Three, single-phase power factor correction (PFC) boost converters for use with three-phase, 3-wire variable frequency drive systems

Diode rectifier front ends with large DC bus capacitors used in Variable Frequency Drives (VFDs) draw discontinuous current from the power system resulting in poor input power factor and high input current distortion. In case of single-phase AC to DC rectifiers, the single-phase boost converter is popular and effective in improving the input power factor and reducing the input current harmonics. However, the same topology does not lend itself for easy use with three-phase 3-wire system since there is no neutral in the system and the boosted voltage necessary for satisfactory operation is beyond the safe voltage level for Variable Frequency Drives (VFDs). This paper discusses a novel idea of using 3, single-phase boost converters in a three-phase, 3-wire system, commonly found in many commercial and industrial locations. To resolve the high DC bus voltage associated with boosting line-line voltage, the method relies on boosting line-neutral voltage instead. The neutral point for the proposed topology is obtained from a zigzag autotransformer rated at only 0.1pu of rated load VA. Experimental results from a 480V, 15hp system are given to prove the concept.