Regenerative Braking

Project 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 Works

Part 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

Sources

1. http://auto.howstuffworks.com/auto-parts/brakes/brake-

types/regenerative-braking.htm

2. http://www.hybridcars.com/components/regenerative-braking.html

3. http://www.hybridcars.com/related-technologies/hydraulic-

hybrids.html

4. http://www.railway-technical.com/brake1.shtml

5. http://www.shorpy.com/node/5734

6. http://www.railwaygazette.com/news/single-view/view//regenerative-

braking-boosts-green-credentials.html

7. http://www.railway-

energy.org/static/Regenerative_braking_in_DC_systems_103.php

8. http://privatenrg.com/

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