An optimized active interphase transformer for auto-connected 12-pulse rectifiers results in clean input power

This paper proposes an optimized 12-pulse diode/SCR rectifier topology with lower kVA magnetics and fewer component count. The proposed system consists of an autotransformer (0.18 P/sub a/), two diode/SCR rectifier bridges and a new active interphase transformer. The new active interphase transformer combines the function of two zero sequence blocking transformers (ZSBT), and a conventional interphase transformer into one component wound on the same core. Further, an additional auxiliary winding is added on to the same core to facilitate active current shaping or input current for clean input power. A low kVA two-switch PWM-VSI is employed to control the auxiliary winding current to realize near sinusoidal utility line currents under varying load condition. The proposed system is suitable for the utility interface of high power AC motor drive systems to meet the current IEEE-519 harmonic current limits. The proposed system is very rugged and, in the event the active control were to fail, the system reverts to 12-pulse operation with 5th and 7th harmonics cancellation. Further the active PWM unit is of low kVA (0.15P/sub 0/) and is not directly exposed to line transients. Analysis and design of the proposed system is examined in detail and simulation results are shown.