Power factor correction in single phase AC-DC conversion: control circuits for performance optimization

AC-DC conversion with power factor correction may use several well known power circuits (boost, half-bridge and full-bridge), or some single stage converters, in the case of switch mode power supplies. All of them present the same control problem: an accurate control of the input current and the simultaneous control of the voltage across the energy storage capacitor. The control of the voltage at the storage capacitor presents a high response time or a reduced gain, in order to avoid a significant distortion of the input current, with a dominant harmonic at the double of line frequency. In the case of switch mode power supplies, the storage capacitor is designed to perform a required stand-on time and, consequently, is bulky and expensive. This paper presents a survey of the more recent pulse width modulators used in the PFC circuits, namely UCI modulators and the design objectives of those control circuits and their main limitations. It is also presented a new technique for capacitor voltage sampling that permit an important reduction of the response time of the voltage regulators. The stability conditions for PI regulators with sampled feedback are presented. Experimental results obtained with a full-bridge single stage converter are also presented.