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4 phase ac motor

Discussion in 'Electronic Design' started by colin, Jun 11, 2007.

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  1. colin

    colin Guest

    Hi,

    I have a ac mains capacitor run induction motor wich I am going to rewind to
    be used with a lower voltage higher frequency inverter.

    It has 16 slots in the stator wich makes it difficult to wind for 3 phase,
    it was wound with 2 pole pairs before wich I aim to folow.
    however I have 4pwm outputs so I thinking about 4 phase,
    makes it realy easy to wind,
    where each phase peak power would be 22.5' from the next,
    ie not like some stepper motors where the the are 4 windings but only 2
    seperate or real phases as the other 2 are opposites.

    however its difficult to work out the drive,
    as at a first look the 4 phases dont always add upto zero unlike 3 phase.

    theoretically this would mean the center conection would need to be held at
    a constant voltage,
    and the equivalent of delta configuration (quad ?) would not work.

    is there an easy way round this?
    or how would trying to work out a 3 phase winding pattern to fit onto a 16
    slot rotor work out ?
    best shot at it so far I came up with was also not balanced,
    but trial and error aproach makes it a bit tedious.

    also Im looking for constant power drive, I could of course use any drive
    waveform to acheive this.

    any one have any ideas ?

    would be easier if I could find a 3phs ac motor wich could run upto 30kprm
    from low voltage ~24v drive,
    <50W

    most 3 phase motors seem to start at quite large size, Idealy it would be 2"
    square.

    at the moment im using a spindle motor out of an old fairly large disc
    drive, but the drive is not smooth enough.

    I have a small aircraft motor, wich is 3phase, but it has slip rings to
    excite the rotor wich is a shame,
    im not sure theyd last long at such high speed.

    Colin =^.^=
     
  2. I found this link some time ago:

    http://www.slmti.com/inm/default.asp

    They run on 200 V L-L, and they appear to be mostly three phase. I was
    impressed by the 2 HP motor that is 4.25" long, 3.28" dia. It is rated at
    11,450 RPM, but might be able to go faster.

    The motors I have rewound had 24 and 36 slot stators, even though they were
    single phase, so it was easy to make them three phase. Even one very small
    fan motor I rewound had IIRC 6 or 12 slots, so I was still able to make it
    three phase.

    I think you are correct that a multiple of three phases is ideal because
    the sum of the voltages is zero at all angles, and the power remains
    constant. Split phase capacitor run motors are essentially two-phase, which
    is really the same as four phase. So, you might be able to wind a single
    phase two pole motor with a smaller pole pair at 90 degrees. You would just
    need a large H-bridge for the main pole pair, and a smaller H-bridge,
    driven at 90 degrees, for the second pair. Once the motor is up to speed,
    you may not even need the second set of poles. Single phase motors run
    quite well. It's just harder to get them started, and they may not run as
    well at low speeds, as three phase types.

    There are some commercial sewing machine motors that are three phase, and
    rather small. The smallest 3 phase motor I have seen was about 1/4 HP (I
    did find a 1/6 HP). Smaller motors seem to be PSC or shaded pole.

    Some new appliances use three phase motors with integrated V/F controller
    modules like the IRADS series. I think they are used in washing machines
    but may also be in blenders, so they might be about the size you are
    looking for.

    Paul
     
  3. colin

    colin Guest

    cool thanks for that link.

    I need it to run with very little torsional vibration so I want to get as
    good as I can.
    i also want it to be fairly quiet as it will have to run in my study
    overnight !

    Ive written a little computer program to help optimise the turns to get 3
    phase onto 16 slots,
    4 of the poles are actually slightly narower wich is odd, and is doing my
    head in trying to see if i can make use of this.

    2 phase is not realy what I was refering to as 4 phase, thats like saying a
    center tapped transformer is 2 phase,
    so I gues by your definition i would be talking about 8 phase ! lol

    I have a dspic33 wich is driving a bunch of 50v 50amp fets.
    ive only implmeneted 3 of the 4 pwm channels so if I can assure myself i
    have the sums correct I may go for 3 phase windings.

    4(8) phase seemed quite good til i realised the problems, id already started
    winding some coils, maybe i can use them for the 3 phase, or at least enough
    to try it and see if it will turn ok. (ive done 3 of the 4 phases lol) but
    hardly filled anywhere near the winding space for testing purposes.

    atm I have a seperate windings covering 2 poles, so i can reconect them if i
    get it wrong lol.

    yes thats a point there are coming common in many new appliances, i think
    they are switched reluctance too, im not sure wich motor type would be best,
    I need low power, but real smooth, im thinking induction would be smoothest.

    id rather stick to low voltage as it tends to retain the magic smoke a bit
    better.

    Colin =^.^=
     
  4. Jasen

    Jasen Guest

    use 2 phase (plus two inverses)

    Bye.
    Jasen
     
  5. colin

    colin Guest

    oops 45', not 22.5'
    so positive peak would be at 0,45,90,135, then negative peak at 180 ...
    changing the polarity of one or two of the phases would mean the negative
    peaks wernt all together,
    but no combination gives an even distribution, maybe it only works well for
    odd nimbers maybe 5 would work ?
    I gues no one uses 4 true phases, however it looked like it would make the
    motor winding more compact.
    yes this is how 4 phase stepper motors seem to be,
    when used with open collector drivers,
    but seems to be wastefull of the windings.
    the peaks are 90' apart.

    It still needs 3 or more lines to drive it,
    I have a full 3phase bridge so il just try and make it 3 phase.

    Incidently the motor is out of an old 8" shugart sa801 floppy drive lol.
    seemed a shame to cut the windings out as it looked so nicely made.
    thanks
    Colin =^.^=
     
  6. I just did a quick Excel spreadsheet showing the sum of sines for each of
    three phases (120 degrees), and "four phase" (90 degrees), and it appears
    that the sum is zero in both cases for all angles. So I think the motor
    will run smoothly if you wind it for four phase. It will have 2 pole pairs,
    or four poles, if you want it to to run at 3600 RPM at 60 Hz, which would
    be like a two pole 3 phase motor.

    I'm not 100% sure of this and don't have time to think it through now, but
    a 2 pole three phase motor can be made with three "belts", each 120 degrees
    apart, while a 2 pole 4 phase motor needs four belts, each at 90 degrees. I
    think the correct term for two phases at 90 degrees is actually 2 phase,
    rather than four phase, because the phases at 180 degrees are just the
    reverse polarity. A three phase motor can have just three winding belts
    because the opposite phase is composed of the vector sum of the other two
    phases. Again, please verify this, as it does seem confusing.

    Good luck,

    Paul
     
  7. colin

    colin Guest

    came up with a solution wich im going to try, posted in a.b.s.e ...

    Colin =^.^=
     
  8. colin

    colin Guest

    sum of sines I didnt think was constant, maybe its the sum of the square
    wich is constant,
    wich seems to be the case in my simulation in a.b.s.e. wich is important for
    torque ripple,
    sum of sines is important for current balance in the neutral connection wich
    seems to go out of the window for 4 phase or 2 phase.
    4 phase is 45'. 90' is only 2 phase.
    a center tapped winding is only 1 phase.
    or at least my use of 4 phase is for 45' phases.

    for 3 phase i prefer not to use vector sum of the 2 phases instead of the
    oposite polarity of the other phase.
    current density is lower for the same magnetizing force.

    Colin =^.^=
     
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