Precise ripple cancellation technique for power-factor pre-regulator circuits

Power-factor pre-regulators generally suffer from poor dynamic response due to the need to limit the propagation of output voltage ripple at double line frequency into the voltage control loop and to achieve a satisfactory power factor performance. Ripple cancellation methods have been proposed to eliminate the double-line-frequency signal from the sampled output voltage before it propagates into the voltage control loop. However, these methods generally employ idealized formulations that give rise to accurate ripple estimation over a limited range of operating conditions only. In this paper, a new ripple estimation/ cancellation circuit that does not rely on such idealized formulations is proposed. It consists of an independent amplitude tuner circuit and a phase shifter circuit that can provide accurate ripple estimation over a wide range of operating conditions. The proposed circuit is analyzed in detail and verified theoretically by computer simulation. It is shown that ripple cancellation provides a way to decouple the pre-regulator's power factor from its controller's bandwidth and load condition, thus both fast dynamic response and constant near-unity power factor can be achieved.