Question Bank Drives and Control TE Electronics Unit -1 1. 2. 3. 4. 5. 6. State essential part of electric drives and state its functions.[8] What is a drive? Explain different types of drives and procedure for selection of it.[8] What are the parameters to be varied for speed control of DC Series motor? What are the parameters to be varied for speed control of separately excited DC motor? Explain with neat diagram how the speed control is achieved by a 3-phase fully controlled converter. Draw output voltage waveforms for α= 300.Write output equations for the converter.[10] A 220V, 1200rpm, 15A separately excited DC motor has a armature resistance and inductance of 1W and 52 mH respectively. This motor is controlled by a single phase full converter with a Ac voltage source of 230V 50 Hz. Find Speed at α= 300 and α= 600.[8] Why are dual converters important? With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase dual mode dual converter. Why are dual converters important? With the help of a neat circuit diagram and relevant waveforms, explain the operation of a three-phase dual mode dual converter. With the help of a neat circuit diagram and relevant waveforms, explain the Symmetrical Angle Control (SAC) technique for power factor improvement in AC-DC converters. With the help of a neat circuit diagram and relevant waveforms, explain the Symmetrical Angle Control (EAC) technique for power factor improvement in AC-DC converters. With the help of a neat circuit diagram and relevant waveforms, explain the Symmetrical Angle Control PWM technique for power factor improvement in AC-DC converters. What is input power factor of the converter? Explain various methods used to improve input power factor and compare them. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase semi converter-based separately excited DC motor drive. Derive expressions for the motor armature current and torque in terms of the firing angle, motor speed, field current and motor parameters. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase full converter-based separately excited DC motor drive. Derive expressions for the motor armature current and torque in terms of the firing angle, motor speed, field current and motor parameters. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase Dual converter-based separately excited DC motor drive. Derive expressions for the motor armature current (circulating current) and torque in terms of the firing angle, motor speed, field current and motor parameters. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a three-phase semi converter-based separately excited DC motor drive. Derive expressions for the motor armature current and torque in terms of the firing angle, motor speed, field current and motor parameters. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a three-phase full converter-based separately excited DC motor drive. Derive expressions for the motor armature current and torque in terms of the firing angle, motor speed, field current and motor parameters. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a Three-phase Dual converter-based separately excited DC motor drive. Derive expressions for the motor armature current (circulating current) and torque in terms of the firing angle, motor speed, field current and motor parameters. Draw a neat circuit diagram of 1 semiconverter drive for separately excited dc motor. Explain its operation with suitable wave forms. [10] Draw a neat circuit diagram of chopper fed dc drive. Explain its operation with suitable waveforms. [8] What are the advantages and disadvantages of 3phase dc drive over 1 phase dc drive? [6] Draw a neat circuit diagram of 3 phase full converter dc drive. Explain its operation with suitable waveforms. [10] What are the effects of discontinuous armature current for dc motor drive.[4] 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. Explain over voltage and over current protection for D.C. motor. 25. Explain ‘Field failure and under voltage protections for D.C. motor.[4] 26. Write short note: a) DC motor performance parameters. b) PWM converter drive. c) Digital control of DC motor 27. A 230V, 1000rpm, 10A separately excited DC motor is fed from a single-phase semiconverter operating from the 230V, 50Hz mains. If Ra = 0.75, calculate the firing angle to obtain rated torque for a motor speed of 500rpm. [6] 28. The Speed of a separately excited motor is controlled by a single phase semi converter. The Field current which is also controlled by a semi converter is set to the maximum possible value. The ac supply voltage to the armature and field converters is 1-phase 208 V, 60 Hz. The armature resistance Ra= 0.25Ω, the field resistance Rf= 147Ω and the motor voltage constant K v= 0.7032 V/A rad/sec. T he load torque is TL= 45 Nm at 1000 rpm. The viscous friction and no-load losses are negligible. The inductances of the armature and field circuits are sufficient enough to make the armature and field currents continuous and ripple free. Determine: [10] a) The field current b) The delay angle of the converter in the armature circuits αa and c) The input power factor of the armature circuit converter. 29. The Speed of a separately excited motor is controlled by a single phase semi converter. The Field current which is also controlled by a semi converter is set to the maximum possible value. The ac supply voltage to the armature and field converters is 1-phase 208 V, 60 Hz. The armature resistance Ra= 0.12Ω, the field resistance Rf= 220Ω and the motor voltage constant K v= 1.055V/A rad/sec. T he load torque is TL= 75 Nm at 700 rpm. The viscous friction and no-load losses are negligible. The inductances of the armature and field circuits are sufficient enough to make the armature and field currents continuous and ripple free. Determine: [10] a) The field current b) The delay angle of the converter in the armature circuits αa and c) The input power factor of the armature circuit converter. 30. The Speed of a separately excited motor is controlled by a single phase Full converter. The Field current which is also controlled by a full converter is set to the maximum possible value. The ac supply voltage to the armature and field converters is 1-phase 208 V, 60 Hz. The armature resistance R a= 0.5Ω, the field resistance Rf= 345 Ω and the motor voltage constant K v= 0.71 V/A rad/sec. T he load torque is TL= 45 Nm at 1000 rpm. The viscous friction and no-load losses are negligible. If delay angle of the armature converter is αa= 450 and the armature current Ia = 55 A Determine: [12] a) Torque developed by the motor Td b) The speed ω c) The input power factor of the drive. d) If the polarity of the motor back emf is reversed find αa to maintain the armature current constant at same value of Ia = 55 A e) Power fed back to supply during regenerative braking. 31. The Speed 20 HP, 300 V, 1800 rpm of a separately excited motor is controlled by a three phase full converter drive. The Field current which is also controlled by a full converter and is set to the maximum possible value. The ac supply voltage to the armature and field converters is 3-phase; Υ connected 208 V, 60 Hz. The armature resistance Ra= 0.35Ω, the field resistance Rf= 250Ω and the motor voltage constant K v= 1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature and field circuits are sufficient enough to make the armature and field currents continuous and ripple free. Determine: [10] a) The delay angle of the converter in the armature circuits αa if motor supplies rated power at rated speed b) The no load speed if the delay angles are the same as in (a) and armature current at no-load is 10 % of the rated value. c) Speed regulation 32. The Speed 20 HP, 300 V, 1800 rpm of a separately excited motor is controlled by a three phase semi converter drive. The Field current which is also controlled by a semi converter and is set to the maximum possible value. The ac supply voltage to the armature and field converters is 3-phase; Υ connected 208 V, 60 Hz. The armature resistance Ra= 0.35Ω, the field resistance Rf= 250Ω and the motor voltage constant Kv= 1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature and field circuits are sufficient enough to make the armature and field currents continuous and ripple free. Determine: [10] a) The delay angle of the converter in the armature circuits αa if motor supplies rated power at rated speed b) The no load speed if the delay angles are the same as in (a) and armature current at no-load is 10 % of the rated value. c) Speed regulation 33. The Speed 20 HP, 300 V, 900 rpm of a separately excited motor is controlled by a three phase full converter drive. The Field current which is also controlled by a full converter and is set to the maximum possible value. The ac supply voltage to the armature and field converters is 3-phase; Υ connected 208 V, 60 Hz. The armature resistance Ra= 0.15Ω, the field resistance Rf= 145Ω and the motor voltage constant K v= 1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature and field circuits are sufficient enough to make the armature and field currents continuous and ripple free. Determine: [10] a) The delay angle of the converter in the armature circuits αa if the field converter is operated at maximum field current and the developed torque is Td = 106 Nm at 750 rpm. b) If the field converter is operated at maximum field current and the developed torque is T d = 106 Nm The delay angle of the converter in the armature circuits αa=0 determine Speed c) For the same load as in (b) determine delay angle of the field circuit converter if the speed is increased to 1800 rpm 34. The Speed 20 HP, 300 V, 900 rpm of a separately excited motor is controlled by a three phase semi converter drive. The Field current which is also controlled by a semi converter and is set to the maximum possible value. The ac supply voltage to the armature and field converters is 3-phase; Υ connected 208 V, 60 Hz. The armature resistance Ra= 0.15Ω, the field resistance Rf= 145Ω and the motor voltage constant K v= 1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature and field circuits are sufficient enough to make the armature and field currents continuous and ripple free. Determine: [10] d) The delay angle of the converter in the armature circuits αa if the field converter is operated at maximum field current and the developed torque is T d = 106 Nm at 750 rpm. e) If the field converter is operated at maximum field current and the developed torque is Td = 106 Nm The delay angle of the converter in the armature circuits αa=0 determine Speed f) For the same load as in (b) determine delay angle of the field circuit converter if the speed is increased to 1800 rpm 35. A 210 V, 1200 rpm, 10A separately excited motor is controlled by a single phase fully controlled converter with an a.c. source ‘voltage of 230 V, 50Hz. Assume that sufficient inductance is present in the armature circuit to make the motor current continuous and ripple free for any torque greater than 25 percent of rated torque Ra = 1.5 i) What should be the value of the filing angle to get the rated torque at 800 rpm? ii) Compute the filing angle for the rated braking torque at – 1200 rpm. iii) Calculate the motor - speed at the rated torque and α = 165º for the regenerative braking in the second quadrant. [10] Unit -2 36. Write short note: a) PWM converter drive. b) c) d) e) Digital control of DC motor Phase locked loop control of DC drive Microcomputer control of DC Drive Mechanical time constant and electrical time constant of DC motors 37. What are the advantages of closed loop control of DC Drives? 38. Derive and explain the principle of closed loop control of DC drives using suitable block diagram for separately excited DC Motor. 39. Derive and explain the principle of closed loop control of DC drives using suitable block diagram for DC Series Motor. 40. Draw and explain the operation of closed loop control of separately excited DC Motor with inner-current loop and field weaking. 41. Explain the principle of Phase locked loop control of DC drive using suitable block diagram for separately excited DC Motor. 42. Explain the principle of Microcomputer control of DC drive using suitable block diagram and flow chart for separately excited DC Motor. 43. Explain briefly the braking methods of dc motor. 44. Explain the operation of closed loop control of separately excited DC Motor with inner-current loop. 45. Problems 15.21 to 15.27 from power electronics circuits, devices and applications- M H Rashid 46. Example 15.12 from power electronics circuits, devices and applications- M H Rashid. Unit-3 47. Explain any two of the following methods for speed control of induction motors : [16] a) Variable frequency PWM-VSI drive. b) Stator voltage control. c) Slip power. 48. With the help of the appropriate torque-speed characteristics, explain how electromagnetic braking is achieved for 3-phase induction motors fed from a constant V/f variable voltage variable frequency drive. [8]. 49. Draw the torque- speed characteristics of the polyphase induction-motor. Also explain the following operating regions. i) Motoring region ii) Generating region iii) Braking region [6] 50. Explain PWM techniques for the speed control of IM.[8] 51. Draw circuit diagram of transistorized stator control of IM. Draw waveform for output voltage, current and sequence of pluses.[8] 52. A 4 pole, 415V, 50Hz, three-phase induction motor has a rated speed of 1460rpm. Calculate its speed, slip and slip frequency under constant V/f control for a stator frequency of 40Hz, the load torque being equal to 60% of rated motor torque. [8] 53. What is static Kramer drive and static Scherbius drive? [6] 54. What are the different speed control methods of Induction motor? Explain it in brief. [12] 55. Draw the circuit diagram and explain the operation of rotor resistance control using chopper. [8] 56. Explain with suitable block diagram the control of induction motor using microprocessor. 57. With the help of a circuit diagram and the motor torque – speed characteristic, explain stator voltage speed control of induction motors.[8] 58. What do you understand by soft start? State and explain the soft start methods employed for motors. [4] 59. Justify “The speed range of an induction motor is restricted to above 30% of full range while operating with slip power regulation system. [4]. 60. What is V/f control in speed control of IM? Explain its limitations.[8] 61. Compare VSI and CSI for IM drive.[8] 62. Explain the induction motor operation, when the V/f ratio is held constant. Also derive the expression for maximum torque. [8] 63. Explain various protection circuits used for AC motors.[8] 64. Explain Vector control of IM drive.[8] 65. Explain Briefly the braking method of Induction motor.[8] Unit-4 66. What are the various types of synchronous motors? What is self controlled mode of synchronous motor? [4] 67. Why CSI drive is preferred for synchronous motors? Explain the operation of CSI drive of a synchronous motor. [12] 68. What is self control mode of synchronous motor.[4] 69. Explain the salient pole synchronous motor with vector diagram.[8] 70. Draw and explain briefly the torque speed characteristics of synchronous reluctance motor at constant voltage and frequency.[8] Unit-5 71. Draw and explain the operation of three - phase brushless d.c. motor drive. Also explain the related waveforms. [8] 72. Explain the operation of Brushless DC motor drive. [8] 73. Draw and explain the operation of three-phase BLDC motor drive. Also Explain the related waveforms.[8] 74. Explain PF improvement using Multistep converters. [8] 75. Explain the driver circuits of permanent Magnet and hybrid stepper motor.[8] 76. Explain microstepping in stepper motors. [8] 77. Draw the circuit diagram and explain the working of chopper drive (unipolar) for stepper motor.[4] 78. With the help of a neat circuit diagram and relevant waveforms, explain the operation of a bipolar voltage chopper drive for P. M and hybrid stepper motor. [10] 79. Write short note (any three): [16] a) VCVF drives. b) Microprocessor based stepper motor drive. c) Start up consideration of Induction motor. d) synchronous motor drive Unit -6 80. Write short notes on 81. 82. i) fuzzy logic based induction motor speed control.[8] ii) fuzzy logic based wind generation system. [8] Write short note on Neuro Fussy system. [8] Explain Neural network based PWM controller. [8]