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%PID Control with Gradual approaching input value 
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; 
error_1=0;error_2=0;ei=0; 
 
kp=0.50;ki=0.05; 
rate=0.25; 
rini=0.0; 
 
for k=1:1:1000 
time(k)=k*ts; 
rd=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; 
 
M=2; 
if M==1   %Using simple PID 
   rin(k)=rd; 
   error(k)=rin(k)-yout(k); 
end 
if M==2   %Using Gradual approaching input value  
if rinird+0.25 
   rini=rini-k*ts*rate; 
else 
   rini=rd; 
end    
   rin(k)=rini;    
   error(k)=rin(k)-yout(k); 
end 
 
%PID with 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 
   u(k)=10; 
end 
if u(k)<=-10 
   u(k)=-10; 
end 
%----------Return of PID parameters------------ 
rin_1=rin(k); 
u_3=u_2;u_2=u_1;u_1=u(k);    
y_3=y_2;y_2=y_1;y_1=yout(k); 
    
error_2=error_1; 
error_1=error(k); 
end 
figure(1); 
plot(time,rd,'b',time,yout,'r'); 
xlabel('time(s)');ylabel('rd,yout'); 
figure(2); 
plot(time,u,'r'); 
xlabel('time(s)');ylabel('u'); 
figure(3); 
plot(time,rin,'r.'); 
xlabel('time(s)');ylabel('rin');