Near unity input displacement factor for voltage source PWM drives

More and more PWM rectifiers are now used to replace traditional diode or thyristor types in AC drive systems. To minimize the switching frequency, while keeping the input current close to sinusoidal, this paper presents a topology composed of two identical front-end voltage source rectifiers in series and a three-winding transformer. This topology uses the transformer connection to remove the harmonics of the order 6k±1 (k=1,3,5,···). Additional harmonics lower than 23^rd are eliminated by a suitable PWM-SHE switching pattern. Among known PWM switching patterns, the PWM-SHE produces the lowest switching losses, yet eliminates the required harmonics. The resulting converter system presents all the advantages associated with active front-end rectifiers. The main purpose is to ensure near unity power factor operation. A simple control structure is used. Simulation and experimental results confirm the feasibility and advantage of the proposed drive system