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Electric Vehicle University - 205a REGENERATIVE BRAKING

THE CENTRAL QUESTION ...
How does the electric motor serve to brake my EV and what are the underlying principles that enable braking to happen?

COURSE ABSTRACT
The use of regenerative braking as a mechanism for capturing and reusing a vehicle’s kinetic energy is presented. Basic kinetic energy concepts are discussed, the characteristics of an electric motor that allows it to become a generator are explored, the system diagram for a regenerative braking system is considered, and driving with regen is examined. To obtain a copy of the EVU study guide for this and other available EVU courses, please complete the form on this page.

Course level: Intermediate

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Electric Vehicle University - 205a REGENERATIVE BRAKING

1. 1. 1
2. 2. 2 Regenerative Braking, part 1 EV-205a This course is presented as part of Evannex University—a free, open learning environment that presents concise, video-based mini-courses for those who have interest in electric vehicles (EVs) …
3. 3. Kinetic energy - 1 From Wikipedia: “the energy it possesses due to its motion” “work required to accelerate an object” “the body maintains it KE unless its speed changes” “”the same amount of work is done …” 3
4. 4. Kinetic energy - 2  Kinetic energy—equation  KE = (Mass x velocity squared)/2  Physics — energy cannot be destroyed  So, when speed (v) changes  KE must be transformed into something else
5. 5. Kinetic energy of a car  A moving car:  has a very large mass  has a velocity  KE is large at high speed  How do we stop a conventional car?  stop providing energy to the motor  depress the brake pedal  Energy is dissipated as heat
6. 6. For ICE vehicles …  As braking occurs, a significant amount of heat is created  There is no easy way to recover this heat energy, and it is lost  For an ICE vehicle  80 percent of the energy input to propel the car forward is lost to heat and other affects as the car is brought back to zero velocity
7. 7. For EVs  Braking can recapture as much as 40 to 50% of the vehicle’s kinetic energy, but NOT if you use the conventional braking paradigm  Instead, control electronics recognizes that:  power to the electric motor has been discontinued  regenerative braking is then initiated
8. 8. The Electric Motor The stator The rotor Current creates a magnetic field AC causes field to vary between N and S The rotor “chases” the magnetic field and rotates 8 Source: Tesla Motors
9. 9. Motor to generator  when an electric motor receives electric energy as input, it converts the energy derived from an electromagnetic field into mechanical energy transmitted by the motor’s rotor  if input to the motor is electrical energy, output will be mechanical rotation  but if the electric input stops and the mechanical rotation derived for the KE is used as ‘input’  the motor becomes a generator and produces electrical energy as output
10. 10. 10 … a free study guide for all EVU mini-courses is available for download from our website … For a complete list of mini- courses and the study guide, visit: www.evannex.com

THE CENTRAL QUESTION ... How does the electric motor serve to brake my EV and what are the underlying principles that enable braking to happen? COURSE ABSTRACT The use of regenerative braking as a mechanism for capturing and reusing a vehicle’s kinetic energy is presented. Basic kinetic energy concepts are discussed, the characteristics of an electric motor that allows it to become a generator are explored, the system diagram for a regenerative braking system is considered, and driving with regen is examined. To obtain a copy of the EVU study guide for this and other available EVU courses, please complete the form on this page. Course level: Intermediate

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