Digital Control of PFC Rectifier with Combined Feedforward and PI Regulator

This paper presents an analysis of a method for controlling power factor correction (PFC) rectifiers to achieve unity power factor and high quality of the input current. The duty cycle estimation is based on a combination of two terms: feedforward and PI. The feedforward term is calculated with a digital model of the converter using input voltage, input current and reference current values. The PI term is then added to compensate for non-idealities of the model including factors, like digital and sensing delays. The analytical equations and characteristics of the proposed combined method are derived and the performance is compared with a standard PI regulator. The results demonstrate that the combined method features significantly better phase margin and can provide unity power factor and low total harmonic distortion (THD) for wide range of load conditions even with significant digital delay.