loop index 'i' is changed inside of a FOR loop

Dear MATLAB users,

I need an explanation on the reason why the i in line 23 is red-underlined in the program and the error discription is "loop index 'i' is changed inside of a FOR loop". I tried to remove line 23 so that line 4 could stand for line 23 but the iteration values of P and Q were in complex instead of scalar. Please what could be the problem and what is the way out? Thank you

% while (V_tolerance > 1e-7 || V_angle_tol > 1e-7 || w_tolerance > 1e-7)

.

.

.

.

% Computing V

4 for i = 1:nbus

sumyv = 0;

for k = 1:nbus

if i ~= k

sumyv = sumyv + YBUS(i,k)* V(k); % Vk * Yik

end

end

% calculating the active and reactive power at the generator buses

23 for i = 1:nbus

for j = 1 : nbus

if type(i) == 2 % Computing Pi & Qi for Generator buses

delta(i) = ((Pm(i) - P(i))/Dpu);

P(i) = P(i) + V(i)*V(j)*(G(i,j)*cos(delta(i)-delta(j)) + ...

B(i,j)*sin(delta(i)-delta(j)))+ PO(i)-PL(i)

Q(i) = Q(i) + V(i)*V(j)*(G(i,j)*sin(delta(i)-delta(j)) - ...

B(i,j)*cos(delta(i)-delta(j)))+ QO(i)-QL(i)

end

end

end

V(i) = (1/YBUS(i,i))*((P(i)-1i*Q(i))/conj(V(i)) - sumyv); % Compute Bus Voltages

V_mag(i) = abs(Vprev(i)) + acc1*(abs(V(i))-abs(Vprev(i)));

V_ang(i) = angle(Vprev(i)) + acc2*(angle(V(i))-angle(Vprev(i)));

delta(i) = delta_prev(i) + acc3*(delta(i) - delta_prev(i));

% V(i) = Vprev(i) + acc1*(V(i)-Vprev(i));

V(i) = V_mag(i)*exp(1i*V_ang(i));

if (i == 1 || i == 2)

V_mag(i) = 1;

[x, y] = pol2cart(angle(V(i)),V_mag(i));

V(i)= x+1i*y;

end

if i == 3

[a, b] = pol2cart(0,abs(V(i)));

V(i)= a+1i*b;

end

end

[Torsten]

The loop indices in line 4 and line 23 cannot both be named "i" because the loop starting at line 4 ha snot yet been closed when the loop at line 23 starts.

[Kamilu Sanusi]

@Torsten, It was already closed with end before the % calculating the active and reactive power at the generator buses i.e

end

% calculating the active and reactive power at the generator buses.

May be like this:

for i = 1:nbus

sumyv = 0;

for k = 1:nbus

if i ~= k

sumyv = sumyv + YBUS(i,k)* V(k); % Vk * Yik

end

V(i) = (1/YBUS(i,i))*((P(i)-1i*Q(i))/conj(V(i)) - sumyv); % Compute Bus Voltages

end

% calculating the active and reactive power at the generator buses

Answer 1

[Sulaymon Eshkabilov]

Because this part of your code is outside of the set loop:

end % Wrongly placed
...
     V(i) = (1/YBUS(i,i))*((P(i)-1i*Q(i))/conj(V(i)) - sumyv); % Compute Bus Voltages
       
        V_mag(i) = abs(Vprev(i)) + acc1*(abs(V(i))-abs(Vprev(i)));
        V_ang(i) = angle(Vprev(i)) + acc2*(angle(V(i))-angle(Vprev(i)));
        delta(i) = delta_prev(i) + acc3*(delta(i) - delta_prev(i));
        

[Kamilu Sanusi]

@Sulaymon Eshkabilov, Pls what do you mean? It was used to closed that loop

[Sulaymon Eshkabilov]

See the previous loops where one "end" is missing:

4 for i = 1:nbus
        sumyv = 0;
        for k = 1:nbus
            if i ~= k
                sumyv = sumyv + YBUS(i,k)* V(k);  % Vk * Yik
            end
        end
        % calculating the active and reactive power at the generator buses
        "end" is missing

[Kamilu Sanusi]

@Sulaymon Eshkabilov, thank you for reply. I tried it but it was rather leading to results far from the expected, though it does not converge as well. Expected result is:

delta = [ 0.268; 0.1774; 0; 0;x]; x = cant say but I am seeing the results staying at

delta = 1e-2* [ 0.3; 0.17644; 0; 0;x];

Please, I would appreciate if you can help me look at it, I think I am close to the result, may be one syntax error is not making it converge. Pls kindly help me with your email so that i send it. For protection of my research I cant upload the whole program here. My email is [e-mail]

Thank you

Answer 2

[Sulaymon Eshkabilov]

% See the below given answer:    

Or you had better combine two loops to make your simulation more efficient, e.g.:

...       
for i = 1:nbus
        sumyv = 0;
        for k = 1:nbus
            if i ~= k
                sumyv = sumyv + YBUS(i,k)* V(k);  % Vk * Yik
            end
        % end
        % calculating the active and reactive power at the generator buses
%  23     for i = 1:nbus 
%           for j = 1 : nbus
            if type(i) == 2     % Computing Pi & Qi for Generator buses
               delta(i) = ((Pm(i) - P(i))/Dpu);
               P(i) = P(i) + V(i)*V(j)*(G(i,j)*cos(delta(i)-delta(j)) + ...
                B(i,j)*sin(delta(i)-delta(j)))+ PO(i)-PL(i)
               Q(i) = Q(i) + V(i)*V(j)*(G(i,j)*sin(delta(i)-delta(j)) - ...
                B(i,j)*cos(delta(i)-delta(j)))+ QO(i)-QL(i)
            end
        end 
    %   end
        V(i) = (1/YBUS(i,i))*((P(i)-1i*Q(i))/conj(V(i)) - sumyv); % Compute Bus Voltages
       
        V_mag(i) = abs(Vprev(i)) + acc1*(abs(V(i))-abs(Vprev(i)));
        V_ang(i) = angle(Vprev(i)) + acc2*(angle(V(i))-angle(Vprev(i)));
        delta(i) = delta_prev(i) + acc3*(delta(i) - delta_prev(i));
%         V(i) = Vprev(i) + acc1*(V(i)-Vprev(i));
        V(i) = V_mag(i)*exp(1i*V_ang(i));
         if (i == 1 || i == 2)
           V_mag(i)  = 1;
            [x, y] = pol2cart(angle(V(i)),V_mag(i));
            V(i)= x+1i*y;
        end
        if i == 3
            [a, b] = pol2cart(0,abs(V(i)));
            V(i)= a+1i*b;
        end    
  end