Optimum Third Current Harmonic During Nondead Zone and Its Control Implementation to Improve PF for DCM Buck PFC Converter

A buck power factor correction (PFC) converter is widely used in low-power applications for its high efficiency in the entire universal input voltage range. However, because of the inherent dead zone, the input power factor (PF) is not high. A buck PFC converter operating in a discontinuous conduction mode is introduced. When the duty cycle is constant during the line cycle, the input current contains a large amount of negative third harmonic, especially at a low input voltage. By proposing an optimum third harmonic injection during the nondead zone and its control implementation, a higher PF and a lower output voltage ripple within the entire universal input voltage range are achieved. The experimental verifications are carried out on a 120-W prototype with universal input.