If statement four variables

Hi all, Thanks for your time in advance.

I have vectors which contain the kWh output of a wind turbine and demand data for a house beside that turbine, i want to create an if statement which will

• If battery is fully charged && windpower>demand then Charge battery until is full
• If battery is fully charged && wind<demand then Battchg=wind-demand
• If battery is empty && wind>demand then Battchg=wind-demand
• If battery is empty && wind<demand then import=demand-wind

I've been trying to implement this without any success for the last week. I'm relatively new to Matlab so apologies for the stupidity of this. What I've done so far is this

range=2000;  %specify amount of data steps
D=importdata('data1.mat');  %import demand data
demand=D(1:range)'; % create demand vector
time=0:1:(range-1); % simple time vector
W=xlsread('wind_data');  % read wind data from excel
wind=W(1:range)';  %create wind vector
rho=1.2754; %assumed at 10degrees
R=2; %wind turbine radius
wind_p=(1/2*(pi*R^2)*(wind.^3))';   %simple windo power no efficiency etc.
subplot(2,1,1);
plot(time,demand,time,(wind_p/1000));   %wind power from kw to kwh
ax=gca;                                               %add axis 16/11/2016
ax.YLabel.String = 'demand/wind power in kw';
ax.YLabel.FontSize = 12;
ax.XLabel.String = 'time (s)';
ax.XLabel.FontSize = 12;
cap=10;
chg=cumsum(wind_p/1000);   %cumulative battery charge assuming 100% efficiency
chg(chg>cap)=cap;   %battery can only hold value of cap
chg_per=(chg/cap)*100;  %percentage charge
subplot(2,1,2);
plot(time,chg_per);  % plotting battery  charge
ax=gca;                                                   
ax.YLabel.String = 'battery charge percentage';
ax.YLabel.FontSize = 12;
ax.XLabel.String = 'time (s)';
ax.XLabel.FontSize = 12;
import=(0:range-1)';   %creating vector for if statement
export=(0:range-1)';   %creating vector for if statement
diff=wind_p>demand;

if chg_per==100 & diff==1
    export=wind_p-demand;
    if chg_per==100 & wind<demand
        chg=wind-demand;        
elseif chg_per~=100 & diff==0
    import=wind_p-demand;
    end
end

[ILONA DOMAGALA]

Did exactly as instructed by Geoff Hayes still not getting proper battery charge/discharge Can anyone help please ?

if true
  eps=0.05;
if abs(chg_per-100) < eps  % only true if fully charged to 99.5%+ therefore full
  if wind_p > demand   % only true if wind > demand
      export=wind_p-demand   % exporting only if 100% charged
  else
      chg=wind_p-demand   %  always charging
  end
elseif abs(chg_per) < eps  % only true if charge is less than 0.05%
  if wind_p < demand    %  only true if demand > wind
      import=demand-wind_p   % importing only if 0% charged
  else
      chg=wind_p-demand   % discharging if battery is not less than 0.05% and demand > wind
  end
end
end

Answer 1

[Geoff Hayes]

Ilona - diff is a built-in MATLAB function, so I would avoid using it as a name for a variable. I don't understand the first if statement: If battery is fully charged && windpower>demand then Charge battery until is full. If the battery is fully charged, why would you charge the battery until full?

Regardless, your if statements would look something like this

 if abs(chg_per-100) < eps 
    if wind_p > demand
        % do something
    else
        % do something else
    end
 elseif abs(chg_per) < eps
    if wind_p > demand
        % do something
    else
        % do something else
    end
 end

The above assumes that chg_per is the battery charge. Note that since this variable is a double, we cannot compare it to 100 (this sort of comparison is only valid for integers) and so we use a check to see if it is very close to 100 where eps is a small number. Likewise, if chg_per is less than eps, we assume that the battery is empty.

[ILONA DOMAGALA]

I did exactly as instructed and still do not get the proper charge/discharge behaviour, am I missing something ? Please kindly have a quick look Thanks in advance

if true
eps=0.05;
if abs(chg_per-100) < eps  % only true if fully charged to 99.5%+ therefore full
  if wind_p > demand   % only true if wind > demand
      export=wind_p-demand   % exporting only if 100% charged
  else
      chg=wind_p-demand   %  always charging
  end
elseif abs(chg_per) < eps  % only true if charge is less than 0.05%
  if wind_p < demand    %  only true if demand > wind
      import=demand-wind_p   % importing only if 0% charged
  else
      chg=wind_p-demand   % discharging if battery is not less than 0.05% and demand > wind
  end
end

[Geoff Hayes]

Ilona - while the above code looks fine, without access to your data file (and so values for your variables) I cannot tell why the code is not working. I suggest that you use the MATLAB debugger to step through the code and see what is happening. Details for debugging can be found at debugging process and features.