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Bridging Theory in Practice

Bridging Theory in Practice. Transferring Technical Knowledge to Practical Applications. Introduction to Motor Control. Introduction to Motor Control. Introduction to Motor Control. Intended Audience: Individuals with an interest in learning about electric motors and how they are controlled

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Bridging Theory in Practice

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  1. Bridging Theory in Practice Transferring Technical Knowledge to Practical Applications

  2. Introduction to Motor Control

  3. Introduction to Motor Control

  4. Introduction to Motor Control Intended Audience: • Individuals with an interest in learning about electric motors and how they are controlled • A simple understanding of magnetics is assumed Topics Covered: • What is an electric motor? • What are some common types of electric motors? • How do these electric motors work? • How these motors are controlled. Expected Time: • Approximately 90 minutes

  5. Agenda Introduction to Electromagnets and Electric Motors What Is Motor Control?               What Are Some Common Types of Motors?           Permanent Magnet DC Motors Stepper Motors Brushless DC Motors Summary of Motors and Motor Control Circuits    

  6. Agenda • Introduction to Electromagnets and Electric Motors • What Is Motor Control?               • What Are Some Common Types of Motors?           • Permanent Magnet DC Motors • Stepper Motors • Brushless DC Motors • Summary of Motors and Motor Control Circuits    

  7. What Is a Permanent Magnet? A piece of iron or steel which produces a magnetic field Found in nature as magnetite (Fe3O4) lodestones Magnetic field causes the permanent magnet to attract iron and some other materials Two ends of the permanent magnet are usually designated North and South Opposite magnet ends attract and like magnet ends repel

  8. What Is an Electromagnet? Electromagnets behave like permanent magnets… … but their magnetic field is not permanent Magnetic field is temporarily induced by an electric current

  9. How Do You Make an Electromagnet? Start with an iron bar

  10. How Do You Make an Electromagnet? Start with an iron bar Wrap a wire around the iron bar

  11. How Do You Make an Electromagnet? Start with an iron bar Wrap a wire around the iron bar Connecting a battery causes a current to flow in the wire - + Current

  12. How Do You Make an Electromagnet? Start with an iron bar Wrap a wire around the iron bar Connecting a battery causes a current to flow in the wire The current induces a magnetic field creating an electromagnet - + SOUTH NORTH Current

  13. How Do You Make an Electromagnet? Reversing the current direction, reverses the polarity - + NORTH SOUTH Current

  14. - + Current How Do You Make an Electromagnet? • Reversing the current direction, reverses the polarity • If the current is stopped, the induced magnetic field decays to 0 NORTH SOUTH

  15. Electromagnets andElectric Motors We can use electromagnets in electric motors to convert electrical energy to mechanical work… Electric Motor • Electric motors are used to perform a mechanical task by using electricity • Open a sunroof • Lift a power antenna • Control windshield wiper Electric Energy + - 12V

  16. What Is an Electric Motor? An electric motor has two basic parts: The stationary part is called the stator. The rotating part of the electric motor is called the rotor. ROTOR STATOR

  17. ROTOR What Is an Electric Motor? • Electrical energy creates a rotatingmagnetic field inside the motor causing the rotor to rotate, creating mechanical motion STATOR

  18. Where Are Electric Motors Used? Electric motors are used in many different automotive applications: Sunroof Brakes Power steering Fuel pump Water pump Hybrid and electric vehicles Cruise control Throttle plate control Air vents Others Power windows Power seats Power mirrors Fans Windshield wipers Windshield washer pumps Starter motor Electric radio antennae Door locks Information gauges

  19. Agenda • Introduction to Electromagnets and Electric Motors • What Is Motor Control? • What Are Some Common Types of Motors?           • Permanent Magnet DC Motors • Stepper Motors • Brushless DC Motors • Summary of Motors and Motor Control Circuits    

  20. What Is Motor Control ? • The controlled application of electrical energy to a motor to elicit a desired mechanical response • Start / Stop • Speed • Torque • Position • Significant amount of electronics may be required to control the operation of some electric motors

  21. Control of Electromagnetics Much of the physical design of an electric motor and its control system are related to the switching of the electromagnetic field There is a mechanical force which acts on a current carrying wire within a magnetic field The mechanical force is perpendicular to the wire and the magnetic field The relative magnetic fields between the rotor and stator are arranged so that a torque is created, causing the rotor to rotate about its axis

  22. Agenda • Introduction to Electromagnets and Electric Motors • What Is Motor Control?               • What Are Some Common Types of Motors?     • Permanent Magnet DC Motors • Stepper Motors • Brushless DC Motors • Summary of Motors and Motor Control Circuits    

  23. Types of Electric Motors • There are many different types and classifications of electric motors: Permanent magnet DC motor Stepper motor Brushless DC motor Wound field motor Universal motors Three phase induction motor Three-phase AC synchronous motors Two-phase AC Servo motors torque motors Shaded-pole motor split-phase induction motor capacitor start motor Permanent Split-Capacitor (PSC) motor Repulsion-start induction-run (RS-IR) motor Repulsion motor Linear motor Variable reluctance motor Unipolar stepper motor Bipolar stepper Full step stepper motor Half step stepper motor Micro step stepper motor Switched reluctance motor Shaded-pole synchronous motor Induction motor Coreless DC motor Others......

  24. Permanent Magnet DC Motor Similar in construction to the introductory example Metallic contacts (brushes) are used to deliver electrical energy Rotational speed proportional to the applied voltage Torque proportional to the current flowing through the motor Advantages: Low cost (high volume demand) Simple operation Disadvantages: Medium efficiency Poor reliability (brush, commutator wear out) Strong potential source of electromagnetic interference

  25. Stepper Motor Full rotation of electric motor divided into a number of "steps" For example, 200 steps provides a 1.8o step angle A stepper motor controller can move the electric motor one step (in either direction) by applying a voltage pulse Rotational speed is controlled by changing the frequency of the voltage pulses Advantages: Low cost position control (instrument gauges) Easy to hold position Disadvantages: Poor efficiency Requires digital control interface High motor cost

  26. Brushless DC Motor Similar to a permanent magnet DC motor Rotor is always the permanent magnet (internal or external) Design eliminates the need for brushes by using a more complex drive circuit Advantages: High efficiency High reliability Low EMI Good speed control Disadvantages: May be more expensive than "brushed" DC motors More complex and expensive drive circuit than "brushed" DC motors

  27. Agenda • Introduction to Electromagnets and Electric Motors • What Is Motor Control?               • What Are Some Common Types of Motors?           • Permanent Magnet DC Motors • Stepper Motors • Brushless DC Motors • Summary of Motors and Motor Control Circuits    

  28. How Does a Permanent Magnet DC Motor Work? "DC Motors" use magnets to produce motion Permanent magnets NORTH SOUTH

  29. NORTH SOUTH How Does a Permanent Magnet DC Motor Work? • "DC Motors" use magnets to produce motion • Permanent magnets • An electromagnet armature

  30. NORTH SOUTH Permanent Magnet DC Motor Rotating Armature • Electromagnet armature is mounted on axle so that it can rotate

  31. NORTH SOUTH Permanent Magnet DC Motor Commutator and Brushes • Electromagnet armature is mounted on axle so that it can rotate • A commutator makes an electrical contact with the motor's brushes

  32. Permanent Magnet DC Motor Commutator Structure Commutator is comprised of two "near-halves" of a ring

  33. Permanent Magnet DC Motor Commutator Structure • Commutator is comprised of two "near-halves" of a ring • Mounted on the armature's axle to rotate with the rotor Armature

  34. Permanent Magnet DC Motor Commutator Structure • Armature's windings are connected to the commutator

  35. Permanent Magnet DC Motor Commutator and Brushes • Armature's windings are connected to the commutator • Brushes connect the commutator to the battery

  36. NORTH SOUTH - + Permanent Magnet DC Motor Electromagnet Polarization • Current flows through the armature's windings, which polarizes the electromagnet

  37. NORTH SOUTH - + Permanent Magnet DC Motor Rotation • The like magnets (NORTH-NORTH and SOUTH-SOUTH) repel • As the like magnets repel, the armature rotates, creating mechanical motion

  38. NORTH SOUTH - + Permanent Magnet DC Motor Rotation Direction? • What direction will the armature spin? • Clockwise? Counterclockwise? Counterclockwise ? Clockwise ?

  39. To determine the direction of the motor's rotation, we need to use the "Left Hand Rule" Permanent Magnet DC Motor Rotation Direction? Magnetic Field Current Force

  40. Left Hand Rule Start with two opposite ends of a magnet SOUTH NORTH

  41. B Left Hand Rule:Magnetic Field • The magnetic field (B) is from the NORTH pole to the opposite SOUTH pole • The pointing finger follows B into screen SOUTH NORTH

  42. Left Hand Rule:Current Flow • Current flows in a wire through the magnetic field from left to right • The middle finger follows I1 right, or I2 left SOUTH I1 I2 NORTH

  43. Left Hand Rule:Force • The force, F, acting on each wire is in the direction of the thumb • The wire with I1 is pushed up, I2 down F1 SOUTH I1 I2 NORTH F2

  44. Left Hand Rule:Force • The magnitude of F is give by: | F | = | I | *  * | B | where  is the length of the wire in B F1 SOUTH I1 I2 NORTH F2 

  45. Left Hand Rule:Current Loop • If the current flows in a loop, the force(s) will cause the loop to rotate F SOUTH I NORTH F

  46. NORTH SOUTH - + Permanent Magnet DC Motor Rotation • Magnetic field is from right to left • Imagine current flows out of the screen in this cross section

  47. NORTH SOUTH - + Permanent Magnet DC Motor Rotation • Magnetic field is from right to left • Imagine current flows out of the screen in this cross section • The force causes the armature to rotate clockwise

  48. NORTH SOUTH - + Permanent Magnet DC Motor Rotation • At some point, the commutator halves will rotate away from the brushes • Momentum keeps the electromagnet and the commutator ring rotating

  49. NORTH SOUTH - + Permanent Magnet DC Motor Rotation • When the commutator halves reconnect with the other brush, the current in the windings is reversed

  50. NORTH SOUTH - - + + Permanent Magnet DC Motor Rotation • When the commutator halves reconnect with the other brush, the current in the windings is reversed • The polarity is reversed and the armature continues to rotate

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