DC Motors and H-Bridges Presented By: Sean Huang, Daniel Simon, and - - PowerPoint PPT Presentation

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DC Motors and H-Bridges Presented By: Sean Huang, Daniel Simon, and - - PowerPoint PPT Presentation

Aug 02, 2023 480 likes •972 views

DC Motors and H-Bridges Presented By: Sean Huang, Daniel Simon, and Scott Smith [1] [2] 1 Presentation Outline 1. Electric Motors 2. A (Brief) Review of E&M Physics 3. Brushed DC Motors 4. Controlling DC Motors 5. H-Bridges 6.

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DC Motors and H-Bridges

Presented By: Sean Huang, Daniel Simon, and Scott Smith

[1] [2]

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Presentation Outline

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  • 1. Electric Motors
  • 2. A (Brief) Review of E&M Physics
  • 3. Brushed DC Motors
  • 4. Controlling DC Motors
  • 5. H-Bridges
  • 6. Brushless Motors and Control
  • 7. References and Further Reading
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Electric Motors

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What are Electric Motors?

  • Turn electrical energy into mechanical energy.
  • Useful in wide range of embedded applications from automotive to medical.
  • Vary from extremely complex to incredibly simple.

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[3]

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Many Different Types of Motors

Electric Motors DC Motors AC Motors Brushless Motors Brushed Motors

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A (Brief) Review of E&M Physics

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A Brief Review of Ohm’s Law

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Ohm’s Law: V = I * R I = V / R = 9 / 3000 = 0.003 A = 3 mA

[4]

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A Brief Review of Magnets

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N S

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A Brief Review of Magnets

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N S

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A Brief Review of Magnets

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N S I

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A Brief Review of Lorentz Forces

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N S I

F = IL x B Lorentz Force:

In which direction is the force?

[5]

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A Brief Review of Lorentz Forces

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N S I

F = IL x B Lorentz Force:

In which direction is the force?

[5]

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Brushed DC Motors

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How do Brushed DC Motors Work?

[6]

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How do Brushed DC Motors Work?

[6]

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Commutator Ring [6]

How do Brushed DC Motors Work?

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Commutator Ring Brushes [6]

How do Brushed DC Motors Work?

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[6]

How do Brushed DC Motors Work?

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[7]

How do Brushed DC Motors Work?

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How do Brushed DC Motors work?

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Adding additional coils increases motor stability.

[8]

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Controlling DC Motors

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Goals:

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  • 1. Be reliable (Doesn’t blow up)
  • 2. Control Speed/Torque
  • 3. Control Direction
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One (Naive) Approach

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One (Naive) Approach

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??

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One (Naive) Approach

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  • Not enough power

(usually)

  • No directional control
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Better Approach

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Better (Dangerous) Approach

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I

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Better (Dangerous) Approach

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I

[13]

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Better (Dangerous) Approach

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I

[9]

Henry

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Better Approach

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  • Fixes the power supply

problem, but

  • Back EMF Sparks
  • Still no directional control
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Better Approach

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I

[10]

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Better Approach

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I

[10]

I

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Better Approach

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I

[10]

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Better Approach

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I

  • Doesn’t blow up
  • Control Speed (PWM)
  • Still doesn’t control direction

[10]

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H-Bridges

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H-Bridge Components

  • 4 switches centered around a load
  • 4 flyback diodes
  • Power supply
  • Ground

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[11]

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Powering the Motor

  • Create a path for current to flow through motor
  • Switches turned on/off independently using I/O
  • If switch is off (open), no current will flow through the switch
  • If switch is on (closed), current will flow through the switch

○ Current will flow through the load if the diagonally-paired switches are on simultaneously

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[11] [11]

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H-Bridge Hazards (Shoot-through)

  • If both switches on one side are on (closed), we’ll get a short circuit
  • Can happen when trying to reverse the direction of the motor

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[11]

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Hazard Handling

  • Delay is present when toggling the switches
  • Delay can cause both switches on one side to be on/off simultaneously
  • Perform “turn off” before “turn on”

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[11] [11] 1 1 1 1 [11]

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H-Bridge Hazards (Back EMF)

  • Sudden change in current creates large voltage on motor

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V -> inf I -> 0 [11]

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  • Diodes create a loop that reduces current change
  • Smaller current change means smaller voltage across the motor (no back

EMF)

Flyback Diodes

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I = i V = v [11] [11] 1 1

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Controlling Motor Speed with PWM

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[11] [11] 1 1 [11]

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Brushless Motors and Control

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How do Brushless DC Motors Work?

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Switch the position of the magnets and coils.

[8]

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Brushless Control

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[12]

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Brushless Motors

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Brushed Motors

  • Cheap
  • Easy to use
  • Requires few wires
  • Simple control circuitry
  • Long lifespan
  • Very high efficiency
  • Low noise generation
  • High power to size

ratio

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Recommended Further Reading

Brushed DC Motors: http://pcbheaven.com/wikipages/How_DC_Motors_Work/ Brushless DC Motors: https://www.renesas.com/us/en/support/technical-resources/engineer-school/brushl ess-dc-motor-01-overview.html H-Bridges: http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/ Brushless Control: https://www.digikey.com/en/articles/techzone/2016/dec/how-to-power-and-control-b rushless-dc-motors

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References

[1] DC Motor Photo: https://www.surpluscenter.com/Electrical/DC-Motors/DC-Motors-Face-Mount/1-2-HP-90-Volt-DC-Motor-10-3114.axd [2] H-Bridge Hardware Photo: https://www.robotshop.com/en/l298-dual-h-bridge-dc-motor-controller.html [3] Toy Photo: https://www.walmart.com/ip/Vroom-Rider-Dirt-Bike-Motorcycle-Battery-Powered-Riding-Toy-Orange/33154659 [4] Simple Circuit: https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/simple-series-circuits/ [5] Right Hand Rule Photo: https://en.wikipedia.org/wiki/Lorentz_force#/media/File:Regla_mano_derecha_Laplace.svg [6] DC Motor Still Image and Slow GIF: https://www.explainthatstuff.com/electricmotors.html [7] Alternate Fast DC Motor GIF: https://www.electricaleasy.com/2014/01/basic-working-of-dc-motor.html [8] Better Brushed Motor Photo and Brushless Motor Photo: https://www.renesas.com/us/en/support/technical-resources/engineer-school/brushless-dc-motor-01-overview.html [9] Shock photo: https://dawsonpower.com/blog/2014/09/how-to-help-an-electric-shock-victim/ [10] Flyback Diode Photo:https://resources.altium.com/bill-of-materials-blog/why-you-should-use-a-flyback-diode-in-a-relay-to-prevent-electrical-noise-in-your-circuits [11] H-Bridge Photos and Tables: http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/ [12] Brushless Motor Control:: https://www.digikey.com/en/articles/techzone/2016/dec/how-to-power-and-control-brushless-dc-motors [13] Motor Spec sheet: http://hades.mech.northwestern.edu/index.php/Brushed_DC_Motor_Theory

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