A phase-controlled 12-pulse rectifier with unity displacement factor without phase shifting transformer

This paper presents a three-phase 12-pulse phase-controlled rectifier with unity displacement factor, low line current harmonic content, two quadrant operation and the absence of a phase shifting transformer. The circuit is composed by two three-phase 6-pulse rectifiers parallel connected by four balancing reactors. One is a conventional thyristor rectifier with a lag firing angle (/spl alpha/). The other is an active rectifier composed by GTOs or IGBTs and diodes, operating with a lead (and symmetrical) firing angle (-/spl alpha/). The 12-pulse operation with line frequency modulation provides a 5-level line current with reduction or cancellation of certain harmonics. Circuit operation, theoretical analysis, key equations, along with experimental and simulation results are presented.