How to set integrator to make it reset its state to zero when the output negative and the state is negative?

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耘岑 2023-3-4

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https://ww2.mathworks.cn/matlabcentral/answers/1922985-how-to-set-integrator-to-make-it-reset-its-state-to-zero-when-the-output-negative-and-the-state-is-n

评论：耘岑 2023-3-5

I am now trying to use simulink to model the TCP network by Misra’s Nonlinear Model, whose mathematic equation is below.

I am now working with the model below, which is the queue of the router.

As you can see, there is an integrator in the subsystem. I wanna it to keep reset its state to be zero when the output is negative because at the very begining, the r(t)-C may be negative. But the queue length can never be negative. With time goes, the r(t)-C may be positive, and integrator can work natrually. And since the queue is positive, the r(t)-C to be negative is OK because that means the output rate is larger than input rate.

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Answer 1

Paul 2023-3-4

Hi 耘岑,

If the queue length can never be negative, how is it that the model is resulting in a negative queue length?

In any case, perhaps it would be easiest to use the Limit output feature of the Integrator block with a lower limit set to 0 and the upper limit set to inf. There's also an Integrator Limited block that could apply as well. I don't know if it is any different than the garden variety Inetegrator block other than the default setting for the 'Limit output' parameter.

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耘岑 2023-3-5

Thank you for helping, that's actually what I want. It seems that I misunderstand the integrator limited as an integrator folloed with a saturation before.

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