Page 274 - Solutions Manual to accompany Electric Machinery Fundamentals

legend ('Ea line','Vt line',4);
hold off;
grid on;
(d) A MATLAB program to calculate and plot the terminal characteristic of this generator is shown
be low.

% M-file: prob8_27d.m
% M-file to calculate the terminal characteristic of a
% cumulatively compounded dc generator without armature
% reaction.

% Get the magnetization curve. This file contains the
% three var iables if_values, ea_values, and n_0.
clear all
load p87_mag.dat;
if_values = p87_mag(:,1);
ea_values = p 87_mag(:,2);
n_ 0 = 1800;

% First, initialize the values needed in this progr am.
r_f = 20; % Field resistance (ohms)
r_adj = 10; % Adjustable resistance (ohms)
r_a = 0.21; % Armature + series r esistance (ohms)
i_f = 0:0.02:6; % Field current (A)
n = 1800; % Generator speed (r/ min)
n_f = 1000; % Shunt field turns
n_ se = 25; % Series field turns

% Calculate Ea versus If
Ea = interp1(if_values,ea_values,i_f);

% Calculate Vt versus If
Vt = (r_f + r_adj) * i_f;

% Find the point where the difference between the two
% lines is exactly equal to i_a*r_a. This will be the
% point where the line line "Ea - Vt - i_a*r_a" goes
% negative.
i_a = 0:1:55;
fo r jj = 1:length(i_a)

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

% Get the voltage difference
diff = Ea_a - Vt - i_a(jj)*r_a;

% 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

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