getfod.m

控制系统计算机辅助设计——MATLAB语言与应用(源代码）

function [K,L,T]=getfod(G,method)
%GETFOD computes the variables in the FOPDT system
%
%[K,L,T]=getfod(G,method) computes the values for the system
%      Gr=K exp(-L s)/(T s + 1)
%      two methods can be used
%     method = 1, transfer function based
%     method = 2, frequency response based method.

%Designed by Professor Dingyu Xue
%Northeastern University, Shenyang 110004, P R China
%first drafted in 1998, revised for LFC book, 2002
K=dcgain(G);
if nargin==1
   [Kc,Pm,wc,wcp]=margin(G); ikey=0;
   L=1.6*pi/(3*wc); T=0.5*Kc*K*L; 
   if finite(Kc), x0=[L;T]; 
      while ikey==0, 
         u=wc*x0(1); v=wc*x0(2);
FF=[K*Kc*(cos(u)-v*sin(u))+1+v^2;
    sin(u)+v*cos(u)];
J=[-K*Kc*wc*sin(u)-K*Kc*wc*v*cos(u),...
   -K*Kc*wc*sin(u)+2*wc*v;
   wc*cos(u)-wc*v*sin(u), wc*cos(u)]; 
         x1=x0-inv(J)*FF; 
         if norm(x1-x0)<1e-8, 
            ikey=1; else, x0=x1;
      end, end
      L=x0(1); T=x0(2);
   end
elseif nargin==2 & method==1
   [n1,d1]=tfderv(G.num{1},G.den{1}); 
   [n2,d2]=tfderv(n1,d1);
   K1=dcgain(n1,d1); K2=dcgain(n2,d2);
   Tar=-K1/K; T=sqrt(K2/K-Tar^2); L=Tar-T;
end
%tfderv is internal to getfod
function [e,f]=tfderv(b,a)
f=conv(a,a); na=length(a); nb=length(b);
e1=conv((nb-1:-1:1).*b(1:end-1),a);
e2=conv((na-1:-1:1).* a(1:end-1),b);
maxL=max(length(e1),length(e2));
e=[zeros(1,maxL-length(e1)) e1]-...
  [zeros(1,maxL-length(e2)) e2];