The Study On Soft Switching PFC Techniques

Most power electronics equipments are connected to the power system through rectifiers. The traditional diode and thyristor rectifiers are the main sources of the harmonics in power system. In Recent years, many countries and international organization have proposed regulations on the harmonics of power equipment. Active power factor correction circuit can effectively reduce the harmonics of the rectifier and can meet the harmonics standard.The PFC converters with middle or large out power usually work under continuous-conduction-mode (CCM), which have the advantage of low current stress on the switch. However, there exists severe diode reverse recovery problem in the single phase and three-phase CCM PFC converters. It may lead to high switching loss and cause severe EMI problems.Compound Active-Clamp and Minimal Voltage Active-Clamp topologies are proposed in this paper. These two topologies can effectively suppress the diode reverse recovery, meanwhile create zero-voltage switching for all the switches. These two topologies can also eliminate the unwanted voltage oscillation in the traditional active clamp topology. The theoretical analysis and design details of these two active clamp PFC circuit are proposed. According to Intel's SSI (Server System Infrastructure) specification DPS (V2.0), a lkW PFC converter with compound active clamp and a lkW PFC converter with minimal voltage active clamp are built to test the theory.On the basis of single phase compound active clamp and minimal voltage active clamp topology, two kinds of active clamp soft switching techniques are proposed, and a family of compound active clamp switching cells and minimal voltage active clamp switching cells are got. Using those cells can produce a family of active clamping single-phase converter. The concepts of compound active clamp and minimal voltage clamp are extended to three-phase PFC converter and a family ofcompound active clamp three-phase PFC converter and a family of minimal voltage active clamp three-phase PFC converter are got.To reduce the number of the auxiliary circuits, two kinds of simple active clamp three phase PFC converters are proposed. An improved space vector modulation (SVM) for the two kinds of simple active clamp three phase PFC converter is proposed. A detailed theoretical analysis of the compound active clamp three phase boost PFC converter is given. A DSP controlled prototype is build to test the proposed theory. All the switches in the converter realize ZVS. The voltage stress on the switches is low. The compound active clamp three-phase PFC has a high efficiency.Theoretical analysis and experimental results show that the compound active clamp and minimal voltage active clamp are two promising soft switching techniques for both single-phase and three-phase PFC converters.