Page 273 - Solutions Manual to accompany Electric Machinery Fundamentals

% Calculate the Ea v alues modified by mmf due to the
% armature current
i_a = 20;
Ea _a = interp1(if_values,ea_values,i_f + i_a * n_se/n_f);

% Find the point where the difference between the
% enhanced Ea line and the Vt line is 4.2 V. This will
% be the poin t where the line "Ea_a - Vt - 4.2" goes
% negative.
di ff = Ea_a - Vt - 4.2;

% This code prevents us from reporting the first (unstable)
% location sat isfying the criterion.
was_pos = 0;
for ii = 1:length(i_ f);
if diff(ii) > 0
wa s_pos = 1;
end
if ( diff(i i) < 0 & was_pos == 1 )
bre ak;
end ;
en d;

% We have the intersection. Tell user.
disp (['Ea_a = ' num2str(Ea_a(ii)) ' V']);
disp (['Ea = ' num2str(Ea(ii)) ' V']);
disp (['Vt = ' num2str(Vt(ii)) ' V']);
disp (['If = ' num2str(i_f(ii)) ' A']);
di sp (['If_a = ' num2str(i_f(ii)+ i_a * n_se/n_f) ' A']);

% Plot the c urves
figure(1);
plot(i_f,E a,'b-','LineWidth',2.0);
hold on;
pl ot(i_f,Vt,'k--','LineWidth',2.0);

% Plot intersections
plot([i_f(ii) i_f(ii)], [0 Vt(ii)], 'k-');
plot([0 i_f(ii)], [Vt(ii) Vt(ii)],'k-');
pl ot([0 i_f(ii)+i_a*n_se/n_f], [Ea_a(ii) Ea_a(ii)],'k-');

% Plot compounding triangle
plot([i_f(ii) i_f(ii)+i_a*n_se/n_f],[Vt(ii) Vt(ii)],'b-');
plot([i_f(ii) i_f(ii)+i_a*n_se/n_f],[Vt(ii) Ea_a(ii)],'b-');
plot( [i_f(ii)+i_a*n_se/n_f i_f(ii)+i_a*n_se/n_f],[Vt(ii) Ea_a(ii)],'b-
') ;

xlabel('\bf\itI_{F} \rm\bf(A)');
ylabel('\bf\itE_{A} \rm\bf or \itE_{A} \rm\bf(V)');
title ('\bfP lot of \itE_{A} \rm\bf and \itV_{T} \rm\bf vs field
current');
axis ([0 5 0 150]);
set(gca, 'YTick',[0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
150]')
set(gca,'XTick',[0 0.5 1.0 1.5 2. 0 2.5 3.0 3.5 4.0 4.5 5.0]')

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