1 three phase controlled rectifiers. 2 3 phase controlled rectifiers operate from 3 phase ac supply...

1

Three Phase Controlled Three Phase Controlled RectifiersRectifiers

2

3 Phase Controlled Rectifiers3 Phase Controlled Rectifiers

• Operate from 3 phase ac supply Operate from 3 phase ac supply voltage.voltage.

• They provide higher dc output voltage.They provide higher dc output voltage.

• Higher dc output power.Higher dc output power.

• Higher output voltage ripple frequency.Higher output voltage ripple frequency.

• Filtering requirements are simplified Filtering requirements are simplified for smoothing out load voltage and for smoothing out load voltage and load current.load current.

3

• Extensively used in high power Extensively used in high power variable speed industrial dc drives.variable speed industrial dc drives.

• Three single phase half-wave Three single phase half-wave converters can be connected converters can be connected together to form a three phase half-together to form a three phase half-wave converter.wave converter.

4

3-Phase Half Wave 3-Phase Half Wave ConverterConverter(3-Pulse Converter) (3-Pulse Converter) with RL Loadwith RL LoadContinuous & ConstantContinuous & ConstantLoad Current OperationLoad Current Operation

6

Vector Diagram of Vector Diagram of 3 Phase Supply Voltages3 Phase Supply Voltages

V A N

V C N

V B N

1 2 00

1 2 00

1 2 00 RN AN

YN BN

BN CN

v v

v v

v v

7

3 Phase Supply Voltage 3 Phase Supply Voltage EquationsEquations

We deifine three line to neutral voltages

(3 phase voltages) as follows

8

0

0

0

sin ;

Max. Phase Voltage

2sin

3

sin 120

2sin

3

sin 120

sin 240

RN an m

m

YN bn m

m

BN cn m

m

m

v v V t

V

v v V t

V t

v v V t

V t

V t

9

van vbn vcn van

10

io=Ia

Constant Load Current

Ia

Ia

Each thyristor conducts for 2/3 (1200)

11

To Derive an Expression To Derive an Expression for the Average Output for the Average Output Voltage of a 3-Phase Half Voltage of a 3-Phase Half Wave Converter with RL Wave Converter with RL Load for Continuous Load Load for Continuous Load CurrentCurrent

12

01

02

03

0

306

5 150

6

7 270

6

2Each thytistor conducts for 120 or radians

3

T is triggered at t

T is triggered at t

T is triggered at t

13

5

6

6

If the reference phase voltage is

sin , the average or dc output

voltage for continuous load current is calculated

using the equation

3sin .

2

RN an m

dc m

v v V t

V V t d t

14

5

6

6

5

6

6

3sin .

2

3cos

2

3 5cos cos

2 6 6

mdc

mdc

mdc

VV t d t

VV t

VV

15

0 0

0

Note from the trigonometric relationship

cos cos .cos sin .sin

5 5cos cos sin sin

6 63

2co

cos 150 cos sin 150 sin3

2 cos 30

s .cos sin sin6 6

.cosm

dc

mdc

A

VV

B A B A B

VV

0sin 30 sin

16

0 0

0 0 0 0

0 0

0 0

0

0

0

0

0 0

Note: cos 1

cos 180 30 cos sin 180 30 sin3

2 cos 30 .cos sin 30 sin

cos 30 cos sin 30 sin3

2 cos 30 .cos sin 30 s

80 30 cos 30

sin 180 30 sin 30

in

mdc

mdc

VV

VV

17

032cos 30 cos

2

3 32 cos

2 2

3 3 33 cos cos

2 23

cos2

Where 3 Max. line to line supply voltage

mdc

mdc

m mdc

Lmdc

Lm m

VV

VV

V VV

VV

V V

18

max

The maximum average or dc output voltage is

obtained at a delay angle 0 and is given by

3 3

2Where is the peak phase voltage.

And the normalized average output voltage is

mdmdc

m

ddcn n

VV V

V

VV V

cosc

dmV

19

15 26

2 2

6

1

2

The rms value of output voltage is found by

using the equation

3sin .

2

and we obtain

1 33 cos 2

6 8

mO RMS

mO RMS

V V t d t

V V

20

3 Phase Half Wave3 Phase Half Wave Controlled Rectifier Output Controlled Rectifier Output Voltage Waveforms For RL Voltage Waveforms For RL Load Load at Different Trigger Anglesat Different Trigger Angles

21

0

0

300

300

600

600

900

900

1200

1200

1500

1500

1800

1800

2100

2100

2400

2400

2700

2700

3000

3000

3300

3300

3600

3600

3900

3900

4200

4200

V an

V 0

V 0

V an

= 300

= 600

V bn

V bn

V cn

V cn

t

t

=300

=600

22

=900

23

3 Phase Half Wave3 Phase Half Wave Controlled Rectifier With Controlled Rectifier With R Load and RL Load with R Load and RL Load with FWDFWD

24

a a

b b

c c

RV 0

L

R V 0

+

T 1

T 2

T 3

n n

T 1

T 2

T 3

25

3 Phase Half Wave3 Phase Half Wave Controlled Rectifier Output Controlled Rectifier Output Voltage Waveforms For R Voltage Waveforms For R Load Load or RL Load with FWDor RL Load with FWDat Different Trigger Anglesat Different Trigger Angles

26Prof. M.

0

0

300

300

600

600

900

900

1200

1200

1500

1500

1800

1800

2100

2100

2400

2400

2700

2700

3000

3000

3300

3300

3600

3600

3900

3900

4200

4200

V s

V 0

V a n

= 0

= 1 5 0

V b n V c n

t

V a n V b n V c n

t

=00

=150

27

0

0

300

300

600

600

900

900

1200

1200

1500

1500

1800

1800

2100

2100

2400

2400

2700

2700

3000

3000

3300

3300

3600

3600

3900

3900

4200

4200

V 0

= 3 0 0

V a nV b n V c n

t

V 0

= 6 0 0

V a nV b n V c n

t

=300

=600

28

To Derive An To Derive An Expression For The Average Expression For The Average Or Dc Output Voltage Of A 3 Or Dc Output Voltage Of A 3 Phase Half Wave Converter Phase Half Wave Converter With Resistive Load Or RL With Resistive Load Or RL Load With FWDLoad With FWD

29

01

0 01

02

0 02

0

306

30 180 ;

sin

5 150

6

150 300 ;

sin 120

O an m

O bn m

T is triggered at t

T conducts from to

v v V t

T is triggered at t

T conducts from to

v v V t

30

03

0 03

0

0

7 270

6

270 420 ;

sin 240

sin 120

O cn m

m

T is triggered at t

T conducts from to

v v V t

V t

31

0

0

0

0

0

0

180

30

0 0

180

30

180

30

3.

2

sin ; for 30 to 180

3sin .

2

3sin .

2

dc O

O an m

dc m

mdc

V v d t

v v V t t

V V t d t

VV t d t

32

0

0

180

30

0 0

0

0

3cos

2

3cos180 cos 30

2

cos180 1, we get

31 cos 30

2

mdc

mdc

mdc

VV t

VV

VV

33

Three Phase SemiconvertersThree Phase Semiconverters

• 3 Phase semiconverters are used in Industrial 3 Phase semiconverters are used in Industrial dc drive applications up to 120kW power dc drive applications up to 120kW power output.output.

• Single quadrant operation is possible.Single quadrant operation is possible.

• Power factor decreases as the delay angle Power factor decreases as the delay angle increases.increases.

• Power factor is better than that of 3 phase Power factor is better than that of 3 phase half wave converter.half wave converter.

34

3 Phase Half Controlled 3 Phase Half Controlled Bridge Converter Bridge Converter (Semi Converter) with (Semi Converter) with Highly Inductive Load & Highly Inductive Load & Continuous Ripple free Load Continuous Ripple free Load CurrentCurrent

36

Wave forms of 3 Phase Wave forms of 3 Phase Semiconverter for Semiconverter for > 60 > 6000

39

0 0

1

3 phase semiconverter output ripple frequency of

output voltage is 3

The delay angle can be varied from 0 to

During the period

30 210

7, thyristor T is forward biased

6 6

Sf

t

t

40

1

1 1

If thyristor is triggered at ,6

& conduct together and the line to line voltage

appears across the load.

7At , becomes negative & FWD conducts.

6The load current contin

ac

ac m

T t

T D

v

t v D

1 1

ues to flow through FWD ;

and are turned off.mD

T D

41

1

2

1 2

If FWD is not used the would continue to

conduct until the thyristor is triggered at

5, and Free wheeling action would

6

be accomplished through & .

If the delay angle , e3

mD T

T

t

T D

ach thyristor conducts

2for and the FWD does not conduct.

3 mD

42

0

0

0

We deifine three line neutral voltages


sin ; Max. Phase Voltage

2sin sin 120

3

2sin sin 120

3

sin 240

RN an m m

YN bn m m

BN cn m m

m

v v V t V

v v V t V t

v v V t V t

V t

V

is the peak phase voltage of a wye-connected source.m

43

3 sin6

53 sin

6

3 sin2

3 sin6

RB ac an cn m

YR ba bn an m

BY cb cn bn m

RY ab an bn m

v v v v V t

v v v v V t

v v v v V t

v v v v V t

44

Wave forms of 3 Phase Wave forms of 3 Phase Semiconverter for Semiconverter for 60 6000

48

To derive an Expression for To derive an Expression for the Average Output Voltage the Average Output Voltage of 3 Phase Semiconverterof 3 Phase Semiconverter for for > > / 3 and / 3 and Discontinuous Output Discontinuous Output Voltage Voltage

49

76

6

76

6

For and discontinuous output voltage:3

the Average output voltage is found from

3.

2

33 sin

2 6

dc ac

dc m

V v d t

V V t d t

50

max

3 31 cos

23

1 cos2

3 Max. value of line-to-line supply voltage

The maximum average output voltage that occurs at

a delay angle of 0 is

3 3

mdc

mLdc

mL m

mdmdc

VV

VV

V V

VV V

51

17 26

2

6

The normalized average output voltage is

0.5 1 cos

The rms output voltage is found from

3.

2

dcn

dm

acO rms

VV

V

V v d t

Power ElectronicsPower Electronics 5252

17 26

2 2

6

1

2

33 sin

2 6

3 sin 23

4 2

mO rms

mO rms

V V t d t

V V

53

Average or DC Output Average or DC Output Voltage of a 3-Phase Voltage of a 3-Phase Semiconverter for Semiconverter for / 3, / 3, and Continuous Output and Continuous Output VoltageVoltage

54

562

6 2

For , and continuous output voltage3

3. .

2

3 31 cos

2

dc ab ac

mdc

V v d t v d t

VV

55

15 262

2 2

6 2

1

22

0.5 1 cos

RMS value of o/p voltage is calculated by using

the equation

3. .

2

3 23 3 cos

4 3

dcn

dm

ab acO rms

mO rms

VV

V

V v d t v d t

V V

56

Three Phase Full ConverterThree Phase Full Converter

• 3 Phase Fully Controlled Full Wave 3 Phase Fully Controlled Full Wave Bridge Converter.Bridge Converter.

• Known as a 6-pulse converter.Known as a 6-pulse converter.

• Used in industrial applications up to Used in industrial applications up to 120kW output power.120kW output power.

• Two quadrant operation is possible.Two quadrant operation is possible.

60

• The thyristors are triggered at an interval The thyristors are triggered at an interval of of / 3. / 3.

• The frequency of output ripple voltage is The frequency of output ripple voltage is 6f6fSS..

• TT11 is triggered at is triggered at t = (t = (/6 + /6 + ), T), T66 is is already conducting when Talready conducting when T11 is turned ON. is turned ON.

• During the interval (During the interval (/6 + /6 + ) to () to (/2 + /2 + ), ), T T11 and T and T66 conduct together & the output conduct together & the output load voltage is equal to load voltage is equal to vvab ab = (v= (van an – v– vbnbn))

61

• TT22 is triggered at is triggered at t = (t = (/2 + /2 + ), T), T66 turns off turns off naturally as it is reverse biased as soon as Tnaturally as it is reverse biased as soon as T22 is triggered.is triggered.

• During the interval (During the interval (/2 + /2 + ) to (5) to (5/6 + /6 + ), T), T11 and Tand T22 conduct together & the output load conduct together & the output load voltage voltage vvOO = v = vacac = (v = (vanan – v – vcncn))

• Thyristors are numbered in the order in which Thyristors are numbered in the order in which they are triggered. they are triggered.

• The thyristor triggering sequence is 12, 23, The thyristor triggering sequence is 12, 23, 34, 45, 56, 61, 12, 23, 34, ………34, 45, 56, 61, 12, 23, 34, ………

62

0

0

0



sin ; Max. Phase Voltage

2sin sin 120

3

2sin sin 120

3

sin 240

RN an m m

YN bn m m

BN cn m m

m

v v V t V

v v V t V t

v v V t V t

V t

V

is the peak phase voltage of a wye-connected source.m

63

The corresponding line-to-line

supply voltages are

3 sin6

3 sin2

3 sin2

RY ab an bn m

YB bc bn cn m

BR ca cn an m

v v v v V t

v v v v V t

v v v v V t

64

To Derive An Expression For The Average To Derive An Expression For The Average Output Voltage Of 3-phase Full Converter Output Voltage Of 3-phase Full Converter

With Highly Inductive Load Assuming With Highly Inductive Load Assuming Continuous And Constant Load CurrentContinuous And Constant Load Current

65

2

6

6. ;

2

3 sin6

dc OO dc

O ab m

V V v d t

v v V t

The output load voltage consists of 6 The output load voltage consists of 6 voltage pulses over a period of 2voltage pulses over a period of 2 radians, Hence the average output radians, Hence the average output voltage is calculated as voltage is calculated as

66

2

6

mL

max

33 sin .

6

3 3 3cos cos

Where V 3 Max. line-to-line supply vo

The maximum average dc output voltage is

obtained for a delay angle

ltage

3 3

0,

3

dc m

m mLdc

m

m mdmdc

V V t d t

V VV

V

V VV V

L

67

1

22

2

6

The normalized average dc output voltage is

cos

The rms value of the output voltage is found from

6.

2

dcdcn n

dm

OO rms

VV V

V

V v d t

68

1

22

2

6

1

22

2 2

6

1

2

6.

2

33 sin .

2 6

1 3 33 cos 2

2 4

abO rms

mO rms

mO rms

V v d t

V V t d t

V V


VVnn/V/Vml-lml-l for controlled 3-phase for controlled 3-phase full converterfull converter


ExampleExample


Continued..Continued..

72

Three Phase Dual Three Phase Dual ConvertersConverters

• For four quadrant operation in many For four quadrant operation in many industrial variable speed dc drives , 3 industrial variable speed dc drives , 3 phase dual converters are used.phase dual converters are used.

• Used for applications up to 2 mega Used for applications up to 2 mega watt output power level.watt output power level.

• Dual converter consists of two 3 phase Dual converter consists of two 3 phase full converters which are connected in full converters which are connected in parallel & in opposite directions across parallel & in opposite directions across a common load.a common load.

76

Outputs of Converters 1 & 2Outputs of Converters 1 & 2

• During the interval (During the interval (/6 + /6 + 11) to () to (/2 /2 + + 11), the line to line voltage ), the line to line voltage vvabab appears across the output of appears across the output of converter 1 and converter 1 and vvbcbc appears across appears across the output of converter 2the output of converter 2

77

0

0

0



sin ;

Max. Phase Voltage

2sin sin 120

3

2sin sin 120

3

sin 240

RN an m

m

YN bn m m

BN cn m m

m

v v V t

V

v v V t V t

v v V t V t

V t

78

The corresponding line-to-line

supply voltages are

3 sin6

3 sin2

3 sin2

RY ab an bn m

YB bc bn cn m

BR ca cn an m

v v v v V t

v v v v V t

v v v v V t

79

• If If vvO1O1 and and vvO2O2 are the output voltages are the output voltages of converters 1 and 2 respectively, of converters 1 and 2 respectively, the instantaneous voltage across the the instantaneous voltage across the current limiting inductor during the current limiting inductor during the interval (interval (/6 + /6 + 11) ) t t ( (/2 /2 + + 11) is given by) is given by

To obtain an Expression for To obtain an Expression for the Circulating Currentthe Circulating Current

80

1 2

3 sin sin6 2

3 cos6

The circulating current can be calculated by

using the equation

r O O ab bc

r m

r m

v v v v v

v V t t

v V t

81

1

1

6

6

1

max

1.

13 cos .

6

3sin sin

6

3

t

r rr

t

r mr

mr

r

mr

r

i t v d tL

i t V t d tL

Vi t t

L

Vi

L

82

Four Quadrant OperationFour Quadrant Operation

Conv. 2 Conv. 2 InvertingInverting

2 2 > 90> 9000

Conv. 2 Conv. 2 RectifyingRectifying

2 2 < 90< 9000

Conv. 1 Conv. 1 RectifyingRectifying

1 1 < 90< 9000

Conv. 1 Conv. 1 InvertingInverting

1 1 > 90> 9000

83

• There are two different modes of There are two different modes of operation.operation. Circulating current free Circulating current free

(non circulating) mode of operation (non circulating) mode of operation Circulating current mode of Circulating current mode of

operationoperation

84

Non Circulating Non Circulating Current Mode Of OperationCurrent Mode Of Operation

• In this mode of operation only one In this mode of operation only one converter is switched on at a timeconverter is switched on at a time

• When the converter 1 is switched on,When the converter 1 is switched on,

For For 11 < 90 < 9000 the converter 1 operates the converter 1 operates in the Rectification modein the Rectification mode

VVdcdc is positive, I is positive, Idcdc is positive and hence is positive and hence the average load power Pthe average load power Pdcdc is positive. is positive.

• Power flows from ac source to the loadPower flows from ac source to the load

85

• When the converter 1 is on,When the converter 1 is on,

For For 11 > 90 > 9000 the converter 1 operates the converter 1 operates in the Inversion modein the Inversion mode

VVdcdc is negative, I is negative, Idcdc is positive and the is positive and the average load power Paverage load power Pdcdc is negative. is negative.

• Power flows from load circuit to ac Power flows from load circuit to ac source.source.

86


For For 22 < 90 < 9000 the converter 2 operates the converter 2 operates in the Rectification modein the Rectification mode

VVdcdc is negative, I is negative, Idcdc is negative and the is negative and the average load power Paverage load power Pdcdc is positive. is positive.

• The output load voltage & load current The output load voltage & load current reverse when converter 2 is on.reverse when converter 2 is on.

• Power flows from ac source to the loadPower flows from ac source to the load

87


For For 22 > 90 > 9000 the converter 2 operates the converter 2 operates in the Inversion modein the Inversion mode

VVdcdc is positive, I is positive, Idcdc is negative and the is negative and the average load power Paverage load power Pdcdc is negative. is negative.

• Power flows from load to the ac source.Power flows from load to the ac source.• Energy is supplied from the load circuit Energy is supplied from the load circuit

to the ac supply.to the ac supply.

88

Circulating Current Circulating Current Mode Of OperationMode Of Operation

• Both the converters are switched on Both the converters are switched on at the same time.at the same time.

• One converter operates in the One converter operates in the rectification mode while the other rectification mode while the other operates in the inversion mode.operates in the inversion mode.

• Trigger angles Trigger angles 11 & & 22 are adjusted are adjusted such that (such that (11 + + 22) = 180) = 18000

89

• When When 11 < 90 < 9000, converter 1 operates , converter 1 operates as a controlled rectifier. as a controlled rectifier. 22 is made is made greater than 90greater than 900 0 and converter 2 and converter 2 operates as an Inverter. operates as an Inverter.

• VVdcdc is positive & I is positive & Idcdc is positive and P is positive and Pdcdc is positive.is positive.

90

• When When 22 < 90 < 9000, converter 2 operates , converter 2 operates as a controlled rectifier. as a controlled rectifier. 11 is made is made greater than 90greater than 900 0 and converter 1 and converter 1 operates as an Inverter. operates as an Inverter.

• VVdcdc is negative & I is negative & Idcdc is negative and is negative and PPdcdc is positive. is positive.

1 three phase controlled rectifiers. 2 3 phase controlled rectifiers operate from 3 phase ac supply...

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