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

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.

Answer 1

[Paul]

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.

[耘岑]

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.