index must be a positive integer or logical.

Hi all,

Currently I'm trying to create a battery simulation in matlab simulink. I'm still in the middle of myresearch so I'm trying different things. I came across this book: 'Electric Vehicle Technology Explained' by James Larminie & John Lowry. I wanted to try one of their scripts for battery simulation but I keep getting the following error:

    Attempted to access open_circuit_voltage_LA(0,6); index must be a positive integer or logical. 
Error in TEST (line 28)
V(0)= open_circuit_voltage_LA(0,NoCells) - I(1)*Rin;

I was hoping you guys could help me out and explain to me the problem and solution. Thanks a bunch, I'll post the code down below.

CODE:
% M file for Figure 2.15
% Simple battery discharge experiment for a large 5 cell NiCad
% battery.
% Form some arrays for holding data.
% Time will run from 0 to 10000 seconds
T=(0:50:50000);
DoD=zeros(1,1001); % Depth of discharge, start off fully charged.
V=zeros(1,1001); % Battery voltage will be calculated at each time
			% step, so fill array with zeros initially.
I=linspace(100,100,1001); % Make current constant, and = 20 amps
NoCells=6	;% 6 cell battery
Capacity=50;  % This is the normal "10 hour" capacity
k=1.12		;% Peukert coefficient, not much greater than 1.
deltaT = 50;	% Take 50 second time steps, OK for constant current
% Calculated values
Rin= (0.022/Capacity)*NoCells;	% Internal resistance
PeuCap= ((Capacity/10)^k)*10; % See equations 2.7 to 2.9
% Starting voltage set outside loop
V(0)= open_circuit_voltage_LA(0,NoCells) - I(1)*Rin;
for n=2:1001
 I_cor= (I(n))^k; % Current corrected by Peukert
 DoD(n)= ((PeuCap * DoD(n-1)) + ((I_cor * deltaT)/3600))/PeuCap;
 if DoD(n)>1 
    DoD(n)=1;
 end
 V(n)=open_circuit_voltage_LA(DoD(n),NoCells) - I(n)*Rin;
 % We will say that the battery is "dead" if the
 % depth of discharge exceeds 99%
 if DoD(n)>0.99
    V(n)=0;
    end
end
C=zeros(1,1001);
C(1)=0;
for n=2:1001
 if V(n)>0
    C(n)=C(n-1)+ ((I(n)*deltaT)/3600);
 else 
    C(n)=C(n-1);
 end
end
for n=1:1001
 I(n)=5;
end
V2=zeros(1,1001);
% Starting voltage set outside loop
V2(1)= open_circuit_voltage_LA(0,NoCells) - I(1)*Rin;
for n=2:1001
 I_cor= (I(n))^k; % Current corrected by Peukert
 DoD(n)= ((PeuCap * DoD(n-1)) + ((I_cor * deltaT)/3600))/PeuCap;
 if DoD(n)>1 
    DoD(n)=1;
 end
 V2(n)=open_circuit_voltage_LA(DoD(n),NoCells) - I(n)*Rin;
 % We will say that the battery is "dead" if the
 % depth of discharge exceeds 99%
 if DoD(n)>0.99
    V2(n)= 0;
    end
end
C2=zeros(1,1001);
C2(1)=0;
for n=2:1001
 if V2(n)>0
    C2(n)=C2(n-1)+ ((I(n)*deltaT)/3600);
 else 
    C2(n)=C2(n-1);
 end
end
for n=1:1001
 I(n)=50;
end
V3=zeros(1,1001);
% Starting voltage set outside loop
V3(1)= open_circuit_voltage_LA(0,NoCells) - I(1)*Rin;
for n=2:1001
 I_cor= (I(n))^k; % Current corrected by Peukert
 DoD(n)= ((PeuCap * DoD(n-1)) + ((I_cor * deltaT)/3600))/PeuCap;
 if DoD(n)>1 
    DoD(n)=1;
 end
 V3(n)=open_circuit_voltage_LA(DoD(n),NoCells) - I(n)*Rin;
 % We will say that the battery is "dead" if the
 % depth of discharge exceeds 99%
 if DoD(n)>0.99
    V3(n)= 0;
    end
end
C3=zeros(1,1001);
C3(1)=0;
for n=2:1001
 if V3(n)>0
    C3(n)=C3(n-1)+ ((I(n)*deltaT)/3600);
 else 
    C3(n)=C3(n-1);
 end
end
plot(C,V,'b.',C2,V2,'r.',C3,V3,'m.');
axis([0 55 7 14]);
end

Answer 1

[Image Analyst]

Have you seen the FAQ on this? http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F

I think that describes it well enough that you can figure it out using the debugger.

[Michel de Jongh]

Thanks for your reply.

I did indeed found that FAQ but in my understanding I did made sure that the index are real, positive integer numbers, or logicals. I'm pretty sure that I'm missing something obvious.

[Image Analyst]

OK, I tried to run it but after removing the extra "end" I could not get past this line:

V(0)= open_circuit_voltage_LA(0,NoCells) - I(1)*Rin;

You should provide open_circuit_voltage_LA and any other data necessary to demonstrate the error.

[Michel de Jongh]

That is the exact line that I keep getting stuck on. This is the exact code I got from the book mentioned above. (except for the extra end btw) I believe it is supposed to calculate open_circuit_voltage_LA.

I didn't get any other data with this code. Even when I state that open_circuit_voltage_LA = 6; I still get the same error.