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Optimal Power flow(OPF) is allocating loads to plants for minimum cost while meeting the network constraints. It is formulated as an optimization problem of minimizing the total fuel cost of all committed plant while meeting the network(power flow ) constraints. The variants of the problems are numerous which model the objective and the constraints in different ways.
The basic OPF problem can described mathematically as a minimization of problem of Minimizing the total fuel cost of all committed plants subject to the constraints.
function [Pgg P V Ybus]=pflow(busdata,linedata);
% formation of Y bus
j=sqrt(-1);
nl = linedata(:,1); nr = linedata(:,2); R = linedata(:,3);
X = linedata(:,4); Bc = j*linedata(:,5); a = linedata(:, 6);
nbr=length(linedata(:,1)); nbus = max(max(nl), max(nr));
Z = R + j*X; y= ones(nbr,1)./Z; %branch admittance
for n = 1:nbr
if a(n) <= 0 a(n) = 1; else end
Ybus=zeros(nbus,nbus); % initialize Ybus to zero
% formation of the off diagonal elements
for k=1:nbr;
Ybus(nl(k),nr(k))=Ybus(nl(k),nr(k))-y(k)/a(k);
Ybus(nr(k),nl(k))=Ybus(nl(k),nr(k));
end
end
% formation of the diagonal elements
for n=1:nbus
for k=1:nbr
if nl(k)==n
Ybus(n,n) = Ybus(n,n)+y(k)/(a(k)^2) + Bc(k);
elseif nr(k)==n
Ybus(n,n) = Ybus(n,n)+y(k) +Bc(k);
else, end
end
end
basemva = 100; accuracy = 0.01; maxiter =3;
ns=0; ng=0; Vm=0; delta=0; yload=0; deltad=0;
nbus = length(busdata(:,1));
for k=1:nbus
n=busdata(k,1);
kb(n)=busdata(k,2); Vm(n)=busdata(k,3); delta(n)=busdata(k, 4);
Pd(n)=busdata(k,5); Qd(n)=busdata(k,6); Pg(n)=busdata(k,7); Qg(n) = busdata(k,8);
Qmin(n)=busdata(k, 9); Qmax(n)=busdata(k, 10);
Qsh(n)=busdata(k, 11);
if Vm(n) <= 0 Vm(n) = 1.0; V(n) = 1 + j*0;
else delta(n) = pi/180*delta(n);
V(n) = Vm(n)*(cos(delta(n)) + j*sin(delta(n)));
P(n)=(Pg(n)-Pd(n))/basemva;
Q(n)=(Qg(n)-Qd(n)+ Qsh(n))/basemva;
S(n) = P(n) + j*Q(n);
end
end
for k=1:nbus
if kb(k) == 1, ns = ns+1; else, end
if kb(k) == 2 ng = ng+1; else, end
ngs(k) = ng;
nss(k) = ns;
end
Ym=abs(Ybus); t = angle(Ybus);
m=2*nbus-ng-2*ns;
maxerror = 1; converge=1;
iter = 0;
% Start of iterations
clear A DC J DX
while maxerror >= accuracy & iter <= maxiter % Test for max. power mismatch
for i=1:m
for k=1:m
A(i,k)=0; %Initializing Jacobian matrix
end, end
iter = iter+1;
for n=1:nbus
nn=n-nss(n);
lm=nbus+n-ngs(n)-nss(n)-ns;
J11=0; J22=0; J33=0; J44=0;
for i=1:nbr
if nl(i) == n | nr(i) == n
if nl(i) == n, l = nr(i); end
if nr(i) == n, l = nl(i); end
J11=J11+ Vm(n)*Vm(l)*Ym(n,l)*sin(t(n,l)- delta(n) + delta(l));
J33=J33+ Vm(n)*Vm(l)*Ym(n,l)*cos(t(n,l)- delta(n) + delta(l));
if kb(n)~=1
J22=J22+ Vm(l)*Ym(n,l)*cos(t(n,l)- delta(n) + delta(l));
J44=J44+ Vm(l)*Ym(n,l)*sin(t(n,l)- delta(n) + delta(l));
else, end
if kb(n) ~= 1 & kb(l) ~=1
lk = nbus+l-ngs(l)-nss(l)-ns;
ll = l -nss(l);
% off diagonalelements of J1
A(nn, ll) =-Vm(n)*Vm(l)*Ym(n,l)*sin(t(n,l)- delta(n) + delta(l));
if kb(l) == 0 % off diagonal elements of J2
A(nn, lk) =Vm(n)*Ym(n,l)*cos(t(n,l)- delta(n) + delta(l));end
if kb(n) == 0 % off diagonal elements of J3
A(lm, ll) =-Vm(n)*Vm(l)*Ym(n,l)*cos(t(n,l)- delta(n)+delta(l)); end
if kb(n) == 0 & kb(l) == 0 % off diagonal elements of J4
A(lm, lk) =-Vm(n)*Ym(n,l)*sin(t(n,l)- delta(n) + delta(l));end
else end
else , end
end
Pk = Vm(n)^2*Ym(n,n)*cos(t(n,n))+J33;
Qk = -Vm(n)^2*Ym(n,n)*sin(t(n,n))-J11;
if kb(n) == 1 P(n)=Pk; Q(n) = Qk; end % Swing bus P
if kb(n) == 2 Q(n)=Qk;
if Qmax(n) ~= 0
Qgc = Q(n)*basemva + Qd(n) - Qsh(n);
if iter <= 7 % Between the 2th & 6th iterations
if iter > 2 % the Mvar of generator buses are
if Qgc < Qmin(n), % tested. If not within limits Vm(n)
Vm(n) = Vm(n) + 0.01; % is changed in steps of 0.01 pu to
elseif Qgc > Qmax(n), % bring the generator Mvar within
Vm(n) = Vm(n) - 0.01;end % the specified limits.
else, end
else,end
else,end
end
if kb(n) ~= 1
A(nn,nn) = J11; %diagonal elements of J1
DC(nn) = P(n)-Pk;
end
if kb(n) == 0
A(nn,lm) = 2*Vm(n)*Ym(n,n)*cos(t(n,n))+J22; %diagonal elements of J2
A(lm,nn)= J33; %diagonal elements of J3
A(lm,lm) =-2*Vm(n)*Ym(n,n)*sin(t(n,n))-J44; %diagonal of elements of J4
DC(lm) = Q(n)-Qk;
end
end
DX=A\DC';
for n=1:nbus
nn=n-nss(n);
lm=nbus+n-ngs(n)-nss(n)-ns;
if kb(n) ~= 1
delta(n) = delta(n)+DX(nn); end
if kb(n) == 0
Vm(n)=Vm(n)+DX(lm); end
end
maxerror=max(abs(DC));
end
V = Vm.*cos(delta)+j*Vm.*sin(delta);
deltad=180/pi*delta;
i=sqrt(-1);
k=0;
for n = 1:nbus
if kb(n) == 1
k=k+1;
S(n)= P(n)+j*Q(n);
Pg(n) = P(n)*basemva + Pd(n);
Qg(n) = Q(n)*basemva + Qd(n) - Qsh(n);
Pgg(k)=Pg(n);
Qgg(k)=Qg(n); %june 97
elseif kb(n) ==2
k=k+1;
S(n)=P(n)+j*Q(n);
Qg(n) = Q(n)*basemva + Qd(n) - Qsh(n);
Pgg(k)=Pg(n);
Qgg(k)=Qg(n); % June 1997
end
yload(n) = (Pd(n)- j*Qd(n)+j*Qsh(n))/(basemva*Vm(n)^2);
end
busdata(:,3)=Vm'; busdata(:,4)=deltad';
Pgt = sum(Pg); Qgt = sum(Qg); Pdt = sum(Pd); Qdt = sum(Qd); Qsht = sum(Qsh);
Pgg=abs(Pgg);
vv=abs(V);
[1]郗忠梅, 李有安, 赵法起,等. 基于Matlab的电力系统潮流计算[J]. 山东农业大学学报:自然科学版, 2010(2):4.
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