Adaptive Internal Model Control Based Ripple Rejection for Improved Response of PFC Rectifiers

A simple and effective method is proposed to eliminate double-line frequency component in the outer voltage control loop of rectifiers with power factor correction (PFC). An adaptive notch filter based on the internal model principle (IMP) of control theory is introduced between the feedback error ADC and the digital PI voltage loop controller of the rectifier. It effectively identifies the exact double-line frequency based on the output voltage feedback signal and accordingly adjust the filter notch frequency to allow exact ripple rejection with a high Q factor. The elimination of double-line frequency component in voltage control loop allows a high bandwidth controller to be used and a very fast load transient response obtained. The frequency adaptation not only enables a universal PFC rectifier for either 50Hz or 60Hz input line voltage it also compensates small line frequency variations and especially relatively large clock frequency variation in internal oscillator of the controller IC. As a result of this adaptive method, cost effective digital ASIC controllers or microcontrollers can be used for this application without the need of an expensive quartz crystal clock source. The effectiveness of the proposed method is verified with extensive simulations in Plecs.