DC Motor Control

Discussion in 'The Projects Forum' started by Padderick, Apr 10, 2012.

  1. Padderick

    Thread Starter New Member

    Jan 7, 2012
    Hi everybody,

    can anybody tell me why it is possible when you have got a separately excited DC Motor control loop to compare the controlled speed with the armature current directly? Or do I need a special transfer function after the speed control to transform speed to current? Maybe you already did a Matlab simulation!? would be fine if you can help me!

    Thanks for help. Pad
  2. jimkeith

    Active Member

    Oct 26, 2011
    In your attachment you show a velocity loop driving a current loop--it is perhaps THE CLASSICAL way of doing it, but not necessarily the only or even best way. No, you cannot compare the velocity with the current directly.

    The current loop may be bypassed or eliminated so that the output of the velocity regulator may vary the 'error voltage' (motor PWM or phase delay angle directly, depending upon power control technique). However this implies that you have no control over current.

    To maintain control over the current, I have often used the parallel loop technique in which the the two loop outputs are connected together in a wired NOR arrangement so that either one may limit the error voltage--in either case, the unused regulator runs into saturation as it has lost control, so either the velocity regulator or the current regulator is in control at any given time. In this case, the current regulator is simply performing a current limit function.

    The beauty of this is that it is stable over a broader range of conditions and generally avoids the need for tweaking.
    Last edited: Apr 10, 2012
  3. Padderick

    Thread Starter New Member

    Jan 7, 2012
    I think I do not understand exactly what you mean, can you send me a schematic? So the structure I showed you is not possible, also not if i would implement another transfer function?