Analysis of Interphase Currents in 12 Pulse Rectifiers Using Switching Functions

Many large PWM inverter drives use a 12 pulse diode or thyristor front end rectifier connected directly to the dc link capacitor with little or no dc inductance and rely entirely on the source inductance to provide the current smoothing. If the bridges are arranged in parallel there may be very high ripple in the dc current supplied by each bridge. This paper uses frequency domain analysis to solve for the harmonic currents in each of the two 6 pulse groups simultaneously to allow for the interphase currents flowing between them. The procedure outlined here can cope with unbalanced supply voltages and discontinuous current by using the appropriate switching functions.