%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%   spwmnat2.m  -  Determines switching angles for bi-state.
%                  SPWM ( natural sampling )
%                  Re: Fig 6-5 of Rashid
%                  Plots Fourier spectrum.
%                  Uses alf.m
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clear;
global cglob
cglob = zeros(1,5);
angle = zeros(1,1); time = zeros(1,1);
x = zeros(1,1024); y = zeros(1,1024);
N=4; T=1/60; Tc=T/(2*N-1);
%  T  - period of fundamental     N  - chops/half cycle
%  MI - modulation index          Ac - amplitude of carrier
MI=0.9; Ac=10; A=MI*Ac;
if MI>1 | MI<0; disp( 'CAUTION: MI>1 or MI<0'); end
m=8*Ac*N/T; w=2*pi/T;
for i=1:511; x(i)=Ac; end
for k=1:N
td = (k-1)*Tc; x0 = Tc/2; cglob = [ m w A 2*Ac td ];
alfa = fzero( 'alf', x0 );
alfa = alfa + td; time = [ time; alfa ];
angle = [ angle; alfa*360/T ];
x0 = 0.75*Tc; cglob = [ -m w A -4*Ac td ];
alfa = fzero( 'alf', x0 );
alfa = alfa + td; time = [ time; alfa ];
angle = [ angle; alfa*360/T ];
end 
angle = [ angle; 180 ]; time = [ time; T/2 ];
t = linspace(0,T/2,512); k = length( time );
y = A*sin( w*t ); n=2;
for i=1:512
if n > k-2, break, end
if t(i) < time(n); x(i)=Ac;
elseif t(i) >= time(n) & t(i) <= time(n+1); x(i)=-Ac;
else; x(i)=Ac; n=n+2;
end
end
for i=1:512; x(i+512)=-x(i); y(i+512)=-y(i); end
alphas = angle'             % Display alphas to screen
disp('Hit any key to continue'); pause
t=linspace(0,T,1024); clf; figure(1);
subplot(211), plot(t',x',t',y'); title('SINUSOIDAL PWM WAVEFORM');
xlabel('TIME- s'); ylabel('OUTPUT WAVE FORM'); grid;
fn = abs( fft(x) ); fnn = 100*fn/max(fn);
subplot(212), plot( [0:100], fnn(1:101) );
title('FOURIER SPECTRUM OF SPWM WAVEFORM');
xlabel('HARMONIC NUMBER'); ylabel('PERCENT');
text(0.15, 0.65, ['MI = ',num2str(MI),'  N = ', ...
num2str(N)], 'sc');