Hybridization of Ultra-capacitors and Batteries for ...

Futuristic Trends In Mechanical Engineering, 4th & 5th December, 2010 – PIET Limda

Hybridization of Ultra-capacitors and Batteries for Modern Automotive Energy Storage System Nityam P Oza Lecturer, Mechanical Engineering Department Parul Institute of Engineering and Technology, Limda E-Mail ID : [email protected]

Prashant K Shah Associate Professor, Electrical Engineering Department, Parul Institute of Engineering and Technology, Limda E-Mail ID : [email protected]

Ramesh N. Barot Senior Lecturer, Mechanical Engineering Department Parul Institute of Engineering and Technology, Limda E-Mail ID : [email protected]

ABSTRACT Since the automobile invented, battery plays a very vital role of supply and storage of electrical energy for key systems, which are required to operate vehicle like starter motor, Ignition circuit, Lighting, Air conditioner, Wiper, Various Gauges. Today, surplus in all above requirements features of modern automobile like Electronic power steering, Automatic air conditioning, Electronic suspension, four wheel drive, seat heating and cooling, Multi media system, GPRS system, TV, Telephone demands for lots of electrical energy volume with high power. Current battery technology can cope with high energy volume but, the second requirement, for high power it does not perform well. Apart from power problem, the battery fails to satisfy modern vehicle need for cold starting, High cycle life in turn less cost, environment hazards ( Lead ). In contrast, ultra capacitor can provide very high power, higher life cycle, and safety with deficit of lower energy density. Hybridization of battery and ultra capacitor together leads us to make automobile electrical storage system that meet the requirement of high power, high energy volume, higher life cycle, safety, higher recharging efficiency and environment friendly of modern automobile.

KEY WORDS: Ultra capacitor; Battery; Hybrid Energy storage system.

INTRODUCTION This paper is about application of hybrid electrical energy storage concept in automobile. Battery and ultra capacitor together meets the almost all requirement of more power, high energy density, minimum cost, safe operation, higher regeneration efficiency, high cycle life of modern automotive energy storage and supply system. HISTORY OF AUTOMOTIVE ELECTRICAL STORAGE SYSTEM:

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Lead Acid batteries were invented by French Physicist Plante and are the oldest type of rechargeable type of battery. Despite having a very low energy to weight/volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power to weight ratio. This feature along with their low cost make them attractive for use in motor vehicles to provide the high current required for automobile starter motors. Today 90 percentage of the total car manufactured uses conventional lead Acid Batteries. Lead as used in this kind of batteries is very toxic and cause brain and kidney damage, hearing impairment and learning problems in children during long term exposure. As environmental concerns are

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extremely important for the manufacturers in current scenario, they are forced to search alternative arrangements that can meet environment concerns and also can provide a relatively large energy to weight/volume which is considered to be very important advantage for a modern automobile sector. In view of this battery manufacturers have developed various batteries like Nickel Hydrogen, Nickel Cadmium, Nickel Metal Hydride, Lithium Ion Batteries having a power to weight ratio 75 watt per Kg., 150 W/Kg., 250 W/Kg., 340 W/Kg and energy to weight ratio 50Wh/Kg; 60 Wh/Kg, 80 Wh/Kg; 160 Wh/Kg. Among this Lithium Ion battery is giving a hope but it is not suited because of relatively higher cost and stability problems and less life cycle; manufacturers are forced to look at new energy storage device, which can provide high power to weight ratio, high energy per weight and relatively longer life cycle with lower cost. HYBRID CONCEPT Ultra capacitors fulfill all requirements like high power to weight ratio, longer life cycle with moderate cost. Apart from this they are environmental very safe with higher recharging efficiency. In spite of all this advantages, they could not replace lead acid battery completely as having a lower energy to weight ratio. Hence, hybrid concept of featuring benefits of both the technologies can provide a feasible and alternative solution with greater advantages. For that, combining high energy lead-acid batteries and ultra capacitors can create a system that has the excellent energy, self-discharge, availability, and low cost associated with lead-acid technology, and the high charge acceptance, high efficiency, cycle stability, and excellent low-temperature performance of the ultra capacitor. With this concept, apart from above advantage ultra capacitors can also play a valuable role simplifying the wiring required and reducing cost.

and accidents, needs to be incorporated into the design of future power systems. 3. It is particularly important to provide the power required for computer-based processing systems in vehicles, where a poor quality power supply can cause a shutdown that stops the vehicle. 4. Centralized power control requires that a separate wire be run from the central control box (which contains fuses, relays, and switches) to the device being powered. Each wire must carry the full current of the load, and must be routed through the vehicle, sometimes over long, circuitous routes. 5. It is prudent to design a backup power source into the electronic box, which allows soft fail and a safer shutdown. This backup concept is very common in industrial and commercial computer based systems. Power is generated in one location, and is distributed via a limited number of common power buses. Control signals are also distributed over a limited number of common communications buses. Power and signal are delivered to a local distribution node, which incorporates intelligent electronic controls, and possibly energy storage. The local processor controls local use of power without the need to run multiple wires long distances to each specific point-of-use. Where local power is used intermittently, energy storage at the local power node by a device such as an ultracapacitor can provide that power, while the vehicle's power bus need only supply the average power. This use of a local power buffer significantly reduces the size of the main power bus wire. By reducing the size of individual wires, the length of high-current-carrying wires and the total number of wires in the vehicle, the system becomes less complex, Integrating local energy storage is also a proven strategy for making controllers more resistant to power problems.

1. Modern automobile has become more and more dependent on electrical subsystems as features proliferate. X-by-Wire functions such as power steering and electrical braking, fast heating, computer control modules, powered/heated/air-conditioned seating, navigation systems, and audio-video entertainment systems place huge loads on the power system of the vehicle. Also to run these applications electrical power is necessary this creates another problem of wire web occupying more space in vehicle along with more cost. Fig 1 Hybrid energy storage/supply concept

2. The availability and reliability of electrical power for robust operation, as well as during failure modes

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INTRODUCTION TO ULTRACAPACITOR As shown in figure 2, a capacitor consists of two electrodes, or plates, separated by a thin insulator. When a voltage is applied to the electrodes, an electric field builds up between the plates. A capacitor's energy is stored in such an electric field, without requiring any sort of chemical reaction. Thus a capacitor has an almost unlimited lifetime. It's also fast. Depending

about 60 grams. The innovation is going on to replace the activated carbon with a dense, microscopic forest of carbon nanotubes that is grown directly on the surface of the current collector. This can lead to a device that can hold up to 50 percent as much electrical energy as a comparably sized battery. This feat would allow ultra capacitors to supplant batteries in a number of mainstream applications. APPLICATIONS

Fig 2 Construction of Ultra capacitor

on its physical structure, typical charge and discharge times are on the order of a microsecond; sometimes they are as quick as a pico-second. Three main factors determine how much electrical energy a capacitor can store: the surface area of the electrodes, their distance from each other, and the dielectric constant of the material separating them. However, one can push conventional capacitor designs only so far. Ultra Capacitors functions differently. They are coated with two aluminum electrodes with a 100-micrometer-thick layer of carbon. The carbon is first chemically etched to produce many holes that extended through the material, as in a sponge, so that the interior surface area is about 100 000 times as large as the outside. (This process is said to “activate” the carbon.) Interior is filled with an electrolyte and used a porous insulator, one similar to paper, to keep the electrodes from shorting out. When a voltage is applied, the ions are attracted to the electrode with the opposite charge, where they cling electro statically to the pores in the carbon. At the low voltages used in ultra capacitors, carbon is inert and does not react chemically with the ions attached to it. Nor do the ions become oxidized or reduced, as they do at the higher voltages used in an electrolytic cell. Today, ultra capacitors can store 5 percent as much energy as a modern lithium-ion battery. Ultra capacitors with a capacitance of up to 5000 farads measure about 5 centimeters by 5 cm by 15 cm, which is an amazingly high capacitance relative to its volume. The D-cell battery is also significantly heavier than the equivalently sized capacitor, which weighs

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Power Train System design engineers can take advantage of the power of ultracapacitors to conserve energy by allowing the engine to stop while the vehicle is stationary, and then to be restarted nearly instantly on "tip in" of the throttle... The use of engine start/stop and regenerative braking has been estimated to produce between 7 and 15% increased fuel efficiency while reducing pollution by even more. Announced programs (see Below )for integrating ultra capacitors into vehicle power trains include BMW, VW, Honda, Nissan, and Toyota, among others. These vehicles run the gamut from concept to production-intent, and include systems for hybrid trucks, buses, and passenger vehicles. Announced programs Honda FCX V3 and Civic IMA both uses ultra capacitor along with fuel-cell Volkswagen hybrid has incorporated ultracapacitor with fuel cell In regenerative braking of MAN diesel electric city bus. In regenerative braking of Nissan Hybrid electric diesel truck In regenerative braking of BMW X5 hybrid prototype In regenerative braking of Toyota Prius hybrid Modern Drive Features Power steering, most essential feature of any modern vehicle, let the driver to negotiate curve and park vehicle with finger tip load application. Power to drive this feature comes from power from mechanically/electrically driven pump. Most of the time, this device is idle, in other words working intermittently. But in contrast the pump, which drives this application, draws power constantly. This will cause a loss of power decreasing efficiency of the system. Moreover, this feature is optimum used during parking and negotiating curve where vehicle speed will be low. Hence power requirement is a brief, high power pulse of less than one to two seconds. But, instead of using mechanical drive When electrically

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driven, these loads only draw power when actually used, effectively eliminating losses. The profile for a typical electrically powered steering event is a one- to three-second ramp to approximately 2,000 watts for several hundred milliseconds, which quickly returns to quiescent. In centralized power architecture, the power required can be supplied by the central energy storage, but this would require a very heavy and costly power cable. The voltage drop due to the high current could require that either the cable or the energy storage system be oversized. Using ultra capacitor with battery in distributed power concept eliminates the requirement of oversized battery, heavy costly power cable with high efficiency. Automotive Subsystems Another application is mechanical latches for doors, trunks and bonnets. To operate this device mechanical connection from the handle to latch is provided. They could be activated by solenoid eliminating mechanical connection. Having the power module in the door eliminates the heavy cabling associated with centralized energy storage architecture, and provides an added safety function as the door can still be opened in an accident where the central power source is disabled or disconnected. Hybrid Vehicles Today, Hybrid Electric Vehicle (HEV) technology is the most promising technology which boasts for higher efficiency by combination of the best characteristics of fuel-driven engines, electric motor drives, and energy storage components. .Mild or full hybrid vehicles have a combustion engine that functions as the primary power source, and an electric motor with a power storage system that functions as the secondary power source. Designers are able to size the combustion engine for cruising power requirements thanks to the presence of the secondary power source that handles the peak power demands for acceleration. Conventional Batteries have its own problem (listed below) as a secondary power source. Even though the fuel cell is capable of being dynamic enough to handle transients, it is large and costly if sized to meet the maximum load. Therefore, it is more cost-effective to have a hybrid design with a fuel cell and a bank of ultra capacitors, which can handling very dynamic loads such as initial acceleration and absorbs braking energy. Using only batteries to provide the electrical power storage has drawbacks in the hybrid applications. Starting in cold weather will be difficult. Batteries require a sophisticated charge equalization management.

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Under extreme conditions batteries have very limited cycle life, which results in cost replacement throughout the life of the vehicle. Batteries are limited in their ability to capture and provide bursts of high power during short duration events such as Acceleration and regenerative braking, which reduces the efficiency of the hybrid electric drive system design. Can not meet current requirement of passenger of fun and safe driving. Additionally, regenerative braking energy is captured by the secondary power system, and that energy is applied for further acceleration or for the basic energy needs of supplementary electrical systems by using the secondary source. Ultracapacitor, as secondary power source not only improves the recharging efficiency but also reduces charging time. Mini hybrid vehicles use a power generator that delivers the power required to handle start/stop idling only. Finally, in the micro hybrid concept, there is a power generator and power energy storage source to handle start/stop idling, fuel consumption reduction due to energy recuperation/acceleration assist, and to power some additional features like fast windshield heating. CONCLUSION As such, ultracapacitors have the potential to make non-traditional power trains more palatable to the average consumer or vehicle fleet owner, and thereby to help make a reality the promise of an efficient, clean, affordable, and fun automotive. REFERENCE Adrian Schneuwly. “Ultracapacitors fill automotive power gaps” Andrew Burke Marshall Miller University of California – Davis, California 95616. “Update of Ultracapacitor Technology and Hybrid Vehicle Applications: Passenger Cars and Transit Buses” Miller John M..”Ultracapacitors Challenge the Battery” Miller John M. and Michael Everett. “Ultracapacitor Augmentation of the Vehicle Electrical System to Reset its Power. Budget” Supramaniam Srinivasan. “Fuel cells: from fundamentals to applications ”

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