Auxiliary supply assisted harmonic suppression for 12-pulse phase-controlled rectifiers

A 12-pulse phase-controlled rectifier has been used for high power applications. It consists of two sets of 6-pulse rectifiers. Basically they operate in parallel, but they operate alternately if load is light. The commutation of the DC current between the two rectifiers is examined and it is found that harmonic distortion of the input current is automatically minimized if they operate in the boundary between continuous and discontinuous conduction modes. An auxiliary voltage supply (AVS) is applied to forces the rectifiers to operate in the boundary conduction mode at any load conditions. It is found that AVS is required a bi-directional power flow. A simple AVS arrangement using a diode rectifier and a PWM inverter is proposed. Application of AVS to a conventional 12-pulse rectifier installing an interphase reactor is discussed. It is concluded that an interphase reactor is unnecessary if AVS is applied to reduce the input current harmonics.