lesson14et438a.pdf - lesson14et438ax LESSON 14 TRANSFER FUNCTIONS OF DC MOTORS 1 ET 438a Automatic Control Systems Technology LEARNING OBJECTIVES After

lesson14et438a.pdf - lesson14et438ax LESSON 14 TRANSFER...

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10/28/2015 1 L ESSON 14: T RANSFER F UNCTIONS OF D C M OTORS ET 438a Automatic Control Systems Technology 1 lesson14et438a.pptx L EARNING O BJECTIVES 2 lesson14et438a.pptx After this presentation you will be able to: Write the transfer function for an armature controlled dc motor. Write a transfer function for a dc motor that relates input voltage to shaft position. Represent a mechanical load using a mathematical model. Explain how negative feedback affects dc motor performance.
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10/28/2015 2 S TEADY -S TATE O PERATION OF S EPARATELY E XCITED D C M OTORS 3 lesson14et438a.pptx Consider steady-state model w m i a = armature current e b = back emf e a = armature terminal voltage w m = motor speed (rad/sec) T = motor torque T f = static friction torque R a = armature resistance L a = armature inductance J m = rotational inertia B m = viscous friction Review the steady-state relationships Of machine S TEADY -S TATE O PERATION OF S EPARATELY E XCITED D C M OTORS 4 lesson14et438a.pptx Relationships of Separately Excited Dc Motor i a T -T f D T D i a K T =D T/ D i a Torque-Current Curve Back EMF Curve w m e b D T D i a K T =D T/ D i a Speed-Torque Curve T w m D T Dw m w m =w nl ( Dw m / D T)T w nl
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10/28/2015 3 S TEADY -S TATE M OTOR E QUATIONS 5 lesson14et438a.pptx Developed Torque m - N T i K T f a T = T = motor torque K T = torque constant T f = motor friction torque i a = armature current KVL in Armature Circuit V e R i e b a a a = w m = shaft speed (rad/s) e b = back emf K e = back emf constant Back EMF V K e m e b w = Developed Power W T P m w = e a = armature voltage e b = back emf R a = armature resistance P = shaft power 6 lesson14et438a.pptx S TEADY -S TATE M OTOR E QUATIONS Combining the previous equations gives: e T a f a T m K K R ) T T ( e K = w e a a a m K R i e = w If the load torque is zero (T=0) then the above equation (1) gives the no-load speed (1) (2) e T a f a T nl K K R ) T ( e K = w
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10/28/2015 4 S TEADY -S TATE M OTOR O PERATION 7 lesson14et438a.pptx Example 14-1: An armature-controlled dc motor has the following ratings: T f =0.012 N-m, R a =1.2 ohms, K T =0.06 N-m/A, K e =0.06 V-s/rad. It has a maximum speed of 500 rad/s with a maximum current of 2 A. Find: a) maximum output torque, b) maximum mechanical output power, c) maximum armature voltage, d) no-load speed at maximum armature voltage.
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  • Fall '17
  • tola
  • DC MOTORS, Electric motor

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