nrlfppg.m

% Program for Newton-Raphson Load Flow Analysis
%   Bus number 1 is assumed to be slask bus..

Y = ybusppg();              % Get Y-Bus..
busdata = busdata30();      % Get Bus Data..
baseMVA = 100;              % Base MVA..
bus = busdata(:,1);         % Bus Number..
type = busdata(:,2);        % Type of Bus 1-Slack, 2-PV, 3-PQ..
V = busdata(:,3);           % Specified Voltage..
del = busdata(:,4);         % Voltage Angle..
Pg = busdata(:,5);          % PGi..
Qg = busdata(:,6);          % QGi..
Pl = busdata(:,7);          % PLi..
Ql = busdata(:,8);          % QLi..
Qmin = busdata(:,9);        % Minimum Reactive Power Limit..
Qmax = busdata(:,10);       % Maximum Reactive Power Limit..
nbus = max(bus);            % To get no. of buses..
P = Pg - Pl;                % Pi = PGi - PLi..
Q = Qg - Ql;                % Qi = QGi - QLi..
P = P/baseMVA;              % Converting to p.u..
Q = Q/baseMVA;
Qmin = Qmin/baseMVA;
Qmax = Qmax/baseMVA;
Tol = 10;     % Tolerence kept at high value.
Iter = 1;  % iteration starting
Psp = P;
Qsp = Q;
G = real(Y);    % Conductance..
B = imag(Y);    % Susceptance..

pv = find(type == 2 | type == 1); % Index of PV Buses..
pq = find(type == 3); % Index of PQ Buses..

npv = length(pv); % Number of PV buses..
npq = length(pq); % Number of PQ buses..

while (Tol > 1e-5)   % Iteration starting..
    P = zeros(nbus,1);
    Q = zeros(nbus,1);
    % Calculate P and Q
    for i = 1:nbus
        for k = 1:nbus
            P(i) = P(i) + V(i)* V(k)*(G(i,k)*cos(del(i)-del(k)) + B(i,k)*sin(del(i)-del(k)));
            Q(i) = Q(i) + V(i)* V(k)*(G(i,k)*sin(del(i)-del(k)) - B(i,k)*cos(del(i)-del(k)));
        end
    end
    
    % Checking Q-limit violations..
    if Iter <= 7 && Iter >= 2
        for n = 2:nbus
            if type(n) == 2
                if Q(n) < Qmin(n)
                    V(n) = V(n) + 0.01;
                elseif Q(n) > Qmax(n)
                    V(n) = V(n) - 0.01;
                end
            end
         end
    end
    
    % Calculate change from specified value
    dPa = Psp-P;
    dQa = Qsp-Q;
    dQ = zeros(npq,1);
    k = 1;
    for i = 1:nbus
        if type(i) == 3
            dQ(k,1) = dQa(i);
            k = k+1;
        end
    end
    dP = dPa(2:nbus);
    M = [dP; dQ];       % Mismatch Vector
    
    % Jacobian
    % J1 - Derivative of Real Power Injections with Angles..
    J1 = zeros(nbus-1,nbus-1);
    for i = 1:(nbus-1)
        m = i+1;
        for k = 1:(nbus-1)
            n = k+1;
            if n == m
                for q = 1:nbus
                    J1(i,k) = J1(i,k) + V(m)* V(q)*(-G(m,q)*sin(del(m)-del(q)) + B(m,q)*cos(del(m)-del(q)));
                end
                J1(i,k) = J1(i,k) - V(m)^2*B(m,m);
            else
                J1(i,k) = V(m)* V(n)*(G(m,n)*sin(del(m)-del(n)) - B(m,n)*cos(del(m)-del(n)));
            end
        end
    end
    
    % J2 - Derivative of Real Power Injections with V..
    J2 = zeros(nbus-1,npq);
    for i = 1:(nbus-1)
        m = i+1;
        for k = 1:npq
            n = pq(k);
            if n == m
                for q = 1:nbus
                    J2(i,k) = J2(i,k) + V(q)*(G(m,q)*cos(del(m)-del(q)) + B(m,q)*sin(del(m)-del(q)));
                end
                J2(i,k) = J2(i,k) + V(m)*G(m,m);
            else
                J2(i,k) = V(m)*(G(m,n)*cos(del(m)-del(n)) + B(m,n)*sin(del(m)-del(n)));
            end
        end
    end
    
    % J3 - Derivative of Reactive Power Injections with Angles..
    J3 = zeros(npq,nbus-1);
    for i = 1:npq
        m = pq(i);
        for k = 1:(nbus-1)
            n = k+1;
            if n == m
                for q = 1:nbus
                    J3(i,k) = J3(i,k) + V(m)* V(q)*(G(m,q)*cos(del(m)-del(q)) + B(m,q)*sin(del(m)-del(q)));
                end
                J3(i,k) = J3(i,k) - V(m)^2*G(m,m);
            else
                J3(i,k) = V(m)* V(n)*(-G(m,n)*cos(del(m)-del(n)) - B(m,n)*sin(del(m)-del(n)));
            end
        end
    end
    
    % J4 - Derivative of Reactive Power Injections with V..
    J4 = zeros(npq,npq);
    for i = 1:npq
        m = pq(i);
        for k = 1:npq
            n = pq(k);
            if n == m
                for q = 1:nbus
                    J4(i,k) = J4(i,k) + V(q)*(G(m,q)*sin(del(m)-del(q)) - B(m,q)*cos(del(m)-del(q)));
                end
                J4(i,k) = J4(i,k) - V(m)*B(m,m);
            else
                J4(i,k) = V(m)*(G(m,n)*sin(del(m)-del(n)) - B(m,n)*cos(del(m)-del(n)));
            end
        end
    end
    
    J = [J1 J2; J3 J4];     % Jacobian
    
    X = inv(J)*M;           % Correction Vector
    dTh = X(1:nbus-1);
    dV = X(nbus:end);
    del(2:nbus) = dTh + del(2:nbus);
    k = 1;
    for i = 2:nbus
        if type(i) == 3
            V(i) = dV(k) + V(i);
            k = k+1;
        end
    end
    Iter = Iter + 1;
    Tol = max(abs(M));
end
    
Iter = Iter - 1; % Number of Iterations took..
V;
Del = 180/pi*del;
E1 = [V Del]; % Bus Voltages and angles..
disp('------------------------------');
disp('|  Bus  |    V    |  Angle   | ');
disp('|  No   |   pu    |  Degree  | ');
disp('------------------------------');
for m = 1:nbus
    fprintf('%4g', m), fprintf('    %8.4f', V(m)), fprintf('    %8.4f', Del(m)); fprintf('\n');
end
disp('-----------------------------');