Week-11 Challenge: Braking
- For a defined driving cycle, calculate the energy required for braking.
The drive cycle is created using the user input values of time and velocity which is entered in the excel sheet and the data is imported to matlab.
Energy required for both accleration and deceleration is same. It is in the form of kinetic energy stored .
KE=1/2 mv^2
Where m-mass of the vehicle, v-velocity of the vehicle.
And the velocity is given by two components -initial velocity Vi and final velocity Vf.
The total amount of energy required for braking is found to be 302kJ.
Link: https://drive.google.com/file/d/101tur6pxbCfFhvy-5L9671dyXAdPMvex/view?usp=sharing
2. Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?
The braking torque in an electric motor differs in starting conditions low speed and high-speed conditions. There are different factors affecting the motor. The rate of discharge capacity of the battery is higher than charging rate then the discharge can be twice as that of the charging rate. Power converters indirectly affects the motor. The power converter circuit is bidirectional and 3 phase inverters which convert regenerating braking energy back to DC current for the battery and this reduces the efficiency of the power converter. At low speeds, regenerative braking is very high and as speed increases, the regenerative braking reduces as the effectiveness of inverter plays an important role and the overall efficiency reduces resulting in reduced braking torque.
Hence, for the effective braking at high speeds, the combination of Hydraulic(mechanical) brake and regenerative(electrical) braking. There are different approaches to coordinating between the hydraulic and regenerative braking. One of the brake control strategies involves series connection where the both brakes are connected together which implies both the brakes are used and the next one in the parallel connection where other two brakes are operated individually without relying on one another depending on the braking requirements,
While coordinating the use of two brakes electromagnetic torque oscillation at low speed, the braking torque higher than the power absorption capacity of the electric source. Below the certain speed limit, the KE is also very low, there is no regenerative braking and this situation requires a use of mechanical brake using brake pedal that required braking torque is obtained. It results in braking that complies with drivers' input on the brake pedal.
This hydraulic (mechanical)system can provide large and stable torque and the torque response of motor braking system is accurate and fast and it reduces the fluctuation of the vehicle. The braking stability of EVs with an electro-hydraulic braking system can be influenced by braking force distribution between hydraulic and regenerative force braking. When the regenerative braking capacity is less than the actual braking required, mechanical brakes are applied at most times.
Two main control strategies are series and parallel. It is chosen based on driver comfort and efficiency.
The braking is applied one after the other. One after other regenerative and hydraulic braking is applied.In the parallel operation both the brakes are applied in parallel. Simultaneous operation is possible.
3.Make a MATLAB program that plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots
The contour plot is used for representing a 3-dimensional surface by plotting constant z slices into a 2-dimensional format and the value of z comes from the line connecting the corresponding (x,y) coordinates.
A Matlab program is used to plot the motor, speed, torque, and efficiency values which determines the performance of the motor.
link:https://drive.google.com/file/d/1jIElaqbvPP70ME_z-fx6sNyHPganphTk/view?usp=sharing