第8讲现代控制系统分析设计(6)

例8_19

已知开环系统传递函数

H(s)?k(s?2) 22(s?4s?3)解：

num=[1 2]; den1=[1 4 3];

den=conv(den1,den1); figure(1);

rlocus(num,den);

%title('Root locus'); [k,p]=rlocfind(num,den) %Checking the stability k=55;

figure(2); num1=k*[1 2]; den=[1 4 3];

den1=conv(den,den);

[num,den]=cloop(num1,den1,-1); impulse(num,den);

%title('Impulse Response (k=55)'); %Checking the stability figure(3); k=k+1; k=56;

num1=k*[1 2]; den=[1 4 3];

den1=conv(den,den);

[num,den]=cloop(num1,den1,-1); impulse(num,den);

%title('Impulse Response (k=56)');

Error in ==> D:\\MATLABR11\\toolbox\\control\\rlocfind.m

On line 58 ==> [k,poles] = rlocfind(tf(a,b),varargin{:});

642Imag Axis0-2-4-6-4-3-2-1Real Axis012回目录 4．控制系统的频域分析 例8_20

典型二阶系统

2?n H(s)?22s?2??ns??n绘制出?取不同值时的Bode图。

wn=6;

kosi=[0.1:0.1:1.0]; w=logspace(-1,1,100); figure(1); num=[wn.^2]; for kos=kosi

den=[1 2*kos*wn wn.^2];

[mag,pha,w1]=bode(num,den,w); subplot(2,1,1); hold on;

semilogx(w1,mag); subplot(2,1,2); hold on;

semilogx(w1,pha); end;

subplot(2,1,1); grid on;

xlabel('Frequency (rad/sec)'); ylabel('Gain dB'); subplot(2,1,2); grid on;

xlabel('Frequency (rad/sec)'); ylabel('Phase deg'); hold off;

6Gain dB4200123456Frequency (rad/sec)789100-50-100-150-200Phase deg0123456Frequency (rad/sec)78910 回目录

例8_21

有系统

H(s)?绘制出系统的Bode图。 k=100; z=[-4];

p=[0 -0.5 -50 -50];

[num,den]=zp2tf(z,p,k); %subplot(2,1,1); grid on;

%subplot(2,1,2); %grid on;

bode(num,den);

title('Bode plot'); 6100(s?4)s(s?0.5)(s?50)2

Gain dB4200123456Frequency (rad/sec)Bode plot78910Magnitude (dB)Phase (deg)2000-200-90-180-270-101210101010Frequency (Hz)回目录