Working around looping problem

Hi,

So I am modelling the acceleration and coasting speed of an electric car over time. I have managed to model the max acceleration of the car. What I am trying to do is, once it reaches this max speed (8 m/s) the motor should switch off until it reaches 4 m/s where it will accelerate again before this process repeats. Here's what I currently have:

 for n=1:500

%Motor Current I(n)=(Ebat-(((vel(n)*G)/WheelRadius)*Ke))/R;

%Motor Torque
T(n)=Kt*I(n);

%Motor RPM
RPM(n)=(vel(n)*G)/(WheelRadius)*60/(2*3.14);

%Car velocity during acceleration, taking into account rolling resistance
%and aerodynamic drag. Once these are equal to the max motor speed, car
%will travel at fixed velocity
vel(n+1)=(vel(n)+dT*((G/WheelRadius)*T(n)-CoeffRoll*mass*g-DensityAir*FrontalArea*CoeffDrag*(vel(n))^2)/(mass));

PowerIn(n)=(NoLoadCurrent+I(n))*Ebat;
PowerOut(n)=T(n)*(G*vel(n)/WheelRadius);
Efficiency(n)=PowerOut(n)/PowerIn(n);

d(n+1)=d(n) + (50/501)*vel(n); % Compute distance travelled.
end;

Now, if I put an if statement in here telling the motor to switch off once it reaches max speed, it will just decelerate for one iteration before accelerating back to maximum speed again over and over.

Does any one have any idea where to go with this?

Thanks!!

Answer 1

[Doug Hull]

Use Simulink for time based simulation. This is simple enough though that you can do this in MATLAB.

Put a flag that gets toggled at the top speed but does not toggle back until the bottom speed.

Doug

[Mark Kelly]

Ok, how would I go about that? I know what you mean but am unsure how to implement it. Sorry for the vagueness! Thanks

[AJ von Alt]

I think Doug had something like this in mind:

flagMotorOn = true;
minVelocity = 11;
maxVelocity = 22;

    ...

if( vel(n) >= maxVelocity )
    flagMotorOn = false;
elseif( vel(n) <= minVelocity )
    flagMotorOn = true;
end

if( flagMotorOn )
    % update calculations with motor turned on
else
    % update calculations with motor turn off
end

[Mark Kelly]

That makes sense. I understand now! Thanks very much to you both.