Practical digital current regulator

[MechatronO]

Consider a DC motor, being switched by a H bridge that is controlled by a PI current regulator.

As long as the error (SetCurrent-Current) is positive everything is good. However, when this goes negative we have a problem as you couldn't set a negative duty cycle.

How is this solved in practice? Using the other transistors to reverse the current?

I tried using solely an I regulator which off course works kind of, but as expected performs very poor.

Maybe it could be solved by ignoring the P part when we overshoot the setpoint?

 

[berkeman]

Consider a DC motor, being switched by a H bridge that is controlled by a PI current regulator.

As long as the error (SetCurrent-Current) is positive everything is good. However, when this goes negative we have a problem as you couldn't set a negative duty cycle.

How is this solved in practice? Using the other transistors to reverse the current?

I tried using solely an I regulator which off course works kind of, but as expected performs very poor.

Maybe it could be solved by ignoring the P part when we overshoot the setpoint?

What are you controlling? The motor's speed? That is usually done with PWM on the drive voltage. Is the motor intended to be uni-directional?

 

[Baluncore]

MechatronO, as you point out, duty cycle can only range between zero and one.
Anything below zero must clamp at zero.
Anything above one must clamp at one.

 

[meBigGuy]

You either have to clamp the signal as Baluncore suggested, or condition the signal to remain in range, or redesign the system to allow reverse directions if that is what you need.

 

[alphy]

I would suggest considering the use of a PID (Proportional-Integral-Derivative) controller instead of just a PI controller. This would take into account both the proportional and integral components of the error to provide a more robust and accurate control of the current. Additionally, using additional transistors to reverse the current may introduce complications and potential failure points, so it would be important to carefully consider the design and implementation of such a solution.

Furthermore, it may be beneficial to explore other control strategies or algorithms that are specifically designed for DC motor control, as they may provide better performance and stability than a generic PI controller. Additionally, incorporating feedback from motor speed or position sensors can also improve the accuracy and responsiveness of the current regulation.

In terms of handling negative error values, one approach could be to limit the error to zero when it becomes negative, instead of completely ignoring the P component. This would prevent any drastic changes in the duty cycle and help maintain stability of the system.

Overall, it is important to carefully consider the specific requirements and limitations of the application in order to select the most appropriate and effective digital current regulator. Experimenting with different control strategies and fine-tuning the parameters can also help improve the performance of the system.