Unity-power-factor control based on precise ripple cancellation for fast-response PFC preregulator

Power-factor preregulators are commonly used in electronic equipments for minimizing the injection of current harmonics into the mains power line. However, the bandwidth of conventional preregulators are usually configured to be very small in order to achieve near-unity power factor, and this inevitably gives rise to poor dynamic response. Ripple estimation/cancellation method is used to eliminate the double-line frequency component from the sampled output voltage before it propagates into the voltage control loop, hence, the requirement of small bandwidth is not mandatory. The existing ripple estimation circuits, however, are only accurate under specific conditions, beyond which power factor will be degraded. In view of this, a new ripple estimation/ cancellation network consisting of an amplitude tuner and a phase shifter based on switched-resistor circuits is proposed and verified experimentally on a 200-W boost power-factor preregulator. It is shown that the proposed ripple estimation network not only provides accurate ripple estimation over a wide range of operating conditions, it also gives a way to decouple the power factor of a preregulator from its controller bandwidth. With the aid of the proposed ripple estimation network, the desired features of fast dynamic response and unity power factor are both achieved.