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

2. Outline Power Electronics Converters for DC Drives
Controlled Rectifier Fed DC Drives
Single Phase
Two-quadrant
Four-quadrant
Three Phase
References
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

3. 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

4. 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

5. Controlled Rectifier Fed – Single-phase DC DrivesQ1 Q2 Q3 Q4 
Controlled Rectifier Fed – Single-phase DC Drives
Two-quadrant drive
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

6. Controlled Rectifier Fed – Single-phase DC Drives
supply + Va  ia
Two-quadrant drive
For continuous current:
Armature voltage
where Vm = peak voltage
Armature current
Field voltage
90o
180o 
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

7. Controlled Rectifier Fed – Single-phase DC Drives
supply + Va  ia + Ea 
Two-quadrant drive
For Quadrant 1 operation:
 positive  Ea and Va positive
a  90
Ia positive
Rectifier delivers power to motor, i.e. forward motoring. 
90o
180o  Q1
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

8. Controlled Rectifier Fed – Single-phase DC Drives
supply  Va + ia  Ea +
Two-quadrant drive
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. 
90o
180o  Q4
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

9. Controlled Rectifier Fed – Single-phase DC DrivesQ1 Q2 Q3 Q4 
Four-quadrant drive
Converter 1 for operation in 1st and 4th quadrant
Converter 2 for operation in 2nd and 3rd quadrant
Limited to applications up to 15 kW
Single-phase
supply + Va  ia
Two rectifiers connected in anti-parallel across motor armature
Converter 1
Converter 2
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

10. 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 and
(Vm = peak supply voltage)
Hence, firing angles of both converters must satisfy the following:
Armature current
Field voltage + V1 
Converter 1
Converter 2 V2
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

11. Controlled Rectifier Fed – Three-phase DC DrivesQ1 Q2 Q3 Q4 
Two-quadrant drive
Limited to applications up to 1500 kW
Regeneration (Q4) only be achieved with loads that can drive the motor in reverse (-ve )
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

12. Controlled Rectifier Fed – Three-phase DC Drives
supply + Va  ia
For 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)
90o
180o 
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

13. Three-phase Controlled Rectifier 2Q DC Drive – Example
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

14. Controlled Rectifier Fed – Three-phase DC DrivesQ1 Q2 Q3 Q4 
Four-quadrant drive
Converter 1 for operation in 1st and 4th quadrant
Converter 2 for operation in 2nd and 3rd quadrant
Ia +ve,
Va +ve or -ve
Ia -ve,
Va +ve or -ve
Converter 1
Converter 2
3-phase
supply + Va  ia
Two rectifiers connected in anti-parallel across motor armature
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

15. Controlled Rectifier Fed – Three-phase DC Drives
Four-quadrant drive For continuous current:
where VL-L, m = peak line-to-line voltage.
Similar to single-phase drive: + Va  ia
Converter 1
Converter 2
Converter 2:
Ia -ve,
Va +ve
Converter 1:
Ia +ve,
Va +ve T Q1 Q2 Q3 Q4 
Converter 2:
Ia -ve,
Va -ve
Converter 1:
Ia +ve,
Va -ve
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

16. 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 + Va 
Converter 1
Converter 2 ia L1 L2
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

17. Three-phase Controlled Rectifier 4Q DC Drive – Example
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

18. Controlled Rectifier Fed – Three-phase DC DrivesQ1 Q2 Q3 Q4 
Four-quadrant drive
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 M1 M2 R1 R2
+ Va -
3-phase
supply ia ia
Dr. Ungku Anisa, July 2008
EEEB443 - Control & Drives

19. Rectifier Fed DC Drives Problems
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

20. 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

21. Rectifier Fed DC Drives Problems
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

22. Rectifier Fed DC Drives Problems
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

23. 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

24. Three-Phase Full-Converter
Figure 10.5
Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004
4/10/2017
EEL 4242 by Dr. M.H. Rashid

25. Waveforms and Conduction Times
Figure 10.5
Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004
4/10/2017
EEL 4242 by Dr. M.H. Rashid