Improving Light-Load Efficiency of AC/DC Boost PFC Converters by Nonlinear Control Scheme

Power supply units (PSUs) with an equally shared load current are widely employed for data processing equipment like servers due to their advantages such as easy extension of power processing capability and simple thermal management. This paper presents a method to improve light-load efficiency by reducing load-independent losses such as capacitive turn-on and core losses and reduce the THD of input current of a boost PFC converter used in applications to high performance server power supply units. The conventional system constant frequency and 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 gain scheduling has been used to improve dynamic response under light load condition with discontinuous conduction mode (DCM) operation with lower switching frequency.