Electric Vehicle University - 205b REGENERATIVE BRAKING
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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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Electric Vehicle University - 205b REGENERATIVE BRAKING
- 1. 1
- 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. 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. 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. 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. 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. 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. Regen in PHEVs 8 Source: http://www.cvel.clemson.edu/auto/systems/regenerative_braking.html
- 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. 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. 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 … 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
Notes de l'éditeur
- Before we proceed with part 2 of this EVI mini-course, let’s take a quick look back at what we covered in part 1. >> 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 electric motor into a generator >> the torque or rotational energy of the wheels drives the generator which produces electric current that recharges the EV battery
- It’s now time to examine the regenerative braking system and its major components. >> New tech, right? >> Nope. Original patent by C.J Paulson in 1908! >> As we discussed in part 1, regenerative braking takes advantage of the “duality” of the electric motor >> The core components of a regenerative braking system are the same components you learned about in earlier EVU mini-courses: >> an energy source, which in the case of EVs is the battery >> a motor/generator >> and a control system that provides the “intelligence” necessary to effect the energy capture The diagram on the right of your screen depicts the regen system components when they are passive, that is, when the accelerator is depressed and the car is moving forward. The battery passes power to the motor which transforms the power into rotational energy that drives the wheels. Control electronics coordinates all of this. Now let’s look at what happens when the driver takes his foot off the accelerator. ————————————- Study Guide http://www.slideshare.net/divyanshu2k/regenerative-braking-system-32602945 http://www.jameshalderman.com/links/book_adv_elec_electronics_1/ci/handouts/adv_e&e_chap_27_images.pdf http://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking.htm
- >> 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 Bottom line—the flow of energy from the battery to the wheels is reversed during regen, as depicted in the diagram. The system components remain the same, but the flow of energy changes direction. ————- for highly technical students, a patent application for the regen control system http://www.faqs.org/patents/app/20120138395
- The control electronics for regenerative braking is a combination of hardware and software that: >> 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 (e.g., state of charge of the battery) A more detailed discussion of the technology that allows the controller to do its work — involving images like the one shown on the right of your screen —is beyond the scope of this EVU mini-course. Those students who would like to delve further should examine study guide materials for more detailed information. —————————- Energy loss function http://www.cecube.co.uk/papers/regeneration_2.htm
- >> Are there situations 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 generative braking controller monitors the battery charge and will only invoke regen if capacity exists for the re-charge. >> Can the driver control the amount of regen? >> In some EVs, yes. For example, in the Tesla Model S, regen can be set to either “standard” or “Low.” On the “Low” setting, region is less evident to the driver >> Are there Limitations: >> regen less efficient at very low speed, and >> although it serves to reduce speed nicely, regen is no substitute for conventional brakes for emergency stopping ————————————————- A highly technical discussion of regen (engineers only): http://www.controleng.com/single-article/energy-efficiency-regenerative-braking/6ff87f94ef12313dc983ac33fd29a7ba.html
- The diagram shown on your screen is representative of a typical PHEV regenerative braking arrangement. During acceleration or steady state driving, an ICE motor and/or an electric motor — depending on the PHEV architecture — drives the wheels and propels the vehicle forward. At slow speeds, the PHEV may be in battery-depleting mode, and the ICE will be inoperative. During braking, the ICE is disengaged, and the rotational energy of the wheels becomes input to the electric motor, transforming it into generator, that passes electricity back to the PHEV battery.
- The first time your drive an EV with regen, you’ll encounter >> a new and slightly odd experience >> when you remove your foot from the accelerator >> the car slows perceptively without touching the brake >> it feels slightly like downshifting a convention manual transmission, but much smoother >> you can come to an almost complete stop without ever touching the brakes
- >> after some practice, you unconsciously begin to judge stopping distance and remove your foot from the accelerator accordingly, allowing regen to do all of the braking work >> your brake lights will come on during regen according to an algorithm defined by the EV manufacturer >> in some cases brake lights are triggered by the number of kWs that are generated as regen occurs. If kWs generated are below a certain number, for example, applying regen at low speed, the brake lights do not come on. >> the EV comes to a near stop (2 - 3 mph) without touching the brake pedal >> because you can now drive without using your brakes, in many instances, brake wear is dramatically reduced.
- Let’s summarize: >> Kinetic energy 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, and this provides the basis for regenerative braking >> regen allows an EV to capture kinetic energy and transform it to electrical energy to recharge the battery >> regen represents a different driving experience, but one that you adapt to very quickly. Within weeks, you’ll won’t how you ever drove without it. a It’s really a very cool feature that distinguishes EVs from ICE vehicles.