Multilevel AC/DC/AC converter for AC drives

A novel pulse width modulation (PWM) scheme for a multilevel AC/DC/AC converter is proposed. A power factor corrector using the hysteresis current control techmque is presented to improve the power quality at the rectifier side. The circuit configuration of the adopted five-level rectifier has two AC power switches and one diode bridge. The proposed control scheme of the fivelevel rectifier is based on a look-up table that is implemented by programmable array logic (PAL). According to the proposed control method, the line current will follow the reference current with unity power factor. The reference supply current is derived from a DC link voltage regulator and an output power estimator. A three-level diode clamped voltage source inverter is used to reduce the output voltage harmonics and blocking voltage of each power device in each leg. The high power factor and low current distortion at the input of the rectifier and the low total harmonic distortion at the output of the inverter are verified by the experimental results.