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Cody Hyman HC399. Regenerative Braking. 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

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what is regenerative braking
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
Regen Braking Principles in Electric Transportation
  • EVs use their drive motors to convert kinetic energy into electromagnetic energy
    • Motors 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 works part 1 the mechanical aspect
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 EV
    • Instead 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
Diagram of a Regen Braking System

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

part 2 brake control circuitry
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
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
Mechanical Methods
  • Hydraulic Regenerative Braking
    • Slows 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

A 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 vehicles
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
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
DC Railway Regeneration Estimates

% Energy recapture figures for DC Catenary Locomotives

Source: Institute for Futures Studies and Technology Assessment

regen braking in road vehicles
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
  • Priusregen efficiency ≈ 30%
road vehicle efficiency data
Road Vehicle Efficiency Data

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

cars with regenerative braking
Cars with Regenerative Braking
  • Toyota Prius
  • Honda Insight
  • Ford Escape Hybrid
  • Tesla Roadster
  • Chevy Volt
    • It actually does have regen braking*

Toyota Prius

Tesla Roadster

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

regenerative braking is not all that new
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
Benefits of Regen Braking
  • Increase of overall energy efficiency of a vehicle
    • Increases vehicle range
    • Cuts down on pollution related to electricity generation
  • Increases the lifespan of friction braking systems
    • Less use of traditional mechanical brakes leads to less wear over time
the downsides
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 necessary
    • Safety
    • Motor braking power decreases as the kinetic energy of the vehicle decreases
conclusion
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
sources
Sources
  • http://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking.htm
  • http://www.hybridcars.com/components/regenerative-braking.html
  • http://www.hybridcars.com/related-technologies/hydraulic-hybrids.html
  • http://www.railway-technical.com/brake1.shtml
  • http://www.shorpy.com/node/5734
  • http://www.railwaygazette.com/news/single-view/view//regenerative-braking-boosts-green-credentials.html
  • http://www.railway-energy.org/static/Regenerative_braking_in_DC_systems_103.php
  • http://privatenrg.com/
  • http://cleantech.com/news/4201/delhi-metro-earns-carbon-credits-re