Current-forced neutral injection in a three-phase rectifier/converter

A new three-phase rectifierkonverter with low harmonic input currents and minimal DC voltage ripple is described. The device achieves continuous input line currents by injecting a triangular thrd harmonic current, derived from the DC link current, into the neutral point of a delta-star transformer at the supply. It uses a conventional six-pulse phase controlled converter, with an additional bridge of four devices in the DC link. The additional bridge also cancels much of the DC voltage ripple, allowing a much smaller DC link inductance to be used. A prototype lOkW system, suitable for such applications as DC motor drives, load-commutated inverters, exciters for AC generators, and low-power DC links is described. Experimental results obtained from this system are compared with ideal theoretical predictions.