a single stage soft-switched ac/dc power factor corrected

A single stage soft-switchedAC/DC power factorcorrected converter withgalvanic isolation

Zhi Zhang1a), Xueliang Liu1, and Zhiping Wang21 School of Electronic Engineering, Dongguan University of Technology,

Dongguan 523808, China2 Guangdong Institute of Automation, Guangzhou 510007, China

a) [email protected]

Abstract: This paper describes a single-stage AC/DC Power Factor Cor-

rection (PFC) converter with galvanic isolation, and an active-clamp circuit

is used to achieve zero-voltage-switching (ZVS) for both main and auxiliary

switches. The ZVS operation principle of the system is illustrated in detail.

Simulation and experimental results based on a 85 kHz, 3000W prototype

circuit show that the proposed converter has low component count, galvanic

isolation, simple control, high power factor and high conversion efficiency in

a wide load range.

Keywords: power factor correction, zero-voltage-switching, isolation

Classification: Power devices and circuits

References

[1] D. S. Gautam, et al.: “An automotive onboard 3.3-kW battery charger forPHEVapplication,” IEEE Trans. Veh. Technol. 61 (2012) 3466 (DOI: 10.1109/TVT.2012.2210259).

[2] F. Musavi, et al.: “An LLC resonant DC–DC converter for wide output voltagerange battery charging applications,” IEEE Trans. Power Electron. 28 (2013)5437 (DOI: 10.1109/TPEL.2013.2241792).

[3] L. Huber, et al.: “Effect of valley switching and switching-frequency limitationon line-current distortions of DCM/CCM boundary boost PFC converters,”IEEE Trans. Power Electron. 24 (2009) 339 (DOI: 10.1109/TPEL.2008.2006053).

[4] F. Musavi, et al.: “A high-performance single-phase bridgeless interleaved pfcconverter for plug-in hybrid electric vehicle battery chargers,” IEEE Trans. Ind.Appl. 47 (2011) 1833 (DOI: 10.1109/TIA.2011.2156753).

[5] L. Huber, et al.: “Performance evaluation of bridgeless pfc boost rectifiers,”IEEE Trans. Power Electron. 23 (2008) 1381 (DOI: 10.1109/TPEL.2008.921107).

[6] J. W. Yang and H. L. Do: “High-efficiency ZVS AC-DC LED driver using aself-driven synchronous rectifier,” IEEE Trans. Circuits Syst. 61 (2014) 2505(DOI: 10.1109/TCSI.2014.2309837).

[7] S. W. Lee and H. L. Do: “Single-stage bridgeless AC-DC PFC converter usinga lossless passive snubber and valley switching,” IEEE Trans. Ind. Electron. 63(2016) 6055 (DOI: 10.1109/TIE.2016.2577622).

© IEICE 2017DOI: 10.1587/elex.14.20170144Received February 17, 2017Accepted March 24, 2017Publicized April 7, 2017Copyedited April 25, 2017

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LETTER IEICE Electronics Express, Vol.14, No.8, 1–7

http://dx.doi.org/10.1109/TVT.2012.2210259





http://dx.doi.org/10.1109/TPEL.2013.2241792








http://dx.doi.org/10.1109/TIA.2011.2156753








http://dx.doi.org/10.1109/TCSI.2014.2309837




http://dx.doi.org/10.1109/TIE.2016.2577622




[8] S. Cuk: Power electronics Technology Magazine (2010) 22.[9] D. Bortis, et al.: “Comprehensive analysis and comparative evaluation of

isolated true bridgeless Cuk single-phase PFC rectifier system,” IEEECOMPEL (2013) 1 (DOI: 10.1109/COMPEL.2013.6626438).

[10] M. Kim and S. Choi: “A fully soft-switched single switch isolated DC-DCconverter,” IEEE Trans. Power Electron. 30 (2015) 4883 (DOI: 10.1109/TPEL.2014.2363830).

1 Introduction

Isolated AC/DC converters are used in many applications, such as PC’s and

consumer electronics, uninterruptible power supplies, telecommunication power

supplies [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Sever isolated AC/DC converter topologies

with active PFC have been proposed [1, 2]. These topologies has two stages: the

first stage for rectification and power factor correction [3, 4, 5], and the other stage

for galvanic isolation, output voltage regulation and conversion [2]. However, these

topologies suffers from high switch losses with the drawback of many switch

component needed, and this often results in an overall efficiency of less than 90%.

Several single stage schemes have been reported in the literature [6, 7, 8, 9, 10].

They have the features such as lower component, lower cost, smaller size and high

power conversion efficiency than the two stage schemes. A boost-flyback topology

is the most commonly used single stage converter for galvanic isolation [6, 7], but it

is only suitable for small power applications.

The DC-DC converter proposed in [8, 9] can realize galvanic isolation and

could be used for high power applications, but it has the drawback of high voltage

spike across the power switch and limiting its use for high frequency applications.

An passive-clamp circuit is proposed to limit the switch voltage excursion and

realize the soft-switch for power switch and diode [10], but it suffers from excessive

power losses dissipated in RCD snubber.

This paper proposes a single-phase single-stage soft-switched AC/DC isolated

converter, and the basic active-clamp operation of the ZVS single-stage converter

is analyzed and explained. Finally, simulation and experimental results verify the

validity of the analysis. With a rated power of 3000W prototype, an outstanding

efficiency of 94.49% can be achieved.

2 Circuit converter

Fig. 1 shows the single-stage isolated PFC AC/DC topology. The AC/DC top-

ology includes a diode bridge and a isolated boost converter [8, 10]. The proposed

converter consists of switches Q1 and Q2, which are shown with their associated

antiparallel diode. Q1 and Q2 are main and auxiliary switches respectively. During

the turn-off of the main switch Q1, it will produce high voltage spikes at switch Q1,

so a clamp circuit is essential part of the topology [10].

Cr represents the parasitic capacitance of the two switches. L represents the

input inductor. The component Lr, Cp, Cs, together with the main power switch Q1

compose of the hybrid switch [8, 10]. C and Co are the clamp capacitor and output


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capacitor, respectively. The active clamp circuit is composed of the auxiliary switch

Q2 and the clamp capacitor C. With the active-clamp circuit, the main switch Q1

voltage spike is clamped, zero-voltage-switching (ZVS) for both primary (Q1) and

auxiliary (Q2) switches become possible, and high switching frequency, high

conversion efficiency can be reached.

3 Operating principle

Fig. 2 shows the key waveforms for the active-clamp isolated boost converter and

Fig. 3 illustrates the topological operation stages. The following assumptions are

made for the system analysis:

(1) all switch components are ideal;

(2) the clamp capacitance C is larger than the parasitic capacitance Cr;

(3) the resonant Lr is much less than the transformer magnetizing inductance Lm;

(4) energy stored in the resonant Lr is greater than the parasitic capacitance to

completely discharge Cr and turn on Q1’s antiparallel diode;

(5) n = ns/np is the transformer turns ratio between the secondary winding turns

and the primary winding turns.

The five distinct operating modes can be described below.

Fig. 2. Key waveforms of the proposed converter

Fig. 1. Proposed single-stage isolated active-clamp PFC converter


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Mode 1

At t0, the main switch Q1 is turned on, and the auxiliary switch Q2 is turned off.

The input inductor L is being linearly charged, the parasitic capacitor voltage

ucr ¼ udsQ1 ¼ 0, and the resonant inductor current iLr discharge the capacitor Cp.

The diode D2 and D3 are turned on. The capacitor current ics increase and capacitor

voltage ucs decrease.

Mode 2

At t1, main switch Q1 is turned off, and the auxiliary switch Q2 is off, Cr is

charged by the input inductor current iL and resonant current iLr from 0 to uc(udsQ1 ¼ ucr ¼ uc) until time t ¼ t2, the charge time is very short, and the input

inductor iL and resonant current iLr are almost constant.

Fig. 3. Operation stages of proposed isolated converter


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Mode 3

At t2, the antiparallel diode of Q2 starts to conduct, when the Cr is charged to

the point of ucr ¼ uc, since the clamp capacitor C is larger than Cr, the time interval

is very short, the uc almost keeps constant. The auxiliary switch Q2 should be

turned on to achieve ZVS. The input inductor current iL decrease linearly.

The resonant inductor iLr will decrease form a positive to a negative value, and

the capacitor current ics becomes negative, the diode D1, D4 are turned on. The

voltage ucs increase. This stage ends when auxiliary switch Q2 is turned off.

Mode 4

The auxiliary switch Q2 is turned off at t3, and the clamp capacitor C is removed

from the circuit, and the main switch current is negative.

Assuming the energy stored in resonant inductor Lr is greater than the energy

stored in Cr. The ucr voltage will be discharged from uc to 0, and the antiparallel

diode of Q1 starts to conduct. Hence, the resonant Lr must stratify:

Lr � Crðucðt3ÞÞ2iLr ðt3Þ2

: ð1Þ

At time t4, the main switch is turned on for ZVS because the antiparallel diode

of main switch turns on.

Mode 5

At time t5, the switch current is increases from a negative to a positive value.

The input inductor current begins to linearly charge again, and another switch cycle

starts again.

4 Experimental result

A 3000W simulation and experimental prototype of the proposed AC/DC con-

verter has been built and tested to verify the effectiveness of the proposed converter.

The PSIM software is used to illustrate to the operation waveform of the proposed

converter, and the control circuit is implemented with the average current-mode

controller UC3854 from Texas Instruments. The parameters of the experimental

prototype of the AC/DC PFC converter are summarized in Table I.

Fig. 4 shows the simulation and experimental waveforms of input voltage,

input current and output voltage at the rated output power of 3000W. The input

current is close to a sinusoidal waveform, and it is in phase with the input voltage.

A high power factor of 0.993 could be achieved, and the measured THD of the

Table I. System parameters of the proposed converter

Input AC voltage 220V/50HzTurn ratio for primary side winding and

8:9secondary side winding

Output DC voltage 300V Sic switch C3M0065090JPomax 3000W Resonant inductor Lr 5 uH

Switching85K Input inductor L 220 uH

frequency (KHz)Output filter

2200 uF capacitance Cp 6.6 uFcapacitance C0

Clamp capacitance C 100 uF capacitance Cs 2.2 uF


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input current is 3.9%. The output voltage keeps 300V and it contains 100Hz ripple

voltage.

The simulation and experimental waveform of primary capacitor ucp, secondary

capacitor voltage ucs and input current is are given in Fig. 5 respectively.

Fig. 6 shows the gate drive signal ugs and the drain to source voltage uds for

main switch Q1 and auxiliary switch Q2, it indicates that the zero voltage switching

(ZVS) could be achieved for all SiC MOSFETs.

Fig. 7 shows the efficiency of the proposed topology for 220V/50Hz AC input

voltage, a high efficiency is reached over a wide load range, and the maximum

conversion efficiency is achieved by the 3000W prototype is 94.49%.

(a) (b)

Fig. 4. Simulation and experimental waveform of input voltage, inputcurrent and output voltage

(a) (b)

Fig. 5. Simulation and experimental waveform of input current,primary capacitor Cp and secondary capacitor Cs

(a) (b)

Fig. 6. Experimental waveform of gate voltage and drain-sourcevoltage for switch devices Q1 and Q2


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5 Conclusion

A single-stage isolated AC/DC PFC topology with active-clamped zero-voltage

switch is described in this paper. The ZVS operation mode is analyzed in detail, and

the proposed converter can be easily implemented with available control IC’S. The

theoretical analysis is verified by a 3000W simulation and experimental prototype.

A nearly unity power factor, lower than 4% THD current, and greater than 94%

conversion efficiency could be achieved.

Acknowledgments

This work was supported by Guangdong Science and Technology Foundation of

China (grant number 2015A010106018), Distinguished Young Teacher Project of

Education Department of Guangdong Province (YQ2015156, 2014KQNCX217).

Fig. 7. Measured efficiency curve


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a single stage soft-switched ac/dc power factor corrected

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