Using the DC-bus current to improve the power factor in low-cost electric drives

In this paper, a new approach is presented aimed at improving the power factor of pulsewidth-modulation inverters that equip low-power electric motor drives for household appliances. The key feature of the proposed approach consists of exploiting the dc-bus current as a suitable dither generator by means of a high-frequency transformer. Such a strategy is used to force the diode rectifier to draw current from the mains in those periods when, in conventional systems, the diodes are reverse biased, i.e., when the dc-bus capacitor voltage exceeds the ac input voltage. The proposed method allows for elimination of the power-factor controller (PFC) front end, traditionally used to comply with power quality requirements. In comparison with standard PFCs based on a dc/dc converter, the proposed approach represents a cheaper and more feasible solution, not using additional power devices and control circuits.