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 switch mode 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.