Chapter 4: Load Flow Studies

Forming Ybus Matrix

This is a function that can be called by various programs. The function can be invoked by the statement

                                              [yb,ych]=ybus;

where 'yb' and 'ych' are respectively the Ybus matrix and a matrix containing the line charging admittances. It is assumed that the system data of Table 4.1 are given in matrix form and the matrix that contains line impedances is 'zz', while 'ych' contains the line charging information. This program is stored in the file ybus.m. The program listing is given below.

 

% Function ybus
% THIS IS THE PROGRAM FOR CREATING Ybus MATRIX.

function [yb,ych]=ybus

  % The line impedances are

 zz=[0 0.02+0.1i 0 0 0.05+0.25i
    0.02+0.1i 0 0.04+0.2i 0 0.05+0.25i
    0 0.04+0.2i 0 0.05+0.25i 0.08+0.4i
    0 0 0.05+0.25i 0 0.1+0.5i
    0.05+0.25i 0.05+0.25i 0.08+0.4i 0.1+0.5i 0];

 % The line chargings are

 ych=j*[0 0.03 0 0 0.02
    0.03 0 0.025 0 0.020
    0 0.025 0 0.02 0.01
    0  0 0.02 0 0.075
    0.02 0.02 0.01 0.075 0];

 
  % The Ybus matrix is formed here

  for i=1:5
     for j=1:5
        if zz(i,j) == 0
           yb(i,j)=0;
        else
           yb(i,j)=-1/zz(i,j);
        end
     end
  end

  for i=1:5
     ysum=0;
     csum=0;
     for j=1:5
      ysum=ysum+yb(i,j);
      csum=csum+ych(i,j);
   end
   yb(i,i)=csum-ysum;
end