A low cost high power factor three-phase diode rectifier with capacitive load

This paper presents a novel method to improve the power factor of three-phase diode rectifiers with capacitive load, which implementation requires three additional four-quadrant switches rated at very small power. These switches in conjunction with input filter inductors constraint the line current to start increasing every time the corresponding line voltage crosses zero. Besides, they remain at on state during small fractions of the line period and process a small amount of the total rectifier power. Because they commutate at the line frequencies and process a small fraction of the power, the additional losses are small and the overall power converter efficiency is very high. It is also demonstrated that the output DC voltage can be regulated by varying the conduction time of the auxiliary switches. Principle of operation, theoretical analysis, design procedure and example and simulation results are presented. In order to verify the theoretical studies, a laboratory prototype has been built rated at 6 kW and the corresponding experimental results are presented in the paper. The additional switches are rated at a power sixty times less than the total power delivered to the load