%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  shntgen.m - plots terminal characteristic for shunt excited 
%              dc generator. Armature reaction neglected.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear; clf;
VtR=600;      % Rated terminal voltage
PR=60e03;     % Rated output power
Ra=0.25;      % Armature resistance
Pfw=3060;     % F&W losses at speed of analysis (W)
ILR=PR/VtR;   % Rated output current
load eif      % Load stored OCC
m=length(eif); npts=200;
E=eif(1:m,1); If=eif(1:m,2);

% Iterative determination of rated If
IfR=0;
for i=1:50; IfR=interp1( E, If, VtR+(ILR+IfR)*Ra); end

Rfeq=VtR/IfR;    % Total shunt field circuit resistance
IL=linspace(0,1.5*ILR,npts);
  
% Iterative determination of Vt-IL
for i=1:npts
   If1=IfR;
   for j=1:100
      Vt1=interp1(If, E, If1)-(IL(i)+If1)*Ra; 
      If2=Vt1/Rfeq;
      if abs(If2-If1)<= 0.001; Vt(i)=Vt1; break; end;
      If1=If2;
   end
      eff(i)=Vt(i)*IL(i)/(Vt(i)*IL(i)+(IL(i)-If2)^2*Ra+ ...
         Vt(i)*If2+Pfw)*100;
end
subplot(2,1,1); plot(0,0,IL,Vt,ILR,VtR,'o'); grid;
title('Shunt excited dc generator');
xlabel('Load current, A'); ylabel('Terminal voltage, V');
subplot(2,1,2); plot(IL, eff); grid;
xlabel('Load current, A'); ylabel('Efficiency, %');
title('Shunt excited dc generator');