4 Controlled Rectifier DC 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

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


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


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



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 )



5

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


90o



180o



2Vm  6


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 



+

Va

Ea





2Vm

m



+





cos a

Q1 90o

180o

2Vm  7




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


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



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

V1 V2  0

terminal, i.e.: where V1 

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





+ 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 )



11

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


12



Three-phase Controlled Rectifier 2Q DC Drive – Example



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 



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


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


L2

Converter 2 16

Three-phase Controlled Rectifier 4Q DC Drive – Example



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


R1


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


19

Rectifier Fed DC Drives Problems 12-pulse converter – consists of two 6-pulse controlled rectifiers connected in parallel



20


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)



21


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) 



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.



23

Three-Phase Full-Converter

Figure 10.5

Reference: Rashid, M.H, Power Electronics: Circuit, Devices and Applictions, 3rd ed., Pearson, New-Jersey, 2004 11/4/2013

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 11/4/2013

EEL 4242 by Dr. M.H. Rashid

25

4 Controlled Rectifier DC Drives

Recommend Documents