Week-11 Challenge: Braking

STUDENT OF EV BATCH 16 ONLINE COURSE

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

The command script foe calculating energy is

1)Script was written in the command window.

2)Excel sheet in the name of drivingcycle has been created with 50 values for time and velocity has been saved in the same folder where the matlab file is stored.

3)The excel file is then imported to matlab.

4)The script is run and value for breaking energy has been found.

The breaking energy is 2000.5kWh.

https://drive.google.com/file/d/1ccmnwkVqj2ugNNsupHWYSfClIVkXE1Xx/view?usp=drivesdk

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

The low breaking torque ar high speed of electric motor can be explained with the help of torque speed characteristics of electric motor.

• From the above characteristics we can see that initially the torque is high and is in the constant torque region.
• When starting the motor the speed will be less and the motor will be having high torque. This region is called constant torque region and this is the reason for high starting torque
• When the speed crosses critical speed the motor will be in constant power region here because of high speed whenever brake is applied the braking torque will be less.
• So the braking torque produced at the end will be less than the starting torque.

Coordination of electrical and mechanical brakes.

There are two braking control strategies.

1)Series: In this we apply mechanical brakes or regenerative braking one after the other. For low speed regenerative braking is used but it may be limited according to the SOC of the battery

2)Parallel: In this both mechanical brakes and regenerative brakes are applied simultaneously.

ELECTRIC DRIVEN INTELLIGENT BRAKE

It is a type of parallel braking.

From the figure below it is evident that friction brake and regenerative braking is done simultaneously at higher speed.

At low speed the motor torque is high so regenerative braking will take place.

Electrical brakes:

• They are applied for functional braking like controlling the speed or bringing the load to standstill.
• Their application will be smooth and comfortable
• For proper braking electrical braking will not be sufficient, it has to be supplemented by mechanical brakes.
• Application of regenerative braking can be done.
• There won't be any wear and tear in electrical braking.

Mechanical brakes:

• The frictional force between the rotating parts and brake drum provides the required brake.
• There will be wear and tear of equipments.
• Heat loss will be high.
• Safety will be there in mechanical brakes unlike electrical brakes which are only for functional braking.

The controller determines the usage of electrical and mechanical braking system. Usually the electrical brakes are used for low speeds.

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.

Matlab code

Result obtained

https://drive.google.com/file/d/1coVEo7RVj9vkqfWk5l5Jz9NEiR_tYUtW/view?usp=drivesdk