Ultracapacitor Based Energy Storage System for Hybrid and Electric

Vehicles

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CONTENTS Introduction Capacitors and Ultracapacitors Advantages of ultracapacitors Conventional ESS HESS(Hybrid Energy Storage Systems) Design and Working Operation of Proposed Systems Conclusion Reference

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Introduction Using HESS system in place of conventional Energy systems

Ultracapacitors are introduced in to the system, which act as a buffer that gives higher performance to Energy systems

Battery will only provide power directly whenever the Ultracapacitor voltage drops below battery voltage. Therefore, a relatively constant load profile is created for the battery also satisfying the real-time peak power demands

Battery is not used to directly harvest energy from the regenerative braking; thus, the battery is isolated from frequent charges, which will increase battery life.

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Capacitors &

Ultracapacitors

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Capacitors A capacitor is made up of two conductors separated by an insulator called

dielectric

The dielectric can be made of paper, plastic, mica, ceramic, glass, a vacuum or nearly any other nonconductive material

When a potential difference applied across the capacitor, electric field develops across the dielectric causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate

ielectric constant or Permittivity of the mediumA = Area of the platesD = Distance between the plates

Ultracapacitors

Also called Supercapacitors or Double layer capacitors , Invented by engineers at Standard Oil of Ohio(SOHIO) in 1966

High-capacity electro chemical capacitor with capacitance value much higher than other capacitors that bridge the gap between electrolytic capacitors and rechargeable batteries

10 to 100 times more energy per unit volume than electrolytic capacitors Capacitance ranges up to 5000f! Principle:- Energy is stored in ultracapacitor by polarizing the electrolytic solution. The charges are separated via electrode–electrolyte interface Types EDLC(Electrochemical Double Layer), Pseudocapacitors and Hybrid capacitors 6

An ultracapacitor cell basically consists of two electrodes, a separator, and an electrolyte

As ,in order to increase the capacitance, need to change

A, Materials with highest specific surface area used for electrodes eg: Highly porous carbon , Activated carbon, Carbon nanotubes , graphite etc. D, The distance between the plates is in the order of angstroms(10-10 meters) Electrolytic solution with high conductivity and adequate electrochemical stability

Separator is to prevent the charges moving across the electrodes

The amount of energy stored is very large as compared to standard capacitor,the small charge separation created by the dielectric separator.

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Advantages Long life: It works for large number of

cycles without wear and aging High power storage: It stores huge

amount of energy in a small volume Very high rates of charge and

discharge: Ultracapacitor charges within seconds whereas batteries takes hours

High cycle efficiency (95% or more)

Ultra capacitors are able to attain greater energy densities while still maintaining the characteristic high power density of conventional capacitors

Conventional capacitors have relatively high power densities, but relatively low energy densities when compared to batteries, while a battery have low power density and high energy density. Ultracapacitors have moderate energy density and power density

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Activated carbon

Carbon nanotubes

Inside-ultracapacitor

ESS(Energy Storage Systems)

Batteries are most widely used energy storage devices

The Toyota Prius, Honda Insight, and Ford Escape are examples of commercially available HEVs with efficiencies around 40 mi/gal in the market(old models).

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Drawbacks Power density is low, incompatible to meet peak power demands

Batteries with higher power densities are of higher cost and large size Needs intensive thermal management systems, to cool it and also to warm

it up in cold temperatures

It cannot be used for high rate charge discharge operations, which causes unbalance of voltages between individual cells eventually the total capacity decreases

Vehicles in most driving conditions requires instantaneous power input and output, a conventional battery(with cycle life up to 2000times) is inappropriate for this application

in order to solve these problems HESS(Hybrid Energy Storage Systems) have been proposed.

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HESS(Hybrid Energy Storage Systems) The basic idea of HESS is to combine UCs and batteries to achieve a

better overall performance

UCs having higher power density but a lower energy density act as a Buffer or an assistant energy source between battery and the DC link.

There are several conventional HESS configurations proposed , while Most of these combinations share one common feature which is to efficiently combine fast response devices with high power density and slow response components with high energy density.

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Classifications and Topologies HESS can be classified in to PASSIVE and ACTIVE based on power electronic

convertors used in it PASSIVE: Battery pack is directly paralleled with the UC bank , battery voltage

always same as that of UC nominal voltage, battery must charge the UC and provide power to the load side

Passive cascaded battery/UC system 15

ACTIVE: * A DC-DC converter added between the battery pack and the UC bank

* The battery voltage is boosted to a higher level * Small sized battery can be employed, reduces cost * Battery can be more efficiently controlled and stress on battery gets reduced

Active cascaded battery/UC system16

Advantages The Active type topologies are more used The battery supplies average power to the load, and the UC delivers

instantaneous power charge and recovers fast charging from regenerative braking

Drawbacks Battery can not directly charged by breaking energy or by UC due to

unidirectional boost converter Therefore parallel and multi input topologies were used

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Parallel active battery/UC system Multiple-input battery/UC system

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Parallel active battery/UC system Battery and UC are at a Low voltage than DC link Voltage When the Drive train Demands power, The voltage on the battery and UC will level up Supplies power, The voltages are stepped down for recharge

Multiple-input battery/UC system BOOST mode: When input sources supply energy BUCK mode : When recovering braking energy Only one inductor is needed even if more inputs are added

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Design&

Working

DESIGN TOPOLOGIES Design focus on which topology is uses, the basic design considerations include

Voltage strategy Both battery and UC have different voltages of operation

The demand of balancing the system increases with high voltage capacity of the system

A better matched system can be build with a bigger batch of cells ,which in turn increases the cost

Therefore a voltage tradeoff between storage elements by considering that UC are more easier to balance( lower additional cost)

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Effective utilization of stored energy In battery system, the energy delivered is not a function of voltage , but in

HESS energy delivered is a function of voltage because UC obeys law of standard capacitors

Voltage of UC needs to be discharged to half of original voltage in order to

deliver 75% of energy stored If Vuc<Vbatt=Vdc, 100% energy will deliver theoretically but not practically

because of presence of unbalanced cells A 66% reduction in UC voltage considered to discharge 90% of stored

energy, in passive systems which is further limited to 20% But a margin need to be allowed for UC to operate in Regenerative Braking

Conditions ,therefore actual energy discharged limited to a nominal 36%22

Protection from overcurrent Design consideration is to fully utilize the higher power limit of UC to support

accilaration and fully recover energy through regenerative breaking

But there is current surges due to unpredictable Regenerative breaking

Solution is to give a charging and discharging limits to the controller

Mechanical braking is used to absorb extra energy

Trade off between energy and securityCost control

Uc adds extra costs 23

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OPERATION OFPROPOSED

SYSTEM

Proposed system

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OperationMODE 1-Vehicle low constant speed operation

Pconst≥Pdemand

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MODE 2:Vehicle High Constant Speed Operation

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Mode III: Acceleration

Acceleration mode phase I energy flow. Acceleration mode phase II energy flow

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Mode IV: Deceleration (Regenerative Braking)

Regenerative braking phase I energy flow when VUC< VUC tgt Regenerative braking phase I energy flow when VUC ≥ VUC tgt .

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Regenerative braking phase II energy flow

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Conclusion In this seminar, a new HESS design has been proposed. Compared to

the conventional HESS, the new design is able to fully utilize the power capability of the UCs

Much smoother load profile is created for the battery pack

Future work related to this design will focus on the analysis of the

system efficiency in the high-voltage conditions

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REFERENCES  v M. R. Rade, Prof. S. S. Dhamal, “Battery-Ultracapacitor Combination used as

Energy Storage System in Electric Vehicle”, International Conference on Emerging Research in Electronics, Computer Science and Technology – 2015.

v Jian Cao, Member, IEEE, and Ali Emadi, Senior Member, IEEE, “A New Battery/UltraCapacitor Hybrid Energy Storage System for Electric, Hybrid, and Plug-In Hybrid Electric Vehicles”, IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 1, JANUARY 2012.

v Khaligh, Z. Li, “Battery, Ultracapacitor, Fuel Cell, and Hybrid Energy Storage Systems for Electric, Hybrid Electric, Fuel Cell, and Plug-In Hybrid Electric Vehicles: State of the Art”, IEEE Transactions on Vehicular Technology vol. 59, no. 6, pp. 2806-2814, 2010.

 

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