Source impedance and current-control loop interaction in high-frequency power-factor correctors

The authors introduce a model for the input port of the high-frequency power-factor corrector and determine the gain of the current control loop. Both the model and the expression for the loop gain are entirely general and can be used for analyzing the source impedance and current control loop interaction of virtually any corrector with any current control method, operating in continuous or discontinuous inductor current mode, and having any source impedance. Based on the model, the electromagnetic interference filter capacitor and the current-error amplifier can be designed to avoid instability of the current-control loop. The loop gain of a boost corrector with average current control was investigated in detail. The system was found to be unstable at low line voltage and at source inductance values frequently encountered in practical applications. A physical explanation for the instability is given together with recommendations on how to avoid the instability. Test data taken from an experimental boost corrector with average current control are in good agreement with theoretical predictions of the model