PI controller and an integrator.

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Charanraj 2015-5-8

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https://ww2.mathworks.cn/matlabcentral/answers/215758-pi-controller-and-an-integrator

Hi, I am using a discrete control algorithm to control an inverter. In this I have to construct a PI controller and an integrator. My challenge is i have to do all these in an s-function only as a code. So, my system is discrete system with the following values

Matlab integration time, Ti=10^-6 sec Sampling time, Ts=10^-4 sec Count = Ts/Ti=100

So, my for loop count is 100 values either 0to99 or 1to100. I am doing it with the level of a counter, rather using for loop. So the control algorithm is carried out inside the counter loop, as follows-

%global declaration

global count;

global e2;

global e1;

global inte;

global inti;

global PI;

global kp;

global ki;

kp=1; ki=2.5;

%main program

if count<(100-0)

   count=count+1;
else
   e2=desired-measured;   %error
   prop=error;            %for P
   inte=(e2+e1)*Ti/2;     %for I
   inti=sum(inte);        %for I
   PI=kp*prop+ki*inti;    %for PI controller
   %
   % %some blocking for matrix calculations
   %
   x_dot=[x1;x2;x3];          %output of the vector after some control calculations
   state1=sum(x_dot(1));      %for integration
   state2=sum(x_dot(2));
   state3=sum(x_dot(3));
   x=[(state1+state11)*Ti/2; (state1+state11)*Ti/2; (state1+state11)*Ti/2]; %output after integration
   e1=e2;          %for getting the previous count values in the next count
   state11=state1;
   state22=state2;
   state33=state3;

count=0;

end

My queries:

1) Is the PI counter code ok? Or should I sum the PI value ? But there is just simple matrix multiplication after PI controller.

*2) Is the method used for Integrating a vector ok? It is just a vector, x_dot=[x1;x2;x3] and i have to integrate in. When I look the alternate to use the function directly like trapz or quad, I have doubts of using the format inside my for loop, which already is structured to have 100 counts in every 10^-4 seconds.Because, I do not find any example for discrete systems and how to call the integrating time in it. Can I be able to use directly the trapz of each element in the vector for example

x1=trapz(x_dot(1)); x2=trapz(x_dot(2)); x3=trapz(x_dot(3));

or likethis, using the integration time, Ti=10^-4 sec (but remember, this is also my matlab integration time)

x1=trapz(Ti,x_dot(1)); x2=trapz(Ti,x_dot(2)); x3=trapz(Ti,x_dot(3));

Any advices/guidances will b highly useful for learning.

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PI controller and an integrator.

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