controlled rectifiers

1. 1

2. 2
 Operate from 3 phase ac supply voltage.
 They provide higher dc output voltage.
 Higher dc output power.
 Higher output voltage ripple frequency.
 Filtering requirements are simplified for smoothing
out load voltage and load current.
3 Phase Controlled
Rectifiers

3. 3
 Extensively used in high power variable speed
industrial dc drives.
 Three single phase half-wave converters can be
connected together to form a three phase half-wave
converter.

4. 4
Converter
(3-Pulse Converter)
with RL Load
Continuous & Constant
Load Current Operation

5. 5

6. 6
RN AN
YN BN
BN CN
v v
v v
v v



Vector Diagram of
3 Phase Supply Voltages
VAN
VCN
VBN
120
0
120
0
120
0

7. 7
We deifine three line to neutral voltages
(3 phase voltages) as follows
3 Phase Supply Voltage
Equations

8. 8
 
 
 
0
0
0
sin ;
Max. Phase Voltage
2
sin
3
sin 120
2
sin
3
sin 120
sin 240
RN an m
m
YN bn m
m
BN cn m
m
m
v v V t
V
v v V t
V t
v v V t
V t
V t








 

 
  
 
 
 
 
  
 
 
 
 

9. 9
van vbn vcn van

10. 10
io=Ia
Constant Load
Current
Ia
Ia
Each thyristor conducts for 2/3 (1200)

11. 11
To Derive an Expression
for the Average Output
Voltage of a 3-Phase
Half Wave Converter
with RL Load for
Continuous Load
Current

12. 12
 
 
 
0
1
0
2
0
3
0
30
6
5
150
6
7
270
6
2
Each thytistor conducts for 120 or radians
3
T is triggered at t
T is triggered at t
T is triggered at t

  

  

  

 
   
 
 
 
   
 
 
 
   
 
 

13. 13
 
5
6
6
If the reference phase voltage is
sin , the average or dc output
voltage for continuous load current is calculated
using the equation
3
sin .
2
RN an m
dc m
v v V t
V V t d t





 



 
 
 
  
 
 


14. 14
 
 
5
6
6
5
6
6
3
sin .
2
3
cos
2
3 5
cos cos
2 6 6
m
dc
m
dc
m
dc
V
V t d t
V
V t
V
V








 



 
 





 
 
  
 
 
 
 
 
 
 
 
 
   
    
   
 
   
 


15. 15
   
   
   
       
   
0 0
0
Note from the trigonometric relationship
cos cos .cos sin .sin
5 5
cos cos sin sin
6 6
3
2
co
cos 150 cos sin 150 sin
3
2 cos 30
s .cos sin sin
6 6
.cos
m
dc
m
dc
A
V
V
B A B A B
V
V
 
 
  




 
  
 
   
 
   
 
   
 

 
   
 
 
   
   






    
0
sin 30 sin 
 
 
 
 

16. 16
       
       
   
   
       
       
0 0
0 0 0 0
0 0
0 0
0
0
0
0
0 0
Note: cos 1
cos 180 30 cos sin 180 30 sin
3
2 cos 30 .cos sin 30 sin
cos 30 cos sin 30 sin
3
2 cos 30 .cos sin 30 s
80 30 cos 30
sin 180 30 sin 30
in
m
dc
m
dc
V
V
V
V
 
  
 
  
 
 
   
 

 
 
 
 
 
 
 
 
 






17. 17
   
 
   
 
0
3
2cos 30 cos
2
3 3
2 cos
2 2
3 3 3
3 cos cos
2 2
3
cos
2
Where 3 Max. line to line supply voltage
m
dc
m
dc
m m
dc
Lm
dc
Lm m
V
V
V
V
V V
V
V
V
V V




 
 


 
  
 
 
 
 
 
 
 

 

18. 18
 
max
The maximum average or dc output voltage is
obtained at a delay angle 0 and is given by
3 3
2
Where is the peak phase voltage.
And the normalized average output voltage is
m
dm
dc
m
d
dcn n
V
V V
V
V
V V



 
  cos
c
dm
V



19. 19
   
 
1
5 2
6
2 2
6
1
2
The rms value of output voltage is found by
using the equation
3
sin .
2
and we obtain
1 3
3 cos2
6 8
m
O RMS
m
O RMS
V V t d t
V V




 





 
 
  
 
 
 
 
 
 


20. 20
3 Phase Half Wave
Controlled Rectifier Output
Voltage Waveforms For RL
Load
at Different Trigger Angles

21. 21
0
0
30
0
30
0
60
0
60
0
90
0
90
0
120
0
120
0
150
0
150
0
180
0
180
0
210
0
210
0
240
0
240
0
270
0
270
0
300
0
300
0
330
0
330
0
360
0
360
0
390
0
390
0
420
0
420
0
Van

V0

V0
Van


=30
0
=60
0
Vbn
Vbn
Vcn
Vcn
t
t
=300
=600

22. 22
=900