Week-11 Challenge: Braking
1) The braking energy is calculated as ,
E = 1/2 * m* v^2 .
where v = vi-vf
vi = initial speed at which the vehicle is running .
vf = speed at which the vehicle slows down after braking .
For the defined driving cycle ,
| Time (sec) | Speed (kmph) |
| 0 | 0 |
| 1 | 3 |
| 2 | 6 |
| 3 | 9 |
| 4 | 12 |
| 5 | 15 |
| 6 | 18 |
| 7 | 25 |
| 8 | 35 |
| 9 | 50 |
| 10 | 55 |
| 11 | 60 |
| 12 | 50 |
| 13 | 40 |
| 14 | 40 |
| 15 | 41 |
| 16 | 42 |
| 17 | 43 |
| 18 | 44 |
| 19 | 45 |
| 20 | 46 |
| 21 | 47 |
| 22 | 48 |
| 23 | 49 |
| 24 | 50 |
| 25 | 40 |
| 26 | 35 |
| 27 | 30 |
| 28 | 35 |
| 29 | 36 |
| 30 | 37 |
| 31 | 40 |
| 32 | 43 |
| 33 | 47 |
| 34 | 55 |
| 35 | 60 |
| 36 | 63 |
| 37 | 66 |
| 38 | 69 |
| 39 | 70 |
| 40 | 71 |
| 41 | 72 |
| 42 | 73 |
| 43 | 75 |
| 44 | 77 |
| 45 | 78 |
| 46 | 80 |
| 47 | 80 |
| 48 | 79 |
| 49 | 75 |
| 50 | 70 |
| 51 | 65 |
| 52 | 60 |
| 53 | 55 |
| 54 | 50 |
| 55 | 45 |
| 56 | 40 |
| 57 | 30 |
| 58 | 20 |
| 59 | 35 |
| 60 | 50 |
considering the mass of vehicle 1000 kg , the braking enegry is calculated as ,
E = 1/2 * 1000 * ((60-50)*.278)^2
E = 3864.2 Joules .
2a) In EV application there is motor-generator and a battery pack to supply power , as the electric current travels through the motor within a magnetic field , it generates a force . The more current is applied more the motor will rotate .
For regenerative braking a motor will act as a generator i.e. the direction of current is reversed , the electric motor will rather than taking in the current to rotate the armature , the armature is rotate through the field by the deceleration of the vehicle . The electricity produces is used to recharge the battery and the motor can switch between powering the car and regenrating electricity as fast as the driver can accelerate and lift off .
An electric motor can generate high torque during starting but cannot produce high braking torque during braking due to inertia of vehicle . One way to increase the braking torque is by using the regenrative braking.
2b) The mechanical and electrical brakes are cordinated in two types ,
- Series Braking
- Parallel Braking
In series braking first we use regenrative braking and when we require more braking power we use mechanical brakes .
In parallel braking regenerative and mechanical braking is used simultaneously . The energy loss in parallel braking is more than in series braking .
3) Matlab programm for motor speed , torque and efficiency -
Contour -
We can see that maximum efficiency is 95.45% at speed = 151.51 rad/s and torque = 21.21 N-m .
As the speed increases the efficiencies of the motor will be reduced .