Gauss-Seidel Load Flow Program with Matlab Simulation Output

The Gauss-Seidel program is stored in the file loadflow_gs.m. This calls the ybus.m function discussed above. The program allows the selection of the acceleration factor. The program lists the number of iterations required to converge, bus voltages and their magnitudes and real and reactive power. The program listing is given below.

% Program loadflow_gs

% THIS IS A GAUSS-SEIDEL POWER FLOW PROGRAM

clear all

d2r=pi/180;w=100*pi;

% The Y_bus matrix is

[ybus,ych]=ybus;

g=real(ybus);b=imag(ybus);

% The given parameters and initial conditions are

p=[0;-0.96;-0.35;-0.16;0.24];

q=[0;-0.62;-0.14;-0.08;-0.35];

mv=[1.05;1;1;1;1.02];

th=[0;0;0;0;0];

v=[mv(1);mv(2);mv(3);mv(4);mv(5)];

acc=input('Enter the acceleration constant: ');

del=1;indx*=0;

% The Gauss-Seidel iterations starts here

while del>1e-6

% P-Q buses

for i=2:4

tmp1=(p(i)-j*q(i))/conj(v(i));

tmp2=0;

for k=1:5

if (i==k)

tmp2=tmp2+0;

else

tmp2=tmp2+ybus(i,k)*v(k);

end

vt=(tmp1-tmp2)/ybus(i,i);

v(i)=v(i)+acc*(vt-v(i));

end

% P-V bus

q5=0;

for i=1:5

q5=q5+ybus(5,i)*v(i);

end

q5=-imag(conj(v(5))*q5);

tmp1=(p(5)-j*q5)/conj(v(5));

tmp2=0;

for k=1:4

tmp2=tmp2+ybus(5,k)*v(k);

end

vt=(tmp1-tmp2)/ybus(5,5);

v(5)=abs(v(5))*vt/abs(vt);

% Calculate P and Q

for i=1:5

sm=0;

for k=1:5

sm=sm+ybus(i,k)*v(k);

end

s(i)=conj(v(i))*sm;

end

% The mismatch

delp=p-real(s)';

delq=q+imag(s)';

delpq=[delp(2:5);delq(2:4)];

del=max(abs(delpq));

indx=indx+1;

if indx==1

pause

end

'GS LOAD FLOW CONVERGES IN ITERATIONS',indx,pause

'FINAL VOLTAGE MAGNITUDES ARE',abs(v)',pause

'FINAL ANGLES IN DEGREE ARE',angle(v)'/d2r,pause

'THE REAL POWERS IN EACH BUS IN MW ARE',(real(s)+[0 0 0 0 0.24])*100,pause

'THE REACTIVE POWERS IN EACH BUS IN MVar ARE',(-imag(s)+[0 0 0 0 0.11])*100