CHAPTER 1 INTRODUCTION1.1 Electric Vehicles

Anelectric vehicle(EV) use one or moreelectric motorsortraction motorsforpropulsion. Three main types of electric vehicles exist, those that are directly powered from an external power station, those that are powered by stored electricity originally from an external power source, and those that are powered by an on-board electrical generator, such as aninternal combustion engine(hybrid electric vehicles) or ahydrogen fuel cell.EVs includeplug-in electric cars,hybrid electric cars,hydrogen vehicles,electric trains, electric lorries,electric airplanes,electric boats,electric motorcycles and scootersandelectric spacecraft.

1.2 Types :

1.2.1 Plug-In Electric Vehicles : A plug-in electric vehicle (PEV) is anymotor vehiclewithrechargeable battery packsthat can be charged from theelectric grid, and the electricity stored on board drives or contributes to drive the wheels for propulsion.[18]Plug-in electric vehicles are also sometimes referred to as grid-enabled vehiclesand also as electrically chargeable vehicles. 1.2.2 Battery Electric Vehicle : Abattery electric vehicle(BEV) uses chemicalenergystored inrechargeable batterypacksas its only source for propulsion.BEVs useelectric motorsandmotor controllersinstead ofinternal combustion engines(ICEs) for propulsion.1.2.3 Plug-In Hybrid Electric Vehicle : Aplug-in hybrid electric vehicle(PHEV or PHV), also known as a plug-in hybrid, is ahybrid electric vehiclewithrechargeable batteriesthat can be restored to full charge by connecting a plug to an externalelectric power source.A plug-in hybrid shares the characteristics of both a conventional hybrid electric vehicle and anall-electric vehicle: it uses a gasoline engine and an electric motor for propulsion, but a PHEV has a larger battery pack that can be recharged, allowing operation inall-electric modeuntil the battery is depleted.

1.3 HistoryFor the first time it was German inventor, Nikolaus Otto, who made it possible to use combustions engines in cars by the invention of the first four-stroke internal combustion engine in 1862. These types of engines are continuously being used in so-called conventional vehicles. The low-efficiency of ICE (Internal Combustion Engines) and high emission production are the most negative points about these types of vehicles. In the figure 1.1, the recent development in car industry is been shown.

Figure 1.1 : Developments in Car Industry[4]Next were the hybrid vehicles which first commenced in 1997 in Japan by the introduction of Toyota Prius. The main specification of this type of vehicle is the operation of the ICE on its efficient interval by means of a regenerative braking system. Hybrid electric vehicle (HEV) refers to a vehicle with an electric motor, an internal combustion engine, and limited onboard energy storage that improves fuel and engine efficiency. Automotive manufacturers are now turning to plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV). PHEVs and BEVs have more onboard energy storage than HEVs and give owners the ability to charge the vehicle battery from a stationary electrical sourcefor example, an outlet in the garage. A PHEV contains an internal combustion engine, has a limited range in all-electric mode, and uses gasoline for long trips. A BEV has an electric motor, but no internal combustion engine, and it has a larger battery and a range longer than the all-electric range of a PHEV.

1.4 Current Status

1.4.1 Country-wise Status : Most electric vehicles in the world roads were low-speed, low-rangeneighborhood electric vehicles(NEVs). TheRenault-Nissan Allianceis the leading electric vehicle manufacturer with global sales of over 120,000 all-electric vehicles by October 2013,followed byGeneral Motorswith combined global sales since December 2010 of over 70,000 vehicles by January 2014, mostly plug-in hybrids.Mitsubishi Motorsranks third, with global sales of more than 50,000 plug-in electric vehicles since 2009, including over 33,000 all-electric vehiclesand more than 17,000 plug-in hybrids.

TABLE 1.1Market share of 2012 global salesof highway-capable BEVs and PHEVs by country

All-electric carsPlug-in hybrid cars

RankingCountryMarketshare(1)RankingCountryMarketshare(1)

1Japan28%1United States70%

2United States26%2Japan12%

3China16%3Netherlands8%

4France11%4Canada2%

5Norway7%5China2%

Note: Market share as% total global sales of pure electric cars or plug-in hybrids.[18]

1.4.2 Top-Selling Models : The world's top selling highway-capable all-electric car is the Nissan Leaf, with global sales of 100,000 units by mid January 2014, capturing a 45% market share of worldwide pure electric vehicles sold since 2010. The world's top selling all-electric light utility vehicle is theRenault Kangoo Z.E., with global sales of 12,490 units. TheVolt/Ampera familyis the world's best selling plug-in hybrid and second best selling plug-in electric car, with combined sales of about 70,000 units worldwide as of January 2014.

Table 1.2 :Global Sales of the best selling PEVs available for retail sales or leasing (available for retail sales as of Dec 2013)S.NoMODELMARKET LAUNCHGLOBAL SALES

1NISSAN LEAFDEC 2010>100000

2CHEVROLET VOLTDEC 201070000

3TOYOTA PRIUS PHVJAN 201248600

4MITSUBISHI I MiEVJULY 200928000

5TESLA MODEL SJUNE 201225000

6RENAULT KANGOO ZEOCT 201117800

7RENAULT ZOEOCT 201212490

8FORD C Max ENERGIDEC 201210000

NISSAN LEAF CHEVROLET VOLT

1.5 The V2G/G2V Concept :

Vehicle-to-grid(V2G) describes a system in whichplug-in electric vehicles, such aselectric cars(BEVs) andplug-in hybrids(PHEVs), communicate with thepower gridto selldemand responseservices by either delivering electricity into the grid or by throttling their charging rate.Vehicle-to-grid can be used with suchgridablevehicles, that is, plug-in electric vehicles (BEVs and PHEVs), with grid capacity. Since most vehicles are parked an average of 95 percent of the time, their batteries could be used to let electricity flow from the car to the power lines and back, with a value to the utilities of up to $4,000 per year per car.

Fig 1.3 V2G/G2V System [19]Fig 1.4Components of V2G System [9]

PEVs can serve in discharge mode as vehicle-to-grid (V2G) devices and in charge mode as grid to-vehicle (G2V) devices [1]. The V2G concept has attracted attention from grid operators and vehicle owners. This report reviews V2G/G2V technology and requirements, economic costs, challenges, and strategies for V2G interfaces of both individual PEVs and vehicle fleets. For purposes of the paper, V2G is used generically for both V2G and G2V energy flows. The context is PEVswhether purely electric or hybrid.

The connection to the electric power grid offers opportunities for PHEVs for charging the vehicle but also for discharging and thus injecting energy into the grid. In the ideal case, the electricity consumption should match perfectly with wind and solar energy and the generation of conventional power plants. Because of forecasting errors and the intermittent behavior of renewable resources, imbalances occur and generation and demand do not perfectly match. The vehicles can help to match consumption and generation bycharging and discharging on the right moment.

The current status and implementation impact of V2G technologies on distributed systems are reviewed in this report, and points such as impact of V2G/grid-to-vehicle (G2V) technologies on distributed systems, requirements, benefits, challenges, and strategies for V2G interfaces of both individual vehicles and fleets are discussed.

CHAPTER 2

WORKING OF V2G SYSTEM2.1 Components of V2G SystemElements required for V2G are :1) Power connection for electrical energy flow from vehicle to grid, 2) control or logical connection, needed for the grid operator to determine available capacity, request ancillary services or power from the vehicle, and to meter the result, and 3) precision certified metering on board the vehicle.

V2G System consists of six major subsystems as shown in figure 2.1.

Figure 2.1 : Components and Power Flow of a V2G System[1]These subsystems are :1) energy resources and an electric utility2) an independent system operator and aggregator3) charging infrastructure and locations 4) two-way electrical energy flow and communication between each PEV and ISO or aggregator5) on-board and off-board intelligent metering and control and 6) the PEV itself with its battery charger and management.

Figure 2.2 : Infrastructure required to implement PHEV charge control and demand management, including, a PHEV control unit and a remote switch for PHEV control. [12]

2.2 Charging and Discharging of PHEV:

The charging behavior of PEVs is affected by many factors, such as :

a. the type of connection (unidirectional or bidirectional),b. geographical location,c. the number of PEVs being charged in a given vicinity, their charging voltage and current levels, battery status and capacity, charging duration, etc.d. Fast charging can stress the grid distribution network because power is high.e. Injected harmonics and low power factor can be serious problems

V2G/G2V interfaces can reflect any possible charging rates; industry has defined three typical rates , as summarized in Table 2.1 Table 2.1: Charging Power Levels

Source : [1]

2.3 Unidirectional or Bidirectional Power Flow

Power flow between PHEV and grid can be either one way or both ways. Both the methods have their own advantages and disadvantages. Their comparative study is made in the table 2.2 .

2.3.1 Unidirectional Power Flow : The unidirectional power flow requires no hardware other than an outlet and avoids extra EV battery degradation from cycling. A typical circuit is realized using a diode bridge in conjunction with filtering and dcdc conversion. Unidirectional V2G, the basic battery charge process, can provide services based on reactive power and dynamic adjustment of charge rates even without reversal. Properly designed unidirectional chargers can supply or absorb reactive power by means of current phase-angle control. Control complexities outlined in grid interface standards such as IEEE-1547 are avoided since utility backfeed is not possible.

Implementation of this system can be done at almost no additional cost . Basic control can be managed with time-sensitive energy pricing. Research on unidirectional charging has developed optimal charging strategies that maximize benefits to the vehicle owner, aggregator, and utility, and explores the impact on distribution networks . With unidirectional charging, however, PEVs are likely to be connected for relatively short intervals since owners may not need to connect a fully charged vehicle. Some services can only be supported while batteries are charging, so this trades off utility benefits against owner practices. Even so, with a higher penetration of PEVs and active control of charging current, a unidirectional charger can meet most utility objectives while avoiding cost, performance, and safety concerns associated with bidirectional chargers .

2.3.2 Bidirectional Power Flow :

A bidirectional charger has two stages: an active grid connected bidirectional acdc converter that enforces active power factor correction, and a bidirectional dcdc converter to regulate the battery charge or discharge current.

Modes of Operation : When operating in charge mode, the charger should draw a sinusoidal current with a defined phase angle to control power and reactive power. In discharge mode, the charger should return current in a similar sinusoidal form.

Bidirectional V2G is not currently available with existing PEVs. There are several challenges to me addressed before it is realized. These include battery degradation caused by frequent charge and discharge cycling for regulation. There are extra costs for bidirectional converters, metering issues, and interface concerns. Anti-islanding protection and other interconnection issues must also be addressed.

Table 2.2 : Comparison between unidirectional and bidirectional power flow

Source : [1]2.4 Charging-Recharging frequency and strategies :The economic costs, emissions, and distribution system impacts of the V2G concept depend on PEV penetration and charging/discharging strategies.

2.4.1 Uncoordinated Charging/Discharging :Uncoordinated charging indicates that PEV batteries either start charging immediately when plugged in or start after a user-adjustable fixed delay, and continue charging until they are fully charged or disconnected. This charging system is most likely at Level 1(Table 2.1). Uncoordinated charging operations tend to increase the load at peak hours and can cause local distribution grid problems such as extra power losses and voltage deviations that affect power quality. They may lead to overloads in distribution transformers and cables, increased power losses, and reduction in grid reliability and cost.

Halbleib et al. [17] showed that uncontrolled charging can cause an increase in the monthly electric bill of up to 22% due to demand charges, even at only 10% PEV penetration. A simulation study on impacts of uncoordinated PEV charging on the daily peak power and base consumption was carried out in the Danish island of Bornholm, based on 2200 vehicles . The aggregated load in the simulated system is shown in Fig. 4, and peaks increase substantially.

Fig. 2.3 : System base load and total aggregated PEV (2200) charging usinguncoordinated direct charging of all the PEVs[17]

Some utility companies offer a dual tariff (cheap night rates) to PEV owners as a way to reduce peak load .When the user agrees to an adjustable fixed delay, owners can wait for cheap off-peak prices. Off-peak charging takes place during the night when the electricity demand is low and generation is mostly base load. When PEV nightly charging is added, the load factor improves as some portions of the off-peak valley are filled.

2.4.2 Coordinated Smart Charging/Discharging : Advantages of this technique is that it is possible to optimize time and power demand and reduce daily electricity costs, voltage deviations, line currents, and transformer load surges. It can also flatten the voltage profile of a distribution node. Incremental investments and high energy losses can be avoided, and wasting renewable energy and network congestion prevented.Ssmart charging allows attaining the highest PEV penetration level without violating the network technical limits . Coordinated charging system is more suitable for high power level (Levels 2 and 3). Optimization of charging time and energy flows reduces daily electricity cost with little effect on peak capacity needs.

Coordinated charging management concepts can be divided into centralized and decentralized approaches. The decentralized approaches let the PEV optimize its charging behavior based on a price signal broadcast. The drawback of this approach is that the PEV needs to collect and store the trip history. The centralized approaches focus on a centralized unit that directly controls PEV charging.

Smart V2G charging and discharging, in which PEVs are charged from renewable resources and discharged to the grid at peak load, is reported to offer the best potential for maximum utilization of renewable sources to reduce cost and emmissions. A smart metering and control system must be implemented to combine PEVs and renewable energy.

An alternative battery charging strategy is to swap depleted batteries with a fresh pack. If this can be automated, exchanges can be compared to duration of conventional vehicle refueling. This method reduces the impact on distribution systems since more flexible charge timing becomes possible

2.5 PEV Aggregation as a storage of Stored EnergyThe energy stored in an individual PEV is negligible relative to the grid. The aggregation concept has been proposed to provide viable storage and add to the smart grid for better coordination and reliability.

To maintain grid stability, two-way energy flow and communication needs to be controlled between the aggregated vehicles and the grid . An aggregator in a V2G system is shown in Fig. 2.1. It collects individual PEV data, detects and records the SOC of each PEV, and provides an interface to the independent system operator . When the power grid requests power, the power grid operator sends signals to the aggregator to manage PEV discharging. This minimizes charging and discharging costs subject to a number of technical and contractual constraints . Each PEV can be contracted individually or an aggregator can negotiate a contract for a fleet to implement ancillary services , . In the aggregative structure, the aggregator receives ancillary service requests from the grid operator and issues individual power and reactive power commands to contracted vehicles. PEV aggregations can also provide spinning reserves. PEV aggregations can easily start generating within a ten-minute requirement.

CHAPTER-3ADVANTAGES OF V2G SYSTEMS :

3.1 Environmental Advantages :Studies by NREL and the Northwest Power and Conservation Council determined that CO2 emissions would fall significantly if PEVs replace conventional ICE vehicles. When the V2G concept is added PEVs could offer further environmental benefits and directly. reduce greenhouse gas (GHG) emissions.

If electricity is produced from polluting sources, the environmental advantages of PEVs are more limited: GHG emissions range between 0 g/km for renewables and 155 g/km for lower coal-based plants . If PEVs charge their batteries from low quality coal-fired sources, their emissions may be 721% lower than HEVs . Even when powered entirely by coal-fired electricity, PEVs still produce around 25% Fewer GHG emissions than ICE vehicles.

Automotive and oil companies allege that EVs would have a net negative effect on the environment because of lead discharges from battery manufacturing facilities and battery disposal , but this conflicts with results from the existing lead-acid battery market, which dwarfs that of vehicles, and moves to other battery chemistries.

3.2 Ancillary Services :

PHEVs are for the moment more expensive compared to conventional vehicles.Selling energy could be beneficial for these vehicles. The batteries can act as a source of stored energy to provide a number of grid services. The most promising market for these vehicles is probably that of the ancillary services . Possible services for V2G are: supply of peak power,supply of primary, secondary and tertiary control (for frequency regulation and balancing), load leveling, and voltage regulation. PHEVs are able to respond quickly and thus serving for high value electrical services. It is unlikely that each vehicle will be contracted separately because the maximum power output of each vehicle is too low. But a fleet manager or aggregator could conclude a contract for a fleet of PHEVs. The advantage of dealing with an aggregator or fleet manager is that a single party represents amore significant amount of power, that is the accumulated power of the vehicles in the fleet.

3.2.1 Load Leveling and Load Shifting

For load leveling, the demand is shifted from peak hours to off-peak hours. Therefore, dispatching is necessary. PHEVs could discharge during the daily peak loads, replacing the peak capacity generators that are only used during peak demand hours. If these vehicles want to discharge during the peak hours, they will have to charge during the off-peak hours. In the case the energy whichis stored during off-peak hours, is released during peak hours to relieve congestion in the grid infrastructure, supplying peak power and load leveling are the same. Supplying peak power is possibly difficult for PHEVs because of the relatively long duration and the storage limitations. Thus, supplying peak power is generally not profitable as the largest cost is the wear of the batteries [14]. Load leveling is more likely because the vehicle does not necessary need to discharge during peak hours. The total consumption of electricity will not be lowered but shifted to the hours of low electricity consumption which are the off-peak hours to minimize the power losses and to increase grid efficiency. The implementation of smart meters or real-time pricing and coordinated charging is essential.

3.2.2 Frequency Regulation

Frequency regulation is used to balance supply and demand for active power . Currently, frequency regulation is achieved mainly by cycling large generators , which is costly.

The primary reserves regulate the frequency and stabilize the European grid to avoid blackouts. The frequency control is activated automatically and continually. Primary control can only be activated if primary reserves are available. The primary reserves are about 100MW capacity. The response time is smaller than 1 s. Secondary reserves are allocated a day ahead to balance the grid and are adjusted automatically and continually, both upward and downward on a 15 min time base. If the frequency is lower than 50 Hz, the batteries could be discharged (regulation up) and if the frequency is above 50 Hz, the batteries could be charged (regulation down). On average, the regulation up and down are equal. The impact on the battery is a small discharge due to charge and discharge efficiency. The reaction time is a few seconds. These reserves are used for imbalances between nominated and measured power injections and to restore the frequency. There are two types of tertiary reserves: tertiary production and tertiary offtake reserves. These reserves are used for major imbalances and congestions. In contrast to primary and secondary reserves, these are activated manually and only a few times per year. These reserves must deliver their power within 15 min.

Fast charging and discharging rates of PEV batteries makes V2G a promising alternative for frequency regulation.A PEV could provide regulation down by charging its battery. If there is a need for regulation up, the battery could be discharged into the grid. If the PEV is charging at this moment, charging can be stopped rather than transitioning to discharge. For secondary and tertiary frequency control, activation is based on bids. When demand for regulation up arises, the lowest bid is activated first. Because delivering regulation down means charging at a lower price, this can be profitable for PEVs. In and , primary control is expected to have the highest value for V2G.

3.2.3 Voltage Regulation

Voltage regulation is used to balance supply and demand for reactive power. PEVs can respond quickly to regulation signals . This regulation can be controlled independently by each PEV. A voltage control can be embedded in the battery charger. A charger can compensate inductive or capacitive reactive power by properly selecting the current phase angle . When the grid voltage becomes too low, vehicle charging can stop. When the voltage becomes high, charging can start .

3.3 Renewable Energy Supporting and Balancing

V2G thus increases the flexibility for the grid to better utilize intermittent renewable sources.. For example, peak solar radiation occurs a few hours before peak energy draw in many markets .. Wind power is more complex, and unpredictable variations in wind speed make it strongly intermittent, leadingto imbalances . If the energy injected to the grid from renewable resources is too high, centralized power plants must decrease their production to restore balance or the distributed generator units must be curtailed. Vehicles can help match consumption and generation by discharging and charging so the utility does not need to decrease the power output. PEVs also can store excess renewable energy. This stored energy can be used for driving needs or to provide power to the grid at a later time.

CHAPTER 4CHALLENGES TO V2G CONCEPT

There are many benefits of V2G systems, increasing the number of PEVs may impact power distribution system dynamics and performance due to several reasons :

Distribution grid has not been designed for bidirectional energy flow, and this tends to limit the service capabilities of V2G devices.

Challenge in implementing assured and secure communications particularly between the aggregator and the large number of PEVs . A reliable two-way communication infrastructure network is needed to enable V2G technology.

Increasing the number of PEVs may impact power distribution system dynamics and performance through overloading of transformers, cables, and feeders. This reduces efficiency, may require additional generator starts, and produces voltage deviations and harmonics.

Depending upon the different levels of PEV penetration on distribution network investments and incremental energy losses, additional generation investments may be needed to serve the extra PEV demand.

These issues are discussed below in detail :

4.1 Battery Degradation

Battery degradation depends on the amount and rate of energy withdrawn and is a function of discharge depth discharge and cycling frequency. Bidirectional V2G for ancillary services is likely to reduce battery life. For many types of batteries, deeper discharge increases the cell deterioration rate, resulting in a faster Equivalent series resistance increase. The internal resistance tends to increase at low temperatures and at both ends of SOC. Using the battery in the middle SOC range is a good way to slow the degradation.

Battery cycle life greatly varies depending on chemical structure and manufacturing process. Li-ion batteries are the best present candidate for V2G, because of their long cycle life, reasonable deep cycling capability, relatively high energy density, and high efficiency. An Li-ion battery lasts for 20004000 deep cycles, and estimated future Li-ion battery investment for mass production lies in the range of $200500 per kWh [54].A battery investment cost of $300 per kWh and a lifetime of 3000 cycles at a depth of discharge of 80% suggest battery degradation cost of $130 per MWh.

4.2 Effects on Distribution Equipment

Depending on the PEV penetration scenarios, Level 2 and 3 battery chargers can quickly overload local distribution equipment. They increase distribution transformer losses, voltage deviations, harmonic distortion, and peak demand . This calls for additional investments in larger underground cables and overhead lines, and more transformer capacity . The cost could significantly impact the reliability, security, efficiency, and economy of newly developing smart grids due to possible loss of transformer life.

CHAPTER 5

STATUS OF IMPLEMENTATION

The use of Electric Vehicles in Vehicle to Grid mode is still in the process of research. The utilities currently having V2G trials are :

1. PG&E, USA, converting a number of company-owned Toyota Prius to be V2G PHEVs at Google's campus.

2. Xcel Energy, USA, converting six Ford Escape Hybrids to PHEVs with V2G.

A brief description of the on-going V2G Project currently going on in Denmark is given below :

Denmarks Edison Project :Denmark's Edison project, an abbreviation for 'Electric vehicles in a Distributed and Integrated market using Sustainable energy and Open Networks' is an ongoing partially state funded research project on the island ofBornholmin Eastern Denmark. The consortium ofIBM,Siemensthe hardware and software developer EURISCO, Denmark's largest energy companyDONG Energy, the regional energy company stkraft, theTechnical University of Denmarkand the Danish Energy Association, is currently exploring how to balance the unpredictable electricity loads generated by Denmark's many wind farms, currently generating ~20% of the country's total electricity production, by using electric vehicles (EV) and their accumulators. The aim of the project is to develop infrastructure that enables EVs to intelligently communicate with the grid to determine when charging, and ultimately discharging, can take place.[13]At least one rebuild V2G capableToyota Scionwill be used in the project.The project is key in Denmark's ambitions to expand its wind-power generation to 50% by 2020.According to a source of British newspaper The Guardian 'It's never been tried at this scale' previously.

CONCLUSION

In this report, a thorough study has been made of the impact of V2G technologies on distributed systems, the benefits, challenges and strategies for its implementation. Unidirectional/bidirectionalpower flow technologies , charging/recharging frequency and strategies were addressed. PEVs can act as reserve against unexpected outages if proper power electronics control, communication interface between grid operator and vehicle owner and smart metering system is established. Unidirectional V2G is cheaper and has lesser hardware requirements than a bi-directional V2G system.

V2G concept can have several technical advantages reactive power support, active power regulation, sources, current harmonic filtering, peak shaving, and load balancing by valley filling. They also offer possible backup for renewable power sources such as wind and solar power, supporting efficient integration of intermittent power production. These systems can enable ancillary services including voltage and frequency control, and spinning reserves. They reduce utility operating costs and even the vehicle owners. Researchers estimate the potential net returns from V2G methods can range between $90 and $4000 per year per vehicle based on power capacity of the electrical connections, market value, penetration number of PEVs, and PEV battery energy capacity .

Challenges to V2G include battery degradation in bidirectional applications, the need for intensive communication between the vehicles and the grid, effects distribution equipment, infrastructure changes, and social, political, cultural, and technical obstacles. Although V2G can reduce the lifetime of PEVs, it is more economical for the vehicle owners and the grid operator due to its various advantages. It benefits the environment and will accelerate PEV deployment. With on-going research, infrastructure development, and as we move towards achieving a smart grid, we might soon overcome these challenges and realize the benefits offered by V2G system.

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Websites :

[18]http://en.wikipedia.org/wiki/Plug-in_vehicle

[19]en.wikipedia.org/wiki/Electric_vehicle

[20]en.wikipedia.org/wiki/Vehicle-to-grid

19