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
EEEB443 - Control & Drives
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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
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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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 )
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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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
2Vm
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
2Vm 6
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
2Vm 7
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.
2Vm
Va
Va
Ea
+
+
2Vm
cos a
90o
180o
Q4 Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
2Vm 8
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 9
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 10
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
+
3-phase supply
For continuous current:
3VL-L, m
ia
Va
cos a 3VL -L, m
where VL-L, m = peak line-to-line voltage
Va Ea Ia Ra Field voltage V 3VL-L, m cos f f
Armature current
90o
180o
3VL-L, m
(assuming a three-phase supply is used for field excitation) Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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Three-phase Controlled Rectifier 2Q DC Drive – Example
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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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 14
Controlled Rectifier Fed – Three-phase DC Drives
Four-quadrant drive
+
For continuous current:
Va
3VLL, 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 15
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 16
Three-phase Controlled Rectifier 4Q DC Drive – Example
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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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
EEEB443 - Control & Drives
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
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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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)
Dr. Ungku Anisa, July 2008
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)
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
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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.
Dr. Ungku Anisa, July 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 4/5/2019
EEL 4242 by Dr. M.H. Rashid
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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 4/5/2019
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