Week-11 Challenge: Braking
- For a defined driving cycle, calculate the energy required for braking
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ENERGY REQUIRED FOR BRAKING BASED ON A DRIVING CYCLE:-
The driving cycle taken into consideration is the UDDS Cycle which stands for Urban Dynamometer Driving Schedule, ALthough the data is taken for a total driving time for 1370s for simplicity sake on 150s of driving time is considred. The speed which is in miles per hour been converted to meters per second.
The driving cycle is given below-
The equation for kinetic energy from braking is given as,
E=1/2m(Vi-Vf)2
Where
m= mass of vehicle in kg
Vi= initial speed of the vehicle in m/s
Vf= Final speed of the vehicle in m/s
From the drive cycle 10 braking points were obtained The mass is set a constant 1500kg. The energy required for braking is given in the table below.
Therefore the total energy required for braking is 16.8 KW
2. Why electric motor can’t develop braking torque at high speed similar to starting?
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Let us consider torque motor characteristics
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From this curve we have two region, constant torque and constant power region.
At the start the motor achieves peak torque till it reaches a certain motor speed range from where it will rapidly drop. The reason due to the drop in torque is due to the motor shaft reaching critical speed and the area where the peak torque is constant is known as the constant torque region of motor. The region where the torque decreases is known as constant power region as the power generated by the motor will be at its peak.
Since the torque produced at the constant power region is very low, it is not possible to develop enough braking torque in this region The braking torque produced increases as teh speed decreases.
How electric and mechanical brakes are coordinated?
In the electric vehicle 2 types of braking system are used electric brake system and mechanical brake system.
Electric Braking System: In electrical braking the winding of the motor is used to produce a braking torque, A braking torque is developed during the braking operation this braking torque opposes the motion of the rotating member of shaft This is acheived bu suitably changing the electrical connections of the motor\
The motor operates on a speed-torque characteristics depending upon the method of braking employed.
Mechanical Braking System: In mechnaical braking frictional force between the rotating parts and the brake drums produces the required braking. To achieve this mechanical equipment such as brake linings and brake drums are required. Whether electrical or mechanical the braking of the drive should stop the motor at the specified point of time and position.
The electrical braking system used EVs and HEVs is regenerative braking This method uses the motor as a generator during braking developing retarding torque which acts on the running motor and halts it.
The knietic energy and potential energy minus the losses of the motor runs at a constant speed, Thus regenerative braking eliminates the tendency of the load to acclerate the motor.
Mehanical braking system used can be either disc or drum brake system, Where in case of a disc brake system driction pads rub against a disc when the brake pedals is applied and the kinetic energy is converted to heat and slows the vehicle down in a drum brake system a set of brake shoes which are the friction materials press against a drum.
Since the braking torque is very less at high speeds mechanical brakes are applied to slow down the vehicle As the motor reaches the constant torque region the regenarative braking system takes effect where the motor acts as a generator and the negative torque produced charges the battey pack
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.
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MATLAB CODE:
Explanation:
In this matlab script we create arrays for the speed and the torque of the motor using linspace command. For the speed consider a range of values from 0 to 2000 radians per second whereas for the torque consider a range of values from 0 to 300 Nm. these arrays are then used to create 2D grid coordinates using the mesh gird command These coordinates will help inthe creation of the contour plot. in order to find the efficency of the motor We need to consider the various losses that occur in the motor's operation These are
Copper loss, Iron loss, Windage loss, Conduction Loss.
OUTPUT:
Conclusion: All the questions solved with results.