The output value of discrete PID controller is NaN

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lim daehee 2020-5-19

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https://ww2.mathworks.cn/matlabcentral/answers/526551-the-output-value-of-discrete-pid-controller-is-nan

评论： Zheng Zhang 2023-9-8

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?

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Ameer Hamza 2020-5-19

Try to monitor the input of PID blocks. Are the input values finite?

lim daehee 2020-5-19

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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Answer 1

Ankur Bose 2021-9-28

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https://ww2.mathworks.cn/matlabcentral/answers/526551-the-output-value-of-discrete-pid-controller-is-nan#answer_797114

Answered the same question here

https://www.mathworks.com/matlabcentral/answers/527384-i-gain-of-pid-controller-has-nan-value-simulink

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勇刚张 2022-5-19

This method can solve the problem

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 Initially the estimator might not have started which caues attitude not to be published and hence uORB block retutns [0 0 0 0] as quat which are invalid and hence rotation block computes NaN and passes to PID.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.
Reset the PID block using and external signal when values are stored

Zheng Zhang 2023-9-8

您好，能详细说一下您是怎么解决的吗？

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Answer 2

Jonas 2020-5-19

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https://ww2.mathworks.cn/matlabcentral/answers/526551-the-output-value-of-discrete-pid-controller-is-nan#answer_433400

Check the block 'Rotation Order: ZYX'. Does it work properly?

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lim daehee 2020-5-19

编辑：lim daehee 2020-5-19

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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