Limit the chaning rate of a signal

Hello,

I´m working on a Simulation in Simulink for my masters degree in engineering. In this Simulation there is a valve which controlls the flow of water on one side of a plate heat exchanger based on the outlet tempreture of water on the other side of the exchanger. At the moment this valve is controlled by a thermostat, now it shall be controlled by a electrical engine so that the plant can be controlled electronicly and monitored.

My Problem is now that this engine has a maximum chaning speed e.g when the controller jumps from 0 to its maximum value the engine should need 30 seconds to adjust its position so that the valve is opened completly. I tryed many different solutions but none of them works like they are supposed to be.

function y = fcn(u, du,t)
persistent dy_alt y_alt dy
if isempty(dy_alt)
    dy_alt=0;
    y_alt=u;
    dy=0;
end
while du~=0 || y_alt~=u
    if du>0
        dy=0.7;
        dy_alt=dy;
    elseif du<0
        dy=-0.7;
        dy_alt=dy;
    elseif du==0
        dy=dy_alt;
    end
    y=y_alt+dy*t;
    if y==u
        break
    end
end
y=u;
y_alt=y;
end

This is one example of a solution for the problem but it doesent works. The Simulation runs without an error but only until a certain time is reached then it doesnt proceed further.

Has somebody an idea to solve this Problem? Maybe the Solution is easy but i dont see it :/

Answer 1

[Fangjun Jiang]

Use the Simulink Rate Limiter block.

[Klaas Albers]

It seems that it works, thanks a lot!

Sometimes you cannot see the wood for the trees. :D