Injecting 3rd harmonic into the input curent to improve the power factor of DCM buck PFC converter

The conventional Buck PFC converter adopts constant duty cycle control (CDCC), which can improve the PF to some degree. However, the peak and RMS values of the inductor current are large, which also occurs to the switch and diode. This paper derives the expressions of the input current and PF of DCM Buck PFC converter, and based on which, a kind of injecting 3
^rd
current harmonic control (ICHC) is proposed so as to improve the PF in the whole input voltage range. Besides a higher PF, the proposed novel control achieves a lower output voltage ripple, a smaller rms value of the inductor current and a higher efficiency than the conventional control. The experimental results from a 120 W universal input prototype are presented to verify the validity of the proposed method.