1. Controlled Rectifiers

2. Full wave Controlled Rectifier

3. Discontinuous and Continuous Operations

4. Discontinuous Mode

6. Continuous Mode

7. 4-3 controlled full-wave rectifiers
Resistive　load： 　Fig.4-10

8. R-L　load : Fig.4-11

9. 　Fig　4-12

10. R-L　Source　load　：　Fig.4-14
　The　SCRS　may　be　turned　on　at　any　time　that　they　are　forward　biased, which　is　at　an　angle

11. average load current is
　　For　continuous　current　case, the　average　bridge　output　voltage　is
average　load　current　is　
　The　ac　voltage　terms　are　unchanged　from　the　controlled　rectifier　with　an　R-L　load. 　The　ac　current　terms　are　determined　from　circuit.
　Power　absorbed　by　the　dc　voltage　is
Power　absorbed　by　resistor　in　the　load　is

12. Controlled Single-phase converter operating as an inverter：
seeing 　Fig　4-14. 　4-15 .

13. Full-Bridge Thyristor Converters
Identical to single phase and three phase diode rectifiers but with diode replaced by thyristors.
Start analysis with current source load
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 6 Thyristor Converters

14. Average DC output voltage
Assuming AC side inductance is zero
Note that output voltage can go negative for alpha > 90 degrees.
This means negative power flow or inversion
Copyright © 2003
by John Wiley & Sons, Inc.
Chapter 6 Thyristor Converters

15. 3 Phase Controlled Rectifiers
Power Electronics
3 Phase Controlled Rectifiers
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. 15

16. Extensively used in high power variable speed industrial dc drives.
Power Electronics
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. 16

17. Power Electronics
3-Phase Half Wave Converter (3-Pulse Converter) with RL Load Continuous & Constant Load Current Operation 17

18. Power Electronics 18

19. Power Electronics 19

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

21. Power Electronics
=300
=600 21

22. Power Electronics
=900 22

23. Power Electronics
3 Phase Half Wave Controlled Rectifier Output Voltage Waveforms For R Load or RL Load with FWD at Different Trigger Angles 23

24. Power Electronics 24

25. Power Electronics
=00
=150 25
Prof. M.

26. Power Electronics
=300
=600 26

27. Three Phase Semiconverters
Power Electronics
Three Phase Semiconverters
3 Phase semiconverters are used in Industrial dc drive applications up to 120kW power output.
Single quadrant operation is possible.
Power factor decreases as the delay angle increases.
Power factor is better than that of 3 phase half wave converter. 27

28. Power Electronics
3 Phase Half Controlled Bridge Converter (Semi Converter) with Highly Inductive Load & Continuous Ripple free Load Current 28

29. Power Electronics 29

30. Wave forms of 3 Phase Semiconverter for  > 600
Power Electronics
Wave forms of 3 Phase Semiconverter for  > 600 30

31. Power Electronics 31

32. Power Electronics 32

33. Power Electronics 33

34. Power Electronics 34

35. Power Electronics 35

36. Wave forms of 3 Phase Semiconverter for   600
Power Electronics
Wave forms of 3 Phase Semiconverter for   600 36

37. Power Electronics 37

38. Power Electronics 38

39. Power Electronics 39

40. Power Electronics
To derive an Expression for the Average Output Voltage of 3 Phase Semiconverter for  >  / 3 and Discontinuous Output Voltage 40

41. Power Electronics 41

42. Power Electronics 42

43. Power Electronics 43

44. Power Electronics
Average or DC Output Voltage of a 3-Phase Semiconverter for  / 3, and Continuous Output Voltage 44

45. Power Electronics 45

46. Three Phase Full Converter
Power Electronics
Three Phase Full Converter
3 Phase Fully Controlled Full Wave Bridge Converter.
Known as a 6-pulse converter.
Used in industrial applications up to 120kW output power.
Two quadrant operation is possible. 46

47. Power Electronics 47

48. Power Electronics 48

49. Power Electronics 49

50. The thyristors are triggered at an interval of  / 3.
Power Electronics
The thyristors are triggered at an interval of  / 3.
The frequency of output ripple voltage is 6fS.
T1 is triggered at t = (/6 + ), T6 is already conducting when T1 is turned ON.
During the interval (/6 + ) to (/2 + ), T1 and T6 conduct together & the output load voltage is equal to vab = (van – vbn) 50

51. Thyristors are numbered in the order in which they are triggered.
Power Electronics
T2 is triggered at t = (/2 + ), T6 turns off naturally as it is reverse biased as soon as T2 is triggered.
During the interval (/2 + ) to (5/6 + ), T1 and T2 conduct together & the output load voltage vO = vac = (van – vcn)
Thyristors are numbered in the order in which they are triggered.
The thyristor triggering sequence is 12, 23, 34, 45, 56, 61, 12, 23, 34, ……… 51

52. Power Electronics
To Derive An Expression For The Average Output Voltage Of 3-phase Full Converter With Highly Inductive Load Assuming Continuous And Constant Load Current 52

53. Power Electronics
The output load voltage consists of 6 voltage pulses over a period of 2 radians, Hence the average output voltage is calculated as 53

54. Power Electronics 54

55. Power Electronics 55

56. Vn/Vml-l for controlled 3-phase full converter
Power Electronics

57. Three Phase Dual Converters
Power Electronics
Three Phase Dual Converters
For four quadrant operation in many industrial variable speed dc drives , 3 phase dual converters are used.
Used for applications up to 2 mega watt output power level.
Dual converter consists of two 3 phase full converters which are connected in parallel & in opposite directions across a common load. 57

58. Power Electronics 58

59. Outputs of Converters 1 & 2
Power Electronics
Outputs of Converters 1 & 2
During the interval (/6 + 1) to (/2 + 1), the line to line voltage vab appears across the output of converter 1 and vbc appears across the output of converter 2 59

60. To obtain an Expression for the Circulating Current
Power Electronics
To obtain an Expression for the Circulating Current
If vO1 and vO2 are the output voltages of converters 1 and 2 respectively, the instantaneous voltage across the current limiting inductor during the interval (/6 + 1)  t  (/2 + 1) is given by 60

61. Power Electronics 61

62. Four Quadrant Operation
Power Electronics
Four Quadrant Operation
Conv. 2 Inverting
2 > 900
Conv. 1 Rectifying
1 < 900
Conv. 2 Rectifying
2 < 900
Conv. 1 Inverting
1 > 900 62

63. There are two different modes of operation. Circulating current free
Power Electronics
There are two different modes of operation.
Circulating current free
(non circulating) mode of operation
Circulating current mode of operation 63

64. Non Circulating Current Mode Of Operation
Power Electronics
Non Circulating Current Mode Of Operation
In this mode of operation only one converter is switched on at a time
When the converter 1 is switched on,
For 1 < 900 the converter 1 operates in the Rectification mode
Vdc is positive, Idc is positive and hence the average load power Pdc is positive.
Power flows from ac source to the load 64

65. When the converter 1 is on,
Power Electronics
When the converter 1 is on,
For 1 > 900 the converter 1 operates in the Inversion mode
Vdc is negative, Idc is positive and the average load power Pdc is negative.
Power flows from load circuit to ac source. 65

66. When the converter 2 is switched on,
Power Electronics
When the converter 2 is switched on,
For 2 < 900 the converter 2 operates in the Rectification mode
Vdc is negative, Idc is negative and the average load power Pdc is positive.
The output load voltage & load current reverse when converter 2 is on.
Power flows from ac source to the load 66

67. When the converter 2 is switched on,
Power Electronics
When the converter 2 is switched on,
For 2 > 900 the converter 2 operates in the Inversion mode
Vdc is positive, Idc is negative and the average load power Pdc is negative.
Power flows from load to the ac source.
Energy is supplied from the load circuit to the ac supply. 67

68. Circulating Current Mode Of Operation
Power Electronics
Circulating Current Mode Of Operation
Both the converters are switched on at the same time.
One converter operates in the rectification mode while the other operates in the inversion mode.
Trigger angles 1 & 2 are adjusted such that (1 + 2) = 1800 68

69. Vdc is positive & Idc is positive and Pdc is positive.
Power Electronics
When 1 < 900, converter 1 operates as a controlled rectifier. 2 is made greater than 900 and converter 2 operates as an Inverter.
Vdc is positive & Idc is positive and Pdc is positive. 69

70. Vdc is negative & Idc is negative and Pdc is positive.
Power Electronics
When 2 < 900, converter 2 operates as a controlled rectifier. 1 is made greater than 900 and converter 1 operates as an Inverter.
Vdc is negative & Idc is negative and Pdc is positive. 70