Inductive Power Transfer for Electric Vehicles: Potential Benefits for the Distribution Grid Salman Mohagheghi, Member, IEEE, Babak Parkhideh, Student Member, IEEE, and Subhashish Bhattacharya, Member, IEEE
Abstract—It is believed that the latest advances in battery and converter technology, along with government mandates on energy independence and resilience, will pave the way for higher deployment of electric vehicles in the transportation fleet. These vehicles, when equipped with bidirectional energy transfer capabilities, can function as mobile energy resources and be utilized in a vehicle-to-grid (V2G) scheme to temporarily inject energy back into the power grid. The forecasted increase in the number of these vehicles can turn them into a considerable energy resource to be used by the utilities as ancillary services or even for long-term integration with the grid. The energy injection into the power system by electric vehicles has been investigated in the literature for charging stations or single residential charging devices. The need for the vehicle to be stationary during the transfer, and the possible drive and/or change in the driving route in order to go the station are some of the hurdles that may lead to inconvenience and hence lower V2G participation by the vehicle drivers. Moreover, the need for an electrical connection between the vehicle and the station makes implementing remote supervisory control schemes difficult, if not impractical. However, with the advent of inductive charging systems for contactless transfer of energy, new horizons have been opened for seamless integration of these resources of energy into the distribution grid. This paper focuses on the applications of inductive power transfer systems for V2G purposes in the modern distribution grid. It will be shown here that such a scheme could potentially allow for supervisory control and management of the mobile energy resources with the ultimate goal of improving the reliability and security of the power grid without the need for capacity expansion. Index Terms— Inductive power transfer, electric vehicles, hybrid electric vehicle, distribution system, demand response, service restoration.
I. INTRODUCTION
T
HE High dependence of traditional vehicles on the finite sources of fossil fuels, the environmental concerns on vehicular pollution and the need for higher energy efficiency, fuel economy and fuel flexibility have all paved the way for the introduction of Plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV). The former is defined [1] as any hybrid electric vehicle which contains at least a battery storage system of 4 kWh or more to power the motion of the vehicle, a means of recharging the battery system from an
S. Mohagheghi is with the Electrical Engineering and Computer Science Department, Colorado School of Mines, Golden, CO, 80401, USA (email:
[email protected]). B. Parkhideh and S. Bhattacharya are with the NSF Future Renewable Electric Energy Delivery and Management (FREEDM) System Center of North Carolina State University, Raleigh, NC 27606, USA (email:
[email protected])
external source of electricity, and has an ability to drive at least ten miles in all-electric mode, and consume no gasoline. The latter on the other hand denotes any type of vehicle that is solely propelled by electric motors, and has no internal combustion engine (ICE). Such a fleet of electric vehicles, generally referred to here as plug-in electric vehicles (PEV) can be effectively powered by the underutilized electric power grid during the off-peak hours with little need to increase its energy delivery capacity [2]. Traditionally, PEVs have been considered as nonlinear loads for the grid, whose impacts on stability and quality of supply have been studied in detail [2]-[4]. However, new technological advances in power electronics and machine design, together with the government mandates and subsidies for energy independence and resilience of the transportation system, are expected to further accelerate the penetration rate of PEVs into the transportation fleet. At high penetration rates, it is conceptually possible to utilize these vehicles not just as loads but also as energy resources. The energy stored in the batteries of the PEVs can be potentially extracted by discharging the battery for a relatively short duration of time and injecting its energy back into the grid. This service, often referred to as vehicle-to-grid (V2G), can in principle provide peak load shaving, smoothing generation from nondispatchable renewable energy resources and act as a reserve against unexpected outages [5]. As the size of the PEV fleet increases, the bulk energy storage available becomes considerable in size. For instance, Germany is targeting to deploy 1 million EVs by the year 2020, which corresponds to 2.5% of all the passenger cars in the country [6]. Considering the 45 kW continuous electrical power available in Chevy Volt and 80 kW in Nissan Leaf, this could be translated as 45-80 GW of distributed power sources. This power range is comparable to the Germany’s generation capacity which further emphasizes the importance of EVs. The penetration level of EVs in the western states of US almost follows the same pattern [7]. Clearly, utilization of renewable energy resources such as wind and solar is another comparable source of energy; although, their availability is limited due to their intermittent nature. A generation availability index is defined as in (1) and determined based on the data available from US Energy Information Administration (EIA) [8]. A selected set of results for the year 2009 is depicted in Fig. 1. Generation Availability Index (GAI) = Generation Energy (1) (%) Generation Capacity × 8760(h / yr )
Generation Availability Index(%)
30%
24.7
23.9
25.0
25%
20.0
16.5 20%
15.0
12.2 15%
10.0
10%
5.3 3.3
5% 0.5
3.2 0.003
1.9 0.2 0.1
0% US
Germany
Spain
Denmark
5.0
Generation Capacity (GW)
30.0
35%
China
0.0
Australia
Wind Generation Availability Index
Solar Generation Availability Index
Wind Installed Capacity (GW)
Solar Installed Capacity (GW)
Fig. 1. Wind and solar generation availability index for selected countries.
It can be seen in Fig. 1 that despite the diverse regional generation capacities and characteristics, the GAI is less than 35% for all the countries investigated. On the other hand, it has been shown in the past that energy storage can significantly improve the availability factor of renewable resources, [9] . In fact, the amount of centralized energy storage to achieve an hourly dispatch has been found to be around 20% of the power rating of the wind/solar farm, [10][12]. Currently, the size, complexity and economics of utilityscale centralized energy storage control and management may not have been widely accepted and justified. However, with moderate assumptions, the required power and energy available in the EVs –even with today’s battery technologies– can become available in the very near future. Assuming the targeted numbers for Germany in 2020, with only 10% participation of EV owners, a 4.5-8 GW of power, or –as an example– a 2.25-4 GWh of continuous energy can be made available to the utilities. This is considerable enough to maintain all solar and most of wind generation. However, what differentiates the energy stored in electric vehicles from other conventional sources of energy storage is their mobile nature. Like other storage systems, accessibility of these resources depends on the availability of the primary source of energy (charge on the batteries in this case). Although unlike other storage systems, accessibility of PEV energy depends also on the locations of the vehicles. This complicates matters further by adding another constraint to the problem. Traditionally, people have been looking at extracting the stored energy either from locations where a relatively large number of vehicles exist (e.g., charging stations, parking lots) or from individual charging devices at residential units. The common factor in both lies in the fact that the vehicles need to be stationary (i.e., parked). While this is a reasonable assumption in many cases, it undermines a great potential source of energy in the system: vehicles in motion. Furthermore, in order to inject energy back into the grid, it is necessary for the vehicle to drive to the charging station/device, and park the vehicle for the duration of the
power transfer. On top of those, the driver may have to change its normal route to get to the charging station. All this could inconvenience the driver(s) and hence reduce the tendency (or participation level) for taking part in V2G applications. Moreover, when the source of energy is needed fast (e.g., fast reserves) the distances of the vehicles to the charging stations would serve as a limiting factor. Lastly, for the vehicle to be able to transfer power to the grid, the driver (or an operator) needs to be physically present to establish an electrical connection between the vehicle and the station. Connectionless charging stations (based on inductive charging) have been proposed [13]-[16] as a means for contactless energy transfer. Without the need for establishing an actual electrical connection, these systems enable transfer of energy from the power grid to the vehicle and possibly in the reverse direction through the usage of magnetic circuits. Given the right technical specifications, the vehicle can exchange energy with the power grid while driving even close to normal speed. Utilizing this technology can turn the potential energy stored in the batteries of electric vehicles into an accessible source of energy dispersed across the power grid. In addition, a supervisory control scheme can be designed and implemented that remotely controls these individual sources of energy in order to provide an additional source of energy storage for the power grid. This paper focuses on the applications of Inductive Power Transfer (IPT) systems in the distribution grid, and the added values that such installations can provide for the utility, the customers and the power grid itself. The paper provides a brief introduction to V2G benefits and the concept of IPT in sections II and III. In section IV some of the specifications of inductive charging stations as pertained to distribution grid management are discussed. Section V provides a technical insight into the topic of supervisory control of the IPT systems. Some typical applications of the IPT systems in the distribution grid are presented in section VI. Some practical considerations are provided in section VII, and finally concluding remarks appear in section VIII of the paper. II. BENEFITS OF VEHICLE-TO-GRID (V2G) OPERATION A. Additional Resource for Grid Management Energy stored in the battery of PEVs can be utilized as ancillary services for grid management purposes. With very short response times, especially if fast chargers are used, the vehicles’ batteries can quickly inject power into the grid when necessary, whereas a typical peaking power plant could take up to 30 minutes to ramp up to full capacity. A small amount of discharge provided by a large number of vehicles may very well lead to the same behavior as a traditional energy resource. This way, the bulk energy stored in the fleets of PEVs can be theoretically employed to achieve the following: • Frequency regulation – for fast load changes in the order of a minute, assuming the vehicles are equipped with fast chargers • Load following – for slower load changes in the order of 5-30 minutes
•
• •
Spinning reserves – the available energy can be exploited as spinning reserve for immediate response that can reach full output in a matter of a few minutes, supplemental reserve or replacement reserve with a response time of a few minutes to an hour. Voltage control – especially that the converters allow injection of reactive power into the grid Peak shaving – to provide power during the peak load hours
B. Local Integration with Non-Dispatchable Renewable Energy Resources As discussed in the previous section, the energy stored in the batteries of PEVs can also be used in conjunction with renewable energy resources that are inherently nondispatchable, e.g. wind and solar photovoltaics. If and when the vehicles are available for dispatch they can partly alleviate the volatility of these stochastic generation resources by injecting power into the grid when the renewable resource is
not available, or use the excess energy to charge up their batteries when generation exceeds the load. This can potentially help turn the non-dispatchable renewable resource into a dispatchable source of power. Theoretically, the objective can be achieved by using either the vehicles parked at the parking lots and charging stations, the individual vehicles parked at the residential units, or alternatively by utilizing the energy available through mobile vehicles. Regardless of the approach adopted, the energy stored in the vehicles’ batteries can be used to respond to the fluctuations in the nature of the non-dispatchable energy resources, as well as uncertainties in the network demand. A coordinated control structure as shown in Fig. 2 would ideally monitor the capacity of the main energy source, the forecasted load of the network, and the market data associated with energy prices. In return, it would coordinate the charge/discharge process of the individual chargers and/or charging stations.
Fig. 2. Integration of electric vehicles with non-dispatchable energy resources.
C. Environmental Impact By injecting power into the network, PEVs can help reduce the environmental burdens placed on the air, land and water by reducing or delaying construction and development of new power plants and by allowing usage of the current generation and transmission capacity more effectively. Furthermore, this could help reduce the environmental emissions of the power plants during peak hours. Similar to the financial benefits gained from demand response, the utility can take advantage of the PEV storage to defer building new plants and hence save money. As an example, the overall US capacity is close to 900 GW. Assuming the cost of building a power plant is 1 M$/MW with an average lifespan of 50 years, a hypothetical reduction of
1% in the demand would lead to savings of 1 M$/MW × 9000MW / 50 yr = 180 M$/yr. III. PRINCIPLES OF INDUCTIVE POWER TRANSFER Generally, an IPT system consists of two main parts. One part takes the power from the grid and energizes the track. The other part is a so-called pickup coil. The power is induced in the pickup and transferred to the load. A typical IPT system is illustrated in Fig. 3. Compensation circuits in the IPT system are often resonant circuits to increase the induced current (power) which is normally limited by the self-inductance of the track, misalignment, etc. The output of the IPT system is a regulated DC voltage using a combination of a diode bridge and a switched-mode DC/DC converter. The details of the IPT
system shown in Fig. 3 can be found in [14], [15].
Fig. 3. Schematic diagram of a typical IPT system.
Thus far, unidirectional IPT systems have been mainly investigated because of several improvement potentials in the key market of the technology. However, the IPT system can be bidirectional. With minor changes in the resonant circuits (to be symmetrical), and bidirectional converters, two way IPT system can be realized. A general schematic of a bidirectional IPT system is presented in Fig. 4. In this scheme, a switched mode bidirectional converter would replace the DC/DC converter in the conventional IPT. This way it allows for power transfer in both directions. One of the very few examples of this circuit has been presented in [16].
present. Furthermore, in theory, the inductive charging station can allows for charge/discharge of the batteries while the vehicle is driving on the track, which leads to increased convenience for the drivers. Clearly, this requires the usage of fast chargers that can accomplish the energy transfer within the available time-frame. Such convenient realization of energy transfer would increase the participation level of drivers in V2G schemes initiated by the utility, such as demand response. Although, the slower speed of the charger can be compensated for by building longer tracks that increase the contact time with the vehicle. For instance, the track can be built as a side lane on the street, where the vehicles intending to discharge (or charge) their batteries would take a detour and drive over the inductive charging track. The other extreme alternative is of course the park-andcharge or park-and-discharge type of structure where the vehicles would park on the track for the duration of the energy transfer. In order to justify the higher expenses of installing IPT versus the more conventional connection-type chargers, this scheme could be best beneficial in large parking areas such as terminal parking lots where a remotely enabled supervisory controller would charge/discharge the batteries as needed. More explanations are provided in the following section. V. SUPERVISORY CONTROL OF IPT STATIONS
Fig. 4. General schematic of bidirectional IPT system.
The bidirectional flow of power in the IPT if employed for electric vehicles enables the energy transfer from the vehicle’s battery back to the grid. This way, the vehicle can be viewed as a mobile energy resource that can be integrated into the distribution grid for various V2G applications. IV. INDUCTIVE CHARGING STATION SPECIFICATIONS Inductive charging stations provide benefits over the connection-oriented stations. If energy transfer to the grid is desired, the latter requires the driver to change its route and drive to the station, park the vehicle for the duration of the transaction, and connect to and subsequently unplug the electrical connection from the charger. However, the former scheme is connectionless, which means the energy transfer can be more easily enabled through a remote control process, even when the human operator (i.e., driver) is not physically
The traditional power system control where all the generation units were owned and operated by the utility has now transformed into an open system where various sources of energy (utility owned or autonomous) coexist and interact in the same environment with the overall objective of providing a secure reliable network with high quality of supply. Any portion of such a system is typically equipped with thousands of sensors and measurement units that capture the local state of the system and send it to actuators and controllers. The sheer size of the network necessitates the transport of this data and command signals over long distances across the wide geographical area of the grid, essentially forming a networked control system [17]. Depending on the structure of the grid, the number of components to control and the size of the system, the control system can take on the form of a fully centralized, decentralized or hierarchical system [18]. Regardless of the control structure adopted, for distribution systems, due to the high and direct impact that the system has on the end use customers, having a centralized structure that accurately supervises the performance of the system components deems necessary. Such a system would be the heart of the distribution management system (DMS) and would be in charge of ensuring that all the devices are operating within acceptable limits and the system meets the overall operation criteria set forth by the operator. Among other things, such a system which resides in the utility control center would supervise and manage the energy resources in the grid, including but not limited to electric vehicles. Figure 5 shows a typical realization of a supervisory control system for
management of mobile energy resources via IPT-based charging stations.
where the decisions are made based on some predefined rules and conditions. In more complicated structures it is possible for the vehicle to acquire data on the energy market and related issues through its communication gateway in order to assist real-time decision making. VI. POSSIBLE APPLICATIONS OF IPT IN DISTRIBUTION GRID
Fig. 5. Schematic structure of supervisory controller for management of fleets of PEV using IPT-based charging station.
The operation of the IPT-based charging station must be monitored and supervised by the utility at all times. While the station is in normal charging mode it suffices for the utility to only monitor its status and ensure that the system conditions are not violated. If the utility needs power in certain areas of the network through V2G scheme, it will send a signal to the corresponding stations to activate the V2G mode. This signal may contain the bulk amount of energy that the utility requires along with the desired duration. These numbers would normally come from the higher level calculations at the DMS. The station management system would be responsible for control and management of the track converter and the compensation circuit. Discussion on the details of the control circuits are beyond the scope of this paper, nevertheless, in the most complicated scenario it can be imagined that the area of the track be divided into cells of certain length and width, each one being controlled independently so that multiple vehicles can undergo charge and discharge independently at the same time. At the lowest level of control hierarchy, for moving vehicles, it is only reasonable to ensure that any battery discharging action would be pending approval by the driver. This can be a manual procedure (local or remote access) or an automatic one (sitting at the so called vehicle control box)
A. Bulk Energy in Terminal Parking Lots Ancillary Services are the services necessary to support the secure and stable transmission of electric power from producer to the purchaser, maintaining adequate quality standards. Normally, these services are used for various tasks such as keeping the frequency of the system within certain bounds, controlling the voltage profile of the system, maintaining the stability of the system, preventing overloads in the transmission network, and restoring the system or portions of the system after a blackout [19]-[21]. The value of the ancillary services is quantified in terms of their ability to respond when needed, which varies from a few seconds in more sensitive applications such as frequency regulations, to a few minutes for instance in some load following applications. Traditionally, these services are contracted from a range of different Independent Power Producers (IPP) [19]. However, recently the applications of other active networks within the distribution grid in providing ancillary services has also been investigated [22]. Mobile energy resources such as electric vehicles, when equipped with V2G capabilities, can also be viewed as additional resources of energy which may be utilized by the utility as needed. Hence, when a large number of these vehicles are grouped together, they may be able to provide ancillary services to the grid. However, when being used as reserves, the source of energy has to be on standby and ready to be deployed within a few seconds to a few minutes if needed. This criterion rules out the usage of charging stations for this purpose since by definition (and unless specifically designed otherwise), vehicles would enter and leave the charging station and cannot stay parked for a long duration of time. Terminal parking lots, e.g., at the airport, train stations, subway stations, or even large department stores, on the other hand may contain hundreds to thousands of parked vehicles at any point in time. Many of these vehicles may stay idle for a period of days, for instance in airport parking lots. Potentially, the utility can utilize the energy stored in their batteries; and according to its needs (based on the forecasted shortage of supply) and the energy rates, discharge the batteries and maybe even recharge them if necessary. In fact, schemes for optimal charging the batteries (i.e., unidirectional) have been proposed in the literature [23]. In a more sophisticated structure, the driver (via battery management system or any other vehicle controller) may provide information on the duration of the time that the vehicle is available for charge and discharge (i.e., from the time the owner leaves the vehicle until the time he/she returns). During this time frame, the utility can use the available charge on the battery, and depending on the agreed
upon terms either recharge the battery to the initial charge, or some other user-specific level. In either case, the owner of the vehicle would take advantage of the financial incentives for participating in this transaction. In either case, the supervisory nature of control and the remote access to the vehicles’ batteries makes it more practical to implement a system based on IPT. Such a system would be independent of the owner of vehicle to be physically present. Nor it requires an electrical connection. Figure 6 shows a typical schematic diagram of the proposed system. The heart of the system is the Station Management System (SMS) which is responsible for the overall control and management of the charge/discharge process. It would consist of a master controller, a communication module and a local database to store available information on each vehicle. Examples could be the available timeframe for a vehicle, the terms and conditions the vehicle owner has agreed to, etc. SMS would receive the dispatch commands from the utility control center, and generates discharge/recharge signals to be transmitted to the track compensation circuit. The module also receives the required information from the vehicles. The master controller is the core of the SMS and –among other functionalities– would be responsible for generating control commands for charge and discharge of the vehicles. The module receives the required information through the communication module and would provide algorithms (perhaps mathematical optimization-based) for decision making on the charge/discharge process (time, duration, amount, etc) of the batteries.
Fig. 6. Usage of EV batteries for ancillary services in terminal parking lots.
The track compensation circuit would receive the individual charge/discharge commands from the SMS and may provide charge/discharge capabilities through electrical contact, i.e. plugs, or through connectionless electromagnetic contact, i.e. inductive charging. The former would require the driver to plug in the vehicle to one of the outlets, while the latter only requires the driver to park the vehicle on the designated area. Depending on the level of intelligence required on the vehicle’s part, it may be equipped with a local control box that is responsible for providing the required information to the Station Management System. This information may include (but is not limited to) the vehicle ID, the travel schedule (departure and arrival times), the battery type, state of charge of the battery, terms and conditions of the ancillary service program the vehicle is subscribed to (or perhaps a unique identifier for the program terms). The SMS may refer to its local database to retrieve the required information. It should be noted that upon receiving a discharge/charge signal from the SMS, it is not mandatory to comply with the signal. In fact, it is possible for the vehicle to have its own module that might override a signal issued by the Station Management System (based on some customized rules and conditions). Such a module would sit at the vehicle control box. The coordination can be achieved for instance by having a mechanism that in addition to the signal received from the master controller, checks for an approval message from the vehicle control box before activating the discharge/charge process. Such a scheme –which is similar to the demand response in home automation systems, would be practical with the inductive charging scheme where the owner of the vehicle can remotely approve/reject a discharge request by the SMS. B. Service Restoration Distribution networks are prone to different faults and disturbances that –whether temporary or sustained– are normally cleared by the protection system, isolating the faulty part of the network from the healthy section. Depending on the location of the fault, the selectiveness of the protection scheme and the topology of the network, some healthy sections of the network can also be left without electricity as a result of a disturbance. These healthy sections are referred to as the outage area whose loss of power leads to involuntary loss of load and thereby lowering the reliability index of the network. Electric utilities will therefore employ power restoration solutions to further narrow down the faulty area once the disturbance has been isolated and supply electricity to the deenergized healthy sections. This is often achieved by finding switching sequences and alternative sources that can supply those sections through alternative routes [24]. Clearly, the restoration source should be able to supply energy to the loads located in the de-energized healthy section without causing operating constraint violations such as line overloading or abnormal voltage levels. These operating constraints are generally the limiting factor in determining the feasibility of the restoration solutions and choosing one over another [25]. In a more simplified vision, the normally limited capacity of the restoration paths would force a binary solution where
either all or none of the loads in the outage area can be restored. However, in the modern smart grid paradigm, with the introduction of additional sources of energy (e.g., demandresponsive proactive consumers, energy storage systems, and autonomous renewable energy resources) spread across the distribution network, the nature of the service restoration problem changes from an all-or-none solution to somewhere in between where the restoration source may partially energize the outage area. Electric vehicles with bidirectional energy transfer capabilities can be considered as another alternative source of energy that can provide partial support to the grid during service restoration. These devices can theoretically inject power into the network of the restoration path or the outage area, and act as virtual sources that can increase the capacity of the path. Clearly, the utilization of the energy provided by the EVs in terminal parking lots –as described earlier in this section– is one solution; however, the utilities can also utilize the energy provided by mobile vehicles through inductive charging, as described below. Figure 7 illustrates an example where a two-source feeder with a normally open tie switch R3 is being supplied through two sources S1 and S2. Switches R1, R2, R4 and R5 are normally closed. An inductive charging station C is connected to the system to provide bidirectional power transfer for the electric vehicles. In the following diagrams red and green colors for the switches indicate closed and open switches respectively.
Fig. 7. Inductive charging station used for service restoration (normal condition).
If a fault occurs at the section of the feeder supplying L1, switches R1 and R2 open up to isolate the fault, which in addition to isolating L1, results in L2 without electricity (Fig. 8). The service restoration algorithm can send a command to close R3, so that L2 can be supplied from the source S2 (i.e., restoration source). The total load to be supplied by S2 now includes the load on the restoration path, i.e., L3, L4 and C, and the load in the outage area, i.e., L2. For the restoration algorithm to be successful, the restoration source should be able to feed this load. If this is too large for the capacity of S2, then the service restoration algorithm may try to utilize the
energy provided by the vehicles’ batteries.
Fig. 8. Inductive charging station used for service restoration (during fault condition).
The utility may send broadcast messages detectable by the electric vehicles in the vicinity of charging station C so they drive on the inductive charging path and enable partial discharge of their batteries back into the grid. Alternatively, it can target specific vehicles and send dedicated messages to them so they inject energy back to the grid at specified locations. With enough vehicles discharging their batteries through the track (e.g., sufficient participation or high traffic), the capacity of S2 may be sufficient to supply the loads in the restoration and outage areas, so the switch R3 can now be closed re-energizing L2 (Fig. 9).
Fig. 9. Inductive charging station used for service restoration (during service restoration). A broadcast message is shown in the diagram that is detectable by the vehicles in the vicinity of the station.
VII. PRACTICAL CONSIDERATIONS The energy transfer between the vehicle and the grid can be controlled through a local (through permission by the vehicle’s owner) or remote scheme (activation by the utility). In the former case, the utility sends a request to the vehicle but compliance is pending approval by the driver (or an automated control box residing in the vehicle). The latter allows the utility to directly send the control signal to the vehicle and
start the charge/discharge process. There are pros and cons associated with both schemes. The local control scheme provides a higher comfort level for the vehicles’ owners as they ensure they allow for energy transfer at their convenience. Whereas the remote control scheme, although less convenient for the drivers, may provide better assurance for the utility that the required energy transfer is likely to be met. It can be imagined that for applications where the vehicle is mobile, the driver needs to approve the transfer, therefore local control scheme is more appropriate. However, when the vehicles are parked (e.g., terminal parking lots) the utility may be granted access to the charge in the battery. This is similar to the conventional demand response which is roughly classified into a group of direct load control where the utility may unilaterally turn off certain appliances such as heaters, and interruptible load where the utility sends a signal to the customer who then decides whether to reduce its demand or not [26]. Privacy and cyber-security are other issues that needs to be fully addressed. Applications such as the ones described in this paper are very sensitive to cyber-intrusions and unauthorized access to personal data. Any communication channel between the utility and the vehicles’ gateways must be secure with respect to cyber attacks, as the information on mobile resources would typically include their whereabouts and daily driving patterns among other things. VIII. CONCLUDING REMARKS Electric vehicles are expected to appear in large numbers in the transportation fleets in the near future. With the latest advances in battery and converter technology it will be possible to use these vehicles in Vehicle-to-Grid schemes where the vehicle injects energy back into the grid through a bidirectional charger structure. While this scheme is possible through the conventional charging stations, the utilization of inductive power transfer systems for connectionless transfer of this energy to the grid can provide means for seamless integration of these mobile sources of energy into the distribution network. The ability to provide means for a remote supervisory control scheme is one considerable advantage that this technology has over its conventional counterpart. This paper discussed some of the technical considerations, specifications and applications of IPT systems related to management of electric vehicles in a V2G scheme. Using these resources of energy for ancillary services, demand response and service restoration are some examples that were set forth in the paper. With the expected rate of deployment of electric vehicles in the transportation fleets, they can serve as an invaluable asset for improving the reliability and security of the grid, while responding to environmental concerns by postponing capacity expansion projects. IX. REFERENCES [1]
IEEE-USA, Board of Directors, Position Statement: Plug-in Electric Hybrid Vehicles, June 15 2007.
[2]
[3] [4] [5] [6] [7] [8] [9]
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