pfc correction24090

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Journal of EngineeringVolume 14 June 2008Number2

Available online @ iasj.net 2593

converter with two current feedback loop is presented in [3] and [4] , the model used twotransistors signal to generate the pulse width modulation (PWM) of the Buck Boostswitches . A single phase Buck Boost with variable output is presented in [5]. A current

programmed control for cascade two switches Buck- Boost converter is presented in [6]andits provided a variable output . A computer model for common switch mode control with

average and conventional cycle by cycle switching operation mode for Buck Boost is presented in [7]. A two switch Boost interleaved Buck- Boost converter is presented in [8]and it has the capability of producing both step-up and step down conversion with lowerswitches voltage stress.

POWER CIRCUIT DESIGN This work presents a Boost converter with fixed output (400 V , 3kW ) and a power

factor preregulator (UC3854 ) is used in order to improve the power factor (as shown infigure 1) in such a way that the input current is forced to follow the sinusoidal input voltage .Two loops are used to control the output voltage and the input current , the outer voltage loopand the inner voltage loop [9].

AC

source

Bridgerectifier

Co

L D

RL

Rvi

Rvd

Sensing resistor

-

+MULTIPLIER/

DIVIDER

Rs

Full wave rectified AC inputsensing

Vref

Voltagerror

Power circuit

UC 3854 PFC preregulator IC

-

+

Currenterror

PWM

Fig(1) Power factor correction for Boost converter AC/DC Converter(UC3854)

The second converter is the Buck Boost converter shown in figure 2 , the converteris either operate in boost mode in such away that the output voltage is higher than themaximum input voltage or in Buck Boost mode where the output voltage is lower thanthe maximum input voltage. Figure 3 shows the two operation mode of the Buck Boostconverter .

The output inductor employed in the converter provides the energy storage andfiltering . The current flowing through it has a triangular waveform . In selecting theinductance a compromise has to be found between high rating required for diminishingthe ripple , and a low rating required for quick response to load changes.The peak inductor current is the sum of the peak line current and half of the peak to peakhigh frequency ripple current. The inductor must be designed to handle this current level.


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A.M. Shaker Design and simulation of powee factorA. M. Salih Correction for ac/dc convereterK.S. Ismail


ViCo

D2S1

D1 S2

LVo

Full waverectifier

-

+

-

+

1/Kin

Mult/divIref=AB/C^2

B

Vref

A

C

Kff

Rmo R1

Cz

Cp R2

Cvf

Rvf

Voltageerror

amplifier

Currenterror

amplifier

UC3854 PFC IC

PWMgenerator

D b

u c

k

D b

o o s

t

Rvi

Rvd

RL

Rs

Fig (2) Power factor correction for (Fig3 ) The Buck Boost converter

Buck Boost Converter operation modes

BOOST CONVERTER INDUCTOR DESIGN: The Boost converter inductor is decided according to the minimum rms input

voltage then

rmsi

in

peak V P

I 2

(1)

where PEAK I is the maximum input current, in P is the input power to the converter and

rmsiV ,, is the root mean square of the input voltage.

Since in steady state the time integral of the inductor voltage over one time periodsmust be zero [10] , therefore

0)( OFF oiON i t V vt v (2)

where iv is the instantaneous value of the input voltage , ON t is the on time of the switch ,

oV is the output voltage of the converter and OFF t is the off time of the switch.

Dividing both sides by T s Where T s is the switching frequency and rearranging termsyield

d vV

i

o

11

(3)

where d is the duty cycle of the ON time of the boost switch.During the ON period

Time

Time I n p u

t V o

l t a g e

O u

t p u

t V o

l t a g e

I n p u

t V o

l t a g e

I n p u

t C u r r e n

t


5/15



dt di

LV l L (4)

where l di is the inductor ripple current

S o

iS T

V

vdT dt )1( (5)

then

)1( max,max,

o

i

L

S i

V

V

di

T V L (6)

BUCK- BOOST INDUCTOR DESIGN: The value of inductance is decided depending on the worst operating condition ,

i.e, when the ripple is X% and it is in continuous conduction during buck modeoperation [5] . This occurs when the input voltage is at its maximum peak value and the

output is at its minimum value then the peak input current is given by

(max)2

,rmsi

in peak V

P I (7)

peak L I X

i100

(8)

where Li is the peak to peak ripple of inductor current .When the converter operates at buck mode , as the Buck switch is ON then,

dt di

LV vV Loi L (9)

S T d dt 1

where 1d is the duty cycle of the Buck switch , and as

max

2min1

iV V

d (10)

then

)1(maxi

o

L

S o

V V

iT V

L (11)

OUTPUT CAPACITOR:The output capacitance selection depends on the following factors[10],[11]

The switching frequency . The ripple current. The second harmonic ripple current. The output ripple. The output d.c. voltage . The hold up time of the capacitor.


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It should be noted that for a given capacitance the capacitor value is proportional to thevoltage rating and the maximum energy storage capability which is proportional to thesquare of the voltage rating. According to the above factors the capacitor with a certainhold up time is given by [10],[11]

2

min2

2

oo

UP HOLDou t O

V V

t P C (12)

where UP HOLDt is the time hold up by the capacitor and it is in the range of 16 to 50ms[1].

BUCK BOOST CONVERTER CONTROL CIRCUIT : Active PFC performs much better and is significantly smaller and lighter than the

passive PFC circuit. The active PFC can be implemented with a single chipcontroller, making the circuit relatively simple with minimum number ofcomponents .

One of the most popular chip is the Unitrode UC3854 controller which acceptsan ac input voltage of 75-275 rms voltage and a frequency of 50 400 Hz [9] .

The circuit has two control loop one of them is the fast acting internal currentloop . It defines the input current shape to be sinusoidal and force it to be in phase withthe input voltage .The second loop is the external voltage loop which regulates the outputdc voltage.

The principle of operation of Boost PFC is as follows: The rectified sinusoidalinput voltage is fed to a multiplier circuit , providing a current reference to the multiplierand a feed forward signal proportional to the rms value of the line voltage .Thefiltered DC voltage of Boost PFC is compared to a reference voltage V ref andamplified. The error amplifier sense the variation between the output voltage and thefixed dc reference voltage. The error signal is applied to the multiplier .Themultiplier output follows the shape of the input ac voltage. This signal is comparedto the current signal sensed by R s in a Pulse Width Modulation (PWM) circuit. Theinductor current waveform follows the shape of the rectified ac line voltage. Thegate drive signal controls the inductor current amplitude and maintains a constant outputvoltage.

A charge control scheme is adopted in this design of the current loop control of theBuck Boost converter since the input current to the converter is discontinuous and its oneform of average current control [12-14].Charge control uses a reset integrator to controlthe average value of a pulsating circuit variable. Figure 4 show the input current for thetwo cases .

Time

iiii

(a)Boost mode (b)Buck mode Time

Fig(4 ) Input current for Boost and Buck mode


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Figure 5 illustrates the circuit used in charge average current control used to sense thecurrent in the PFC of the Buck- Boost converter. The K iS /1 is hall current sensor which

is proportional to the instantaneous input current. Two capacitors 1C and 2C are used

for integrating the input current alternatively . Transistor 1T

and 2T

employed to quicklydischarge the capacitors. The four diode bridge Da-Dd allows K iS /1 to charge thecapacitor with lower V x to pick up the higher capacitor voltage which represents theaverage input current .

Is1/K

Da Dc

Db Dd

C1

C2

T1

T2

Vx

Cp

Cz R2

R1 D-

+

Fig( 5 ) Charge average current sensing used in buck boost converter

SIMULATION RESULTS:Using the package Orcad 10 the simulation results for the Boost converter given in

figure 6 is shown in figure 7(a, b, and c) when the input voltage is 230 V rms , linefrequency 50 Hz , output voltage 400 V output power 3kW and the switching frequencyis 20kHz . Figure 7 shows the input voltage input current , duty cycle of the boost switch, the output voltage and the input current harmonics. The input current at the first halfcycle is 20-25 times the current of the converter. This problem is solved by using theBuck Boost converter shown in figure 8. Figures 9 ,10 and 11 show the input voltage ,input current output voltage duty cycle of the buck and boost switch and inputcurrent harmonics when the output voltage of the converter is 400V ,250V and 150 Vrespectively.The input current harmonics for these cases is shown in figure 12 and it shows that thecurrent harmonics is lower than the EIC standards .The problem of discontinuous input current in Buck mode operation is solved usingaverage charge current control .

CONCLUSIONS :A power factor correction control for AC/ DC Boost converter is presented and the input

current harmonics is eliminated and it is lower than the standards ,the output voltage andoutput power is fixed in this type of converters .

The problem of high inrush input current is solved by using Buck Boost converter andalso the output voltage and output power can be made variable in this type of converters


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Since the input current in Buck mode of Buck Boost converter is discontinuous , acharge average current control is used to provide the error signal for the inner loopcurrent amplifier. Also the input current harmonics is lower than the standard harmonicscurrent and hence the power factor is within the range 0.993-0.998.

0

Rf 320k

BZX84C6V2/ZTX

D31

Rf1

Cf2Cf1.47u

Cp

450p

C111u

20

Ct

6.8n

R14

220k

R15

75k

R16

1.6k

R17

10k

R2

20k

Rset

10k

0

V3

FREQ = 50VAMPL = 320

VOFF = 0

0

D151N5817

D161N5817

2

1

0

16.Vdc

0

R2127k

0

Rdv10k

RL54

Ri510k

Rs

.025

Rmo4k

910k

R11

910k

Co4000u

C710n

1 2L1

500u

0

0

0

0

V S ENSE GNDSS

ENAPK LMTCA OUT

I SENSEMULT OUT

V/A OUTRSETCT

VRMSIAC

VREFVCC GT DRV

U1

UC3854

20

1B

0

0 0

00

C8470p

Cz

2.5n

IRFP462

R1

4k

Rf 2

91k

D2

C19. 47u 2

1

2

1

BYT30P-600

2

1

C17.47u

C18

0.16u

0.1u

Fig( 6 ) Single phase PFC boost converter schematic(UC3854)

Ti m e

0s 20 ms 40m s 60 ms 80m s 1 00m s 120 ms 1 40m s- I( V3 ) V (D 27 :K ,D 26 :K ) V (R 3: 2) V (V 3: +, V3 :- )

-500

0

50 0

input cur ren t

input vo l tage

output vo l tage

Fig( 7)( a) Boost converter input voltage , input current andoutput voltage Vi=230Vrms,Vo=400V ,Po=3000W , f S=20kHz

I n p u t v o

l t a g e (

V )

, i n p u

t c u r r e n

t ( A )

, o u

t p u

t v o

l t a g e (

V )


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Ti m e

1 0 0 m s 1 0 1 m s 1 0 2 m s 1 0 3 m s 1 0 4 m s 1 0 5 m s 1 0 6 m s 1 0 7 m s 1 0 8 m s 1 0 9 m s 1 1 0 m s

V ( V3 : +, V 3: - ) V (D 1 4: C AT )

0V

2 0 0 V

3 9 8 V

Fig 7 (b)Duty cycle of Boost converter

Vi=230Vrms,Vo=400V Po=3000W , f S=20kHz

F r e q u e n c y

0 H z 5 0 H z 1 0 0 H z 1 5 0 H z 2 0 0 Hz 2 5 0 H z 3 0 0 H z 3 5 0 H z 40 0 H z 4 5 0 H z 5 0 0 H z 5 5 0 Hz 6 0 0 H zI ( V 3 )

0A

5A

10 A

15 A

20 A

Fig7 (c)Input current harmonics for Boost converter

Vi=230Vrms,Vo=400V Po=3000W , f S=20kH

V1

FREQ =50VAMPL = 320VOFF =0 0.47u

0.47u

amplifier parametersvoltage error

15Vdc

5V

0

V c c

VCC

0

0

1 Q

1

C e x t

1 R e x t

/

C e x t

S1 Buck switch

t o

T 2

t o

T 1

Charge average current sensing

Rs

0.025

senseresistor

T3

15v

D1

voltage error parameter s

1 2L

1.8mH

S2

Cext

1n

D5

5k

Rf1910k

0

Rf2

91k

Boost switch

Rf320k

220k

switch gate drive signals mpdified current sensing

1 Q

1.6k

75k

10k

0

Rmo4k

Cz

270p

Rset36k

discharge signal generation

10

R1027k

RLvariable

Cp

47p

1 A

1 B

1 R

d

Cext 1n

Cf10.1u

average current sensing

Cf20.47u

1u

IS1/k

470p

C71n

R62.5k

Co4000u

C9100n

Cvf

0.16u

R54k0

CT1.8n

Da

R1810

0

1N5817

R32k

15k

1N5817

15k

R2110

Dc

gain modificationvariable output

15k

Db0

2 A

0

C111n

0

R413k

0Dd

R2

192k

C121n

0

2 B

2 R

d

2 R e x t

/ C e x t

2 C e x t

2 Q

2 Q

G N D

10

10k

0

10

10

+Vcc

10k

18k

Rext1k

feedforward voltage

+Vcc

20k

0

Rext

1k

10

0

5k

T5

VCC

CLK3

C L R

1

D2 P

R E

4

Q 5

Q 6

U3A

74LS74A

20-55 ohm

Rvi510k

Rdvvariable

Rvf

77k

0

5V

R14k

0

C10100n

V S E NS E G NDSS

ENAPK LMTCA OUT

I SENSEMULT OUT

V/A OUTRSETCT

VRMSIAC

VREF

VCC GT DRV

U1

UC3854

To drive S1

buck switc h

Vcc15Vdc

T6

0

0

T12N2222

0

+VCC

T22N2222

5k

+5

-6

V +

8

V -

4

OUT 7

LM393

10

5k

VCC

0

10k - 27k

12k

+5

-6

V +

8

V -

4

OUT 7

LM393

0

buck and boost switchesdrive signals of

0

+5

-6

V +

8

V -

4

OUT 7

LM393

0

+ 3

- 2

V +

8

V -

4

OUT1 LM393

To drive S2

+ 5

- 6

V +

8

V -

4

OUT7 LM393

Boost switch

+ 5

- 6

V +

8

V -

4

OUT7 LM393

7 4 H C T 1 2 3

in

Vcc

IR2117

Vs

Ho

Vb

com

5V

0

T4

0

+5

-6

V +

8

V -

4

OUT 7

LM393

5k3Vdc

Vff

0

0

I n p u

t v o

l t a g e (

V ) , D u

t y c y c l e

C u r r e n

t ( A )


10/15



Fig8(a ) The connection diagram for PFC single phase Buck Boost converter

Buck Boost Power Circuit

FeedforwardInput Voltage

Voltage error Amplifier

Multiplier/ divider A*B/C 2

Average ChargeCurrent Sensing

Variable OutputGain

Modification

Pulse WidthModulation Drive

Circuit

Output voltage

Buck Switch DriveSignal

Boost Switch DriveSignal

Current sensing

Gain

B A

C

Current Error Amplifiuer

Vref

Fig8(b) Buck Boost Converter block diagram

Ti m e

0 s 2 0 ms 4 0 ms 6 0 ms 8 0 ms 1 0 0m s 1 2 0m sV (R 2:2 ) - I( V1) *2 V (V1 :+, V1: -)

- 5 0 0

0

50 0

i n p u t c u r r e n t * 2

i n p u t v o l t a g e o u t p u t v o l t a g e

Fig9 (a) Buck Boost converter input voltage , input current andout put voltage Vi=230Vrms,Vo=400V ,Po=3000W , f S=20kHz

I n p u

t v o

l t a g e

( V )

, i n p u

t c u r r e n

t ( A )

, o u

t p u

t v o

l t a g e

( V )


11/15



Frequency

0Hz 100Hz 200Hz 300Hz 400Hz 500Hz 600HzI(V1)*.94

0A

10 A

20 A

25 A

Fig9(b )Input current harmonics of Buck Boost converter

Vi=230Vrms,Vo=400V ,Po=3000W , f S=20kHz

Ti m e

0s 2 0m s 4 0m s 6 0m s 8 0m s 1 00 m s 1 20 m s- I( V1 )* 1. V (V 1: +, V1 :- )* 1 V (R 2: 2) *1 .1 3

- 5 0 0

0

50 0

i n p u t c u r r e n t

o u t p u t v o l t a g ei n p u t v o l t a g e

Fig 10(a) Buck - Boost converter input voltage , input current and

out put voltage Vi=230Vrms,Vo=250V ,Po=2000W , f S=20kHz

t ime

60.00ms 61.00ms 62.00ms 63.00ms 64.00ms 65.00ms 66.00ms 67.00ms 68.00ms 69.00msV ( V1 : +, V 1: - ) V ( S1 : 1, S 1: 2 )

0

200

398

buck duty cycle

input vol tage

Fig 10(b) Buck switch duty cycle for Buck - Boost converter

Vi=230Vrms,Vo=250V Po=2000W f S=20kHz

Input voltage , inputcurrent , output voltage

I n p u

t v o

l t a g e (

V )_

, i n p u

t c u r r e n

t ( A )

, o u

t p u

t v o l t a g e (

V )

I n p u t v o

l t a g e (

V ) , D u

t y c y c l e

C u r r e n

t ( A )


12/15



t ime

60.00ms 61.00ms 62.00ms 63.00ms 64.00ms 65.00ms 66.00ms 67.00ms 68.00ms 69.00msV (V 1: +, V1 :- ) V (M 1: g)

0

200

398

boost duty cycle

input vol tage

Fig 10(c) Boost switch duty cycle for Buck - Boost converter


Frequency

0Hz 100Hz 200Hz 300H z 400 Hz 500 Hz 6 00Hz-I(V1)/2.8

0A

5.0A

10.0A

13.6A

Fig10(d) Input current harmonics for Buck - Boost converter


Time

0s 20ms 40ms 60ms 80ms 100ms 120msV (C3 :2 ) - I( V1 ) V (V 1:+ ,V1 :- )

-400

-200

0

200

400

input current*5

input vol tage output vol tage

Fig11(a) Buck - Boost converter input voltage , input current andout put voltage Vi=230Vrms,Vo=150V ,Po=1000W , f S=20kHz

I n p u

t v o

l t a g e ( V

) ,

i n p u

t c u r r e n

t ( A ) , o u

t p u

t v o

l t a g e

( V )

I n p u

t v o

l t a g e (

V ) ,

D u

t y c y c l e

C u r r e n

t A


13/15



Time

80ms 81ms 82ms 83ms 84ms 85ms 86ms 87ms 88ms 89ms 90msV (R 20 :B ) V (V 1: +, V1 :- )

0V

200V

400V

boost duty cycle

Fig 11(b) Boost switch duty cycle for Buck - Boost converterVi=230Vrms,Vo=150V Po=1000W , f S=20kHz

Time

60ms 61ms 62ms 63ms 64ms 65ms 66ms 67ms 68ms 69ms 70msV ( V1 : +, V 1: - ) V ( S1 : 1, S 1: 2 )* 2

100V

200V

300V

400V

1V

buck duty cycle

Fig11 Buck switch duty cycle for Buck - Boost converterVi=230Vrms,Vo=150V Po=1000W , f S=20kHz

Frequency

0Hz 100Hz 200Hz 300Hz 400Hz 500Hz 600HzI(V1)/5

0A

2.00A

4.00A

6.00A

7.03A

Fig 11 (d) Input current harmonics for Buck - Boost converter

Vi=230Vrms,Vo=150V Po=1000W , f S=20kHz

I n p u

t v o

l t a g e (

V ) ,

D u

t y c y c l e

I n p u

t v o

l t a g e (

V ) , D u

t y c y c l e

C u r r e n

t ( A )


14/15



0

0.5

1

1.5

2

2.5

3

1 2 3 4 5 6 7 8 9 10 11 12

boost 400V

buckboost400V

buckboost250V

buckboost150VIEC1000-3-2ClassA limits

Fig` 12 Input current harmonics contents for the different cases

REFERENCES:

* IEC standard IEC 61000-3-2(2001- 10)Ed2.1,Electromagnetic compatibility (EMC) part 3- 2 limits for harmonic current emissions, 2001.

* B. Flud, S. Kern and R.1993 Ridely Combined buck and boost power factorcontroller for three phase i nput IEEE, Poer Electronics and Applications ,1993,fifth European Conference Vol , Issue 13-16 , Sep , pp 144-148 vol .7.

* R. Ridely, S. Kern and B. Flud 1993 Analysis and design of a wide range PFCcircuit for three phase application IEEE , Appl ied power electronics conference ,volume, issues 7-11 march, pp 299-305.

* M. Chanen, K. AL-Haddad and G.Roy1993 , A new single phase buck boost converterwith unity power factor , IEEE, Industry applications society , annual meeting ,Volume , issue 2-8 Oct. 1993 pp 785-792 volume 1.2.

* Y. Zhao,1998 Single phase power factor correction with wide output voltage rangeM.Sc. thesis ,Virginea University .

* G.K. Andersoen and F. Blaabjerg2001 Current programmed control of a single phase two swit ch buck boost power factor correction, IEEE, Applied powerelectronics conference Volume issue 1 pp 350-356.

* G.G. Michael Averaged and cycle by cycle switching model for buck , boost , buck boost and cuk converters with common average switching mo de Texas TechUniversity e mail Michael @ coez.coe.ttu.edu.

* J. Chen , D. Maksimovic and R. Erickson2006 , Analysis and design of a low stress buck boost converter in universal input PFC application IEEE transaction on power electronics , Volume 21, No 2 march.

* C. Silva2001 Power factor correction with the texas instrumentation catalogueUC3854 .

* N. Mohan , T.M. Undeland and W.P1995 . Robbins Powert electronics converters,applications and design John wily and son, Inc . Second Ed ition , New York .

C u r r e n

t ( A )

Harmonic No


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* M. O. Loughlin 2002 UCC3819 , 250 W power factor correction (PFC) boost flower preregulater design , Texas Instrumentation Literature No.SLOA 296,.

* W. Jang , F.C Lee , R. B. Ridley and I. cohen1992 Charge control modeling anal ysisand design IEEE PESC pp 503 -511.

* V. Vorperian 1993 the charge controlled PWM switch IEEE PESC pp 533 -

543.* W. Jang ,y. Jung , G.C .Hua andF.C Lee1993 Power factor correction with flyback

converter imploying charge control IEEE PESC pp 293 -308 , 1993.

pfc correction24090

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