Small-Signal Modeling of Boost Power-Factor Correction Controllers

Electric power is delivered most efficiently when the load draws current at unity power factor. Traditional rectifier/filter power supplies, however, draw currents that are highly non-sinusoidal and thus display a low power factor. An alternative approach, known as offline power factor correction (PFC), achieves near-unity power factor by eliminating the filter capacitor and using switchmode power converter techniques. Power-factor correction circuits are commercially available; however, manufacturers' data sheets frequently provide little theoretical basis for their application. This paper deals with modeling and simulation work to derive the loop gain of a PFC with the goal of improving the tools available to design engineers. An expression has been derived for the loop gain of a PFC under specified operating conditions, and a Matlab script for plotting Bode plots of the loop gain is being developed.