+ Post New Thread
Results 1 to 6 of 6
  1. #1
    Advanced Member level 2
    Points: 10,850, Level: 24
    Mr.Cool's Avatar
    Join Date
    Jun 2001
    Posts
    638
    Helped
    85 / 85
    Points
    10,850
    Level
    24

    sinusoidal trapezoidal back emf

    hi peeps, can anyone tell me what the trade offs are for driving a trapezoidally wound motor with a sineusoidal controller? i have a trap motor and wanted to learn more about space vector modulation (because of its high DC bus utilization characteristics). this modulation technique will produce sine waves as an output, i wonder if i will really get any benifit from the modulation when it is applied to a trap motor. or will it even work? the feedback from the hall effect sensors will look trapezoidal instead of like a sine wave.. maybe the SVPWM won't even deliver sine waves output?

    are there any research papers on this subject?

    thx
    Mr.Cool

    •   Alt18th September 2004, 02:37

      advertising

        
       

  2. #2
    Advanced Member level 2
    Points: 10,850, Level: 24
    Mr.Cool's Avatar
    Join Date
    Jun 2001
    Posts
    638
    Helped
    85 / 85
    Points
    10,850
    Level
    24

    trapezoidal sinusoidal motor difference

    ok.. i think i have the answer. if the motor is a trapezoidal, then the feedback must be converted into a sinusoidal wave shape. this type of PWM technique is known as "simulated sinusoidal pulse width modulation", or SSPWM. yes you can apply this to the controller and create a sinusiodal drive.

    my new question then is, will this in any way improve the motor efficiency? are there any trade-offs ?

    Mr.Cool



    •   Alt20th September 2004, 22:37

      advertising

        
       

  3. #3
    Advanced Member level 2
    Points: 10,850, Level: 24
    Mr.Cool's Avatar
    Join Date
    Jun 2001
    Posts
    638
    Helped
    85 / 85
    Points
    10,850
    Level
    24

    sinusoidal vs trapezoidal drive

    again i answer my own question...

    yes, you will always have efficiency improvments by driving a motor with a sine wave, since the machine is a rotating machine. the trade-off is the DC bus utilization is typically lower, which in the end means you do not reach the same top speed.

    of course there are work arounds for this, name SVM, but now we are diverging from the topic.

    thx anyways.. its amazing what u can find on g00gle

    Mr.Cool



    •   Alt28th September 2004, 02:12

      advertising

        
       

  4. #4
    Member level 3
    Points: 2,158, Level: 10

    Join Date
    Sep 2004
    Posts
    62
    Helped
    2 / 2
    Points
    2,158
    Level
    10

    sinusoidal vs trapizoidal motor winding

    How do you tell whether the motor is trapezoidal or sine-wave type?



  5. #5
    Advanced Member level 2
    Points: 10,850, Level: 24
    Mr.Cool's Avatar
    Join Date
    Jun 2001
    Posts
    638
    Helped
    85 / 85
    Points
    10,850
    Level
    24

    trapezodial sinusodial motor

    first we define a difference between a *motor* being sinusoidal and the electronic feedback being sinusoidal (or trapazoidal).

    in a closed loop controller most people care only what their feedback looks like. a resolver/encoder always (after computation) results in a sinusoidal feedback. hall-effect sensors look like a trapezoidal type.

    the motor could be the same as the feedback method chosen, or could be different. to find out, ask your manufacturer. check the motor datasheet. a trapezoidal motor has a square shaped magnets in the rotor and the stator windings are evenly spaced when they are wound. a sinusoidal motor has a mushroom shaped magnets in the rotor (actually the curve is mathematically cut to be sinusoidal) and the stator windings are sinusoidally wound. which means there are more turns/windings near the center of the pole than there are near the edges.

    the best motor is sinusoidally wound with sinusoidally cut rotor, but it is more expensive to make.

    i'm not entirely sure what the practical method is to determine which type of motor you have.. i'm thinking, clamp a hand drill to the motor shaft (connects easily with re-enforced flexible hosing) and spin the motor. then measure the line-to-line voltage (Back EMF) of the motor on an oscilliscope. the shape of this waveform should tell you. i've never tried this so i can't be sure, but it seems reasonable...

    Mr.Cool



  6. #6
    Member level 3
    Points: 2,158, Level: 10

    Join Date
    Sep 2004
    Posts
    62
    Helped
    2 / 2
    Points
    2,158
    Level
    10

    trapezoid bemf winding motor

    We have two main types (may be more, pls correct me if I'm wrong) of permanent magnet (PM) brushless motor (BLM), i.e. PM-DC-BLM and PM-AC-BLM. We always refer PM-DC-BLM as trapezoidal type and PM-AC-BLM as sinuisoidal type. Apart from the motor structure and winding topology, I agree with you that the shape of the motor's back-EMF waveform will tell whether the motor is sinusoidal type or trapezoidal type. The back-EMF waveform across stator winding (for BLM) actually tells how the magnetic field (generated by rotor, e.g. PM) changes when it's spinned (by drill or latch machine). For BLM, the variation of rotor's magnetic field can be determined either with sensor or sensorless scheme. To drive the motor efficiently, the stator winding should be powered (drived) in such a way that the magnetic fields generated by stator winding and rotor are synchronized. Therefore, in my opinion, if we power a trapezoidal type of PM-BLM with sinusoidal control scheme, the performance of the motor will not be optimum.



+ Post New Thread
Please login