1 / 140

DC Choppers

DC Choppers. 1. Prof. T.K. Anantha Kumar, E&E Dept., MSRIT. 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. Widely used for motor control. Also used in regenerative braking.

sasha
Download Presentation

DC Choppers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DC Choppers 1 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  2. 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. • Widely used for motor control. • Also used in regenerative braking. • Thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control. 2 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  3. Choppers are of Two Types • 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. 3 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  4. Principle Of Step-down Chopper 4 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  5. 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. 5 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  6. 6 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  7. 7 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  8. 8 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

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

  11. 11 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

  13. 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. 13 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  14. Pulse Width Modulation • tON is varied keeping chopping frequency ‘f’ & chopping period ‘T’ constant. • Output voltage is varied by varying the ON time tON 14 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

  16. Variable Frequency Control • Chopping frequency ‘f’ is varied keeping either tONor 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 tOFFload current may become discontinuous 16 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  17. 17 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  18. Step-down ChopperWith R-L Load 18 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  19. When chopper is ON, supply is connected across load. • Current flows from supply to load. • When chopper is OFF, load current continues to flow in the same direction through FWD due to energy stored in inductor ‘L’. 19 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  20. Load current can be continuous or discontinuous depending on the values of ‘L’ and duty cycle ‘d’ • For a continuous current operation, load current varies between two limits Imaxand Imin • When current becomes equal to Imaxthe chopper is turned-off and it is turned-on when current reduces to Imin. 20 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  21. 21 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  22. Expressions For Load CurrentiO For Continuous Current Operation When Chopper Is ON (0  t  tON) 22 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  23. 23 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  24. 24 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  25. 25 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  26. When Chopper is OFF 26 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

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

  29. 29 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  30. 30 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  31. 31 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

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

  34. 34 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

  36. 36 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

  38. 38 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

  40. Principle Of Step-up Chopper 40 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  41. 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. 41 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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

  43. 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. 43 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  44. Expression For Output Voltage 44 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  45. 45 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  46. 46 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  47. 47 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  48. 48 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  49. 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. 49 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

  50. 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. 50 Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

More Related