Week-11 Challenge: Braking

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

ANS =

-The kinetic energy of vehicle is calculated at each ponit of driving cycle.

- Acceleration values are calculated based on initial and final velocities of vehicle.

- Negative values of acceleration i.e. deceleration indicates the braking is applied to the vehicle.

- Braking energy is the change in kinetic energy during braking action.

- Total braking energy is calculated by summing up change in K.E. during each braking action.

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

ans =

- At low speed, maximum torque is constant. However, at high speed, maximum torque deacreses hyperbolically with its speed. Threfore the mechanical brake torque at given vehicle varies with vehicle speed.

- At high speeds, back emf is so close to Vbus that the application motor torque gets limited. Then the bigger the friction torque and additional load, smaler the acceleration torque becomes.

- Peak acceleration torque and peak decceleration are not equal for electric vehicle motor.

- Acceleration is usually higher, at low speed we get higher torque but high speed the value of the torque gets lower.

- After application of brake motor must produce negativr torque and that vlaue if plotted is not same as acceleration torque at starting. This happens beacause motor is in field wakening region. So we have to compromise on torque.

- Thus electric motor cant develope braking torque at high speed similar to starting.

• The regenerative barking configuration can be broadly classified into series braking and parallel braking:

-Series braking:

In series we apply mechanical brake or regenerative brake.

- Parallel braking:

In parallel braking, both mechanical braking and regenerative braking applied.

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.

ans =

code

output plot: