1. Gandhinagar Institute of Technology
“Power Electronics”
Topic :Classification of choppers
Branch : EE (5th sem B3)
Guided by :Prof Supraja gidalluru
Members:
Aniket singh ( )
Dinesh Shirwani ( )
Nayan solanki ( )
Mitesh tanwani ( )

2. Introduction Chopper is a static device.
Power Electronics
Introduction
Chopper is a static device.
A variable dc voltage is obtained from a constant dc voltage source.
Also known as dc-to-dc converter.
Thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control.

3. Choppers are of Two Types
Power Electronics
Step-down choppers.
Step-up choppers.
In step down chopper output voltage is less than input voltage.
In step up chopper output voltage is more than input voltage.

4. Step down Chopper A step-down chopper with resistive load.
Power Electronics
Step down Chopper
A step-down chopper with resistive load.
The thyristor in the circuit acts as a switch.
When thyristor is ON, supply voltage appears across the load.
When thyristor is OFF, the voltage across the load will be zero.
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

5. Principle Of Step-down Chopper
Power Electronics
Principle Of Step-down Chopper

6. Waveforms Of Step Down chopper
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Waveforms Of Step Down chopper

7. Parameters Of Step Down chopper
Power Electronics
Parameters Of Step Down chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

8. Power Electronics

9. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

10. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

11. Power Electronics

12. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

13. Power Electronics
Problem
A Chopper circuit is operating on TRC at a frequency of 2 kHz on a 460 V supply. If the load voltage is 350 volts, calculate the conduction period of the thyristor in each cycle. 13
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

14. Power Electronics 14
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

15. Power Electronics 15
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

16. Power Electronics
Methods Of Control
The output dc voltage can be varied by the following methods.
Pulse width modulation control or constant frequency operation.
Variable frequency control.

17. Pulse Width Modulation
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Pulse Width Modulation
tON is varied keeping chopping frequency ‘f’ & chopping period ‘T’ constant.
Output voltage is varied by varying the ON time tON

18. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

19. Variable Frequency Control
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Variable Frequency Control
Chopping frequency ‘f’ is varied keeping either tON or tOFF constant.
To obtain full output voltage range, frequency has to be varied over a wide range.
This method produces harmonics in the output and for large tOFF load current may become discontinuous

20. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

21. Principle Of Step-up Chopper
Power Electronics
Principle Of Step-up Chopper

22. When the chopper is ON, the inductor L is connected across the supply.
Power Electronics
Step-up chopper is used to obtain a load voltage higher than the input voltage V.
The values of L and C are chosen depending upon the requirement of output voltage and current.
When the chopper is ON, the inductor L is connected across the supply.
The inductor current ‘I’ rises and the inductor stores energy during the ON time of the chopper, tON.
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

23. Therefore voltage across load is given by
Power Electronics
When the chopper is off, the inductor current I is forced to flow through the diode D and load for a period, tOFF.
The current tends to decrease resulting in reversing the polarity of induced EMF in L.
Therefore voltage across load is given by
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

24. Diode D prevents any current flow from capacitor to the source.
Power Electronics
A large capacitor ‘C’ connected across the load, will provide a continuous output voltage .
Diode D prevents any current flow from capacitor to the source.
Step up choppers are used for regenerative braking of dc motors.
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

25. Expression For Output Voltage
Power Electronics
Expression For Output Voltage
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

26. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

27. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

28. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

29. Power Electronics

30. Performance Parameters
Power Electronics
Performance Parameters
The thyristor requires a certain minimum time to turn ON and turn OFF.
Duty cycle d can be varied only between a min. & max. value, limiting the min. and max. value of the output voltage.
Ripple in the load current depends inversely on the chopping frequency, f.
To reduce the load ripple current, frequency should be as high as possible.

31. Classification Of Choppers
Power Electronics
Classification Of Choppers
Choppers are classified as
Class A Chopper
Class B Chopper
Class C Chopper
Class D Chopper
Class E Chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

32. Class A Chopper Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
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Class A Chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

33. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

34. Class B Chopper Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Class B Chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

35. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

36. Class C Chopper Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Class C Chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

37. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

38. Class D Chopper Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Class D Chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

39. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

40. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

41. Class E Chopper Prof. T.K. Anantha Kumar, E&E Dept., MSRIT
Power Electronics
Class E Chopper
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

42. Four Quadrant Operation
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Four Quadrant Operation
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

43. Advantages Reduction in supply harmonic currents.
Reduction in the ripple content of output voltage
Due to increased frequency of output voltage the size of
the filter inductance L is reduced

44. Disadvantages Chopper cannot be tested without connecting load.
Power Electronics
Disadvantages
Chopper cannot be tested without connecting load.
Thyristor T1 has to carry load current as well as resonant current resulting in increasing its peak current rating. 44
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

45. Applications Widely used for motor control.
Used in regenerative braking
D.C motor speed control
DC voltage boosting
Battery operated appliances, cars
Battery chargers

46. Thank you