Regenerative Braking during Differnt Motor Directions.pdf

Vignesh Shenoy

Department of Electronics

Carleton University

1125 Colonel by Drive

Ottawa, ON, Canada, K1S 5B6

Dr. Cheryl Cundell

Instructor, Communication Courses for Disciplines and

Professions

School of Linguistics and Language Studies

236 Paterson Hall, Carleton University

Ottawa, ON, Canada, K1S 5B6

[email protected]

December 1, 2015

Dear Dr. Cundell,

This letter is produced as a requirement of CCDP2100 for Section I.

The attached report is my final technical report. The title of the document is Regenerative

Braking during Different Motor Directions.

The research topic that was used for the vehicle design project in regards to Efficiency of hybrid

cars is regenerative braking and how energy is generated during different motor directions. The

question used as a guide for this design project is; how does the regenerative braking system adapt

to different motor directions. The topic of regenerative braking is significant because it will

describe the process of converting movement energy to electrical energy and methods to improve

the overall efficiency. The enhancement of the regenerative braking system benefits energy

consumption rates and energy production rates. Thank you for reading this technical concept

report, if you have any further questions, please feel free to contact me by email at

[email protected].

Sincerely,

Vignesh Shenoy

mailto:[email protected]

Regenerative Braking during different Motor Directions

Vignesh Shenoy

CCDP – 2100

Cheryl Cundell

December 1st 2015

Vignesh Shenoy -ii- December 1, 2015 Final Technical Report

Abstract

Regenerative braking is a system that utilizes unused momentum of the vehicle slowing down. As

the wheels of a hybrid electric car slow down, their kinetic energy is redirected to turn a motor

generator. The motor generator spins to create an energy carrying current that is distributed to

various electrical components. Electrical Energy is generated to be charged and stored in electrical

components. The Regenerative Braking System distributes energy to produce forward momentum

and to charge the battery unit. However in practical scenarios, hybrid electric vehicles travel

forwards and backwards, while deaccelerating in both directions. The system adapts to the

direction of the motor by adjusting the orientation of the battery and aligning the rectifier circuits

to allow energy flow. Regenerative Brakes improve the overall efficiency of a hybrid electric car

by generating energy while the vehicle is moving in either direction and aligning rectifier circuits

for faster energy flow.

Table of Contents

Abstract ........................................................................................................................................................ ii

List of Figures ............................................................................................................................................... iv

List of Equations ........................................................................................................................................... iv

Nomenclature .............................................................................................................................................. iv

1.0 Introduction ............................................................................................................................................ 1

2.0 Background ............................................................................................................................................. 1

3.0 Discussion ............................................................................................................................................... 2

3.1 Alternating Current to Direct Current Conversion .............................................................................. 2

3.1.1 Kirchhoff’s Current Law in relation to conversion ....................................................................... 3

3.2 Different Circuit Cycles during different motor directions ................................................................. 4

4.0 Conclusion .............................................................................................................................................. 6

5.0 References .............................................................................................................................................. 7

Appendices ................................................................................................................................................... 8

Vignesh Shenoy -iv- December 1, 2015 Final Technical Report

List of Figures 1) Figure 1: Rectifier Circuit Page 4

2) Figure 2: Kirchhoff’s Current Law at a point on a circuit

3) Figure 3: Motor Direction Cycles Page 6

List of Equations 1) Equation 1: Sum of current at a point Page 5

2) Equation 2: General Current Law Page 5

Nomenclature

I Current

Vignesh Shenoy -1- December 1, 2015 Final Technical Report

1.0 Introduction The reason this report was produced as a requirement of CCDP Section I. The purpose of the Final

Technical Report is to describe the relationship between Kirchhoff’s Current Law and the

Regenerative Braking Process. This report addresses the research question

-How does the Regenerative Braking System adjust to different motor directions?

A background section is included to introduce the Regenerative Braking process and its

components. A discussion section follows, explaining the technical concepts involved with

charging and discharging a battery during Regenerative Braking. Definitions and figures

displaying the charging process are included. A Conclusion concludes the report by redefining the

purpose and summarizes key points mentioned.

2.0 Background Hybrid electric cars are vehicles that utilize a combustion engine and an electrical motor to produce

the sufficient kinetic energy (energy relating to motion) needed to create forward momentum [2,

pp. 21]. Regenerative Braking is an electronic system that is implemented in hybrid electric cars

to supply energy to the electrical motor while the vehicle is slowing down [1, pp. 1]. The primary

focus of Regenerative Braking is to store and reuse energy that is lost in regular braking systems.

In regular braking systems, as the wheels slow down, their kinetic energy is lost as heat and sound

[2, pp. 228]. However regenerative braking redirects kinetic energy from the wheels to spin a

motor-generator [2, pp. 280]. A motor-generator is a mechanical component that when spun

creates a voltage carrying current [2, pp. 253]. The current produced from the generator is stored

in a battery unit, which is then consumed by various components such as the electrical motor to

produce forward momentum [1, pp. 253]. In addition, momentum can travel forwards and


backwards, meaning the Regenerative Braking system must adapt to the direction the motor is

generating in order to achieve efficiency. Regenerative Braking improves the efficiency of hybrid

electric cars by generating electrical energy from the deacceleration of the vehicle.

3.0 Discussion

3.1 Alternating Current to Direct Current Conversion The process of Regenerative Braking can be broken down into three stages; deacceleration, energy

generation and quick access storage. Deacceleration is the reduction of speed in the wheels. As

wheels do not stop instantly, Regenerative Braking utilizes the momentum while the wheels

approach a full stop. The unused momentum is channeled to turn a motor-generator [2, pp. 280].

As the motor-generator spins, it generates a current that carries energy from one component to the

next [2, pp. 157]. The current generated is called Alternating Current, otherwise known as AC. AC

current is current moving backwards and forwards, however for current to be used it must travel

in only one direction [2, pp. 156]. Current travelling in one direction is called Direct Current,

otherwise known as DC. Figure 1 displays the electrical circuit that is implemented in a

Regenerative Braking system to produce direct current, known as a Rectifier Circuit. AC current

enters the rectifier circuit and travels through a rectifier. A rectifier is a circuit component that only

allows current to flow in one direction, meaning the current that exits the rectifier is direct current.

The purpose of converting AC current to DC current is to provide constant energy to an electrical

component, such as a battery [2, pp. 156]. The correct conversion is important in order for energy

to be directed to the electrical motor for the production of momentum [2, pp. 157].


Figure 1: Rectifier Circuit [7]

3.1.1 Kirchhoff’s Current Law in relation to conversion As displayed in Figure 1, current enters and exits a rectifier. Since current must flow from one

point of the rectifier to next, Kirchhoff’s Current Law (KCL) states that the value of the current

must be equal. KCL is the theorem that allows current to be converted from AC to DC while

retaining its value of energy [3]. Kirchhoff’s Current Law states that the sum of current entering a

point in the circuit must equal the sum of current leaving. As displayed in Equation 1, the sum

represented by ∑, of I representing current measured in amperes, must equal zero [3]. Figure 2

displays a point on a circuit in the middle. I1 and I2 are currents entering the point, and I3 and I4

are current leaving. Sum of I1 plus I2 must equal sum of I3 plus I4, resulting in Equation 2 [3].

Equation 2 states that I in (current entering) must equal I out (current leaving). Equation 1 and 2

form Kirchhoff’s Current law [3]. KCL justifies AC being converted to DC, to then be stored in

an electrical component.


∑𝐼 = 0 Equation (1)

𝐶𝑢𝑟𝑟𝑒𝑛𝑡𝐼𝑛 = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡𝑂𝑢𝑡 Equation (2)

3.2 Different Circuit Cycles during different motor directions Vehicles can produce forward and backward momentum while in operation. Similarly vehicles can

also deaccelerate while moving forwards or backwards. Regenerative Braking must generate

electrical energy in any motor direction to achieve efficiency. Electrical components within the

system adapt to the direction of the momentum by switching the direction current is flowing.

Figure 3 displays two orientations in which the system draws energy and regenerates energy. On

the right side of Figure 3, the vehicle is in the “On” cycle, representing energy being consumed.

The left side of Figure 3 displays the “Off” cycle, representing when the vehicle is slowing down

and generating energy [6]. The single line on the left of the diagrams represents a capacitor, which

quick access energy that the system can use rather than from the battery, represented by the M in

the diagrams. Q1, Q2, Q3 and Q4 are rectifier circuits within the system that redirect current to its

Figure 2: Kirchhoff’s Current Law at a point on a circuit [4]


appropriate component. During the “On” cycles, in both directions, rectifier circuits are aligned to

allow energy to be drawn from the capacitors to be stored in the battery unit. During the

regenerative “Off” cycles, energy is produced and stored in capacitors where it can power the

battery unit or the electrical motor [6]. When the vehicle switches motor directions, the alignment

of the battery switches to allow faster energy transfer from rectifier circuits. In the forward “on”

cycle, Q1 is activated to allow faster energy from the capacitor and similarly for the backwards

“on” cycle, Q4 is activated. Regenerative Braking adapts to different motor directions by

dynamically switching the positions of rectifier circuits within the system to allow energy

generating [6]. The different positions of the rectifier circuits allows the system to generate

electrical energy faster creating better efficiency for the hybrid electric car.

Figure 3: Motor Direction Cycles [6]


4.0 Conclusion The purpose of the report was to answer the research question on how regenerative braking adapts

to different motor directions as well as describe the technical concepts related to regenerative

braking. The Regenerative Braking process consists of deacceleration, generating electrical energy

and quick access storage. Regenerative Braking converts kinetic energy to electrical energy by

using unused momentum in the wheels while slowing down to generate a current. This current

switches from Alternating to Direct due to Kirchhoff’s Current Law by passing through a rectifier

circuit. Since a motor moves in two directions, rectifier circuits align in two different orientations

to allow energy to be regenerated while moving in either direction. By dynamically changing the

positions of the circuits, Regenerative Braking efficiently generates electrical energy while moving

forwards and backwards.


5.0 References

[1] A. Baker, Vehicle braking. London: Pentech Press, 1986.

[2] J. Larminie and J. Lowry, Electric vehicle technology explained. West Sussex, England: J. Wiley, 2003.

[3] Facstaff.bucknell.edu, 'Kirchhoff's Current Law', 2015. [Online]. Available:

http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Basic/Basic4Ki.html. [Accessed: 02-

Nov- 2015].

[4] Upload.wikimedia.org, 2015. [Online]. Available:

https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Kirchhoff%27s_Current_Law.svg/

250px-Kirchhoff%27s_Current_Law.svg.png. [Accessed: 02- Nov- 2015].

[5] B. Media, 'Green Car Congress: Recent Hybrid Braking Complaints Highlight Regenerative

Braking Design Issues', Greencarcongress.com, 2015. [Online]. Available:

http://www.greencarcongress.com/2010/02/braking-20100208.html. [Accessed: 02- Nov- 2015].

[6] Hassockshog.co.uk, 'Hassock Hog motor controller description', 2015. [Online]. Available:

http://www.hassockshog.co.uk/motor_controller_description.htm. [Accessed: 01- Dec- 2015].

[7] Lessons in Electric Circuits, 'Discrete Semiconductor Circuits', 2015. [Online]. Available:

https://www.ibiblio.org/kuphaldt/electricCircuits/Exper/EXP_5.html. [Accessed: 01- Dec- 2015].


Appendices [1] A. Baker, Vehicle braking. London: Pentech Press, 1986.

Pg. 1:


Pg. 253:


[2] J. Larminie and J. Lowry, Electric vehicle technology explained. West Sussex, England: J. Wiley, 2003.

Pg. 280:


Pg. 228:


Pg. 156:


Pg. 157:


Pg. 21:


[3] Facstaff.bucknell.edu, 'Kirchhoff's Current Law', 2015. [Online]. Available:

http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Basic/Basic4Ki.html. [Accessed: 02-

Nov- 2015].

[5] B. Media, 'Green Car Congress: Recent Hybrid Braking Complaints Highlight Regenerative

Braking Design Issues', Greencarcongress.com, 2015. [Online]. Available:

http://www.greencarcongress.com/2010/02/braking-20100208.html. [Accessed: 02- Nov- 2015].


[6] Hassockshog.co.uk, 'Hassock Hog motor controller description', 2015. [Online]. Available:

http://www.hassockshog.co.uk/motor_controller_description.htm. [Accessed: 01- Dec- 2015].

Regenerative Braking during Differnt Motor Directions.pdf

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