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

A new approach is presented based on the dither effect, aimed to improve the power factor of PWM inverters equipping low power electric motor drives for household appliances. The key feature of the proposed approach is that the DC bus current is used to generate a suitable dither that forces the diode rectifier to draw current from the main, when the DC bus capacitor voltage exceeds the AC input voltage. Therefore, exploiting the presented idea, a traditional PFC front end, based on a DC/DC converter, is not necessary to comply with power quality requirements and only an additional HF transformer is introduced, that marginally affects the cost and size of the whole drive. Experimental results confirm the consistence of the proposed approach.