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%
%  sermtrfw.m - plots developed torque-speed curve for series 
%               excited dc motor with rated voltage applied
%               and series field weakening.
%               Armature reaction neglected.
%
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clear; clf;
VtR=600;                      % Rated terminal voltage
PR=80;                        % Rated output horsepower
Ra=0.25;                      % Armature resistance
Rs=0.03;                      % Series field resistance
NsT=10;                       % Total series field turns
nmR=1200;                     % Rated speed(rpm)
% Rated developed torque & armature current assuming 4% F&W losses
TdR=PR*746/(nmR*pi/30)/0.96; 
IaR=(VtR-sqrt(VtR^2-4*(Ra+Rs)*TdR*nmR*pi/30))/2/(Ra+Rs);

load eif   % Load stored OCC(in shunt field amps) for speed of nmR
m=length(eif); npts=200;
E=eif(1:m,1); If=eif(1:m,2);
% Create Kphip & mmf arrays
Kphip=eif(1:m,1)/(nmR*pi/30);
mmfs=eif(1:m,2)*NsT*IaR/(interp1(E,If,VtR-IaR*(Ra+Rs)));
npts=200; Ia=linspace(1.5*IaR,0.25*IaR,npts);

% Determination of Td-nm
subplot(2,1,1)
Ns=[4 5 7 10];           % Series field turns
for n=1:length(Ns)
for i=1:npts
   Kphi=interp1(mmfs, Kphip, Ns(n)*Ia(i));
   Td(i)=Kphi*Ia(i);
   wm(i)=VtR/Kphi-Td(i)*Ra/Kphi^2;
   if wm(i)>3000*pi/30; break; end
end
nm=wm*30/pi;
plot(0,0,Td(1:i),nm(1:i),TdR,nmR,'o'); 
hold on
title('Series dc motor');
ylabel('Speed, rpm'); xlabel('Torque, N-m');
end
for n=1:i; T(n)=PR*746/0.96/wm(n); end
plot(T,nm,'--'); grid