Light load efficiency improvement for AC/DC boost PFC converters by digital multi-mode control method

This paper presents a method to improve light load efficiency and reduce the THD of input current of a boost PFC converter used in applications to high performance server power supply units. The conventional constant frequency average current mode control scheme will result lower efficiency and high THD current distortion under light load operation. To overcome this problem, this paper proposes a digital multi-mode control scheme with variable switching frequency control. A nonlinear control scheme with modified gain scheduling has been used to improve dynamic response under light load condition with discontinuous conduction mode (DCM) operation with lower switching frequency. A green mode controller has been developed to change its control mode based on the required line current command under various load conditions. The proposed control scheme has been verified by using simulation and realized by using a DSP TMS32028035 in applications to a single-phase 675W boost PFC AC/DC converter. Experimental results are given to illustrate the feasibility of the proposed control scheme.