Improved three-phase high-quality rectifier with line-commutated switches

The paper presents a three-phase diode rectifier with an add-on simple cell with line-frequency commutated ac switches that is able to greatly improve both power factor and output voltage regulation of rectifiers with passive L-C filters. The boost action introduced by the commutation cell allows for a complete compensation of the voltage drop across the input inductors, so as output voltage regulation can be maintained from no-load to full-load. Moreover, as compared to other line-frequency commutated rectifiers, the proposed circuit allows compliance with the low-frequency harmonic limits defined in the technical report IEC 61000-3-4 for any power range. High-efficiency and minimum EMI are obtained due to the low-frequency commutations. A converter prototype was built and tested. The results confirm the theoretical analysis.