What Is An Electrical Grid Information Technology Essay
Everybody wants cleaner greener environment around us and the world. Dependency on natural resources must be reduced, so going electric might be a step closer for greener world. Electric vehicle and hybrid electric vehicle contribute to the transportation 2.0.This change will occur in near future, lots of hybrid electric vehicle are seen now-a-days. The automobile industries are investing on electric and hybrid electric vehicles, as they see the future in going electric. Most of the plug-in electric vehicle uses the power from the grid, how about giving back the power to the grid, this is called vehicle to grid technology. For this lot of research is going on with batteries and in the field of fuel cell. This review paper will have how this technology evolved and what are the developments in this technology.
Supply of electricity from suppliers to consumers in an interconnected network is an electrical grid. In power industry the term "grid" is used for an electricity network, which might support all or any of the following operations.
The figure shown below might give a better idea about the electrical grid. The figure shows the entire generation and distribution of the electricity from source to destination.
Hybrid electric vehicle (HEV) is a vehicle in combination of internal combustion engine propulsion with electrical propulsion system. The first hybrid electric vehicle was built by an Austro-Hungarian automotive engineer; he is none other than Ferdinand Porsche. The most of the concepts that are implemented now are from the military and aerospace industry. As the technology developed there were significant improvements in the field of hybrid vehicles, now the HEV's use technologies such as regenerative braking which improves the efficiency to a far extent. The most of the hybrid electric vehicles use start-stop mechanism which is one of the major improvements in the automotive industry. The typical HEV is as shown in the fig below.
Fig2. Hybrid electric vehicle (Parallel hybrid).
Plug-in hybrid vehicle is a hybrid electric vehicle with rechargeable batteries which can restore charge by plugging it into an external electric power source. Let's go back to see a history of plug-in hybrid, the first hybrid vehicle was Lohner-Porsche Mixte Hybrid developed in 1899 by Ferdinand Porsche. This was a series hybrid vehicle using electric motors one each wheel hub powered by batteries and generator motor. This vehicle could travel 40miles on electric it included generators driven by Daimler IC engine (2.5hp). The maximum speed achieved by this was 25mph. The electric motor drove the vehicle if the speed was below 15mph utilizing the power from the battery pack and if the speed as above this the main engine used to take care of the same. Mixte also broke all the Austrian speed records, which also won a rally in 1901; this was driven by Ferdinand Porsche himself. Later in England George Fisher sold hybrid buses in 1901.Using the same layout many modern cars are developed such as Chevrolet Volt, Cadillac Escalade and many more. From this we know that hybrid concept is no new, but this was not exploited later. Now most of the automobile companies are going hybrid and investing money in this technology.
Introduction to Plug-in Hybrid Vehicles (PHEV)
Plug-in hybrid vehicles are nothing but hybrid cars with added battery. As the term itself says that "plug-in" these are regular cars which can be charged from a voltage source. The battery pack that is used here are rechargeable batteries, the plug from the cars go to the electric grid for charging. Plug-in hybrid vehicles operate in mixed modes that are charge depleting charge sustaining modes.
In Charge-depleting mode, the fully charge PHEV will exclusively operate in all electric mode until a predetermined level, at this point the ICE comes into picture where it takes over the responsibility of the car. Blended mode is also a kind of charge-depleting mode; it is used in vehicles which do not have enough electric power to sustain at higher speeds without the help of ICE powertrain.
Fig3. Plug-in Hybrid Vehicle
In Charge-sustaining mode, is used by most of the Hybrid vehicles, this combines the operation of vehicle's power source in such a manner that it produces maximum efficiency by not allowing the battery's state of charge to go outside the predetermined level.From this we can know that the battery in a HEV can imagined as energy accumulator than as a fuel storage device. If a PHEV has emptied the all-electric range in charge-depleting mode it can automatically switch to charge-sustaining mode.
In Mixed mode, it describes the combination of both modes. Here depending upon the speed the modes change and thus keeping the fuel economy on the higher side. Beyond the all electric range, the vehicle is run on charge sustaining mode similar to conventional Hybrid cars.
Electric Power Storage
The main source of storage in any HEV is the battery, so better the battery the better is the performance of the vehicle. In PHEV the battery typically requires deeper charging and discharging cycles. Lithium iron phosphate batteries are used in most of the automobile industry, TESLA uses these batteries for the power generation. "Ultracapacitors" are also so another source where some plug-in hybrids use this as the source of power, if they require high power density as these can store rapid available energy. State of Charge (SOC) is the defined as the ratio of actual energy in the battery to the maximum energy that can be stored in the battery expressed in percentages. The SOC should on drop below 20%, in order to extend the lifetime of the battery. The stored energy in the battery can be used to fulfill the need of the local demand on a feeder, intern contributing to the "peak shaving" (sending the power back to the grid when there is a high demand). The advantages of "peak shaving" include line losses, transmission congestion, delay transmission and reduce the stress on the power system.
What is V2G?
Vehicle-to-grid is where a system in which electric or plug-in hybrid vehicles will communicate with the power grid by either delivering electricity into the grid or by throttling its charging rate.
In V2G operation mode of the vehicle (PHEV) it allows to operate as a load, standalone source of energy or distributed storage. Care must be taken for the on-board battery unit as this should not exceed its depth of discharge, which intern impacts on the life expectancy of the battery. The stored energy of the PHEV can be taped while parked, large amount of energy can be provided during the day. Electric vehicles can act as distributed energy resources as both supply and demand resources. As we know that most of the vehicles are parked 95% of the time, then if it can provide energy during this time period then lots of energy can be saved. The basic idea here is to use the stored energy rather to drain the energy without using it. This idea can further adapt and can be used as uninterrupted power supply for household appliances.
Need for Networking in V2G Technology
The basic question arises do we need to use networking and why it is needed in V2G, the answer is yes. The reason being that the monitoring the power generated by each feeder at each point to the main power distribution system. An aggregator is required because the power generated by the PHEV is very less and introduces only noise in the grid, so the aggregator accumulates all the energy generated by the few vehicles and then it is transmitted to the nearby aggregator. Aggregation of the power supplied from the PHEV is essential to provide ancillary services, also the exchange of information between the aggregators and between the aggregators and with the independent system operator (ISO) is required to manage the operation of power system better. A novel communication system is designed for V2G technology for tracking the energy produced by each aggregator. The figure below shows the data exchanged between different components in the network.
Fig4. Proposed communication structure prototype.
The proposed solution uses ZigBee technology, for the communication between electric vehicle and parking lot or house. The communication between the parking lot or house is using the internet. ZigBee is used because of the advantage of high flexibility and low cost. To identify each single PHEV SIM technology is used so that the vehicles are uniquely identified and only small thing that needs to be done is inserting the SIM to the PHEV. The data transmission is quite low because it doesn't contain any load as mobile data, this data might contain the SOC, its threshold and the power it is transmitting. One more concern is the range of the communication should be more too; RFID will not do this work so SIM will do all the tasks easily and efficiently as this is already proven technology and can make use of the existing routers and base station for communication purpose.
Voltage Stability a concernâ€¦..
The ability of power system in restoring the bus voltages following disturbances is called voltage stability. A detailed modeling of dynamics is required for short term voltage stability especially for dynamic loads. PHEV is connected to the power electronics interface through the system and thus will be modeled as a constant current load. Of course there are some concerns about line faults or generator tripping which can also be taken care off.
The main concept of V2G and the test resultsâ€¦.
There are different stages of which the hybrid vehicle can work in order to be v2g compatible; we know that a vehicle which can give back power to the grid a vehicle with this type of technology is V2G capable. There are lots of papers that are published in the field of communication networks to manage the charging and discharging of the vehicle in V2G technology. All vehicle to grid technology vehicle should have the 3 main required elements they are power cable connection to the grid for electrical energy flow, logical and control circuitry for communication with the grid, and on-board precision metering.
When a vehicle is in charge mode instead of V2G mode, then a simple charging will occur, where there is transfer of energy from the grid to the vehicle.
Fig5. Test results graph of the v2g vehicle and battery.
Depending upon the charging infrastructure of the battery gets charged to the maximum power level. The battery's upper and lower limits are truncated to preserve the battery life. A test was conducted from one of the Industry-university research team, the SOC of the battery was initially at 78% at 10:00am, then upon charging it for 1hour the battery reaches 90% SOC and then on the battery management system cuts of the charging time as you can see this in the graph below which has been plotted for the same. The plot shows the details of the vehicle power and battery SOC in percentage.
To test the vehicle discharge capability we can put a manual load in the grid. The vehicle was tested by putting some power back to the grid. Upon this the same graphs as shown in the above diagram was plotted, the discharge was started upon 11% SOC of the battery. The figure below shows the graph which is depleting from the charge to discharge area.
Fig6. Vehicle power and battery SOC(%) degradation in discharge cycle.
There is also scare for overcharge of the battery, so regulation must be done in downwards that is removing the power from the grid. The vehicle in the example is designed such that at 90% of SOC it cannot be charged at maximum power and at 96% of SOC the charging completely stops, thereby avoiding the overcharging of the battery. Some statistics of the vehicle is that, this vehicle can be plugged at home and again in parking lot at work can provide V2G regulation services for majority of the day. The revenue of V2G was 21.5hours, it was run for 45miles.
Current and future projects in V2G technology
Since the year 1997 the V2G program is promoting the idea of electric or hybrid vehicles giving back power to the grid when it is not driven. In university of Delaware sits 3 converted Scions which use V2G technology. The Center for Carbon-free Power Integration is keen in promoting this; also the state of Delaware owns 4 of them too. The vehicles that are contributing energy to the national grid will be paid for the same. Dr.Kempton is leading the research team in the university. He has connected five of such Scions to his laptop in the lab which gives the continuous data of the V2G vehicles about their battery charging status and also the power it has given back to the grid. One of the car which was run for about a month has generated revenue of $145 to the university from the state of Delaware. The key part of this is the power cable which is used for transmission of power from and to the grid from the radiator grille to the outlet which leads to the power socket in the parking lot in the university.
In a V2G world ideally there would be such hook-ups at the highways, rest stops and parking lot where the HEV can be recharged, and an overnight charged car can give back power to the grid. Using the internet the power needs of vehicle's battery and the grid can be found out this was said by the professor in the university. To promote V2G technology in the state of Delaware, the state passed a law in 2009 saying that the owner of the vehicle gets paid for the amount of power generated and provided to the national grid upon number of units provided by the individual. The cost of electricity produced by any HEV to the grid with lead acid battery is $0.23/kWh, with nickel metal hydride (NiMH) which is used in Honda EV plus is $0.45/kWh; the vehicle with nickel cadmium (NiCd) battery is about $0.32/kWh. Fuel Cell can produce revenue in the range of $0.09 - $0.38/kWh which is taking care of the cost of hydrogen. Now the converted scions are sold at $75,000, the professor says the price will go down as the production increases and the cars can be sold at $3,000 - $5,000. Also he says that in 30 years of time from now all cars in U.S will go electric and this is because of the rising cost of the gasoline and all the gasoline will be bought by china in the years down the lane.
Key: $net (revenue - cost)
Battery, full function
$267,(510 - 243 )
$720, (775 - 55)
$3,162 ( 4479 - 1317)
$75, (230 - 155)
$311, (349 - 38)
$2,573 (4479 - 1906)
Fuel Cell, on-board Hydrogen
$-50(loss) to $1,226 (2200 - 974 to 2250)
$2,430 to $2,685 (3342 - 657 to 912 )
$-2,984 (loss) to $811 (2567 - 1756 to 5551)
$322 (1500 - 1178)
$1,581 (2279 - 698)
$-759(loss), (2567 - 3326)
Table1. Net profit from V2G vehicle's owner from the full analysis report (University of Delaware).
AC propulsion V2G quick Specs (ebox)
120kW, 220N-m, 1300rpm drive system.
35kWh Li-ion battery pack
Upto 18kW Onboard charger
Maximum of 18kW Bi-directional power converter.
120 - 150miles range.
95mph Top speed
The above statistics are of one of the V2G vehicle that is used in the University of Delaware, the specs are of Toyota scion. AutoPort is the first licensed company to practice V2G technology. USPS (United States Postal Service) vehicles are the testbed for vehicle to grid technology usage. Usage of power electronics can convert electric and hybrid to plug-in or to V2G capable. The reviewing of many electric and hybrid vehicle are being performed by National Renewable Energy Laboratory (NREL) to test and verify the utility connection standards for these vehicles.
An interesting set of ancillary services to the grid can be provided by the Electric vehicle, which may contribute towards the required storage capacity that enables use of renewable energy. The main intention of this paper to know how the vehicle to grid technology emerged? and how it is taking shape now. In this paper we came across many kinds of charging the battery and discharging of the same.
Different batteries give different output with respect to the energy output to the grid, as there is an improvement in the battery technology there will be a significant improvement in EV and V2G technology as well. Fuel cell is another option, but the cost is the concern, that is using hydrogen as source and the implementation cost. We also saw the EV vehicle of University of Delaware converted to perform V2G technology, which is also supported by federal government too.
We have seen vehicle to grid technology can bring an impact to the environment by saving gasoline and making the nature around us greener and cleaner. Having learnt a lot about V2G, the main transformation is to go electric and also give back energy to the grid so as to use this energy for home appliances of provide it to the national grid. I have decided to take a electric car because of this paper and if it is of vehicle to grid technology vehicle then it would be really good, so in near future you can see the V2G car in IIT campus.
After all our intention is to keep our environment greener, V2G is a step closer to achieve greener earth!
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