ex6_3.m

离散控制系统设计的MATLAB 代码

%%%%%%%%%%%%%%%%%% Example 6.3 %%%%%%%%%%%%%%%%%%
%   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                 %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%   ---- Response of a lowpass digital filter ----
%
clear
disp('Example 6.3')

Ts = 0.01;                            % sampling period
G = tf(0.325*[1 0.5385],[1 -0.5],Ts)  % create lowpass filter
w = logspace(-2,0,50)*pi/Ts;          % specify frequency range
figure
bode(G,w),grid                        % frequency response plot
title('Bode plot for Example 6.3')
disp('Click on the frequency response curves to find')
disp('frequency response values')
disp('******>'), pause

t = [0:Ts:10.0-Ts];                   % time array from 0 to 9.99 sec
e = cos(14*pi*t)+cos(50*pi*t)+cos(86*pi*t);  % DT signal
y = lsim(G,e);                        % filter output
t9 = [901:1000]';

figure
subplot(2,1,1)                  % split graphics window
stem(t(t9),e(t9),':'), grid
title('Input and output signals for Example 6.3')
axis([9.5 10.0 -4 4])			% show only last 0.5 s
legend('Input signal')
xlabel('Time (s)')
ylabel('Amplitude')
subplot(2,1,2)
stem(t(t9),y(t9),':*'), grid
axis([9.5 10.0 -4 4])			% show only last 0.5 s
legend('Output signal')
xlabel('Time (s)')
ylabel('Amplitude')
disp('******>'), pause

N = length(y(t9));              % number of data points
Yp = fft(y(t9))/N;              % Compute Fourier Series Coeffs
ff = [0:1/Ts/N:(1.0-Ts)/Ts];    % frequency array

figure
stem(ff,abs(Yp),'*');grid       % magnitude plot
ylabel('Magnitude')
xlabel('Frequency (Hz)')
title('Magnitudes of output Fourier-series coeffs for Example 6.3')
%%%%%%%%%%