PMDC Motor Control Problem


I designed Permanent Magnet Brushed DC Motor Controller hardware (H-Bridge) for Elevator Door Control. I used dsPIC33EP as main controller. Centre door opening and closing application. So there is a door on each side. In this application, spring is connecting between the two doors. One end of spring is connected to right side door right end and another end of spring is connected to left side door left end. As door opens, the spring will pull. For that I require more power (torque to open the door) and it is done fine.

I have simple PWM Control for speed; i have PI Controller for controlling Speed. My PWM Frequency is 20 KHz. I have 24V Brushed PMDC Motor.

Now the problem is braking and door closing (Reverse direction). When i give brake command (Short Armature winding) it will slip and back to door close because of spring is pulled. And door is close very fast when I give door close command. From above i cannot able to control speed while door close. How can i control the speed while door close with spring connected?

Is Permanent Magnet Brushed DC Motor is ok for this type of application?
If not then which motor will work for this type of applications? As BLDC will work?

So please give some solution for above case.

Thanks and Regards,
Nandish Jasani.


  • evanhevanh Posts: 10,223
    edited 2018-08-27 - 17:08:22
    - Why have the spring?

    - Motor braking isn't useful for locking a motor. Remove this control. If you want to lock the doors open then a mechanical brake is probably the best option.

    - Brushed DC works fine for this but I expect the common solution these days will be induction motors paired with what's called Variable Speed Drives.

    Could be the servo loop (with PI function) isn't working right. It should handle all active motion. You do have a feedback velocity measurement, right?

    But probably it's just that you are doing step changes in speed. This can be very difficult to absorb for a servo - huge overshooting is a symptom which could be what you are experiencing. Having a braking override won't be helping. Better to always ramp the target speed. Create a little profile generator that can take any set target speed and ramp to it from the current speed. This then needs an acceleration parameter.

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