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
1
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
2
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
3
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
4
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
5
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

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
2 Vm

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.
2 Vm

Va 


Va
Ea 
+
+
2Vm

cos  a
90o
180o
Q4

Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
2 Vm

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
11
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)
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives
12

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 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 
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
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
17
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
18
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
19
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
20
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
21
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
22
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
EEEB443 - Control & Drives
23
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