ex7_6.m

离散控制系统设计的MATLAB 代码

%%%%%%%%%%%%%%%%%% Example 7.6 %%%%%%%%%%%%%%%%%%
%   Discrete-Time Control Problems using        %
%       MATLAB and the Control System Toolbox   %
%   by J.H. Chow, D.K. Frederick, & N.W. Chbat  %
%         Brooks/Cole Publishing Company        %
%                September 2002                 %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%   ----  Frequency-response performance  ----
%
clear
disp('Example 7.6')

Ts = 0.1;                           % sampling time
Gp = tf(1,[1 1 0])                  % plant in continuous tf form
Gz = c2d(Gp,Ts,'zoh')               % discretize using zero-order hold
Gc = tf(5*[1 -0.9],[1 -0.7],Ts)     % controller in discrete tf form
disp('******>'), pause

figure
margin(Gz*Gc)                       % Figure 7.10(a)
disp('Click on the frequency response curves to find')
disp('frequency response values')
disp('******>'), pause

T = feedback(Gz*Gc,1)               % build CL transfer function T(z)
[mag_CLdB,ph_CL,w] = bodedb(T);     % CL magnitude in dB & phase
lfg_CL = dcgain(T)                  % dc gain as ratio
lfg_CLdB = 20*log10(lfg_CL);        % dc gain in decibels
disp('******>'), pause

bw = bwcalc(mag_CLdB,w,lfg_CLdB)    % closed-loop bandwidth in rad/s
[M_pw,ii] = max(mag_CLdB)           % maximum CL frequency response
wp = w(ii)                          % .....at this frequency (rad/s)
disp('******>'), pause
S = feedback(1,Gz*Gc)               % sensitivity function S(z)
[magS_dB,phS] = bodedb(S,w);        % sensitivity frequency response
[maxS,jj] = max(magS_dB)            % maximum sensitivity magnitude
w(jj)                               % ...at this frequency (rad/s)
disp('******>'), pause

figure
semilogx(w,mag_CLdB(:),w,magS_dB(:),'--'),grid % Figure 7.10(b)
axis([w(1) w(end) -50 10])
xlabel('Frequency (rad/s)')
ylabel('Gain dB')
text(1.05,2.4,'T(\omega)')
text(1.05,-6.0,'S(\omega)')
title('Magnitudes of T(\omega) and S(\omega) versus frequency for Example 7.6')
%%%%%%%%%%