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Help : DC-motor control

Discussion in 'General Electronics' started by Bamse, Nov 2, 2003.

  1. Bamse

    Bamse Guest

    Hello everybody

    I have bought an actuator (LINAK PLC LA12)

    Datasheet is here :

    http://www.linak-us.com/pdf/english/la12_plc_eng.pdf

    STRIPPED ACTUATOR:
    I have removed the circuit that regulates the piston. All that is left is
    the mechanical system between the permanent magnet DC-motor and the piston.

    MICROCONTROLLER (Keil MCB167-NET)
    I have a microcontroller that is able to generate PWM-signals. The
    microcontroller also has an A/D-port, which I will use to gain
    feedback-information that is necessary to regulate the position of the
    piston.

    INTERFACE:
    Between the stripped actuator and the microcontroller, there will be an
    interface. This interface will consist of an amplifier and a H-bridge. The
    H-bridge will control the spin-direction of the motor based on a PWM-signal
    from the microcontroller. I have to build this circuit.

    SOFTWARE FOR MICROCONTROLLER:
    I need to make a software algorithm that regulates the position of the
    piston according to a desired, pre-defined position P. The software sets up
    the right PWM-signal and sends it to the interface. The software receives
    information about the state of the actuator and corrects errors by adjusting
    the PWM-signal. The correction continues until the desired position has been
    acquired.

    How do I make the algorithm? And how do I make the interface?

    Thanks,

    Jakob
     
  2. BobGardner

    BobGardner Guest

    How do I make the algorithm?

    Proportional control.

    read the a/d 0-255. This is position. You know where you want it to be. This is
    demand (also in range 0-255). Compute error=demand-position. Now compute the
    drive signal, which is proportional to the error drive=K*error. A good K might
    be 1 or 1/2. This gives you a drive 0-255 to stick in the pwm register. Repeat
    real fast. If it oscillates, reduce k. Tricks to add integral and derivative
    terms to the drive signal will be gladly explained later is need be.....
     
  3. Bamse

    Bamse Guest

    Thanks alot. I appreciate any help I can get.

    So here is some more info on what I am going to do:

    The yaw system in todays wind turbines are driven by
    motors. The project I am working on is aimed at
    removing the motordriven yaw-system and making the
    pitch-regulation more advanced, that is:

    The goal is to make a yaw-system based on pitch-regulation
    of the rotor blades.

    The wind turbine we are using is Whisper H80. As there is no
    pitch-regulation in this wind turbine, we modify the rotor blades so
    they can be pitched. An actuator (Linak PLC LA12) is mounted
    on each wing. When the piston goes forward/backward, the wing
    is pitched in an angle between 0 degrees and X degrees. When the
    rotor blades are rotating and we pitch one or more blades, the created
    torque/momentum (i dont know what u call it?) will make the nacelle
    rotate (yaw).

    This is the mechanical part of the project.

    We need to make a PID-regulation system where

    1) We want the wind turbine to point in a desired direction (yaw angle)
    2) We calculate how the rotorblades should be pitched
    3) We calculate to which position and with how much speed the pistons should
    move in order to obtain the desired/calculated pitchangles.
    In this calculation we also take into consideration the load that the
    actuators are experiencing.
    4) Based on these calculations, we derive what the PWM-signals should look
    like and send these PWM-signals
    to the actuator.

    The regulation system is going to be implemented as software in a
    microcontroller
    (Keil MCB167-NET). The microcontroller run at 20 MHz.

    Any helpful information will be appreciated :eek:)
     
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