MATLAB:在奈奎斯特图上显示幅值裕度和相角裕度

code

>> num = [0.5];
>> den = [1 2 1 0.5];
>> sys  = tf(num,den)

sys =
 
           0.5
  ---------------------
  s^3 + 2 s^2 + s + 0.5
 
Continuous-time transfer function.

>> [Gm,Pm,Wcg,Wcp] = margin(sys)

Gm =

    3.0035


Pm =

   48.9534


Wcg =

    1.0004


Wcp =

    0.6435

>> nyquist(sys)
>> title(['Gm=',num2str(Gm),',','Pm=',num2str(Pm)])

示意图

因为$RealAxis$和$ImgAxis$刻度不同，所以虚线半径为1的圆看起来是椭圆