Week-11 Challenge: Braking
Q.
- For a defined driving cycle, calculate the energy required for braking.
Ans:-
we required some amount of power which is used for accelerating the vehicle and also for the braking of the vehicle. Here we consider the drive cycle which is predefined as the FTP75 drive cycle.
Work done=kinetic energy =0.5m*v^2
for calculating the energy the formula is E=0.5*m*v^2
m=mass of vehicle =1000kg
v=velocity of vehicle =vf-vi (here the vehicle is decelerating from 100 to 0 speed)
so, vf=final velocity =100 kmph,
vi=intial velocity =0kmph
t=time required from 100 to 0 speed is =10 sec
power required is p=E/t
p=(0.5*1000*(100*0.277)^2)/(10)
=38.36 kw
Energy is required for braking of the vehicle from 100 to 0 speed 10 sec is
E=0.0106 kwhr
The energy required for braking the vehicle from 100 to 0 speed in 1 sec
E=0.106 kwhr
****************************************************************************************************Q 2.
Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?
Ans:-
Braking is as important as acceleration and braking the vehicle certain amount of energy is required when considering the motor application in an EV vehicle the braking of the electric motor itself is braking the vehicle, and electric braking is where the motor inherently applies braking and the propulsion source itself provides the braking power.
Consider the case where an electric vehicle operated by an electric motor took a sec to reach kmph speed and also took 10 sec to reach 100 to 0 speed. We analyze this case to understand why an electric motor can't develop barking torque at a high speed similar to starting.
Case:1-Electric motor took 10 sec to reach 0 to 100kmph
When the vehicle is starting from zero speed at this stage the torque maintained by an electric motor is almost constant, so at low speed, the characteristics of the motor the torque produced are constant hence the motor-operated in a constant torque region, therefore, the vehicle has higher acceleration power possible al low speed the motor torque is high.
Case_ii) The electric motor took 10 sec to reach 100 to 0kmph
When it comes to the braking part where the torque is negative and the speed is positive therefore the power is negative this is called the second quadrant operation of the motor or forward barking stage. When this stage compared with the first quadrant