Re: PID question

Costas Vlachos wrote:
John Popelish wrote:

The one that reads current cannot be involved in the analog current regulation, without slowing it down, though it is fine to use it for monitoring the average current for other purposes. You will have to use the analog signal it digitizes as the feedback for the analog PID current regulator.

John, I think there is a misunderstanding here. The OP *doesn't have* and analogue PID current regulator!

Then he is in trouble. Even if he can sample the current measurement with his ADC 100k times per second, and cycle his PID algorithm for each sample, the gain bandwidth product of the resultant current limit will be something on the order of 5 kHz. An analog PID current regulator based on a jelly bean opamp, like an LM324, would beat that by a mile.

He wants to do it in s/w with the PIC. The only analogue regulator in his setup is for the voltage. He has *one* DAC to provide the voltage set point to the analogue voltage regulator, and reads the current through an ADC. He wants to use that ADC's reading to limit the current digitally by modifying the voltage set point of the analogue voltage regulator using a PID algorithm in s/w. I hope this is now clearer.

Yes. Thank you. We have been talking past each other, I guess. I thought I explained to him that the current regulating loop had to be fast, without emphasizing enough that his digital system is not fast enough for much of a current control.
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Relevant Pages

  • Re: PID question
    ... You will have to use the analog signal it digitizes as the feedback for the analog PID current regulator. ... The only analogue regulator in his setup is for the voltage. ... He wants to use that ADC's reading to limit the current digitally by modifying the voltage set point of the analogue voltage regulator using a PID algorithm in s/w. ...
    (sci.electronics.design)
  • Re: PID question
    ... digitizes as the feedback for the analog PID current regulator. ... The only analogue regulator in his setup is for the voltage. ... What I meant was that you should tune your PID so that the speed of response of the current limiter is such that there are several samples spread along the transition curve ...
    (sci.electronics.design)
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