The virtual flux oriented control of three-level neutral point clamped PWM rectifier

This paper presents a new control strategy for three-level neutral point clamped (NPC) pulse width modulated (PWM) rectifier without power source voltage sensors. Virtual flux is estimated and served as the oriented vector for the control of PWM rectifier. Theoretical principles of this method are presented and the neutral point potential balance control of the rectifier is also discussed. A digital-signal-processor-based experimental system was developed, and several experiments were conducted to examine the controllability. As a result, it is confirmed that unity power factor can be realized and the system exhibits several advantages, such as the low cost, high reliability, low harmonics and low voltage stress of power switches compared with conventional two-level rectifier.