Three-phase single-switch boost PFC converter with high input power factor

Three-phase single-switch boost power-factor-correction (PFC) converter features zero-current turn-on for the switch, no reverse recovery in diode, constant frequency operation, simple control and low cost, and it is suitable for the low-to-medium power conversions. However, the input power factor (PF) is relatively low when the duty cycle is constant in the whole line cycle. This paper analyzes the operation principle of the three-phase single-switch DCM boost PFC converter, and the expressions of the input current and PF are derived, based on which, a variable duty cycle control is proposed so as to improve the PF and reduce the input current harmonics. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. Besides a higher PF and lower input current harmonics, the proposed variable duty cycle control achieves a lower output voltage ripple and a higher efficiency over the constant duty cycle control. A 3kW prototype has been built and tested in the lab, and the experimental results are presented to verify the effectiveness of the proposed method.