# Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

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Dear MATLAB users,

I am trying to run this program to determine delta (delta(1) and delta(2)) which is the main unknown parameter but at line 45, I am experiencing "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side".

Is the placement of line 46 equation the right place to put it in the program?

Is it also neccessary to initialize P to zeros?

Any suggestions on the errors in this program or how to improve it would be so much appreciated. My email is sanusielect@yahoo.com

Thank you

% Main program

Pm1 = (6.593706744511551/Tbase)*1; % 6.593706744511551/Tbase;

Pm2 = (2.337250265694494/Tbase)*1; % 2.337250265694494/Tbase;

Ta1= 0.1*(100*pi)^2/1000;

Ta2= 0.6*(100*pi)^2/1000;

Em = 325;

Dpu = 9;

% Bus data parameters

% 1 2 3 4 5 6 7 8 9 10 11

% Bus E delta Poi Qoi PGi QGi PLi QLi Pm Ta

busdata2 =[1 1 0 0 0 0 0 0 0 Pm1 Ta1;

2 1 0 0 0 0 0 0 0 Pm2 Ta2;];

acc1 = 1.385;

acc2 = 1.412;

acc3 = 1.439;

bus2 = busdata2(:,1) % Bus number.

E = busdata2(:,2)

delta = busdata2(:,3) % Initial Bus Voltage Angles.

PO = busdata2(:,4);

QO = busdata2(:,5);

PG = busdata2(:,6); % PGi, Real Power injected into the buses.

QG = busdata2(:,7); % QGi, Reactive Power injected into the buses.

PL = busdata2(:,8); % PLi, Real Power Drawn from the buses.

QL = busdata2(:,9); % QLi, Reactive Power Drawn from the buses.

Pm = busdata2(:,10);

Ta = busdata2(:,11);

n_bus = max(bus2) % To get no. of buses

P = PG + PO - PL; % Pi = PGi - PLi, Real Power at the buses.

Q = QG + QO - QL; % Qi = QGi - QLi, Reactive Power at the buses.

Eprev = E;

% Initialization of varaiables

I = zeros(2,1)

S = zeros(2,1);

delta_prev = delta;

iteration = 0; % Iteration Starting

E11 = zeros(2000,2);

delta_tolerance = 1;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Ybuskron = [0.1691 - 5.7449i -0.1407 + 6.0026i;-0.1407 + 6.0026i 0.1642 - 5.8042i]; % 2 by 2 matrix

while (delta_tolerance > 1e-7 || E_angle_tol > 1e-7)

for i = 1:n_bus

E(i)=(cos(delta(i))+1j*sin(delta(i)))

45 I(i) = Ybuskron*E(i);

S(i) = E(i)*conj(I(i));

P(i) = real(S);

end

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

E_mag(i) = abs(Eprev(i)) + acc1*(abs(E(i))-abs(Eprev(i)));

E_ang(i) = angle(Eprev(i)) + acc2*(angle(E(i))-angle(Eprev(i)));

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

E(i) = E_mag(i)*exp(1i*E_ang(i));

E11(iteration+1,1:2)= abs(E);

% E_tolerance = max(abs((E)-(Eprev)));

E_angle_tol = max(abs((angle(E))- angle(Eprev)));

delta_tol = max(abs(delta - delta_prev));

Eprev = E; % Vprev is required for next iteration

iteration = iteration + 1; % Increment iteration count

end

delta;

E_ang;

I;

P;

##### 3 Comments

### Accepted Answer

Karim
on 26 Dec 2022

Edited: Karim
on 26 Dec 2022

@Kamilu Sanusi, based on your comments I tried to update the code. The code runs without errors, but you will have to verify wheter or not the outcome is correct. The main change is that in order to perform the matrix multiplication, you needed to delete the indexing (i)

Hence change lines like

I(i) = Ybuskron*E(i)

into

I = Ybuskron*E

Below, I tried to make the necesary changes. Hope it helps.

% this values was not provided, thus i made it a random value

Tbase = rand;

% Main program

Pm1 = (6.593706744511551/Tbase)*1; % 6.593706744511551/Tbase;

Pm2 = (2.337250265694494/Tbase)*1; % 2.337250265694494/Tbase;

Ta1= 0.1*(100*pi)^2/1000;

Ta2= 0.6*(100*pi)^2/1000;

Em = 325;

Dpu = 9;

% Bus data parameters

% 1 2 3 4 5 6 7 8 9 10 11

% Bus E delta Poi Qoi PGi QGi PLi QLi Pm Ta

busdata2 =[1 1 0 0 0 0 0 0 0 Pm1 Ta1;

2 1 0 0 0 0 0 0 0 Pm2 Ta2;];

acc1 = 1.385;

acc2 = 1.412;

acc3 = 1.439;

bus2 = busdata2(:,1); % Bus number.

E = busdata2(:,2);

delta = busdata2(:,3); % Initial Bus Voltage Angles.

PO = busdata2(:,4);

QO = busdata2(:,5);

PG = busdata2(:,6); % PGi, Real Power injected into the buses.

QG = busdata2(:,7); % QGi, Reactive Power injected into the buses.

PL = busdata2(:,8); % PLi, Real Power Drawn from the buses.

QL = busdata2(:,9); % QLi, Reactive Power Drawn from the buses.

Pm = busdata2(:,10);

Ta = busdata2(:,11);

n_bus = max(bus2); % To get no. of buses

P = PG + PO - PL; % Pi = PGi - PLi, Real Power at the buses.

Q = QG + QO - QL; % Qi = QGi - QLi, Reactive Power at the buses.

Eprev = E;

% Initialization of varaiables

I = zeros(2,1);

S = zeros(2,1);

delta_prev = delta;

iteration = 0; % Iteration Starting

E11 = zeros(2000,2);

delta_tolerance = 1;

Ybuskron = [0.1691 - 5.7449i -0.1407 + 6.0026i;-0.1407 + 6.0026i 0.1642 - 5.8042i]; % 2 by 2 matrix

% i added a max iteration counter to run online, since Tbase is a random

% value anyway

while iteration < 2000 && (delta_tolerance > 1e-7 || E_angle_tol > 1e-7)

% incerment the iteration count

iteration = iteration + 1;

E = cos(delta) + 1j*sin(delta);

I = Ybuskron*E;

S = E.*conj(I);

P = real(S);

delta = (Pm - P) / Dpu;

E_mag = abs(Eprev) + acc1 * (abs(E) - abs(Eprev) );

E_ang = angle(Eprev) + acc2 * (angle(E)- angle(Eprev));

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

E = E_mag.*exp(1i*E_ang);

E11(iteration,:) = abs(E);

E_angle_tol = max(abs(angle(E) - angle(Eprev)));

delta_tol = max(abs( delta - delta_prev ));

Eprev = E;

end

delta

E_ang

I

P

### More Answers (1)

Paul
on 26 Dec 2022

##### 3 Comments

Paul
on 26 Dec 2022

Yes, I and E are defined that way and at the start of the loop are both 2 x 1. Nevertheless, inside the loop that starts with

for i = 1:n_bus

the value of i is a scalar and you are trying to assign a 2 x 2 result to single element of I. To illustrate, let's intialize I and E to 2 x 1 with entries something other than zero

I = [5;10];

E = [50;100];

Here is Ybuskron

Ybuskron = [0.1691 - 5.7449i -0.1407 + 6.0026i;-0.1407 + 6.0026i 0.1642 - 5.8042i]; % 2 by 2 matrix;

Here is the relevant part of the loop, displaying the relevant values, using an arbitrary value for n_bus

n_bus = 2;

for i = 1:n_bus

i

disp('E(i)'),E(i)

disp('I(i)'),I(i)

disp('Ybuskron*E(i)'),Ybuskron*E(i)

disp('tyring to assign to I(i)')

I(i) = Ybuskron*E(i)

end

Can't assign a 2 x 2 matrix to a single element E(1).

Would need more information about the algorithm the code is tyring to implement in order for anyone to suggest corrections.

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