regenerative braking - oregon state...
TRANSCRIPT
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%
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