A Unified Analysis of CCM Boost PFC for Various Current Control Strategies

A single phase continuous conduction mode (CCM) boost PFC can be classified by the method in which input current shaping is done: average-current, peak-current and valley-current controlled PFC. The output of voltage compensator is different in above current controllers for the same loading condition. In this paper, a mathematical derivation using Fourier analysis of input current is presented to determine the value of the compensator output. The analysis is applied to determine the boundary condition for CCM operation. Theoretical comparison of the above derivations is supported by simulation results. A small-signal model of the system is required to design the voltage compensator parameters. A unified method of deriving small-signal model and the transfer function of the outer voltage loop is proposed. A design example of a compensator for average-current controlled PFC is given and differences at various points in conjunction with other current controllers are presented.