ex8_21.m

反馈控制系统分析与设计,虽然有点抽象

num=[-6.4750,4.0302,175.7700]; den=[5, 3.5682,139.5021,0.0929,0];
G=tf(num,den);  nW1=0.9*[1,1.2,1]; 
dW1=1.0210*conv([1,0.001],conv([1,1.2],[0.001,1]));
[a,b,c,d]=tf2ss(num,den); p1=-0.1; a_shift=a-p1*eye(size(a));
S=mksys(a_shift,b,c,d); TSS_=augtf(S,[0,nW1; dW1],[1e-5;1],[]);
C_shift=hinf(TSS_);

[af_shift,bf,cf,df]=branch(C_shift); 
af=af_shift+p1*eye(size(af_shift));
Gc=zpk(ss(af,bf,cf,df))

G_o=G*Gc; G_c=feedback(G_o,1);
step(G_c), 
figure, ngrid('new'), nichols(G_o), axis([-360,0,-40,40])

[gg,C_shopt]=hinfopt(TSS_);

[af_shift,bf,cf,df]=branch(C_shopt); 
af=af_shift+p1*eye(size(af_shift));
Gc1=zpk(ss(af,bf,cf,df))

G_o1=G*Gc1; G_c1=feedback(G_o1,1);
step(G_c1), 
figure, ngrid('new'), nichols(G_o1), axis([-360,0,-40,40])

w=logspace(-5,4);
g1=feedback(1,G*Gc); g2=feedback(1,G*Gc1);
[m1,p1]=bode(g1,w); m1=20*log10(m1(:)');
[m2,p2]=bode(g2,w); m2=20*log10(m2(:)');
[m,p]=bode(tf(nW1,dW1),w); m=20*log10(m(:)');
semilogx(w,m,'-',w,m1,'--',w,m2,':'), 
figure; semilogx(w,m+m1,'--',w,m+m2,':')