Seminar on Improved Power Quality AC-DC Converters with High Frequency Transformer Isolation By Prof. Bhim Singh Department of Electrical Engineering Indian

Seminar onSeminar onImproved Power Quality Improved Power Quality AC-DC Converters with AC-DC Converters with

High Frequency Transformer IsolationHigh Frequency Transformer Isolation

ByByProf. Bhim SinghProf. Bhim Singh

Department of Electrical Engineering Department of Electrical Engineering Indian Institute of Technology Delhi Indian Institute of Technology Delhi Hauz Khas, New Delhi-110016, IndiaHauz Khas, New Delhi-110016, India

email:[email protected]:[email protected].: (91)-011-2659-1045Ph.: (91)-011-2659-1045

ClassificationClassification

Improved Power Quality AC-DC Converters Improved Power Quality AC-DC Converters with with

High Frequency Transformer IsolationHigh Frequency Transformer Isolation The control of DC-DC converter is done such

as the input current wave shaping is achieved for AC-DC Diode converter.

The DC-DC converter can be operated in both DCM and CCM mode.

The control technique for DCM and CCM are different.

It works as voltage follower in DCM mode and there is no need of input voltage & current sensing for power factor correction.

ApplicationsApplications

DC Power Supplies, Telecommunication Power Supply, Improved Power Factor ballast, Power Supplies for equipments like computers,

medical equipments, printers, scanners etc. Drives Applications with Power Factor

Improvement at AC side, Electrical Welding, Lighting such as ballasts, CFL etc.

Single-Phase Buck Boost Single-Phase Buck Boost Flyback AC-DC ConverterFlyback AC-DC Converter

vs

Ls

Cs Cd

HFT

Q

is

io

Vo+

LoadCo

Single-Phase Buck Forward Single-Phase Buck Forward AC-DC ConverterAC-DC Converter

vs

Ls

Cs Cd

HFT

Q

is

Lo

Vo+

LoadCo

io

Single-Phase Buck Push-Pull Single-Phase Buck Push-Pull AC-DC ConverterAC-DC Converter

vs Cd

HFT

Cs

Q1Q2

Lois

Ls

Vo+

LoadCo

io

Single-Phase Buck Half-Bridge Single-Phase Buck Half-Bridge AC-DC ConverterAC-DC Converter

vs

Ls

Cs

Cd1

HFT

Cd2

Lo

is

Vo LoadCo+

io

Q1

Q2

Single-Phase Buck Full Bridge Single-Phase Buck Full Bridge AC-DC ConverterAC-DC Converter

vsCs

Q1

Q2

Cd

Q3

Q4

Ld

isLs

HFT Lo

Vo LoadCo+

io

Single-Phase Boost Forward Single-Phase Boost Forward AC-DC ConverterAC-DC Converter

Lo ioHFT

vs

Ls

Cs

Ld

Cd

is

Q

D1

D2

Vo LoadCo+

Single-Phase Boost Push-Pull Single-Phase Boost Push-Pull AC-DC ConverterAC-DC Converter

LoHFT

vs

Ls

Cs

Cd

+-

Ld

Rd

Q1 Q2

is

io

Vo LoadCo+

Single-Phase Boost Half-Bridge Single-Phase Boost Half-Bridge AC-DC ConverterAC-DC Converter

vs

Ls

Cs

Lo

HFT

Vo LoadCo+

is

Ld

Q2

Q1

io

Single-Phase Boost Full Bridge Single-Phase Boost Full Bridge AC-DC ConverterAC-DC Converter

vsCs

Q1

Q2

Cd

Q3

Q4

HFT Lo

is

Ld

Vo+

LoadCo

io

Ls

Single-Phase Buck-Boost Cuk Single-Phase Buck-Boost Cuk AC-DC ConverterAC-DC Converter

vs

Ls

Cs

L1HFTC1

is

Q

L2C2 io

Vo+Co Load

Single-Phase Buck-Boost SEPIC Single-Phase Buck-Boost SEPIC AC-DC ConverterAC-DC Converter

vs

Ls

Cs

Ld HFTCd

Q

is

io

Vo+Co Load

Single-Phase Buck-Boost Zeta Single-Phase Buck-Boost Zeta AC-DC ConverterAC-DC Converter

Qvs Cs Cd

HFTis

C1

Co Load+

ioLs

Lo

Single-phase buck-boost flyback AC-DC

converter in DCM

Single-Phase Buck Boost Flyback AC-DC Converter

Average current mode control in CCM operation

Single-Phase Buck Boost Flyback AC-DC ConverterFLYBACK Converter in DCM

average input current over a switching cycle is given as:

DI2

1i pk1 (1)

where pkI is the peak of input current (that’s switch current) and D is the duty ratio. From Fig.1b pkI is given as:

1rm

spk v

L

DTI (2)

where 1rv is rectified input voltage and mL is transformer magnetizing inductance referred to primary. From eqns (1) and (2), the input current is as:

1rm

s2

1 v2L

TDi (3)

Single-Phase Buck Boost Flyback AC-DC ConverterDesign of Flyback Converter in DCM

Equation (3) presents nicely PFC operation in DCM. It is clear that if duty cycle and switching frequency is kept constant, then input current is a linear function of input voltage. Eqn. (3) can be written as:

tsinIi 11 (4)

where, tsinVv 11r (5)

m

s2

11 2L

TDVI (6)

Since input inductor current is nothing but the rectified ac mains current, thus from Eqn. (4), it is clear that by keeping the duty cycle and switching frequency constant, the average input current in flyback converter in DCM follows the input voltage exactly thus emulating a resistor and is known as voltage follower technique. Therefore, flyback converter behaves as an ideal current shaper, and performs current shaping automatically with no control when operating in DCM.


The design of the converter depends whether it is working in discontinuous or continuous conduction mode. The transfer function of the flyback converter in DCM is given as:

nD

DvV

1

1ro (7)

where n is the turn ratio. From Fig. 1b, for DCM operation, the condition is: 1DD 1 (8) From Eqns. (7) and (8), for the desired maximum duty ratio at minimum input voltage, turn ratio can be obtained by satisfying following inequality as:

o

1

V

V

D)(1

Dn

(9)


In order to ensure DCM of operation at maximum load, following condition must be satisfied

2

1min

os

minLm

)V

V

n

1(4f

RL

(10)

where min1V is the peak value of minimum input voltage. minLR is the minimum value of load resistance and sf is the switching frequency. Output capacitor is selected on the basis of maximum peak-to-peak ripple in output voltage ( vr ) as:

Lv

oo Rr

V

C (11)


Design of Flyback Converter in DCM and CCM Stresses on semiconductor devices in DCM can be given by following equations, Peak current through switch is given as:

m

s1swpk L

DTVI (12)

Peak voltage across switch is given as: o1swpk nVVV (13)

Similarly, peak current through diode is as:

m

s1o2

diopk L

TDVnI (14)

and peak voltage across the diode can be given as:

o1

diopk Vn

VV (15)


Design of Flyback Converter in DCM and CCM For CCM operation, the transfer function is given as:

D)n-(1

DvV 1r

o (16)

Thus in a similar manner as in DCM, for desirable maximum duty ratio, the turn ratio is determined. However, magnetizing inductance of the transformer is defined by satisfying the following inequality [6]:

2

1min

os

maxLm

)V

V(4f

RL (17)

Referring Fig. 2b, switch current at half of the ripple is given as:

max1min

omaxswh ηDV

PI (18)


Design of Flyback Converter in DCM and CCM From Fig 2b, switch peak current for ripple swI is given as:

2Iswpk

swswh

II

(19)

where ,

m

smax1minsw L

TDVΔI (20)

Switch RMS current is given as: 2swswpksw

2swpkmaxswRMS ΔI

3

1IΔI[IDI (21)

Similarly diode current at half of the ripple is given as:

)1(I

max

max

D

I odh

(22)

From Fig 2b, diode peak current for ripple dI is given as:

2

Idpkd

dh

II

(23)

where,

2

max )1(

L

TDVI so

d

(24)


Specifications

Input: RMS1 220VV , 50Hz, Single-Phase AC Supply Output: V110Vo , 1kWPo , Output voltage-ripple less than 2% Switching frequency 50kHz)2/(fs s Design parameters for DCM Transformer turn ratio (n) 1.5:1, Magnetizing inductance H50Lm , 1mHL f ,

800nFC f and 15mFCo .


Source voltage and current in DCM at

100% load

Steady state output voltage in DCM at 100% load


Source voltage and current in CCM at

100% load

Steady state output voltage in CCM at 100% load


TABLE IComparisons of Flyback Converter Operation in DCM and CCM

Quantity

DCM Operation CCM Operation

10% Load 100% Load 10% Load 100% Load

Input Current THD 12% 5.1% 11% 4.4%

PF 0.981 0.997 0.989 0.998

Output Ripple 0.55% 1.73% 0.52% 1.45%

Normalized Current of Switch(pu)

Peak 25.1 6.73 6.53 2.60

Average 0.93 0.71 0.54 0.67

RMS 2.87 1.62 1.35 1.14

Normalized Current of Diode(pu)

Peak 14.5 9.76 10.13 3.95

Average 1.13 1.48 1.29 1.16

RMS 5.27 2.86 2.57 1.90

Control Technique Voltage Mode Control Average Current Control

Size of Converter Small Large

Circuit Simplicity Simple Complex


Test results of AC mains voltage, AC mains current, output DC voltage and output Test results of AC mains voltage, AC mains current, output DC voltage and output DC current waveform of AC-DC flyback converter for load perturbation response on DC current waveform of AC-DC flyback converter for load perturbation response on equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-axis channel-1 1div =85V, channel-2 1div =5A, channel-3 1div= 100V, channel-4 axis channel-1 1div =85V, channel-2 1div =5A, channel-3 1div= 100V, channel-4 1div= 2A)1div= 2A)

Vs (V),

is(A)

Vdc (V)

Idc (A)

Single-Phase Buck-Boost Cuk AC-DC Converter in DCM

Single-Phase Cuk AC-DC Converter Inductors voltage and current waveforms in DCM

Single-Phase Cuk AC-DC Converter

CCM operation

Single-Phase Cuk AC-DC Converter Inductors voltage and current waveforms in CCM

Single-Phase Cuk AC-DC Converter in

DCM Operation To simplify the analysis, all quantities are referred to the primary side of the transformer. Volt-second balance on the inductor gives following equality:

11r

o

d

d

v

'v (1)

where 'vo and 1rv are output voltage (referred to primary) and rectified input voltage respectively. d is the duty ratio and d1 is the off period of switch, during which inductor currents decrease linearly. Assuming 100% efficiency for simplification, the current ratio is:

12

1

d

d

'i

i (2)

where 1i and 'i2 are the input inductor current and output inductor current referred to primary side of the transformer.

Single-Phase Cuk AC-DC Converter in DCM

First stage of Operation When switch is on, two inductor currents increase linearly with the voltage across them equal to input voltage. The equations of input and output inductor currents for the interval sdTt0 (referring to Fig. 1b(i)) are given by:

tL

vii

1

1r1 (3)

t'L

vi'i

2

1r2 (4)

where i is the minimum input inductor current. Second Stage of Operation When switch is off, inductor currents decrease linearly with voltage across them equal to output voltage. Referring to Fig. 1b(ii) and Fig. 1c, inductor currents are given by:

idTL

vt

L

'vi s

1

1r

1

o1 (5)

idT'L

vt

'L

'v'i s

2

1r

2

o2


Third stage of Operation This is the stage when the diode current is zero. Averaged input and output inductor currents over a switching period can be given by [1]:

i)d(ddT2L

vi 1s

1

1r1 (7)

i)d(ddT'2L

v'i 1s

2

1r2 (8)

Sum of the input and output inductor currents is given by:

dd

d1dT

L

v

2

1'ii 1

seq

1r21

(9)

where, 'LL

'LLL

21

21eq

(10)


By substituting the expression in eqn. (2) in to eqn. (9), we get:

dd

d1dT

L

v

2

1

d

d1 1

seq

1r11

i (11)

After simplification it gives:

eq

s2

1r1 2L

Tdvi (12)

It can be written as: tsinIi 11 (13)

where, tsinVv 11r (14)

eq

s2

11 2L

TdVI (15)

Single-Phase Cuk AC-DC Converter Average and peak currents in the semiconductors

and input inductor Average current ( avswi ) and peak current ( pkswi ) of the MOSFET switch over a switching cycle are as:

).d'I(I2

Td-

L

vi 2max1max

s2

eq

1ravsw

(16)

)'I(Ii 2max1maxpksw (17) where 1maxI and 'I2max are the maximum value of input inductor current and output inductor current (referred to primary) respectively. Average current ( 'i avd ), and peak current ( 'i pkd ) of the diode (all referred to primary) are as:

d)-).(1'I(I2

Td

L

v'i 2max1max

s2

eq

oavd

(18)

)'I(I'i 2max1maxpkd (19)

Single-Phase Cuk AC-DC Converter Average and peak currents in the semiconductors

and input inductor

Peak voltage across switch ( pkswV ) and diode ( 'V pkd ) (referred to primary) is

given as: 'VV'VV oinmaxpkdpksw (20)

The average current ( avL1i ) and RMS current ( rmsL1i ) of input inductor are as:

π

2Ii 1max

avL1 (21)

2

Ii 1max

rmsL1 (22)

Single-Phase Cuk AC-DC Converter

Design Description in DCM and CCM Step 1: Conversion ratio Defining the dc voltage conversion ratio (M) as,

1r

o

v

VM (23)

where, tsinVv 11r (24) For 90t , conversion ratio is obtained as the first step of the design. Here 1V is the peak value of input voltage. Step 2: Condition for operation in DCM and CCM Design must ensure the DCM operation, for which following inequality must hold good:

2en)2(M

1K

(25)

where eK is the conduction parameter and n is the transformer primary to secondary turn ratio.

Design Description in DCM and CCM

For CCM, following condition must be satisfied to ensure the continuous conduction mode of operation:

2en)2(M

1K

(26)

eK is calculated for minimum value of M which occurs at minimum output voltage and maximum input voltage in CCM for given range of specification.

Step 3: Equivalent inductance ( eqL ) which is the parallel combination of 1L and 'L2 , is given as:

2

TRKL sLe

eq (27)

where LR is the load resistance. Step 4: Duty Ratio The duty ratio for the given power (load resistance) in DCM is obtained by:

eKM2d (28)

Design Description in DCM and CCM

Step 5: 1L and 'L2 Design 1L can be obtained by considering the specified maximum current ripple for

DCM as:

i

eq1 dr

2LL (29)

where ir is p.u. ripple current. 'L2 can be obtained using expressions for 1L and eqL in eqns. (29) and (10)

respectively. Similarly, for CCM 1L and 'L2 can be obtained by specified maximum current ripple allowed and eqn. (10).

Design Description in DCM and CCM Step 6: Design of energy transfer capacitor C1

It has great influence on input current waveform. To avoid input current oscillations at every line half cycle, it is given by:

)'L(L

1C

212

r1

(30)

where, srL Resonant frequency ( r ) should lie between line frequency ( L ) and switching frequency ( s ).

Step 7: Output Capacitor Output capacitor is chosen according to specified ripple allowed in the output voltage. It can be achieved by following formula:

minLvLo Rr

1C

(31)

where vr is the pu ripple in the output voltage and minLR is the minimum load resistance.

Single-Phase Cuk AC-DC ConverterSpecifications

Input: RMS1 270V160V , 50Hz, Single-Phase AC Supply

Output: 132V98Vo adjustable with nominal value of 120V , 2.6kWPo Output voltage-ripple less than 2%

Switching frequency 50kHz)2/(fs s Design parameters for DCM mode: Transformer turn ratio (n) 1:1, H1500L1 , H4.3L2 , F2.5C1 ,

F10C2 , and 30mFCo .

Single-Phase Buck-Boost Cuk AC-DC Converter

Source voltage and current in DCM at 100% load




Source voltage and current for 100% load in CCM


TABLE IComparisons of Cuk Converter Operation in DCM and CCM at Full Load

Quantity DCM Operation CCM Operation

Input Current THD 5.5% 3.8%

PF 0.998 to 1.0 0.9975 to 1.0

Ripple Factor 1.83% 1.67%

Peak Current Through Device 170A 60A





Test results of AC mains voltage, AC mains current, output DC voltage and output Test results of AC mains voltage, AC mains current, output DC voltage and output DC current waveform of AC-DC cuk converter for load perturbation response on DC current waveform of AC-DC cuk converter for load perturbation response on equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-axis channel-1 1div =175V, channel-2 1div =5A, channel-3 1div= 100V, channel-4 axis channel-1 1div =175V, channel-2 1div =5A, channel-3 1div= 100V, channel-4 1div= 1.75A)1div= 1.75A)

VVs s (V)(V), ,

iiss(A)(A)

VVdc dc (V)(V)

IIdc dc (A)(A)

Single-Phase SEPIC AC-DC Converter in

DCM

Single-Phase SEPIC AC-DC Converter in

DCM

Single-Phase SEPIC AC-DC Converter inCCM

Single-Phase SEPIC AC-DC Converter inCCM

Single-Phase SEPIC AC-DC Converter

Specifications

Input: RMS1 230VV , 50Hz, Single-Phase AC Supply

Output: V110Vo , kW5.1Po

Output voltage-ripple less than 2%

Switching frequency 50kHz)2/(fs s

Transformer turn ratio (n) 1:1, H1200L1 ,

H1.8L2 , F1C1 , and 30mFCo .

PI controller parameters: gain = 0.308,

time constant = 0.03.

Single-Phase SEPIC AC-DC Converter in DCM



Single-Phase SEPIC AC-DC Converter in CCM

Source voltage and current in CCM at 100% load


Single-Phase SEPIC AC-DC ConverterTABLE I

Comparisons of SEPIC Converter Operation in DCM and CCM

Quantity



Input Current THD 10% 6% 3.8% 8.5%

PF 0.994 0.997 0.998 0.995

Output Ripple 0.22% 1.27% 1.1% 0.1%

Normalized Current of Switch

Peak 14.50pu 9.84pu 3.24pu 3.14pu

Average 0.76pu 0.77pu 0.71pu 0.78pu

RMS 4.60pu 2.18pu 1.50pu 1.39pu

Normalized Current of Diode

Peak 15.2pu 10.94pu 3.17pu 3.15pu

Average 1.47pu 1.27pu 0.93pu 0.98pu

RMS 7.22pu 3.34pu 1.68pu 1.56pu




Single-Phase SEPIC AC-DC Converter

Test results of AC mains voltage, AC mains current, output DC voltage and output Test results of AC mains voltage, AC mains current, output DC voltage and output DC current waveform of AC-DC sepic converter for load perturbation response on DC current waveform of AC-DC sepic converter for load perturbation response on equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-axis equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-axis channel-1 1div =150V, channel-2 1div =5A, channel-3 1div= 100V, channel-4 1div= channel-1 1div =150V, channel-2 1div =5A, channel-3 1div= 100V, channel-4 1div= 1.75A)1.75A)

VVs s (V)(V), ,

iiss(A)(A)

VVdc dc (V)(V)

IIdc dc

(A)(A)

Single-Phase Buck-Boost Zeta AC-DC Converter in DCM

Single-Phase Buck-Boost Zeta AC-DC Converter in DCM

Single-Phase Buck-Boost Zeta AC-DC Converter in CCM


Single-Phase Zeta AC-DC ConverterSpecifications

Input: RMS1 220VV , 50Hz, Single-Phase AC Supply

Output: Vo = 48V, 1kWPo , output voltage-ripple less

than 2%

Switching frequency 50kHz)2/(fs s

Transformer turn ratio (n) 5:1, Magnetizing

inductance mL =100μH , fL =3mH , oL =10mH

1C =10μF , oC =22mF , and fC =100nF .






Source voltage and current for 100% load in CCM

Single-Phase Zeta AC-DC Converter

IIdc dc (A)(A)

Test results of AC mains voltage, AC mains current, output DC voltage and output Test results of AC mains voltage, AC mains current, output DC voltage and output DC current waveform of AC-DC zeta converter for load perturbation response on DC current waveform of AC-DC zeta converter for load perturbation response on equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-equivalent resistive load (60W to 200W to 60W). (Scale on X-axis 1div=20ms, Y-axis channel-1 1div =150V, channel-2 1div =3A, channel-3 1div= 100V, channel-4 axis channel-1 1div =150V, channel-2 1div =3A, channel-3 1div= 100V, channel-4 1div= 1.75A)1div= 1.75A)

VVs s (V)(V), ,

iiss(A)(A)

VVdc dc (V)(V)

Single-Phase Zeta AC-DC ConverterTABLE I

Comparisons of Zeta Converter Operation in DCM and CCM

Quantity



Input Current THD 11% 4.98% 9.2% 1.36%

PF 0.993 0.9975 0.994 0.998

Output Ripple 0.62% 1.99% 0.67% 1.98%

Normalized Current of Switch

Peak 9.21 4.15 2.92 1.75

Average 0.92 1.01 0.45 0.62

RMS 2.15 1.71 1.04 0.95

Normalized Current of Diode

Peak 36.90 20.01 14.6 8.73

Average 4.52 3.02 3.24 3.17

RMS 10.45 5.41 5.37 4.57




References• R. W. Erickson, Fundamentals of Power Electronics. New York:

Chapman & Hall, 1997.• A. I. Pressman, Switching Power Supply Design. Second Edition, New

York: McGraw-Hill, 1998.• P. T. Krein, Elements of Power Electronics. New York: Oxford University

Press, 1998.• M. H. J. Bollen, Understanding Power Quality Problems: Voltage Sags

and Interruptions. New York: IEEE Press Series on Power Engineering, 2000.

• D. Boroyevich and S. Hiti, Three-phase PWM converter: Modeling and Control Design. Seminar 9, IEEE APEC’96, 1996.

• M. F. Schlecht and B.A Miwa, “Active power factor correction for switching power supplies,” IEEE Trans. Power Electron.,vol.2, pp.273- 281, October 1987.

• M. Kravitz,“Power factor correction circuit for power supplies,” U.S. Patent 4,961,044, Oct. 1990.

• J. Sebastian, M. Jaureguizar, and J. Uceda, “An overview of power factor correction in single-phase off-line power supply systems,” in Proc. IEEE IECON’94, 1994, pp. 1688 -1693.

• R. Redl, I. Balogh, and N.O. Sokal, “A new family of single-stage isolated power-factor correctors with fast regulation of the output voltage,” in Proc. IEEE PESC’94, 1994, pp. 1137 –1144.

• J. Sebastian, J. A. Cobos, J.M. Lopera and J. Uceda, The determination of the boundaries between continuous and discontinuous conduction modes in PWM DC-to-DC converters used as power factor preregulators,” IEEE Trans. Power Electron., vol. 10, pp. 574 -582, Sept. 1995.

• A. Zak, “Multi-channel single stage high power factor AC to DC converter,” U.S. Patent 5,619,404, April 1997.

• H. Mao, F. C. Y. Lee, D. Boroyevich, “Review of high-performance three-phase power-factor correction circuits,” IEEE Trans. Ind. Electron., vol. 44, pp. 437-446, August 1997.

• G. A. Karvelis, S. N. Manias and G. Kostakis, “A comparative evaluation of power converters used for current harmonics elimination,” in IEEE HQP’98, 1998, pp. 227-232.

• H. Wei and I. Batarseh, “Comparison of basic converter topologies for power correction,” in IEEE SOUTHEASTCON’98, 1998, pp. 348-353.

• C. Qiao and K.M. Smedley, “A topology survey of single-stage power factor corrector with a boost type input-current-shaper,” IEEE Trans. Power Electron., vol. 16, pp. 360-368, May 2001.

• L.Huber, J. Zhang, M.M. Jovanovic and F.C. Lee, “Generalized topologies of single-stage input-current-shaping circuits,” IEEE Trans. Power Electron., vol. 16, pp. 508-513, July 2001.

• F.L. Williamson, “Universal input/output power supply with inherent near unity power factor,” U.S. Patent 6,343,021, Jan. 2002.

• M. Keller, “Design of a 250 Amp telecom rectifier with true three-phase unity power factor input rectification stage,” in Proc. IEEE INTELEC’02, 2002, pp. 94- 100.

• O. García, J. A. Cobos, R. Prieto, P. Alou and J. Uceda, “Single Phase Power factor correction: A survey,” IEEE Trans. Power Electron., vol. 18, pp. 749-755, May 2003.

Documents

Seminar on Improved Power Quality AC-DC Converters with High Frequency Transformer Isolation By Prof. Bhim Singh Department of Electrical Engineering Indian