AC induction motor versus DC motor in electric vehicles

Discussion in 'Automotive Electronics' started by RMignogna, Jun 27, 2015.

  1. RMignogna

    Thread Starter New Member

    Jun 27, 2015
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    EVs such as the Tesla utilize an AC induction motor. But the batteries are supplying DC. Large industrial applications typically utilize DC motors, but the power supplied is AC. What are the trade-offs and the decision criteria for adopting AC versus DC motors?
     
  2. #12

    Expert

    Nov 30, 2010
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    Induction motors are a lot more reliable than something with carbon brushes. That's why I would want them to power my car. You usually have to wait until the bearings fail to ruin one, and bearings for cars are a well executed science.

    In an industrial setting, massive amounts of power are available and DC motors can be designed for several different torque curves. They are just more versatile.
     
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  3. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Three phase makes life really easy. It's cheaper and less complicated.

    A lot of headway is made with VSD's or variable speed drives. With the event of more complex electronics synthesizing 3 phase is easy. With that variable speed and better energy usage can result. So we are seeing three phase motors in our washers and air conditioning systems. No more multiple windings and therefore less copper. They can also indirectly measure the static pressure and RPM is known.

    Around 1 HP is about as much as a residential service usually sees. >5HP your better off using a 3 phase motor.

    3 phase motors typically require fancy controllers for protection, sometimes starting and fusing which drives up the cost.

    The BLDC motor is yet another.

    When I worked in an industrial environment, we lost a phase and we lost some motors. We then selectively provided more protection to some (ones that I was involved with) and some had the protections in place: e.g low voltage, reversed phase, missing phase, time to trip, time to restart. A piece of equipment that costs $40,000 USD and the compressor costs $10,,000 and it would idle a lot of workers, it makes sense to protect it.

    Backup power was for ventilation, toxic gas monitoring and access systems. Excess power was for convenience: lighting and a couple of pieces of equipment that had long re-start times after a >5 minute unscheduled power down.

    Because money and time was tight and power failures were rare, so no development was allowed for development.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    In the locomotive world from 1980s, power electronics had got to the stage where the 3-phase AC motor became a more efficient alternative to the DC motor.
    They are simpler to construct, they require no mechanical contacts to work (such as brushes) and they are lighter than DC motors for equivalent power, and improved adhesion and traction.
    Also AC traction motors can be microprocessor controlled to a fine degree and can regenerate current down to almost a stop whereas DC regeneration fades quickly at low speeds.
    Max.
     
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  5. crutschow

    Expert

    Mar 14, 2008
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    I would think that few new industrial applications install DC motors any more.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Now brushed motors, DC or Universal are most seen in the automotive world, and power hand tools and home appliances.
    In the CNC arena the AC or BLDC has virtually replaced both servo's and spindles.
    Max.
     
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Crutschow: Can you re-phase your post?
     
  8. crutschow

    Expert

    Mar 14, 2008
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    You don't my mangled grammer, like?
     
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  9. RMignogna

    Thread Starter New Member

    Jun 27, 2015
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    Thanks everyone for replying but now I need to clarify. You said that "DC are most seen in the automotive world" ? I was under the impression that Tesla et.al. were AC. No?

    Overall, am I correct in assuming that it is the more recent power electronics that enable wider AC use? I was thinking of ski lifts for which the prime movers used to be DC but the newer ones all appear to be AC.
     
  10. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    crutch:

    Brain had trouble processing that statement for some reason.
     
  11. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Automotive DC motors: wipers, windows, door locks, convertible tops, the HVAC system.

    Propulsion is an entirely different category.
     
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  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    dc is more available in cars than ac. ac batterys are very espencive, so dc is used mostly. ac motors are also a bit lighter than dc ones, especially at higher frequencies.so now that dc to ac variable frequency drives are getting more efficient, ac motors for moving the car are getting better. if you check into efficency of ac motors, the synchronous motors are much more efficient than induction motors, and newer ones have no brushes for the rotor winding.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    See my post #4, I should have qualified DC in post #6 to automotive auxiliary circuits, not motive power.
    Max.
     
    Last edited: Jul 7, 2015
  14. BR-549

    Well-Known Member

    Sep 22, 2013
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    I like the motor in the wheel strategy. I believe a lot of progress has been made.

    New AC design and control. Efficient regeneration. Light weight.

    True independent wheel velocity and torque.

    How expensive are those AC batteries?
     
  15. panic mode

    Senior Member

    Oct 10, 2011
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    "AC battery" = DC battery + Inverter
    price of inverter as additional component is what makes for price difference
     
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  16. xainnasir

    New Member

    Nov 8, 2012
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  17. crutschow

    Expert

    Mar 14, 2008
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    Ah, another newbie with a Forum thread Lazarus resurrection. :rolleyes:
    If anyone is still around from that year old question, they might look at your recommendations.
     
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