Tune a PID controller

💡 How-to
1

How to tune a PID controller? best practice

  • :one: P = Proportional gain

    • :open_book: P - Background

      • Proportional gain should get you most of the way to the finish line - this is likely the largest win of the 3.
      • Proportional looks at how far you are away from the setpoint and applies force in the opposite direction to push you toward setpoint.

    • :heavy_check_mark: P - How to tune the Proportional gain?

      • Step 1 Zero out the other gains and focus on tuning the P first.
      • Step 2 There is some P gain value above which the loop goes unstable - stay well below that point. Too high proportional gain and you get uncontrollable osscillations.
      • Step 3 Slow reaction to stimulus? Increase proportional gain.
      • Step 4 You’re done setting the P when you’ve got a steady state offset error. This is expected and fine.

  • :two: I = Integral gain

    • :open_book: I - Background

      • If you have a steady state offset from the proportional, you fix that with a little bit of integral.
      • The integral portion of the control loop looks at how far you are away from setpoint for how long (that extra time component is the key difference between P and I).
      • It pushes a little bit if you’re away from setpoint for a little bit of time and pushes ever harder the longer you stay away from setpoint.

    • :heavy_check_mark: I - How to tune:

      • Step 5 Start the I at 0 (zero) and bring it up.
      • Step 6 You know you’ve overdone the I gain when you get a steady state oscillation.
      • Step 7 Often it is typical to end up with something like I=P/20, but your case may of course be different.

  • :three: D = Derivative gain

    • :open_book: D - Background

      • Derivative gain helps predict future errors.
      • It acts as a dampening force, slowing down the system’s response as it approaches the setpoint to minimize overshoot.
      • So it’s basically telling your controller how big the lag is between its action and the actual response of the system. A big D means telling your controller there’s a big lag so it can anticipate that.

    • :heavy_check_mark: D - How to tune?

      • Step 8 Begin with the D gain set to zero and only adjust it after tuning P and I.
      • Step 9 Increase D gain until the loop responds quickly to changes without overshooting the setpoint.
      • Step 10 If the system starts to oscillate or becomes too “jittery,” bring down the D gain.
      • Step 11 Noise affects the performance of the D gain, so use a filter if necessary to remove high-frequency fluctuations.

  • :grey_exclamation:Important remarks for practitioners

    • :mortar_board: Theory tells you:

      • There’s math you can do to theoretically calculate the gains.
      • Most of literature says those of us who tune by feel are dumb and should at least feel bad for doing so.

    • :man_factory_worker: Practice teaches us:

      • In reality the math depends highly on the application, but of course research the math behind it if it interests you.
      • Step 12 Put multiple layers of software and mechanical safeties in place so if the loop were to go unstable, nothing catastrophic would occur.

Source:

This graph is adapted from a comment by @afterburn in response to this youtube video.