Multiple Bode plots in one figure (Linear Analysis Tool)

[Martina]

Hi there,

I am using MATLAB/Simulink 2011b with the Linear Analysis Tool of Simulink Control Design/Control System Toolbox.

I was wondering whether there is a way of plotting several Bode diagrams into a single figure. For example I have a system with parameters. I do a Bode plot, then change some parameters and do another Bode plot. For comparison reasons I would like those two plots to be in the same figure, the same axes to be precise.

Is that possible? How?

(I am aware of the 'Bode' command, but I think I prefer the GUI of the Linear Analysis Tool.)

Thanks in advance!

[Martina]

Any ideas?

[kbid...@gmail.com]

% Example 7.39 - LTR Design for Satellite Attitude Control
% from Feedback Control of Dynamic Systems 6th Edition
% by Gene F. Franklin, J. David Powell, Abbas Emami-Naeini

% Modified to plot multiple bode plots...
% Plant
clear all
close all

F= [0 1;
0 0];
G= [0;
1];
H= [1 0];
J= [0];
sys0= ss(F,G,H,J);
H1= [1 0];
sys= ss(F,G,H1,J);

% LQR
w= logspace(-1,3,1000);
rho= 1;
Q= rho*H1'*H1
r= 1;
[K]= lqr(F,G,Q,r)
sys1= ss(F,G,K,0);
[maggk1,phasgk1,w]=bode(sys1,w);
[gm1,phm1,wcg1,wcp1]=margin(maggk1,phasgk1,w)

% Kalman Filter with LTR

maggk=[];
phsgk=[];
gm=[];
phm=[];
wcg=[];
wcp=[];

qscale=1;

for q=1:1:10
gam=q*qscale*G;
Q1=gam'*gam;
rv=1;
[L]=lqe(F,gam,H,Q1,rv);

aa=F-G*K-L*H;
bb=L;
cc=K;
dd=0;
sysk=ss(aa,bb,cc,dd);
sysgk=series(sys0,sysk);
[maggk(q,:),phsgk(q,:),w]=bode(sysgk,w);
[gm(q),phm(q),wcg(q),wcp(q)]=margin(maggk(q,:),phsgk(q,:),w);
end

figure(1)
semilogx(w,20*log10([maggk1(1,:); maggk(:,:)]))
xlabel('Frequency (rad/sec)')
ylabel('Magnitude (dB)')
title('Bode Magnitude')
% axis([w(1) w(1000) -60 60])
grid on

figure(2)
semilogx(w,[phasgk1(1,:); phsgk(:,:)])
xlabel('Frequency (rad/sec)')
ylabel('Phase (deg)')
title('Bode Phase')
grid on