The output value of discrete PID controller is NaN

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lim daehee
lim daehee on 19 May 2020
Commented: 勇刚 张 on 19 May 2022
I'm trying to control motors with pwm signals.
when I clicked monitor & tune button, I found some outputs of discrete PID controller block is NaN. It is stated below.
Other input from same bus, yawspeed, generate normal value, however, pitch and roll angles have nan value.
I first thought that the problem is from the difference of data type.. so I checked data types of all inputs and outputs and there are no problems with data types.
Is there anyone who know why the nan value is generated?
  2 Comments
lim daehee
lim daehee on 19 May 2020
Nope, I monitored all values including input of PID blocks, however, they are all not inf or nan and it ranges from -0.02~0.02
The output saturation is limited from -0.1~0.1.
Additionally, I changed inputs(pitch_angle, roll_angle)into constant block with a constant value and the model works fine.
However, when inputs are from uORB block, the output of PID block has nan valeu.

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Answers (3)

Ankur Bose
Ankur Bose on 28 Sep 2021
Answered the same question here
https://www.mathworks.com/matlabcentral/answers/527384-i-gain-of-pid-controller-has-nan-value-simulink
  1 Comment
勇刚 张
勇刚 张 on 19 May 2022
This method can solve the problem
  1. Ensure that initial inputs are not NaN. in PX4 thing might happen when you are trying to read from vehicle attitude connected to rotation block. Initially the estimator might not have started which caues attitude not to be published and hence uORB block retutns [0 0 0 0] as quat which are invalid and hence rotation block computes NaN and passes to PID. Eventually this might be fixed but PID will still store NaN.
  2. Reset the PID block using and external signal when values are stored

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Jonas
Jonas on 19 May 2020
Check the block 'Rotation Order: ZYX'. Does it work properly?
  1 Comment
lim daehee
lim daehee on 19 May 2020
I changed pid controller into p controller and it works fine. So I think rotation order worked well. Also, I think d and i controller is the problem, but I don't know why d and i gain caused the problem.

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Kunal Lad
Kunal Lad on 31 Jul 2020
Hey Lim Daehee,
Did you find the solution to this problem as I am facing it too. Share up if possible.
Thanks.

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