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%
%  diffmtr.m - plots developed torque-speed curve for differential 
%             compound excited dc motor with rated voltage applied.
%             Armature reaction neglected.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear; clf;
VtR=600;                      % Rated terminal voltage
PR=80;                        % Rated output horsepower
Ra=0.25;                      % Armature resistance
Rs=0.03;                      % Series field resistance
Nf=250;                       % Shunt field turns
Ns=3;                         % 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 for speed of nmR
m=length(eif); npts=200;
Kphip=eif(1:m,1)/(nmR*pi/30); If=eif(1:m,2);
% Rated If
IfR=table1( [Kphip If], (VtR-IaR*(Ra+Rs))/(nmR*pi/30))+Ns/Nf*IaR;
Rfeq=VtR/IfR;    % Total shunt field circuit resistance
npts=200; Ia=linspace(0,1.5*PR*746/VtR,npts);
% Determination of Td-nm
for i=1:npts
   Kphi=table1([If Kphip], IfR-Ns/Nf*Ia(i));
   Td(i)=Kphi*Ia(i);
   wm(i)=VtR/Kphi-Td(i)*(Ra+Rs)/Kphi^2;
end
nm=wm*30/pi;
subplot(2,1,1); plot(0,0,Td,nm,TdR,nmR,'o'); grid;
title('Differential compound dc motor');
ylabel('Speed, rpm'); xlabel('Torque, N-m');
subplot(2,1,2); plot(0,0,Ia+IfR,nm,IaR+IfR,nmR,'o'); grid;
title('Differential compound dc motor');
ylabel('Speed, rpm'); xlabel('Line current, A');