Controlled Rectifier DC Drives By Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering Dr. Ungku Anisa, July

Controlled Rectifier DC DrivesByDr. Ungku Anisa Ungku AmirulddinDepartment of Electrical Power EngineeringCollege of Engineering

Dr. Ungku Anisa, July 2008 1EEEB443 - Control & Drives

OutlinePower Electronics Converters for DC DrivesControlled Rectifier Fed DC Drives

Single Phase Two-quadrantFour-quadrant

Three PhaseTwo-quadrantFour-quadrant

References

Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 2

Power Electronic Converters for DC DrivesSpeed Control Strategy:

below base speed: Va controlabove base speed: flux control via Vf control

Power electronics converters are used to obtain variable voltageHighly efficientIdeally lossless

Type of converter used is depending on voltage source :AC voltage source Controlled RectifiersFixed DC voltage source DC-DC converters


Controlled Rectifier Fed DC DrivesTo obtain variable DC voltage from fixed AC sourceDC current flows in only 1 directionExample of a drive system


Controlled Rectifier Fed – Single-phase DC Drives

Two-quadrant driveLimited to applications up to 15 kWRegeneration (Q4) only be achieved with loads that can drive

the motor in reverse (-ve )


T

Q1Q2

Q3 Q4


Two-quadrant drive For continuous current:

Armature voltage

where Vm = peak voltage

Armature current

Field voltage


am

a

VV

cos

2

fm

f

VV

cos

2

a

aaa R

EVI

90o 180o

mV2

mV2

Single-phasesupply

+

Va

ia


Two-quadrant drive For Quadrant 1 operation:

positive Ea and Va positivea 90Ia positiveRectifier delivers power to motor,

i.e. forward motoring.


am

a

VV

cos

2

90o 180o

mV2

mV2

Single-phasesupply

+

Va

ia

+

Ea

Q1


Two-quadrant drive For Quadrant 4 operation:

negative Ea negativea > 90 Va negativeIa positive (still in same direction)Rectifier takes power from motor,

i.e. regenerative braking.


am

a

VV

cos

2

90o 180o

mV2

mV2

Single-phasesupply

Va

+

ia

Ea

+

Q4


Four-quadrant driveConverter 1 for operation in 1st and 4th quadrantConverter 2 for operation in 2nd and 3rd quadrantLimited to applications up to 15 kW


T

Q1Q2

Q3 Q4

Converter 1 Converter 2

Single-phasesupply

Single-phasesupply

+

Va

ia

Two rectifiers connected in anti-

parallel across motor armature

Controlled Rectifier Fed – Single-phase DC DrivesFour-quadrant drive

For continuous current:Both converters are operated to produce the same dc voltage across the

terminal, i.e.:

where and

(Vm = peak supply voltage)Hence, firing angles of both converters must satisfy the following:

Armature current

Field voltage


11 cos2

amVV

fm

f

VV

cos

2

a

aaa R

EVI

21 aa

021 VV

22 cos2

amVV

+

V1


V2

+

Controlled Rectifier Fed – Three-phase DC Drives

Two-quadrant driveLimited to applications up to 1500 kWRegeneration (Q4) only be achieved with loads that can

drive the motor in reverse (-ve )


T

Q1Q2

Q3 Q4

Controlled Rectifier Fed – Three-phase DC DrivesFor continuous current:

Armature voltage

where VL-L, m = peak line-to-line voltage

Armature current

Field voltage

(assuming a three-phase supply is used for field excitation)


am

a

VV

cos

3 L,-L

fm

f

VV

cos

3 L,-L

a

aaa R

EVI

90o

mV L,-L3

mV L,-L3

180o

3-phasesupply

+

Va

ia

Three-phase Controlled Rectifier 2Q DC Drive – Example



Four-quadrant driveConverter 1 for operation in 1st and 4th quadrantConverter 2 for operation in 2nd and 3rd quadrant


T

Q1Q2

Q3 Q4


3-phasesupply

3-phasesupply

+

Va

ia

Two rectifiers connected in anti-

parallel across motor armature

Ia +ve,Va +ve or -ve

Ia -ve,Va +ve or -ve


Four-quadrant driveFor continuous current:

where VL-L, m = peak line-to-line voltage.Similar to single-phase drive:


TQ1 Q2

Q3 Q4


+

Va

ia

Converter 1:Ia +ve,Va +ve

Converter 2:Ia -ve,Va +ve 12

1 900

aa

a

Converter 1:Ia +ve,Va -ve 12

1 18090

aa

a

21

2 18090

aa

a

Converter 2:Ia -ve,Va -ve21

2 900

aa

a

am

a

VV

cos

3 ,LL

21 aa


For continuous current:Armature current

Field voltage

Disadvantages:Circulating current

Inductors L1 and L2 added to reduce circulating currents

Slow response


+

Va


ia

L1

L2

fm

f

VV

cos

3 L,-L

a

aaa R

EVI

Three-phase Controlled Rectifier 4Q DC Drive – Example



Four-quadrant driveOne controlled rectifier with 2 pairs of contactorsM1 and M2 closed for operation in 1st and 4th quadrantR1 and R2 closed for operation in 2nd and 3rd quadrant


T

Q1Q2

Q3 Q4

M1

M2

R1

R2+ Va -

3-phasesupply

ia

ia

Rectifier Fed DC Drives Problems1. Distortion of Supply

Controlled rectifier introduces harmonics to supply currents and voltages which cause: heating and torque pulsations in motor resonance in power system network – interaction between rectifier

RL with capacitor banks in systemSolution - eliminate most dominant harmonics by:

install LC filters at input of converters – tuned to absorb most dominant harmonics (i.e. 5th and 7th harmonics)

Use 12-pulse converter – consists of two 6-pulse controlled rectifiers connected in parallel

Selective switching of supply input using self-commutating devices (eg. GTOs, IGBTs) in the converter


Rectifier Fed DC Drives Problems


12-pulse converter – consists of two 6-pulse controlled rectifiers connected in parallel

Rectifier Fed DC Drives Problems2. Low supply power factor

Power factor related to firing angle of rectifierLow power factor especially during low speed operationsSolution:

Employ pulse-width modulated (PWM) rectifiers using GTOs, IGBTs High power factor Low harmonic supply currents Low efficiency - high switching losses (disadvantage)


Rectifier Fed DC Drives Problems3. Effect on motor

Ripple in motor current – harmonics present (most dominant is 6th harmonic) causes torque ripple, heating and derating of motor solution: extra inductance added in series with La

Slow responseDiscontinuous current may occur if

La not large enough Motor is lightly loaded

Effect of discontinuous current Rectifier output voltage increases motor speed increases (poor speed regulation under open-loop operation)


ReferencesRashid, M.H, Power Electronics: Circuit, Devices and

Applictions, 3rd ed., Pearson, New-Jersey, 2004.Dubey, G.K., Fundamentals of Electric Drives, 2nd ed., Alpha

Science Int. Ltd., UK, 2001.Krishnan, R., Electric Motor Drives: Modeling, Analysis and

Control, Prentice-Hall, New Jersey, 2001.Nik Idris, N. R., Short Course Notes on Electrical Drives,

UNITEN/UTM, 2008.Ahmad Azli, N., Short Course Notes on Electrical Drives,

UNITEN/UTM, 2008.


04/18/23 EEL 4242 by Dr. M.H. Rashid 24

Three-Phase Full-Converter

Figure 10.5 Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004

04/18/23 EEL 4242 by Dr. M.H. Rashid 25

Waveforms and Conduction Times

/ 2

( ) / 6

/ 2

/ 6

3

33 sin

6

3 3cos

o dc ab

m

m

V v d

V d

V

Figure 10.5

/ 2 2 2( ) / 6

33 sin

6

1 3 33 cos 2

2 4

o rms m

m

V V d

V

Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004

Documents

Controlled Rectifier DC Drives By Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering Dr. Ungku Anisa, July