Week-11 Challenge: Braking
- For a defined driving cycle, calculate the energy required for braking.
EXPLANATION:
We require some amount of power for the Acceleration and Braking of the Vehicle. Here we consider, FTP75 drive cycle.
Work done=kinetic energy =0.5m*v^2
For Calculating the energy E=0.5*m*v^2
Where mass (m)=2000 kg,
Velocity(V)= Vi+Vf ,
vi=initial velocity, vf= final velocity
In our Case vf=100 and vi=0 , t=10sec
E=(0.5*2000*(100*0.277)^2)
E=767,290
power required(p)=E/t
p=767,290/10
p=76.72Kw
p=76.72/3600=0.021Kwhr is the power required for braking for 10sec
For power required to calculate braking for 1 sec:
P=E/t
p=767290/1
p=0.21kwhr is the power required for braking for 1 sec.
2.Why electric motor can’t develop braking torque at a high speed similar to starting? How electric and mechanical brakes are coordinated?
SOLUTION:
Braking is the important thing as equal to acceleration in an electric vehicle application. When we consider electric motor for EV, the motor inherently applies brakes and the propulsion source itself provides the braking power.
Let us consider two scenarios:
case 1: Electric motor took 10 sec to reach 100 kmph from 0 kmph:
In this case, the motor will works in a constant Torque region because when the motor starts from zero it will produce constant TORQUE. In the constant Torque region, there will possible for higher acceleration at low speed so the motor torque is high. At this stage, both torque and speed might be positive. so power is also positive.
Case 2: Electric motor took 10 sec to reach 100kmph to 0 kmph:
when it comes to braking the torque is negative and the speed will be positive therefore it is in the second quadrant so the power is also Negative. so peak acceleration torque and peak deceleration torque are not equal in an electric motor because at high speed the value of torque is also lower. so the braking torque of an EV motor is not as high as acceleration torque because regenerative braking is not as effective. so, we cannot get all power back to the battery while in regenerative braking because deceleration torque is less compared to acceleration torque.
How electric and mechanical brakes are coordinated?
This is because brake forces are distributed keeping safety in consideration here two axles of the vehicle where brake force is distributed is not equally but almost the same. When the vehicle is running at low speed the electric brakes can be applied but when the vehicle comes to zero speed in less time otherwise if only electric brakes the time is taken for the vehicle to come to rest is large.
The factors decide the type of braking needed for the vehicle at a particular instant of time based on the electric and mechanical brakes that are coordinated.
1) moment of inertia of the vehicle
2) vehicle speed
3) kinetic energy stored in vehicles.
4) time required for braking
5)forces acting on vehicles.
6) mechanical losses like friction and windage losses.
3) Make a MATLAB program that plots the contour of given motor speed, torque, and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.
inner yellow indicates the higher efficiency compare to outer one. As the torque increase efficiency value decrease. for low speed and torque motor efficiency is very high.