Week-11 Challenge: Braking

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

Solution:- During Braking of a Vehicle, the Kinetic Energy possessed by the vehicle gets dissipated in the form of Heat. The total Kinetic energy lost can be calculated as follows

`K.E = ½ * M * DeltaV`

Where,

M = Total mass of the vehicle

`DeltaV` = change in velocity

Below is the Image of the Drive cycle

Matlab program for calculating Braking Energy

Graph of Braking Energy vs Time

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

Solution:- Since from the Torque-Speed characteristics graph we know that at a particular critical speed the Characteristic line takes a curve. Meaning at higher speeds the Torque produced by the motor decreases. This is the main reason why electric motors can’t develop braking torque at higher speeds.

Electrical and Mechanical brakes combined

When a vehicle moves it possess some kinetic energy. While applying only mechanical brake this kinetic energy gets converted into heat and the vehicle gets retarded. To make use of this energy various braking technology is used, among them one is ‘Regenerative Braking’. In this type of braking, the moment the driver removes the pressure on the acceleration pedal the vehicle gets into regenerative mode automatically. In this mode the motor acts as a generator, converting the momentum energy of the vehicle into electrical energy. This happens when the driver of the vehicle wants the vehicle to retard slowly. If there is a sudden retardation then the generator experiences a surge which may get transferred to the battery causing it to get damage. In such case the circuit is cut-off and the mechanical brakes comes into action.

These two types of braking strategies are used in an EV

Series – Both the brakes i.e the Regenerative braking and the mechanical Brakes are applied one after the another

Parallel – Both the Brakes are applied at the same time

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

Solution:- The types of losses that occur in a Motor are as follows

Copper losses = `k_c * T^2`

Iron losses =`k_i * omega`

Windage losses = `k_w * omega^3`

Conduction losses = Assumed to be a constant value of 15

Where,

`k_c` = copper loss coefficient

`k_i`= iron loss coefficient

`k_w`= windage loss coefficient

Below is the matlab code for plotting contour