%PID Controller with Partial differential
clear all;
close all;

ts=0.001;
sys=tf(5.235e005,[1,87.35,1.047e004,0]);
dsys=c2d(sys,ts,'z');
[num,den]=tfdata(dsys,'v');

u_1=0;u_2=0;u_3=0;u_4=0;u_5=0;
y_1=0;y_2=0;y_3=0;
yy_1=0;
error_1=0;error_2=0;ei=0;

kp=0.20;ki=0.05;

sys1=tf([1],[0.04,1]);   %Low Freq Signal Filter
dsys1=c2d(sys1,ts,'tucsin');
[num1,den1]=tfdata(dsys1,'v');
f_1=0;

M=3;
for k=1:1:1000
time(k)=k*ts;

rin(k)=20;  %Step Signal

%Linear model
yout(k)=-den(2)*y_1-den(3)*y_2-den(4)*y_3+num(2)*u_1+...
        num(3)*u_2+num(4)*u_3;
     
if M==1                 %No disturbance signal
   error(k)=rin(k)-yout(k); 
   filty(k)=yout(k);
end

D(k)=5.0*rands(1);      %Disturbance signal
yyout(k)=yout(k)+D(k);

if M==2                 %No filter
   filty(k)=yyout(k);
   error(k)=rin(k)-filty(k);
end
if M==3                 %Using low frequency filter
   filty(k)=-den1(2)*f_1+num1(1)*(yyout(k)+yy_1);
   error(k)=rin(k)-filty(k);
end

%I separation
if abs(error(k))<=0.8
   ei=ei+error(k)*ts;
else
   ei=0;
end
   u(k)=kp*error(k)+ki*ei;

if u(k)>=10       % Restricting the output of controller
   u(k)=10;
end
if u(k)<=-10
   u(k)=-10;
end
%----------Return of PID parameters------------
rin_1=rin(k);
u_5=u_4;u_4=u_3;u_3=u_2;u_2=u_1;u_1=u(k);   
y_3=y_2;y_2=y_1;y_1=yout(k);

f_1=filty(k);
yy_1=yyout(k);

error_2=error_1;
error_1=error(k);
end
figure(1);
subplot(211);
plot(time,rin,'b',time,filty,'r');
xlabel('time(s)');ylabel('rin,yout');
subplot(212);
plot(time,u,'r');
xlabel('time(s)');ylabel('u');
figure(2);
plot(time,D,'r');
xlabel('time(s)');ylabel('Disturbance signal');