Plotting a Nyquist Curve Point by Point

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Julia Hariharan 2020-6-11

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https://ww2.mathworks.cn/matlabcentral/answers/546750-plotting-a-nyquist-curve-point-by-point

编辑： madhan ravi 2020-6-11

I am trying to test the stability of a system that I have mathematically modeled in MatLab. I have a series of Frequency points that I have impedance values for and I form a matrix of their eigenvalues for each frequency point. I want to be able to create a Nyquist curve from these points, but I do not know how to do so without a transfer function. This is what my code looks like now (the two files I run separately include my impedance values):

%Frequency from scan
Sweep;
for k=2:1:50
    F(:,k)
    s=2*pi*F*i
    LineImpedanceCalculation;
end
%Impedance from scan, converted to complex
[a,b]=pol2cart(Zp(:,3),Zp(:,2));
Zp=a+b;
%Line Impedance Calculations
%Impedance Matrix Formulation
num6=0*F;
den6=1;
sys6=num6/den6;
num7=0*F;
den7=1;
sys7=num7/den7;
%Node 1
Z11=Zp+sys1+sys3
Z12n=sys1+sys6+sys7;
Z12=Z12n.'
Z13n=sys3+sys6+sys7;
Z13=Z13n.'
%Node 2
Z21n=sys1+sys6+sys7;
Z21=Z21n.'
Z22=Zp+sys2+sys1
Z23n=sys2+sys6+sys7;
Z23=Z23n.'
%Node 3
Z31n=sys3+sys6+sys7;
Z31=Z31n.'
Z32n=sys2+sys6+sys7;
Z32=Z32n.'
Z33=Zp+sys2+sys1;
%Final Impedance Matrix
for p=1:1:49
Zmat = [Z11(p,:) Z12(p,:) Z13(p,:); Z21(p,:) Z22(p,:) Z23(p,:); Z31(p,:) Z32(p,:) Z33(p,:)]
%Admittance Matrix and Eigenvalues
Ymat = inv(Zmat)
X = eig(Ymat)
%%%where I want to implement my Nyquist curve
plot(abs(X),angle(X))
end