Week-11 Challenge: Braking

1.For a defined driving cycle, calculate the energy required for braking?

In an electric vehicle energy used for the both the accleration & deaclerations, so when we need to apply brake while driving the EV cars, we cannot stop the motor suddenly needed some energy to stop the vehicle moving interia.so this energy is required stop the cars or deaccelerate it on stipilated time.

UDDS drive cycle:

Braking energy:

To reduce the speed from the speed of 80kmph to 20kmph in 20s:97.222KJ

To reduce the speed from the speed of 80kmph to 40kmph in 20s:43.21KJ

Calculation excel attached with UDDS cycle

2.Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?

Regenerative braking is an important tool in the electrical vehicle arsenal & implemented correctly can add more than 25% electric range to a vehcile.important consideration for regenerative braking is how much electrical energy can be recovered to battery or how quickly the battry can accept charge .well there is limitation of charging energy after this limit battery temperature & voltage throws up their own limitations so it unlikely to get same energy which is consumed.

Electric motor genrates torque based on rotation velocity as th evelocity increases from zero there are three phases -1.sharp rise flattening & decreaes with increase speed where the motor has reached its power limit.it also negative velocity,when brakes pedal is pressed regenrative brake torque buuld steadily & after certain time at particular speed peak torque is reached due to recharging limit of battery & motor power limitation.As speed approaches to zero the regenerative braking dropsall together & friction brakes come to play.

Co-ordination of mechanical & electric brake

Blending of electric & mechanical brake is essential for smooth brake experience at low deceleration levels,requested braking can be achived with electrical torque at higher deceleration levels the blending work load increases & sharp changes in electrical torque can cause the friction some difficulty in keeping up,so for desire brekaing proper coordination of mechanical & electricalbrake is very important,so they can be connected in series & parallel connections most the hybrid vehicles use an electro hydraulic system to achieve required breaking ,applied force on brakr is read by pressure sensors which transmits signal to break control unit.control unit calculates desires friction to regen,ratio control unit genrates return signal and breaks performs their individusl task.

3.Make a MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots

>> %motor speed, torque and efficiency values
v = linspace(0,1000);
t = linspace(0,250);
%constants
ki=0.008; %iron loss constant
kc=0.2;  %copper loss constant
kw=0.00001;  %windage loss constant
cl=20; %constant loss
%make meshgrid
[V,T]=meshgrid(v,t);
%loss calculations
copper_loss=kc*(T.^2);
iron_loss=ki*V;
windage_loss=kw*(V.^3);
total_loss=cl+copper_loss+iron_loss+windage_loss;
%power output
p_out=T.*V;
%power input
p_in=p_out+total_loss;
%efficiency
>> eff=p_out./p_in;
>> %efficicency values
>> n=linspace(0.70,0.95,10);
>> %plot contour
%box off
%grid off
>> contour(V,T,eff,n);
>> xlabel('Torque')
>> ylabel('speed')
>> %power
>> p=[8000,10000,15000];
>> hold on
>> contour(V,T,p_out,p);

output

on observing the loops efficiency remains same like innermost loop for different values of torque & speed ,there are hyperbolic lines reperensting 8kw,10kw,15kw powers