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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
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 3
Controlled Rectifier Fed DC DrivesTo obtain variable DC voltage from fixed AC sourceDC current flows in only 1 directionExample of a drive system
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 4
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 )
Dr. Ungku Anisa, July 2008 5EEEB443 - Control & Drives
T
Q1Q2
Q3 Q4
Controlled Rectifier Fed – Single-phase DC Drives
Two-quadrant drive For continuous current:
Armature voltage
where Vm = peak voltage
Armature current
Field voltage
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 6
am
a
VV
cos
2
fm
f
VV
cos
2
a
aaa R
EVI
90o 180o
mV2
mV2
Single-phasesupply
+
Va
ia
Controlled Rectifier Fed – Single-phase DC Drives
Two-quadrant drive For Quadrant 1 operation:
positive Ea and Va positivea 90Ia positiveRectifier delivers power to motor,
i.e. forward motoring.
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 7
am
a
VV
cos
2
90o 180o
mV2
mV2
Single-phasesupply
+
Va
ia
+
Ea
Q1
Controlled Rectifier Fed – Single-phase DC Drives
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.
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 8
am
a
VV
cos
2
90o 180o
mV2
mV2
Single-phasesupply
Va
+
ia
Ea
+
Q4
Controlled Rectifier Fed – Single-phase DC Drives
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
Dr. Ungku Anisa, July 2008 9EEEB443 - Control & Drives
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
Dr. Ungku Anisa, July 2008 10EEEB443 - Control & Drives
11 cos2
amVV
fm
f
VV
cos
2
a
aaa R
EVI
21 aa
021 VV
22 cos2
amVV
+
V1
Converter 1 Converter 2
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 )
Dr. Ungku Anisa, July 2008 11EEEB443 - Control & Drives
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)
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 12
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
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 13
Controlled Rectifier Fed – Three-phase DC Drives
Four-quadrant driveConverter 1 for operation in 1st and 4th quadrantConverter 2 for operation in 2nd and 3rd quadrant
Dr. Ungku Anisa, July 2008 14EEEB443 - Control & Drives
T
Q1Q2
Q3 Q4
Converter 1 Converter 2
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
Controlled Rectifier Fed – Three-phase DC Drives
Four-quadrant driveFor continuous current:
where VL-L, m = peak line-to-line voltage.Similar to single-phase drive:
Dr. Ungku Anisa, July 2008 15EEEB443 - Control & Drives
TQ1 Q2
Q3 Q4
Converter 1 Converter 2
+
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
Controlled Rectifier Fed – Three-phase DC Drives
For continuous current:Armature current
Field voltage
Disadvantages:Circulating current
Inductors L1 and L2 added to reduce circulating currents
Slow response
Dr. Ungku Anisa, July 2008 16EEEB443 - Control & Drives
+
Va
Converter 1 Converter 2
ia
L1
L2
fm
f
VV
cos
3 L,-L
a
aaa R
EVI
Three-phase Controlled Rectifier 4Q DC Drive – Example
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 17
Controlled Rectifier Fed – Three-phase DC Drives
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
Dr. Ungku Anisa, July 2008 18EEEB443 - Control & Drives
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
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 19
Rectifier Fed DC Drives Problems
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 20
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)
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 21
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)
Dr. Ungku Anisa, July 2008 EEEB443 - Control & Drives 22
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.
Dr. Ungku Anisa, July 2008 23EEEB443 - Control & Drives
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