MATLAB Answers

Area under the curve

조회 수: 11(최근 30일)
Bhuvan Khoshoo
Bhuvan Khoshoo 2019년 10월 24일
댓글: Bhuvan Khoshoo 2019년 10월 29일
I have follwing curve resulting from plotting current in capacitor versus time. (Matlab code is attached).
I want to calculate the charge stored in the capacitor. For that I need to calculate the positive area of the curve. As you can see in the zoomed in image, the current plotted has pulses (switching frequency = 20kHz), and I would like to calculate the charge stored in one fundamental cycle (fundamental frequency = 60Hz).
So theoretically, the capacitor is getting charged when the current flows into it. For the curve it means the value of current that is above zero(positive).
I tried calculating the area of the curve by simplifying the curve into traingles and trapezoids, and then taking the coordinate points values (x,y). But I am pretty sure it is not correct since it does not take into account the presence of pulses.
I also tried the trapz(x,y) in matlab but the calculation does not seem right.
And the expression of the current is not a straightforward function, it is defined in terms of switching functions and duty ratios so I am not sure how to use the integral function in Matlab.
Please help.
  댓글 수: 7
Bhuvan Khoshoo
Bhuvan Khoshoo 2019년 10월 25일
I have added the code in the attachements.
Yes, the time series is a vector, sampled at Ts/100 step size, where Ts is switching time period (switching frequency = 20kHz). The current series is also a vector with values corresponding to the time instants.

댓글을 달려면 로그인하십시오.

채택된 답변

Dimitris Kalogiros
Dimitris Kalogiros 2019년 10월 25일
편집: Dimitris Kalogiros 2019년 10월 25일
Change the last section of your program to this:
%% Sizing Capacitor Cf;
%capacitor fundamental current for "a" phase is all the ripple current of ia, considering
%the fundamental compnent of ia, i.e. ia1 flows into converter;
%similar expression for other phases;
icfa = ia-ia1;
icfb = ib-ib1;
icfc = ic-ic1;
% integral of current
Qcfa=zeros(size(t));
for n=2:length(t)
Qcfa(n)=Qcfa(n-1)+icfa(n)*(t(n)-t(n-1));
end
figure(7);
subplot(2,1,1); plot(t,icfa,'-k.'),grid on
xlabel('Time(s)','fontsize',12);
ylabel('Capacitor Current(Amps)','fontsize',12);
xlim([0,T])
figure(7);
subplot(2,1,2); plot(t,Qcfa,'-r.'); zoom on; grid on;
xlabel('Time(s)','fontsize',12);
ylabel('Capacitor charge(Coulomb)','fontsize',12);
xlim([0,T])
Qcfa(n) is the value of capacitor's electric charge at every moment t(n).
  댓글 수: 3
Bhuvan Khoshoo
Bhuvan Khoshoo 2019년 10월 29일
Thanks a lot!! :)
I went with the first method. From the resulting array I needed the maximum value for sizing the capacitor.
Thanks again for the help!!

댓글을 달려면 로그인하십시오.

추가 답변(0개)

태그

제품


릴리스

R2019a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by