Cody Hyman HC399

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

Regen Braking Principles in Electric TransportationEVs 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 AspectVehicle has forward momentumThe 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 EVThe rotors experience opposing torque as current is induced in the motor coilsThis opposing torque slows the vehicleThe generated electrical energy is stored

Diagram of a Regen Braking Systemhttp://static.howstuffworks.com/gif/regenerative-brake-diagram.jpg

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

Part 2: Brake Control CircuitryComplex electronic circuits that handle braking functions Coordinates motor and friction brakes under a wide range of situationsThe controller will take the following parameters into account and determines how the vehicle will brakeSpeed of vehicle Driver input (pedals)Storage medium state-of-charge

Routes and regulates generated powerDepending 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 EnergyRecharging vehicle battery packsState of charge influences how much of the generated current can be safely storedUbiquitous method for hybrid carsCharging an array of capacitors/super-capacitorsPro: Very high charge/discharge rate (high power density)Con: Much lower energy density than batteriesAllows for regen braking if batteries are at a high state of chargeImplemented on some busesNon-electrical methodsFluid compression Flywheels

Mechanical Methods Hydraulic Regenerative BrakingSlows the vehicle by compressing gas and storing it in an accumulatorPressure is used to assist the engine upon forward accelerationPotentially more efficient than electric regenerative brake systems

Source: http://www.hybridcars.com/related-technologies/hydraulic-hybrids.htmlA VW Beetle converted to a hydraulic hybrid that claims up to 80% regeneration efficiency

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

Regenerative Braking in Rail VehiclesDynamic Braking has been frequently used in rail vehicles to reduce brake wearDiesel-Electric locomotives require onboard energy storage for regenerationImpracticalSome electric rail/overhead line locomotives with regenerative braking can send power back through supply linePower can be received by other trains connected to the line or sent back to the grid

Differences Between AC and DC Rail LinesAC LocomotivesCan feed power back into the grid without the need for large power invertersThe New Delhi Metro, after implementing regenerative capabilities, cut down its power consumption by 30%, a total savings of 112MWh between 2004-2007Other AC traction lines in the UK and NZ have achieved improvements of 15-17%

DC LocomotivesCannot easily feed power back to external networks but it can power other trains on the same lineEfficiency depends on the number of nearby locomotives that can receive power from regeneration

DC Railway Regeneration Estimates% Energy recapture figures for DC Catenary LocomotivesSource: Institute for Futures Studies and Technology Assessment

Source: Institute for Futures Studies and Technology Assessment

Regen Braking in Road VehiclesRoad vehicles require onboard energy storage as well as relatively quick braking compared to rail vehiclesRegen braking improves the efficiency in stop and go city traffic more than high speed travelEfficiency gains vary greatly from vehicle to vehicle and under the driving conditionsPrius regen efficiency 30%

Road Vehicle Efficiency DataSource: http://www.privatenrg.com/

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

Cars with Regenerative BrakingToyota PriusHonda InsightFord Escape HybridTesla RoadsterChevy VoltIt actually does have regen braking*Toyota PriusTesla Roadsterhttp://www.nytimes.com/2009/11/22/automobiles/autoreviews/22-chevy-volt.html?_r=1&ref=technology

http://www.nytimes.com/2009/11/22/automobiles/autoreviews/22-chevy-volt.html?_r=1&ref=technology

Regenerative Braking is not All That NewThe electric vehicle in this 1906 had regenerative braking capabilities

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

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

Benefits of Regen BrakingIncrease of overall energy efficiency of a vehicleIncreases vehicle rangeCuts down on pollution related to electricity generationIncreases the lifespan of friction braking systemsLess use of traditional mechanical brakes leads to less wear over time

The DownsidesAdded complexity of brake control systemOnly works for wheels connected to motors Most vehicle operation is done in 2WDFriction brakes are still necessarySafetyMotor braking power decreases as the kinetic energy of the vehicle decreases

ConclusionRegenerative braking is an effective method of improving vehicle efficiency and longevityIs already in use in many EVsThe technology to do it exists and is often well worth itMostly dependent on the wider adoption of EVs or further development of hydraulic regeneration systems

Sourceshttp://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking.htmhttp://www.hybridcars.com/components/regenerative-braking.htmlhttp://www.hybridcars.com/related-technologies/hydraulic-hybrids.htmlhttp://www.railway-technical.com/brake1.shtmlhttp://www.shorpy.com/node/5734http://www.railwaygazette.com/news/single-view/view//regenerative-braking-boosts-green-credentials.htmlhttp://www.railway-energy.org/static/Regenerative_braking_in_DC_systems_103.phphttp://privatenrg.com/http://cleantech.com/news/4201/delhi-metro-earns-carbon-credits-re

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