1、 电子与信息工程学院 本科毕业论文 (设计 ) 外 文 文 献 翻 译 译文题目： single-stage single-switch powerfacter correction AC/DC converter 学生姓名： 专 业： 指导教师： 2010 年 3 月 原文 : 咸宁学院本科毕业论文：外文翻译 - 1 - Single-stage single-switch power factor correctionAC/DC converter Abstract A single-stage single-switch power factor correction AC/DC con
2、verter is proposed in which the power factor correction (PFC) inductor is connedted to a tap on the primary winding ofthe DC/DC flyback converter stage； there is direct energy transfer of a part of the input energy tothe output and theDC-bus voltage feedback. The additional discharge path in the PFC
3、 inductorand DC-bus voltage feedback effectively suppresses the DC-bus voltage and increases the overallefficiency. Experimental results for a 60W converter at a constant switching frequency of 70 kHzare obtained to show the performance of the proposed converter. It is shown that the voltageacross t
4、he DC-bus capacitor can be held below 405V even though the converter operates in a widerange of input voltages (90V-265VAC) and the measured input current harmonics satisfy the IEC。 1 Introduction Many PFC AC/DC converters have been presented inrecent years. PFC techniques can be divided into twocat
5、egories: a single-stage approach and a two-stageapproach. The two-stage approach is the most commonlyused approach. Conventional two-stage PFC convertersinvolve the use of cascading two power-processing stages,responsible for power factor correction and output voltageregualtion. A PFC converter is a
6、dopted at the front-end toforce the line current tracking the line voltage and anotherconventional DC/DC converter is cascaded after the PFCstage to obtain the desired tightly regulated output voltage.This approach can obtain very good performance, such ashigh power factor, and low voltage stress. H
7、owever, due tothe use of two power-processing stages, conversionefficiency is reduced and an additional PFC stage addscomponents and complexity. Consequently the overall costincreases. The two-stage approach has disadvantages oflowpower density, control complexity, and high cost.To reduce the overal
8、l size and cost, a number of siglestagePFC converters have been developed in the literature witches so that the PFC switch anditscontroller can be eliminated. Thesingle-stage approach is specially attractive in low-cost and low-power applicationsdue to its simple power stage and control circuit. How
9、ever,it still has several drawbacks such as high current stress inpower switch and high DC-bus voltage stress. Its majordrawback is a high voltage stress on the DC-bus capacitor.Many single-stage PFC AC/DC converters suffer from highDC-bus voltage stress at light load and high line, whichmakes these
10、 converters impractical. A high DC-busvoltage means high component rating, high cost and lowvoltage stress. Experimental results for a 60W converter ata constant switching frequency of 70 kHz are obtained toshow the performance of the proposed converter. It is hown that the voltage across the DC-bus
11、 capacitor can beheld below 404V even though the converter operates in awide range of input voltages (90V-265VAC) and themeasured input current harmonics satisfy the IEC 61000-3-2Class D requirements. 2 Analysis of proposed converter Figure 1 shows the equivalent circuits of the proposedconverter. T
12、he secondary winding Nb is added in the PFC boost inductor. The first transformer T1 in DC/DC part can be operated either in CCM or DCM depending on the load conditions as in the conventional flyback converter. For simplification, DC/DC part is assumed to operate in CCM for entire line period. The s
13、econd transformer T2 is operated in DCM. According to the operation of T2, When the DC-bus voltage feedback value V1(=np2Vab, np2=N2/Np) is higher than the rectified line input voltage vi, the converter operation enters region A. In region A only T1 is operating and Db is reverse-biased during the o
14、n-time period S. When Vi is higher than V1 and lower 咸宁学院本科毕业论文：外文翻译 - 2 - than V2 the operation converter enters region B. In this region T1 and T2 work like flyback transformers； V2 is determined by Vd+(n1-na)Vo where n1=N1/Ns and na=Na/Nb.When vi is higher than V2 the converter operation enters r
15、egion C. In this region T1 works like a flyback transformer and T2 works like a boost inductor. Since the voltage vi is Vm sin ot in the first quarter of line period, the boundary times tx and ty for three modes are given by Fig. 1 Equivalent circuit 2.1 Region A operation In region A the input volt
16、age vi is lower than the DC-bus voltage feedback value Vl =(N2/Np)Vd. Only the DC/DC part operates. It delivers power from the DC-bus capacitor Cd to the load RL through T1. At to the switch S is turned on. Since the DC-bus voltage Vd is applied across the magnetising inductance Lm1, the magnetising
17、 current iLm1 increases linearly from its lowpeak value ImA,L as follows: At t1 the switch S is turned off and the output diode D1 is on. Since -npVo is applied across the magnetisinginductance Lm1, the current decreases linearly from its highpeak value ImA,H as follows: The diode current iD1 is given by From (3) and (4) the voltage gain is determined as follows: Since the DC/DC part operates in CCM, the duty cycle D does not change with the load variation. From (6) the turn ration np can be determined by The duty cycle D can be obtained as
