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Cody Hyman HC399

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Cody HymanHC399

What is Regenerative Braking?

Conventional braking systems convert kinetic energy into heat, usually via friction. This wastes a great deal of energy!

Regenerative braking systems reclaim and storing the kinetic energy in a reusable manner

Many modern electric drive vehicles including electric locomotives and HEVs have regenerative braking systems

Regen Braking Principles in Electric Transportation EVs use their drive motors to convert

kinetic energy into electromagnetic energyMotors and generators operate under the same

principle and can be used interchangeably.The First Law of Thermodynamics dictates that

the EV will slow down as this occurs. The generated electrical energy can be

dissipated through a resistive network (Dynamic Braking) or stored (Regen Braking)

How Regen Braking WorksPart 1: The Mechanical Aspect Vehicle has forward momentum The wheels are coupled to the rotors of

electric traction motors in an EVInstead of a current being applied to the motor

to turn the rotors, the rotors are turned by the wheels of the EV

The rotors experience opposing torque as current is induced in the motor coils

This opposing torque slows the vehicle The generated electrical energy is stored

Diagram of a Regen Braking System

http://static.howstuffworks.com/gif/regenerative-brake-diagram.jpg

Part 2: Brake Control Circuitry Complex electronic circuits that handle

braking functions Coordinates motor and friction brakes under a wide

range of situations The controller will take the following parameters

into account and determines how the vehicle will brake○ Speed of vehicle ○ Driver input (pedals)○ Storage medium state-of-charge

Routes and regulates generated power Depending on the desired output, the brake

controller must be able to supply vehicle batteries or capacitors with the proper polarity, current, and voltage for safe charging (depends on battery state of charge)

Options for storing the Energy Recharging vehicle battery packs

State of charge influences how much of the generated current can be safely stored

Ubiquitous method for hybrid cars Charging an array of capacitors/super-

capacitors Pro: Very high charge/discharge rate (high

power density) Con: Much lower energy density

than batteries Allows for regen braking if batteries are at a

high state of charge Implemented on some buses

Non-electrical methods Fluid compression Flywheels

Mechanical Methods Hydraulic Regenerative

BrakingSlows the vehicle by

compressing gas and storing it in an accumulator

Pressure is used to assist the engine upon forward acceleration

Potentially more efficient than electric regenerative brake systems

Source: http://www.hybridcars.com/related-technologies/hydraulic-hybrids.html

A VW Beetle converted to a hydraulic hybrid that claims up to 80% regeneration efficiency

Regenerative Braking in Rail Vehicles Dynamic Braking has been frequently

used in rail vehicles to reduce brake wear

Diesel-Electric locomotives require onboard energy storage for regeneration Impractical

Some electric rail/overhead line locomotives with regenerative braking can send power back through supply line Power can be received by other trains

connected to the line or sent back to the grid

Differences Between AC and DC Rail Lines AC Locomotives

Can feed power back into the grid without the need for large power inverters

The New Delhi Metro, after implementing regenerative capabilities, cut down its power consumption by 30%, a total savings of 112MWh between 2004-2007

Other AC traction lines in the UK and NZ have achieved improvements of 15-17%

DC Locomotives Cannot easily feed power back to external networks but it

can power other trains on the same line Efficiency depends on the number of nearby locomotives

that can receive power from regeneration

DC Railway Regeneration Estimates

% Energy recapture figures for DC Catenary Locomotives

Source: Institute for Futures Studies and Technology Assessment

Regen Braking in Road Vehicles Road vehicles require onboard energy

storage as well as relatively quick braking compared to rail vehicles

Regen braking improves the efficiency in stop and go city traffic more than high speed travel

Efficiency gains vary greatly from vehicle to vehicle and under the driving conditions

Prius regen efficiency ≈ 30%

Road Vehicle Efficiency Data

Source: http://www.privatenrg.com/

Cars with Regenerative Braking Toyota Prius Honda Insight Ford Escape Hybrid Tesla Roadster Chevy Volt

It actually does have regen braking*

Toyota Prius

Tesla Roadsterhttp://www.nytimes.com/2009/11/22/automobiles/

autoreviews/22-chevy-volt.html?_r=1&ref=technology

Regenerative Braking is not All That New

The electric vehicle in this 1906 had regenerative braking capabilities

Image source: http://www.shorpy.com/node/5734

Benefits of Regen Braking Increase of overall energy efficiency of a

vehicleIncreases vehicle rangeCuts down on pollution related to electricity

generation Increases the lifespan of friction braking

systemsLess use of traditional mechanical brakes

leads to less wear over time

The Downsides Added complexity of brake control

system Only works for wheels connected to

motors Most vehicle operation is done in 2WD

Friction brakes are still necessarySafetyMotor braking power decreases as the

kinetic energy of the vehicle decreases

Conclusion Regenerative braking is an effective

method of improving vehicle efficiency and longevity

Is already in use in many EVs The technology to do it exists and is

often well worth it Mostly dependent on the wider adoption

of EVs or further development of hydraulic regeneration systems

Sources1. http://auto.howstuffworks.com/auto-parts/brakes/brake-types/

regenerative-braking.htm2. http://www.hybridcars.com/components/regenerative-

braking.html3. http://www.hybridcars.com/related-technologies/hydraulic-

hybrids.html4. http://www.railway-technical.com/brake1.shtml5. http://www.shorpy.com/node/57346. http://www.railwaygazette.com/news/single-view/view//

regenerative-braking-boosts-green-credentials.html7. http://www.railway-energy.org/static/

Regenerative_braking_in_DC_systems_103.php8. http://privatenrg.com/9. http://

cleantech.com/news/4201/delhi-metro-earns-carbon-credits-re