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Unit I Introduction to Solid State Drives.pptx

  2. UNIT I DRIVE CHARACTERISTICS Dr.P.Subha Karuvelam Professor (CAS)/EEE Government College of Engineering Tirunelveli – 627007.
  3. Electric Drives • Systems employed for motion control are called as Drives. • It may employ any of prime movers such as diesel or petrol engines, gas or steam turbines, steam engines, hydraulic motors and electric motors, for supplying mechanical energy for motion control. • Drives employing electric motors are called as Electrical Drives.
  4. Parts Of Electric Drives
  5. Parts of Electric Drives Power Modulator : • The power modulator regulates the output power of the source. • It controls the power from the source to the motor in such a manner that motor transmits the speed torque characteristic required by the load. • During the transient operations like starting, braking and speed reversing the excessive current drawn from the source.
  6. POWER MODULATOR(Cont’d) This excessive current drawn from the source may overload it or may cause a voltage drop. Hence the power modulator restricts the source and motor current The power modulator converts the energy according to the requirement of the motor  e.g. if the source is DC and an induction motor is used then power modulator convert DC into AC.  It also selects the mode of operation of the motor, i.e., motoring or braking.
  7. CONTROL UNIT Control Unit : • Consists of linear and digital integrated circuits and transistors • The control unit controls the power modulator which operates at small voltage and power levels. The control unit also operates the power modulator as desired. • It also generates the commands for the protection of power modulator and motor. An input command signal which adjusts the operating point of the drive, from an input to the control unit.
  8. SENSING UNIT Sensing Unit : • It senses the certain drive parameter like motor current and speed. • It mainly required either for protection or for closed loop operation.
  9. ADVANTAGE OF ELECTRIC DRIVES Advantages of Electrical Drive: • The electrical drives are available in a wide range of torque, speed and power. • They are adaptable to almost conditions such as explosive any operating and radioactive environment, submerged in liquids, vertical mounting and so on. • The electrical drive does not pollute the environment.
  10. ADVANTAGE OF ELECTRIC DRIVES(Cont’d) • It can operate in all four quadrants of speed torque plane. • They can be started instantly and can immediately be fully loaded. i.e., there is no need to refuel or warm up the motor. • They have flexible control characteristic and can be employed to automatically control the drive.
  11. ADVANTAGE OF ELECTRIC DRIVES(Cont’d) • Because of the following advantages, the mechanical energy already available from a non-electrical prime mover is sometimes first converted into electrical energy by a generator and back to a mechanical energy of an electrical motor. • Electrical link thus provides between the non-electrical prime mover and the load impact to the drive flexible control characteristic.
  12. Disadvantage Of Electric Drives Disadvantages of Electrical Drive: • The power failure completely disabled the whole of the system. • The application of the drive is limited because it cannot use in a place where the power supply is not available. • It can cause noise pollution. • The initial cost of the system is high.
  13. CLASSIFICATION OF ELECTRIC DRIVES Generally classified into 3 categories: • Group drive • Individual Drive • Multimotor Drive
  14. Group drive If several group of mechanisms or machines are organized on one shaft and driven or actuated by one motor, the system is called a group drive or shaft drive. Advantage : Most Economical Disadvantage : • Any Fault that occurs in the driving motor renders all the driving equipment idle. • Efficiency low because of losses occurring in the energy transmitting mechanisms (Power loss). • Not safe to operate. Also Noise level at the working spot is high.
  15. Individual Drive: • If a single motor is used to drive or actuate a given mechanism and it does all the jobs connected with this load , the drive is called individual drive. • All the operations connected with operating a lathe may be performed by a single motor. • Each motor is driven by its own separated motor with the help of gears , pulleys etc.
  16. Multi Motor Drive: • Each operation of the mechanism is taken care of by a separate drive motor. • The System contains several individual drives each of which is used to operate its own mechanism. • Applications: Complicated metal cutting machine tools, Paper making industries, rolling machines etc
  17. Multi Motor Drive: Separate motors are provided for actuating different parts of the driven mechanism. Advantage : • Each Machine is driven by a separated motor it can be run and stopped as desired. • Machines not required can be shut down and also replaced with a minimum of dislocation. • There is a flexibility in the installation of different machines.
  18. Multi Motor Drive: • In the case of motor fault, only its connected machine will stop where as others will continue working undisturbed. • Absence of belts and line shafts greatly reduces the risk of a accidents to the operating personnel. Disadvantage: • Initial high cost
  19. Dynamics of motor-load system • When an electric motor rotates, it is usually connected to a load which has a rotational or translational motion. • The speed of the motor may be different from that of the load. To analyze the relation among the drives and loads, the concept of dynamics of electrical drives is introduced.
  20. Dynamics of motor-load combination Drive J = Polar moment of inertia of motor load (kg-m2) m = Instantaneous angular velocity (rad/sec) T = Instantaneous value of developed motor torque (N-m) T1 = Instantaneous value of load torque referred to motor shaft (N-m)
  21. Dynamics of motor-load System • Now, from the fundamental torque equation • For the drive with constant inertia Motor Torque = Load Torque + Dynamic Torque
  22. Dynamics of motor-load System • Dynamic torque J(dωm/dt) present during the transient operations. • During Acceleration • During Deceleration
  23. COMPONENTS OF LOAD TORQUE Divided into 3 components 1. Friction Torque - 2. Windage Torque – 3. Torque required to do useful mechanical work.
  24. COMPONENTS OF LOAD TORQUE 1. Friction Torque Present at the motor shaft and also in various parts of the load. TF is the equivalent value of various friction torques referred to the motor shaft. 2. Windage Torque (TW): When motor runs, wind generates a torque opposing the motion is known as windage torque.
  25. COMPONENTS OF LOAD TORQUE 3. Torque required to do useful mechanical work. • Nature of this torque depends upon particular application. • It may be some function of speed, it may be time invariant or time variant, its nature may also change with the load’s mode ofoperation.
  26. Friction Torque 3 Components are 1. Static Friction Friction at zero speed is Stiction or static friction 2. Viscous Friction Varies linearly with speed B – Viscous friction coefficient 3. Coulomb Friction Independent of spped
  27. Windage Torque  Proportional to the square of the speed
  28. COMPONENTS OF LOAD TORQUE For finite speed,
  29. Common Load Torques 1. Fan and Centrifugal pumps 2. Traction 3. Coiler Drives 4. Diesel Electric Locomotive 5. Excavators 6. Hoist
  31. Fan and Centrifugal Loads Windage torque predominates
  32. Traction Drives Comprises of  Windage torque  Viscous friction  Coulomb friction  Stiction
  33. Coiler Drives Motor will operate at Constant Power  Steel Mill  Paper Mill  Plastic Mill  To maintain the tension of the steel, paper, plastic strip the motor operated in Constant power mode
  34. Diesel Electric Locomotive Act as torque converter AB – To limit the motor speed within permissible value CD – Limit on maximum torque for 1. To limit maximum current 2. To prevent wheel slipage 3. To prevent draw bar fracture
  35. Excavators When load torque is high, the motor will simply stop. To prevent the mechanical damage to the excavator
  36. Hoist For low speed hoist, load torque is mainly due to gravitational force Gravity is constant and independent of speed For high speed hoist, viscous friction and windage plays active role
  38. Classification of load torques Various load torques can be classified into broad categories. • Active load torques • Passive load torques
  39. Active Load Load torques which has the potential to drive the motor under equilibrium conditions are called active load torques Retain their sign if the drive rotation is changed Torque due to gravity, tension, compression and tension due to elastic body.
  40. Passive loads Always oppose the motion and change their direction on the reversal of motion Friction, Cutting, drilling etc
  41. Steady and Transient state stability of Electric Drive • The drive is said to be in equilibrium if • Stable system: If the system can able restore the stable speed after a small disturbance in supply, load or part of the drive
  42. Steady and Transient state stability of Electric Drive • Changes from the state of equilibrium takes place slowly and the effect of either the inertia or the inductance is insignificant – Steady state stability. Sudden and fast changes from the equilibrium state so effect of both inertia and inductance can not be neglected- Dynamic or transient stability.
  43. Steady and Transient state stability of Electric Drive • Criteria for steady state stability:- • At time ‘t’
  44. Steady State Stability
  45. Steady State Stability
  46. Steady State stability In new speed, Hence acceleration will occur and speed of the motor increases.
  47. Steady State stability In new speed, Hence deceleration will occur and speed of the motor decreases.
  50. Modes of Operation
  51. Speed – Torque Curves with different speed settings
  52. Modes of Operation 1. Increase in speed in same direction 2. Decrease in speed in same direction 3. Speed Reversal
  53. Increase in speed in same direction
  54. Decrease in speed in same direction
  55. Speed Reversal
  56. Speed Reversal
  57. Choice or selection of drives Steady State Operating conditions requirements: Nature of speed torque characteristics, speed regulation, speed range, efficiency, duty cycle, quadrants of operation, speed fluctuations if any, ratings etc Transient operation requirements: Values of acceleration and deceleration, starting, braking and reversing performance. Requirements related to the source: Types of source and its capacity, magnitude of voltage, voltage fluctuations, power factor, harmonics and their effect on other loads, ability to accept regenerative power Capital and running cost, maintenance needs life.  Space and weight restriction if any. Environment and location. Reliability.