A compact autotransformer based 12-pulse rectifier circuit

Three-phase diode bridges used in rectifier type loads such as motor drives draw line currents that are rich in harmonics. A popular harmonic current reduction method specifically geared towards such loads is to increase the number of rectification pulses. The wye-delta transformer based 12-pulse rectification scheme is one such example. This scheme suffers from drawbacks such as bulky magnetics. Other schemes use autotransformer based solutions to reduce bulk. However, these need zero-sequence current blocking transformers for proper operation. Also, all these schemes use accessories like interphase transformers and inductors to promote equal current sharing between the diode bridges. This paper presents a compact autotransformer topology suitable for 12-pulse rectification. It differs from conventional schemes by achieving harmonic current reduction without the need for equal current sharing between the diode bridges. This eliminates the need for impedance matching inductors and zero-sequence current blocking devices further reducing size and cost. The paper presents the concept and principle of operation. It establishes guidelines for designing the autotransformer. A simple model is developed and simulated to investigate the concept. Finally, the paper presents experimental results obtained from operation of a proof-of-concept prototype connected to a 3-O, 230 V/15 HP motor drive load. The results show that the proposed scheme satisfies the performance benchmark specified in the IEEE 519-1992 guidelines for voltage sources with impedance 2% or less.