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Electric Vehicle University - 205b 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 - 205b REGENERATIVE BRAKING

  1. 1. 1
  2. 2. 2 Regenerative Braking, part 2 EV-205b 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. A quick look back … Kinetic energy (KE) is lost when a car decelerates due to braking in conventional ICE cars, KE is lost as heat during braking in an EV KE is recaptured by converting the EV electric motor into a generator the torque (rotational energy) of the wheels drives the generator which produces electric current 3
  4. 4. Regenerative Braking  New tech, right?  Nope. Original patent in 1908!  Regenerative braking takes advantage of the “duality” of the electric motor  The core elements:  an energy source  motor/generator  control system While the accelerator is pressed … Battery Motor Generator Control Electronics
  5. 5. Regenerative Braking  Control electronics sense that the accelerator has been released  electric power to the motor is cut  rotational energy from the wheels becomes input to drive the motor, transforming it into a generator  control electronics coordinate all of this When the accelerator is released … Battery Control Electronics Motor Generator
  6. 6. Control Electronics monitors the rotational speed of the wheels determines how much torque is available to be converted into electrical energy provides rotational energy as input to the electric motor, transforming it into a generator conditions the electric energy from generator and effects transfer to the battery monitors other conditions 6 Source: http://www.electronicspoint.com/threads/regenerativ e-braking.244550/, regenerative controller schematic for a scooter
  7. 7. Additional Facts Are there situation when regen is inoperative? Yes. If the battery is full (at capacity) regen is disabled because there is no place for the electricity to go How does this happen? The braking control monitors the battery charge and will only invoke region if capacity exists for the re-charge. Can the driver control the amount of regen? In some EVs, yes. Limitations: less efficient at very low speed not able to accommodate emergency stopping 7
  8. 8. Regen in PHEVs 8 Source: http://www.cvel.clemson.edu/auto/systems/regenerative_braking.html
  9. 9. Regen—Driving Characteristics  it is a new and slightly odd experience  remove your foot from the accelerator  the car slows without touching the brake  feels slightly like downshifting a convention manual transmission, but much smoother  you can come to an almost complete stop without ever touching the brakes
  10. 10. Regen—Driving Characteristics  after some practice, you unconsciously begin to judge stopping distance and remove your foot accordingly  brake light will go on according to an algorithm defined by the EV manufacturer  the EV comes to a near stop (2 - 3 mph) without touching the brake pedal  obvious benefits for brake wear
  11. 11. Summary Kinetic energy (KE) is lost as heat when a conventional vehicle decelerates due to braking an electric motor can be either a motor or a generator, depending on the type of “input” it experiences regen allows an EV to capture kinetic energy and transform it to electrical energy to recharge the battery regen represents a different driving experience
  12. 12. 12 … 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

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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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