Regenerative BrakingProject Members:Akhil S (10)Akhil.R (12)Nidheeesh T T (4)

Project Guide:Prof. GaneshAssistant ProfessorDept. of Mechanical Engg.GECBH

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

Regenerative 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 Regenerative 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 Regenerative 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 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

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

Theoretical potential

Potential if additional technologies are used

Potential without additional technology

Main lines 15% 11% 2%

Regional lines 35% 25% 10%

Local lines 45% 32% 16%

Freight lines 20% 14% 3%

Source: Institute for Futures Studies and Technology Assessment

% Energy recapture figures for DC Catenary Locomotives

Regenerative Braking in Road Vehicles

Road vehicles require onboard energy storage as well

as relatively quick braking compared to rail vehicles

Regenerative 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 regenerative 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*

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

Toyota Prius

Tesla Roadster

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 Regenerative 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

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

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-cr

edits-re

Thank You!!!