PWM rectifier instead of the line voltage vector. As a result, the AC voltage sensors and phase locked circuit will be eliminated and the costs of PWM rectifier can be reduced. According to the design principle of AC motor flux observer, a modified virtual grid flux observer and the grid voltage estimation method are proposed, which solves the DC drift problem caused by a wrong initial value selecting of integer in virtual flux oriented vector control for PWM rectifier. Finally based on Matlab/Simulink, this paper constructs virtual flux oriented current decoupling control simulation model of three-level PWM rectifier without grid voltage sensor. The reliability of the observer has been proved. The good dynamic and static performances of the control scheme have been showed by simulation.