Road Trials on Hybrid Electric Vehicles

Prof. R. Arockiasamy, Mr. S. K. Sud and Mr. Sendhil Solai

Abstract-- EVs are the promise of future transportation inurban as well as rural areas. Ideal EVs of the future will have noengine, no chemical batteries and will derive the required energyfrom conventional power grid or from non-conventionalgenerating stations ranging from solar, nuclear, micro hydel,wind generators, biomass/biogas plants or wave generators. Theproblem at that time will be an economically viable storagemedium. Such a medium is on the horizon for some time. Typicalcontestants are flywheel, Li-ion, ultra caps and Zn-air. Thepresent technology available does not support economic use ofthe above storage mediums. However in special circumstancessuch as remote or hilly area transportation or defence, Li-ion andflywheel can be considered.

Index Terms-- AC motor drives, Batteries, Battery chargers,DC motor drives, Digital control, Motor protection, Road vehicleelectric propulsion

I. INTRODUCTION

T HIS document will focus on Hybrid Electric Vehicles fortransportation. The various subsystems of an EV and test

experiences will be briefly explained.

How the Electric Vehicles (EVs) contribute toenvironmental protection?

Electric vehicles are not burning fossil fuels. Electric motorsare efficient and do not have reciprocating motion. Henceheat, emission, noise and vibration are negligible. Thefollowing energy storage mediums are generally used.

Lead acid 40 watt hr/kg

Nickel MH 70 watt hr/kg

Ultra Capacitor 2.7 watt hr/kg

Lithium Ion 70 watt hr/kg

Flywheel 200 watt hr/kg

Zinc Air 200 watt hr/kg

However, the stored energy per Kg does not result inreasonable range. Most vehicles are limited to 65 to 90 Km.Further increase in battery size results in reduced payload.

emission of pollutants? This point needs to be examinedcarefully. What is the best fuel for this generator? The enginecan operate from either CNG or LPG. In such a case,emissions are negligible. What then about using diesel, whichis generally available everywhere? In case of diesel generator,if the engine speed is adjusted to an optimum value and if theload is fixed and optimum, emissions is shown to benegligible. In our case, using a diesel generator, the videocapture and analyzer test shows exhaust is without smoke andis clear except at starting. Thus at the best operating point(SFC) there is minimum or negligible emissions. We considerthis diesel hybrid as the ideal solution until revolutionarystorage devices appear on the scene. Such a vehicle withonboard diesel generator charger is named as Diesel HybridElectric Vehicle.

Have we come back to the same old internal combustionengine? No, while we do have an engine the differences are:1) Capacity is almost 1/3rd size of the engine in a

conventional vehicle.2) Engine is operated at constant optimum speed

and load.3) Engine is operated when required.4) Pollution is negligible.

In a conventional vehicle engine is running all the time.Pollution / un-burnt fuel is significant during idle stop andslow traffic. In a hybrid vehicle emission is negligible. Fuelsaving in excess of 30% is obtained. Thus the extra investmentis recovered in a short time.

Block diagram of an EV:

Fig 1: EVPower Mode

In order to increase the range the AH consumed will have tobe made up. A small engine generator is installed on boardthe vehicles to continuously charge the batteries. Will it cause0-7803-9794-0/06/$20.00 C 2006 IEEE

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The electric motor (in our case a DC shunt) is carefullydesigned and fits through a flange to clutch-gear side of thepower train. An electronic controller adjusts speed and torqueas per foot pedal position. Energy is drawn from a bank ofbatteries (240V in our case) as shown in Fig 1. In general allEVs give a range of 65 to 90 km before recharge. A quick topup recharge gives a daily range of 250km. However this rangeis a flexible design option.

It is now recognized globally that only Hybrid EV iseconomically viable at present due to power to weight ratio ofstorage devices. In HEV a generator-set charges the batterywithout damaging it. The electronics and its design mustprovide for that eventuality. We have achieved this as percharacteristic in fig 2 using a micro controller and IGBT.

C1-agiaig Cri-eni Full VoltagD

4tmi=. cufrent

Mlin Current

% MEEX VDltage

-----H --E

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Uharo omp]

Fig 2: Taper Charging

Design challenges in auxiliary storage devices:

A sophisticated electronic controller takes power from the DCbus or auxiliary energy storage device and feeds the electricmotor, which is the main drive. The motor is coupled to abraking compressor and steering pump on non-drive end andclutch gear on the drive end. The energy storage device,which feeds power to DC line, is a lead acid battery bank.Other researchers have used Ni-Cd, Ni-MH, Ultra capacitorsand flywheel energy storage. BARC, Mumbai is associatedwith us in developing flywheel energy storage system. Thewell-known advantages of electric vehicles are zero pollution,minimal noise and vibration and minimal release of heat toatmosphere.

The major challenge in the design of electric vehicles is thelimited range and some what long duration of charging, apartfrom the weight. In order to get higher range, we can increasethe storage energy by increasing the ampere-hour capacity ofthe battery bank. However this cuts in to passenger capacityof the vehicle.

Advanced pulsed charging techniques can be used to chargethe battery faster. However effect of fast charging on life ofbatteries is to be studied comprehensively.

While batteries are to be handled delicately, the temperature ofthe electrolyte should be maintained in an optimum range andnot allowed to exceed 50°C. It is recognized that HybridVehicle is economically feasible at present. The weight of thebattery used depends on the designer. One can use a

conservative heavy weight battery and an engine generatorrated at 25% of motor capacity or one can use lower weight ofbatteries and use an engine generator rated 500o of motorrating. The life of the battery is affected by this choice andhas to be assessed practically.

Regenerative Braking:

Let us assume the vehicle is running at 60 kmph in 5th gear. Ifwe change the gear to 4th, motor speed increases and armaturevoltage increases to say 280V in case of a 240 V system.Instead of drawing current from battery as in power mode,current flows into battery through the reverse diode connectedacross the IGBT. The energy is transferred from motor nowoperating as generator to battery as shown in fig 3. In our testruns we have seen the energy consumption per km decreasingby 25%, a clear saving of fuel (electricity), when regenerativebraking is used.

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Fig 3: EVRegeneration Mode

As the speed of the vehicle decreases, we have to change tolower gear. In addition the field current is increased to boostthe reverse current using a micro controller and IGBT asshown in fig 4. If regenerative current exceeds safe limit, fieldis decreased.

Fig 4: Field Control

The current capacity during regeneration depends on thechoice of the battery bank and its design. Question is, if thecurrent going into the battery is say at C2 rating, will it

Field

convert to useful energy stored or will it be wasted as heat?The specifications by manufacturers are silent on several ofthese aspects. Typical waveform of power and regenerativecurrent while negotiating a flyover is shown in fig 5.

15G ................. ..=

100

Fig 5: Regenerative current

Electronic Controller:

This is the heart of any electric drive and requires a section toitself for appropriate justification. In our case it is a choppercircuit with two IGBT's in parallel. A micro controller, Halleffect transducers and IGBT's form the core of the controller.

Protection:

To prevent break down or worse, various levels of protectionand safe guards are provided as per automotive safetyrequirements. We have two levels of protection and twolevels of safe guards. Conventional protection units are

moulded case circuit breakers (DC) followed by HRC fuses.The special protection using Hall probes and electronics isbuilt into the controller.

The two test vehicles with us are giving flawless performancefor the last four years.

Results:

Battery Placement:

Choice and placement of batteries is a major challenge andwill have to be given due attention once the vehicle runs

reliably. Our paramount concern was reliable performance.

The batteries must be ventilated at all times, running or at rest.Dust, oil, grease, water need not find their way to batteries.Charging rate, a crucial deterrent to battery life must be keptunder strict control. Long term testing can give us some hints.For example a 300AH cell can be charged at 150 amps or

more for 30 minutes to an hour depending on its state ofcharge and temperature. After 65 to 7500 charge it will haveto be less than 10 hrs rate.

Batteries don't require jerks and rough handling, a cradle likesupport and motion through shock absorption pads can do a lotof good. Removal of batteries will have to be allowed forreplacement or repair. Watering and monitoring cell voltagewill have to be considered. In short, the design, manufacture,placement, and maintenance of batteries are the key to success

of EVs.

Electric Motor: 20kw to 90kw

The drive can be DC motor, Permanent Magnet motor,Induction motor or Reluctance motor. The appropriateelectronic controller must prove its reliability. Functionally themotor occupies the space vacated by the engine. Motor may beas close to differential as possible. The end cover is modifiedto look like the engine side cover. A flange similar to the one

fixed to engine shaft is fitted to motor shaft and it carries theflywheel, which, is part of the dry clutch. The rest of thepower train is conventional. The non-drive end is designed topower the compressor, alternator, steering pump and some

cooling fans. Available compressors do not fit the requirementof electric vehicles. Presently an arrangement designed by us

is being used.

When operated as Battery vehicles following performance isobtained.

Range / chargeWithout With

Passengers Km I Kmph Regen Regenday250 40 6075

25 250 40 60 7550 250 60 60 75

1100 1250 160 165\0 175

When operated as Hybrid EV, the following performance isobtained

Passengers Kmph Energy / km25 42 0.25 units50 60 0.40 units100 65 0.5 units

Transportation in Remote areas:

Remote area here means that there is no grid supply and it isnot economical to carry fuel or gas. The concept proposedhere assumes the presence of local resource such as microhydel, solar, wind or biogas power generation. The result isavailability of electricity as an alternate source of energy or

fuel. We propose to use this resource to develop a transportlink between village clusters. This will activate or assisteducation and other economic activities. The system consistsof small generating units say a solar farm. The panels charge a

set of station batteries during the day. During the night, energyis transferred to the EV. The following day the vehicle carrieschildren to school and local produce to other locations andvice versa. In hilly terrain, power from micro hydel can beused to run small vehicles linking hamlets.

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L50 t-

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Fig 6: 50 passenger HybridEV

Fig 7: 100 passenger HybridEV

Opening EV market:

Lukewarm efforts are on globally to develop and deploy EVswith noble objective and reducing health hayard. Currenttechnologies go beyond environmental aspects in saving fuel(a depleting commodity) and providing comfort to passengers.

While subsides assist deployment to some extent, opening themarket thro' appropriate policies will load to large scaledeployment and avoid the need for subsides.

Conclusion:

Transport vehicles let out pollutants harmful to all livingbeings. Conventional fuels will not last forever.

Consider electricity as a fuel for road vehicles. Electricity maybe generated by any available resource namely Coal, Oil, Gas,Hydro, Nuclear, Wind, Solar, Wave, Micro hydel or Biogas.However, current problems are mainly related to weight, lifeand cost of batteries. Disposal or recycling must be feasiblefor the chosen battery. The motor and controller must beefficient, reliable and economical.

Lightweight body structure can contribute to viability of EVs.The EVs shown in figs 6, 7 and 8 developed at IIT Delhi areunder trial and meet some of these challenges. The technologydeveloped results in a reliable, economical and pollution freetransportation solution. The Principal Investigator wasconferred the Bimal Bose Award and Vasvik IndustrialResearch Award for his work in Power Electronics andElectric Vehicles.

Acknowledgements:

Several eminent scientists and Govt. officers have providedencouragement and support leading to road worthy vehicles.Demo rides by Hon'ble Chief Minister of Delhi Smt. ShielaDikshit and a group of High Court Judges gave us a shot in thearm. Prof. MGK Menon, Chairman Vasvik Award Committee,Prof. C.S. Jha, Prof. P.V. Indiresan, and Prof. S.C. Dutta Roygave continuous encouragement and support. Many Govt.officers from Oil Industry Development Board and NCT ofDelhi provided assistance during difficult times. EicherMotors, Tata Motors, Sundram Clayton, Society ofAutomobile Engineers and Crompton Greaves have providedgenerous assistance. We are grateful to the personalities andorganizations mentioned above.

Fig 8: 100 passenger HybridEV

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Prof. R. ArockiasamyBorn in Tamil Nadyu in 15th June 1940. graduatedfrom Madras University in the year 1963. receivedD.I.C. of Imperial College and PhD, LondonUniversity in the year 1969. Joined faculty ofElectrical Engineering, IIT Delhi. Working in thearea of Power Electronics, Electrical Drives,Hybrid Electric Vehicles, Theft free energydistribution. Received Bimal Bose Award (1996)and Vasvik Industrial Research Award in 2002.Has been a member, union public servicecommission from 1985 to 1991. CurrentlyEmeritus Fellow with IIT Delhi.

Mr. S.K. SudBorn in 1946 in Lahore.Completed his Bachelor1967 and Master Degree in 1969from University ofRoorkee. After working in field of ScientificInstruments he joined Institute of Technology,Delhi faculty in 1971. His experience includesteaching, R&D in the area of Computerizedinstrumentation and controls. Presently engaged indevelopment of small hydro-generator controllersand Hybrid Electric Vehicles with Eco FriendlyTransportation Group, IIT Delhi. Currentlyemployed as Chief Design Engineer at IIT Delhi.

Mr. Sendhil Solai graduated from AmravatiUniversity with a degree inComputer Science and Engineering.His employment experience mirrors hismultidisciplinary technical interests, whichinclude domains like data communicationnetworks, electronic automation and automotiveengineering.