ex6_18.m

反馈控制系统设计与分析（matlab程序）

G=tf(100,conv([1,1],[1,0.2,1])); wn=30;
Gs=std_tf(1,wn,3); 
Gc=inv(G)*feedback(Gs,1,1); zpk(Gc)

G_c=feedback(G*Gc,1); step(G_c)

ngrid('new'); nichols(G); 
nichols(G*Gc), axis([-360,0,-40,40])

rho=[0.05,0.1,0.15,0.2,0.5,1]; t=0:0.01:1;
f1=figure; f2=figure; ngrid('new'); 
for i=1:length(rho)
   G.den{1}=conv([1,1],[1,rho(i),1]); 
   G_o=G*Gc; G_c=feedback(G_o,1);
   figure(f1); step(G_c,t); hold on
   figure(f2); nichols(G_o);
end
figure(f2), axis([-360,0,-40,40])