Implementation of Active Inter Phase Transformer in 12-Pulse Converter & Getting the Performance like 24-Pulse Converter

Abstract

Harmonics is one of the most severe problems in variable frequency drives. Harmonics are generated due to switching action of the power electronics converters, which are known as non-linear loads. Variable frequency drives are made up of two power sections, a rectifier section and an inverter section. The six pulse diode bridge rectifier is most widely used as an AC-to-DC converter. But major disadvantage of diode bridge rectifier is that it will distort utility line current. To minimize the harmonics we place the filter which increases the cost, size & volume. To mitigate harmonics from utility line currents interphase reactor is implemented for paralleling of converters. It ensures equal sharing of current among the parallel connected converters. There are two type of interphase transformer uncontrolled & controlled (Active IPT). Here a new active interphase transformer (controlled) for 12-pulse diode bridge rectifier with reduced kVA is implemented. This system draws near sinusoidal currents from the utility. Simulations are done for 2 schemes. In scheme I low kVA PWM VSI injects triangualr shaoed current into the secondary of Active interphase reactor of a 12-pulse diode bridge rectifier. This modification result in near sinusoidal utility line currents with less than 1% THD. In scheme II Boost Power Factor Controller circuit connected across auxiliary winding of Active IPT to meet IEEE-519 harmonic current limit. This system is very rugged and in the event active control fails this system will revert to 12-pulse operation with 5th&7th harmonics cancellation. Simulation & Experimental results are provided for 50 kVA, 415 V 12-pulse rectifier system with an auto transformer arrangement. The resulting system draws clean power from the utility & is suitable for powering larger kVA ac motor drive system.