A high-power PWM adjustable speed drive with low current harmonics

An approach recently introduced to correct the power factor of single-phase and three-phase diode rectifiers is extended to high-power PWM adjustable speed drive. The proposed AC/DC stage of the converter is based on a new three-phase diode rectifier, obtained by properly connecting three single-phase diode rectifiers. The power factor of each single-phase rectifier is corrected by using a passive correction technique based on a resistive-capacitive branch connected at the DC-terminals of the rectifier. The design of the passive branches for the power factor correction is performed by substituting the PWM inverter-motor group with a simple resistor and having in mind the nominal power of the drive. Analyses of performances of the new PWM adjustable speed drive scheme are developed with the help of PSPICE simulations. Some considerations on the possibility to reduce additional costs and to improve efficiency of the new scheme are also developed.