%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%   spwm3ph.m  -  Determines switching angles for SPWM
%                 ( bi-state, natural sampling ) for
%                 use in 3-phase inverters.
%                 Triangular carrier symmetric about zero.
%                 Plots Fourier spectrum.
%                 Uses alf.m
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clear;
global cglob
cglob = zeros(1,5);
angle = zeros(1,1); time = zeros(1,1);
N=15; T=1/60; Tc=T/(2*N-1);
%  T  - period of fundamental     N  - chops/half cycle
%  MI - modulation index          Ac - amplitude of carrier
MI=1.0; 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 ];
x = zeros(1,1024); y = zeros(1,1024);
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
clc; alphas = angle'             % Display alphas to screen
disp('Hit any key to continue'); clf; pause
t=linspace(0,T,1024);
% Generate the a-b-c switching patterns wrt dc link midpoint.
xa=x/2; xb=zeros(1,1024); xc=xb; xphi=xb;  
for i=1:341; xb(i)=xa(i+683); end
for i=1:683; xb(i+341)=xa(i); end
for i=1:341; xc(i)=xb(i+683); end
for i=1:683; xc(i+341)=xb(i); end
V=[ 0 T -Ac/2-1 Ac/2+1 ]; axis(V); figure(1);
plot(t,xa); grid; title('PHASE a SWITCHING PATTERN');
xlabel('TIME - s'); ylabel('NODE a POTENTIAL wrt SOURCE MID-POINT');
pause;
% Generate phase a voltage

for i=1:1024; xphi(i)=(2*xa(i)-xb(i)-xc(i))/3; end
% Pulse mitigation to remove short state durations.
ND = 2;   %  min allowable switch time in degrees( 1 deg min )
k = length(xphi); kp = fix( ND/360*1024 ); if kp<1; kp=1; end
for i=1:k-kp
if xphi(i+1)>xphi(i) & xphi(i+kp)~=xphi(i+1);  xphi(i+1)=xphi(i); end
if xphi(i+1)<xphi(i) & xphi(i+kp)~=xphi(i+1);  xphi(i+1)=xphi(i); end
end
V=[ 0 T -Ac Ac ]; axis(V);
subplot(211), plot(t',xphi'); grid;
title('PHASE VOLTAGE WAVEFORM');
xlabel('TIME - s'); ylabel('OUTPUT WAVE FORM');
text(0.15,0.65, ['MI = ',num2str(MI), ' N = ',num2str(N)], 'sc'); 
fn = abs( fft(xphi) ); fnn = 100*fn/fn(2);
axis; subplot(212), plot( [0:100], fnn(1:101) );
title('FOURIER SPECTRUM OF PHASE VOLTAGE WAVEFORM');
xlabel('HARMONIC NUMBER'); ylabel('PERCENT');