Modeling and simulation of off-line boost power factor correction (PFC) circuits

Electric power is delivered most efficiently from utilities to end users when the load draws current at unity power factor. Traditional ac-to-dc power supplies that use a rectifier/filter topology, however, draw currents that are highly non-sinusoidal and rich in harmonics and thus display a low power factor. An alternative approach, known as offline power factor correction, eliminates the filter capacitor and uses switchmode power converter techniques to achieve power factors close to unity. Commercially-available integrated circuits may be combined with external discrete components to make a complete offline power-factor correction circuit; however, the manufacturers' data sheets frequently provide little theoretical basis for their application information. This paper deals with modeling and simulation work to derive the transfer functions of the voltage- and current-control loops, with a primary focus on the current-control loop. The transfer function of the current-control loop has been derived for specified operating conditions, and a Matlab script for plotting Bode plots of these transfer functions is developed.