MATLAB: Phase shift

imaginary parts of complex x and/or y arguments ignoredMATLABphase delayphase shift

I need to simulate a parallel RC circuit with R variable. When I plot it, it seems that are no phase between voltage and current and come Warning: Imaginary parts of complex X and/or Y arguments ignored . and when I calcute this phase (phi), there is something. Can someone help me how to plot with this phase delay? Thanks Flavia Here is my code
                  f=0.1; %Hz
fs=1000;% Abtastfrequenz in Hz
ta=1/fs;
t=0:ta:100;
T=10;
U=100*sqrt(2)*sin(2*pi*f*t); %V
C=-2*pi*f*1e-6*i; %Kapazität in F
R=15e6*(1+exp(-(t/T+log(5/3))))-14e6; % Widerstand in M Ohm
Y=(1./R)+C;
Z=1./Y;
I=U./Z;
plot(t,I/2e-7,'r',t,U,'g');
grid on
hold on
Im=imag(U./I);
Re=real(U./I);
phi=angle(Im./Re);
figure
plot(t,phi*180/pi);

Best Answer

C incluedes 1e-6*i so C will normally be complex. Y adds C to a calculation, so Y will normally be complex. Z has 1/Y so Z will normally be complex. I has something ./ Z, so I will normally be complex.
You then plot t vs I, so you are plotting a real value against a (usually) complex value. plot() requires that the coordinates to it be real, with the one exception that if you use plot(P) and P is complex, then real(P) will be plotted against imag(P); this exception never applies if you specify the x (or t) coordinate as you do in this plot() call.
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