im_perf.m

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%
%  im_perf.m - calculates induction motor performance ( I1, PF,
%              3Td, Ps, efficiency ) based on equivalent circuit
%              of Fig. 6.17.
%              Reads equivalent circuit parameters from im_data.m
%              Assumes F&W losses vary as nth power of speed.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear; clf;
im_data,
V1=230/sqrt(3); f=60; p=6;  % Phase voltage, frequency, poles
Pfw=224; n=2.8;  % Total F&W losses at syn. speed, speed dependence
npts=200; s=linspace( 0.00001,1,npts); s=fliplr(s);
I1=zeros(1,npts); TTd=I1; PF=I1; Ps=I1; eff=I1; nm=I1;
ws=2/p*2*pi*f; ns=120*f/p;   % Synchronous speed
% Empirical adjustment of R2pr & X2pr for fr variation
R2pr0=R2pr; X2pr0=X2pr; smax=R2pr/sqrt(R1^2+(X1+X2pr)^2);
for i=1:npts
  %if s(i) > smax
  %R2pr=(0.5+0.5*sqrt(s(i)/smax))*R2pr0;
  %X2pr=(0.4+0.6*sqrt(smax/s(i)))*X2pr0;
  %else; R2pr=R2pr0; X2pr=X2pr0; end
Z2=R2pr/s(i)+j*X2pr; Zm=j*Rc*Xm/(Rc+j*Xm);
Zin=R1+j*X1 + Z2*Zm/(Z2+Zm);
I11=V1/Zin; I1(i)=abs(I11); PF(i)=cos(angle(I11));
I2pr=abs(Zm/(R2pr/s(i)+j*X2pr+Zm)*I11); TPin=3*V1*I1(i)*PF(i);
TTd(i)=3*I2pr^2*R2pr/s(i)/ws; nm(i)=(1-s(i))*ns;
PPo=TTd(i)*(1-s(i))*ws - Pfw*(nm(i)/ns)^n;
if PPo<0; break; else;
Ps(i)=PPo; eff(i)=100*Ps(i)/TPin; end
end
subplot(2,1,1), plot(nm,TTd); grid; title('Developed torque');
xlabel('Speed, rpm'); ylabel('Torque, N-m');
subplot(2,1,2), plot(nm,Ps/746); grid; title('Output power'); 
xlabel('Speed, rpm'); ylabel('Output power, hp');
figure(2); subplot(2,1,1);
plot(nm,I1); grid; title('Input current');
xlabel('Speed, rpm'); ylabel('Current, A');
subplot(2,1,2); plot(nm,eff); grid; title('Efficiency');
xlabel('Speed, rpm'); ylabel('Efficiency, %');
figure(3); subplot(2,1,1);
plot(nm,PF); grid; title('Input power factor');
xlabel('Speed, rpm'); ylabel('Power factor');