ex5_25.m

反馈控制系统设计与分析（matlab程序）

G=tf(1,[1,1]); T=[0.1:0.1:1]; x=[]; y=[];
w=[0,logspace(-3,1,100),logspace(1,2,200)]';
for i=1:length(T)
   set(G,'Td',T(i)); [x0,y0]=nyquist(G,w); 
   x=[x,x0(:)']; y=[y,y0(:)'];
end
plot(x,y), axis('square')

n=1:6; T=1; x=[]; y=[]; G0=tf(1,[1,1]);
for i=1:length(n)
   [nP,dP]=pade(T,n(i)); G=G0*tf(nP,dP);
   [x1,y1]=nyquist(G,w); 
   x=[x,x1(:)]; y=[y,y1(:)];
end
plot(x,y), axis('square')

n=1:6; T=1; x=[]; y=[]; G0=tf(1,[1,1]);
for i=1:length(n)
   [nP,dP]=paderm(T,0,n(i)); G=G0*tf(nP,dP);
   [x1,y1]=nyquist(G,w); 
   x=[x,x1(:)]; y=[y,y1(:)];
end
plot(x,y), axis('square')