Single-Stage Power-Factor-Correction Techniques

To reduce the component counts and the cost, the single-stage power factor correction (PFC) techniques have attracted more and more attention. A single-stage PFC converter combines the PFC stage and a DC/DC converter into one stage with a shared switch and controller, which is analyzes and researches in this dissertation. The dissertation includes six chapters.In chapter one, the passive PFC approach, the active two-stage PFC approach and the active single-stage PFC approach are analyzed and compared. The single-stage PFC converter suits for low power applications. It is the researching trend and the hot-point of the PFC techniques.In chapter two, a topological study of representative single-stage PFC converters are presented. In single-stage PFC approach, to comply with IEC1000-3-2 input harmonic current limits and provide tight output regulation, there are two important issues of concern. One issue is how to implement the input current shaper (ICS). Another issue is how to control the energy-storage capacitor voltage below 450V. The single-stage PFC converters are classified as the Boost type and the Buck-Boost type. And the Boost type can be classified as 2-terminal ICS cell and 3-terminal ICS cell. The general structures of Boost type and the translation rule of 2-terminal and 3-terminal ICS cell are presented. Several new PFC topologies were derived from some existing topologies using the translation rule.In chapter three, three single-stage PFC converters with the negative feedback of energy-storage capacitor voltage by transformer windings are analyzed. The three converters have similar performances, and they can be translated each other, which verified the translation rule. The analysis and experiment results show that with the negative feedback of energy-storage capacitor voltage by transformer windings have good performances, and very simple.Chapter four proposes a novel single-stage forward PFC converter. The operation principle is analyzed and parameters design is discussed. Compared with other topologies, this topology has some advantages, such as simple structure, low input current harmonics and low energy-storage capacitor voltage.The DCM flyback single-stage PFC converter is analyzed in chapter five. The theoretic analysis and parameters design are presented based on the "loss-free resistor" concept. This chapter presents the loss analysis of the flyback PFC circuit with RCD snubber.The loss analysis shows that the leakage inductance has a great influence on the efficiency of converter and the voltage rating of components, which limits the applications of the DCM flyback converter. By analysis and simulation with active clamp flyback converter, it can be found that the magnetic energy of transformer can flow bi-directionally. If the duty cycle is constant, when the main switch is on, there is some energy of magnetic and leakage inductorfeedback to the input source, which results in distorted input current and low input power factor. However if the active clamp flyback converter is designed to operate in CCM, and the duty cycle is controlled to make the input current track input voltage, the input power factor can be improved.