Regenerative Braking

1. Regenerative Braking
Project Members:
Akhil S (10)
Akhil.R (12)
Nidheeesh T T (4)
Project Guide:
Prof. Ganesh
Assistant Professor
Dept. of Mechanical Engg.
GECBH

2. 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

3. 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)

4. 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

5. Diagram of a Regenerative Braking
System
http://static.howstuffworks.com/gif/regenerative-brake-diagram.jpg

6. 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)

7. 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

8. 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

9. 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

10. 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

11. DC Railway Regeneration
Estimates
% Energy recapture figures for DC Catenary Locomotives
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

12. 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%

13. Road Vehicle Efficiency Data
Source: http://www.privatenrg.com/

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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