Page 345 - Solutions Manual to accompany Electric Machinery Fundamentals

% fire = Firing angle in degrees

% vu
if ( vin > vx )
vu = 100;
else
vu = 0;
end

% vv
if ( vin >= vy )
vv = 0;
else
vv = 100;
end

% Caclulate vout
vout = vv - vu;

v
Now we need a MATLAB program to generate the input voltage   tv in and the reference voltages   t
x
and  tv y . After the voltages are generated, function vout will be used to calculate v out   t and the
v
v
frequency spectrum of v out  t . Finally, the program will plot   tv in ,   t and  t , v out   t , and the
y
x
spectrum of v out  t . (Note that in order to have a valid spectrum, we need to create several cycles of the
60 Hz output waveform, and we need to sample the data at a fairly high frequency. This problem creates
4 cycles of v out  t and samples all data at a 20,000 Hz rate.)

% M-file: probs1_15a.m
% M-file to calculate the output voltage from a PWM
% modulator with a 500 Hz reference frequency. Note
% that the only change between this program and that
% of part b is the frequency of the reference "fr".

% Sample the data at 20000 Hz to get enough information
% for spectral analysis. Declare arrays.
fs = 20000; % Sampling frequency (Hz)
t = (0:1/fs:4/15); % Time in seconds
vx = zeros(size(t)); % vx
vy = zeros(size(t)); % vy
vin = zeros(size(t)); % Driving signal
vu = zeros(size(t)); % vx
vv = zeros(size(t)); % vy
vout = zeros(size(t)); % Output signal
fr = 500; % Frequency of reference signal
T = 1/fr; % Period of refernce signal

% Calculate vx at fr = 500 Hz.
for ii = 1:length(t)
vx(ii) = vref(t(ii),T);
vy(ii) = - vx(ii);
end

% Calculate vin as a 50 Hz sine wave with a peak voltage of
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