Virtual flux based direct power control for three-level 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. The relationship between instantaneous power and voltage vectors is derived mathematically. Virtual flux is estimated and used to calculate the phase of the power source voltage and instantaneous power. On these bases, a direct power control (DPC) scheme for three-level PWM rectifier is presented. An optimal switching table is established, vector switching scheme and balance strategy for the neutral point potential are discussed. Variable switching frequency and dynamic process of the startup are also analyzed. Experimental results have verified the theoretical approach and the three-level PWM rectifier with proposed DPC based on virtual flux exhibits several advantages, such as simple algorithm, low costs and excellent dynamic performance.