Small-signal modeling and fast response control strategy for DCVM Cúk converters in PFC applications

Cúk Converter operating in discontinuous capacitor voltage mode is an inherent PFC converter in which, unity power factor can be achieved using constant duty cycle and switching frequency. In this paper, a reduced-order switch network modeling technique is applied to Cúk converter operating in DCVM in order to derive small-signal model of the converter assuming a dc voltage source as the input source of the converter. This model is extended to derive the small-signal behavior of the converter while operating as a PFC converter. The validity of the proposed model is confirmed by both simulation and experimental results. Afterwards, a new control strategy is proposed in which switching frequency is a function of load effective resistance. This control strategy considerably improves transient response of the converter to load variations besides stabilizing voltage stress on semiconductor switches. Experimental results are presented to demonstrate the features of proposed control algorithm.