Matlab Function Block in Simulink Model_ using persistent variables to hold previous values

Hi there!

I have this MATLAB Function Block within a Simulink Model: the function takes a voltage measurment from the Simulink model as an input and it outputs the drive signal for a switch.

I would like to be able to fire the switch when some condition is TRUE, and then keep the switch ON until the measured voltage is higher by N voltages than its value when the switch is first fired.

I am using persistent variables to store the voltage measurment (at the moment the switch is fired) and the previous drive signal. I am not sure why my code does not function properly. I would appreciate your suggestions. Thanks

Here the piece of the code inside the MATLAB Function Block:

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persistent prev_Volt;
persistent prev_G;
if isempty(prev_G)
    prev_G = 0;
end
if isempty(prev_Volt)
    prev_Volt = measured_Volt;
end
if (ARM==1) 
    G = 1; %fire the switch
    if prev_G == 0
        prev_Volt = measured_Volt; % update prev_volt only when G transitions from 0 to 1
    elseif measured_Volt > (prev_Volt + N)
        G = 0; prev_Volt = measured_Volt; %Reset the switch when it exceeds N voltage higher than when it was initially fired
    end
else
    G = 0;
end

% Store the current value of G for the next time step
prev_G = G;
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Answer 1

[madhan ravi]

change prev_DcBusVolt to pre_Volt

[HASSAN ABDELGABIR]

This was just a typo error! I edited the question

[madhan ravi]

Puh. You make too many typos (Change GR to G). MATLAB doesn’t care if it’s typo or not. If G is a gate signal, then I would suggest you to have it’s value as Boolean than double.You say when G transition from 0 to 1 but only check if previous G value is equal to 0 and forgot about the current G value.

 if (prev_G == 0) && (G == 1) % change your code to this

I don’t have access to Simulink at the moment. But I would simply prefer implementing this logic in Simulink directly.

Note: when comparing for conditions make sure ARM and measured_Volt are (Boolean or int) or float. If it’s float you need to make floating point comparison with tolerances, otherwise the if - condition won’t be executed.