Controlled Rectifier DC Drives By Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering Dr.
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Transcript Controlled Rectifier DC Drives By Dr. Ungku Anisa Ungku Amirulddin Department of Electrical Power Engineering College of Engineering Dr.
Controlled Rectifier DC Drives
By
Dr. Ungku Anisa Ungku Amirulddin
Department of Electrical Power Engineering
College of Engineering
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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Outline
Power Electronics Converters for DC Drives
Controlled Rectifier Fed DC Drives
Single Phase
Two-quadrant
Four-quadrant
Three Phase
Two-quadrant
Four-quadrant
References
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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Power Electronic Converters
for DC Drives
Speed Control Strategy:
below base speed: Va control
above base speed: flux control via Vf control
Power electronics converters are used to obtain variable
voltage
Highly efficient
Ideally lossless
Type of converter used is depending on voltage source :
AC voltage source Controlled Rectifiers
Fixed DC voltage source DC-DC converters
Dr. Ungku Anisa, July 2008
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Controlled Rectifier Fed DC Drives
To obtain variable DC voltage from fixed AC source
DC current flows in only 1 direction
Example of a drive system
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Controlled Rectifier Fed
– Single-phase DC Drives
Two-quadrant drive
Q2
Q1
Q3
Q4
T
Limited to applications up to 15 kW
Regeneration (Q4) only be achieved with loads that can drive
the motor in reverse (-ve )
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Controlled Rectifier Fed
– Single-phase DC Drives
Two-quadrant drive
For continuous current:
Armature voltage
2Vm
Va
cos a
ia
+
Singlephase
supply
Va
2 Vm
where Vm = peak voltage
Va Ea
Armature current I a
Ra
Field voltage
Dr. Ungku Anisa, July 2008
Vf
2Vm
cos f
EEEB443 - Control & Drives
90o
180o
2 Vm
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Controlled Rectifier Fed
– Single-phase DC Drives
Two-quadrant drive
ia
Singlephase
supply
For Quadrant 1 operation:
positive Ea and Va positive
a 90
2V
Ia positive
Rectifier delivers power to motor,
i.e. forward motoring.
Va
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
+
Va
Ea
2Vm
m
+
cos a
Q1
90o
180o
2 Vm
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Controlled Rectifier Fed
– Single-phase DC Drives
Two-quadrant drive
ia
Singlephase
supply
For Quadrant 4 operation:
negative Ea negative
a > 90 Va negative
Ia positive (still in same direction)
Rectifier takes power from motor,
i.e. regenerative braking.
2 Vm
Va
Va
Ea
+
+
2Vm
cos a
90o
180o
Q4
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
2 Vm
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Controlled Rectifier Fed
– Single-phase DC Drives
Four-quadrant drive
Converter 1 for operation in 1st and 4th quadrant
Q2
Q1
Converter 2 for operation in 2nd and 3rd quadrant
Q3
Q4
T
Limited to applications up to 15 kW
+
Singlephase
supply
ia
Singlephase
supply
Va
Converter 1
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
Converter 2
Two rectifiers
connected in antiparallel across
motor armature
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Controlled Rectifier Fed
– Single-phase DC Drives
Four-quadrant drive
For continuous current:
Both converters are operated to produce the same dc voltage across the
terminal, i.e.:
where V1
V1 V2 0
2Vm
cos a1
and
V2
2Vm
cos a 2
(Vm = peak supply voltage)
Hence, firing angles of both converters must satisfy the following:
a1 a 2
Va Ea
Armature current I a
Ra
2Vm
Field voltage V f
cos f
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
+
V1
Converter 1
V2
+
Converter 2
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Controlled Rectifier Fed
– Three-phase DC Drives
Two-quadrant drive
Limited to applications up to 1500 kW
Regeneration (Q4) only be achieved with loads that can
Q2
Q1
Q3
Q4
T
drive the motor in reverse (-ve )
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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Controlled Rectifier Fed
– Three-phase DC Drives
Armature voltage
Va
Va
cos a
3VL-L, m
where VL-L, m = peak line-to-line voltage
Armature current I Va Ea
a
Ra
Field voltage
+
3-phase
supply
For continuous current:
3VL-L, m
ia
Vf
3VL-L, m
cos f
90o
180o
3VL-L, m
(assuming a three-phase supply is used for
field excitation)
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Three-phase Controlled Rectifier
2Q DC Drive – Example
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Controlled Rectifier Fed
– Three-phase DC Drives
Four-quadrant drive
Converter 1 for operation in 1st and 4th quadrant
Q2
Q1
Converter 2 for operation in 2nd and 3rd quadrant
Q3
Q4
Ia +ve,
Va +ve or -ve
Ia -ve,
Va +ve or -ve
Converter 1
Converter 2
+
3-phase
supply
Va
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
ia
T
3-phase
supply
Two rectifiers
connected in antiparallel across
motor armature
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Controlled Rectifier Fed
– Three-phase DC Drives
Four-quadrant drive
+
For continuous current:
Va
3VL L, m
ia
Va
cos a
Converter 1
Converter 2
where VL-L, m = peak line-to-line voltage.
Similar to single-phase drive: a1 a 2
90 a 2 180
a1 a 2
0 a 2 90
a1 a 2
Dr. Ungku Anisa, July 2008
Converter 2:
Ia -ve,
Va +ve
Converter 2:
Ia -ve,
Va -ve
EEEB443 - Control & Drives
Converter 1:
Ia +ve,
Va +ve
Q2
Q1
Q3
Q4
0 a1 90
a 2 a1
T
Converter 1:
Ia +ve,
Va -ve
90 a1 180
a 2 a1
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Controlled Rectifier Fed
– Three-phase DC Drives
For continuous current:
Armature current I a
Field voltage
Vf
Va Ea
Ra
3VL-L, m
cos f
L1
Disadvantages:
+
Circulating current
Va
Inductors L1 and L2
added to reduce
circulating currents
Slow response
Converter 1
Dr. Ungku Anisa, July 2008
ia
EEEB443 - Control & Drives
L2
Converter 2
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Three-phase Controlled Rectifier
4Q DC Drive – Example
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Controlled Rectifier Fed
– Three-phase DC Drives
Four-quadrant drive
Q2
Q1
Q3
Q4
T
One controlled rectifier with 2 pairs of contactors
M1 and M2 closed for operation in 1st and 4th quadrant
R1 and R2 closed for operation in 2nd and 3rd quadrant
ia
M1
ia
3-phase
supply
+
R2
Dr. Ungku Anisa, July 2008
R1
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Va
M2
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Rectifier Fed DC Drives Problems
1.
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 system
Solution - 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
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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Rectifier Fed DC Drives Problems
12-pulse converter – consists of two 6-pulse controlled rectifiers
connected in parallel
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Rectifier Fed DC Drives Problems
2.
Low supply power factor
Power factor related to firing angle of rectifier
Low power factor especially during low speed operations
Solution:
Employ pulse-width modulated (PWM) rectifiers using GTOs,
IGBTs
High power factor
Low harmonic supply currents
Low efficiency - high switching losses (disadvantage)
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EEEB443 - Control & Drives
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Rectifier Fed DC Drives Problems
3.
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 response
Discontinuous 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)
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References
Rashid, 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.
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Three-Phase Full-Converter
Figure 10.5
Reference:
Rashid, M.H, Power Electronics: Circuit, Devices and
Applictions, 3rd ed., Pearson, New-Jersey, 2004
10/30/2015
EEL 4242 by Dr. M.H. Rashid
24
Waveforms and Conduction Times
3
Vo ( dc )
3
/ 2
/ 6
3 Vm sin d
6
/ 2
/ 6
3 3Vm
Vo ( rms )
vab d
3
cos
/ 2
3 Vm
/ 6
3Vm2 sin 2 d
6
1 3 3
cos 2
2 4
Figure 10.5
Reference:
Rashid, M.H, Power Electronics:
Circuit, Devices and Applictions,
3rd ed., Pearson, New-Jersey, 2004
10/30/2015
EEL 4242 by Dr. M.H. Rashid
25