Regenerative Braking, part 2

EV-205b

This course is presented as part of Evannex Universitya free, open learning environment that presents concise, video-based mini-courses for those who have interest in electric vehicles (EVs)

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 brakingin an EV KE is recaptured by converting the EV electric motor into a generatorthe torque (rotational energy) of the wheels drives the generator which produces electric current

Before we proceed with part 2 of this EVI mini-course, lets 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

Regenerative BrakingNew tech, right?Nope. Original patent in 1908!Regenerative braking takes advantage of the duality of the electric motorThe core elements:an energy sourcemotor/generatorcontrol system

While the accelerator is pressed BatteryMotorGeneratorControlElectronics

Its 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 lets look at what happens when the driver takes his foot off the accelerator.

-Study Guide

http://www.slideshare.net/divyanshu2k/regenerative-braking-system-32602945http://www.jameshalderman.com/links/book_adv_elec_electronics_1/ci/handouts/adv_e&e_chap_27_images.pdfhttp://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking.htm

Regenerative BrakingControl electronics sense that the accelerator has been releasedelectric power to the motor is cutrotational energy from the wheels becomes input to drive the motor, transforming it into a generatorcontrol electronics coordinate all of this

When the accelerator is released

BatteryControlElectronicsMotorGenerator

>> 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 linethe 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 systemhttp://www.faqs.org/patents/app/20120138395

Control Electronicsmonitors the rotational speed of the wheelsdetermines how much torque is available to be converted into electrical energyprovides rotational energy as input to the electric motor, transforming it into a generatorconditions the electric energy from generator and effects transfer to the batterymonitors other conditions

Source: http://www.electronicspoint.com/threads/regenerative-braking.244550/, regenerative controller schematic for a scooter

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 functionhttp://www.cecube.co.uk/papers/regeneration_2.htm

Additional FactsAre 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 goHow 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 speednot able to accommodate emergency stopping

>> 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

Regen in PHEVs

Source: http://www.cvel.clemson.edu/auto/systems/regenerative_braking.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.

RegenDriving Characteristicsit is a new and slightly odd experienceremove your foot from the acceleratorthe car slows without touching the brakefeels slightly like downshifting a convention manual transmission, but much smootheryou can come to an almost complete stop without ever touching the brakes

The first time your drive an EV with regen, youll 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

RegenDriving Characteristicsafter some practice, you unconsciously begin to judge stopping distance and remove your foot accordinglybrake light will go on according to an algorithm defined by the EV manufacturerthe EV comes to a near stop (2 - 3 mph) without touching the brake pedalobvious benefits for brake wear

>> 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.

SummaryKinetic 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 experiencesregen allows an EV to capture kinetic energy and transform it to electrical energy to recharge the battery regen represents a different driving experience

Lets 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, youll wont how you ever drove without it. aIts really a very cool feature that distinguishes EVs from ICE vehicles.

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

OlharesRouletBeats d'Amor, track 12014-05-18T14:02:41118051.055OlharesRouletBeats d'Amor, track 12014-05-18T14:02:41118051.055