Td=1; N=[100, 1000, 10000, 1:10];
Gc=tf(Kp*[Ti*Td,Ti,1]/Ti,[1,0]);
G_c=feedback(G*Gc,1); step(G_c), hold on
for i=1:length(N)
   nn=Kp*([Ti*Td,0,0]+conv([Ti,1],[Td/N(i),1]))/Ti;
   dd=[Td/N(i),1,0]; Gc=tf(nn,dd);
   G_c=feedback(G*Gc,1); step(G_c)
end
figure; [y,t]=step(G_c); err=1-y; plot(t,err)