1 Overview. With the promotion and application of electric vehicles and the
construction of charging stations, people's understanding of electric vehicles
and charging stations is no longer limited to transportation tools and "gas
stations", but they hope to develop a wider range of applications. Although most
of the charging stations currently operating and under construction at home and
abroad only have the single function of supplying energy to electric vehicles,
the United States, Germany and other countries are already conducting research
on V2G (Vehicle to Grid) related technologies. V2G refers to the two-way
exchange of energy and information between electric vehicles and the power grid
as a mobile energy storage unit under controlled conditions. The electric
vehicle (charging station) not only obtains energy from the power grid, but also
realizes the transfer of energy to the power grid when necessary. The power grid
sends electricity back, thereby improving the reliability of grid operation.
Electric vehicles containing distributed mobile energy storage units have the
advantages of complementing the large power grid, relieving grid power supply
shortages and improving grid reliability. With the development of technology,
the mobile energy storage application of electric vehicle power batteries can
further reduce the investment and operating costs of the power system. The
combination of ultra-large power stations and decentralized micro power stations
can reduce investment in transmission and distribution lines and improve the
operation of the power system. safety and economy. In particular, compared with
many distributed power sources, the biggest advantage of electric vehicle power
battery mobile energy storage is that when a large-scale power outage occurs in
a large power grid, the electric vehicle power battery mobile energy storage can
still maintain normal operation, which can Improve the disaster resilience of
power systems. Overall, the application advantages and feasibility of 2V2G
technology are that the peak-to-valley differences of major power grids are
increasing day by day, and the contradiction between the power grid's peak
shaving capabilities and the objective peak shaving needs is very acute. V2G's
participation in power system peak shaving is important for coping with the
increasing demand for peak shaving. Serious peak load regulation issues are of
extremely great significance. 2.1 Advantages of V2G technology application (1)
Adjustment of capacity can be guaranteed. 90% of electric vehicles can
participate in V2G services 24 hours a day. Even during peak traffic periods,
more than 80% of the vehicles are parked, and private electric vehicles are
parked most of the time. (2) Fast response speed. The charging and discharging
of electric vehicles with bidirectional power adjustment function can reach ms
level, while the traditional peaking power supply has to take into account the
life of mechanical components, and the fastest response time is around s level.
(3) The response power reserve margin is small. The inaccurate response of
traditional peak shaving and frequency modulation to AGC signals requires a
larger response power reserve margin for power grid dispatching, while V2G
responds quickly and accurately to peak shaving and frequency modulation
commands, which can reduce the power reserve margin. (4) High overall
efficiency. The charging and discharging efficiency of the battery is higher
than the average comprehensive energy efficiency of general pumped storage power
station operation. (5) It has obvious social and economic benefits. Electric
vehicles can take advantage of off-peak power from the grid and provide services
when the grid is at its peak. 2.2 Feasibility of V2G technology application
Electric vehicles/charging stations have a two-way power exchange function,
which can not only transmit power to the grid (i.e., the discharge state of
electric vehicles), but also absorb power from the grid (i.e., the charging
state of electric vehicles); secondly, electric vehicles / The charging station
has a two-way communication function and can remotely receive instructions and
send power information. The peak shaving instructions are sent to the electric
vehicle by the grid dispatcher through the communication network in the charging
station. The response of the electric vehicle is monitored, recorded and fed
back to the charging station through the communication network ( Backend
management system). If electric vehicles develop to a certain scale and have
relevant policy and technical support, peak shaving instructions can also be
sent directly to electric vehicles through wireless communication, and the
responses of electric vehicles can be monitored and recorded (the response
results of each electric vehicle should also be fed back through wireless
communication To the charging station background management system). Therefore,
electric vehicles can achieve organized and planned peak shaving according to
the requirements of the grid. 3 Basic ideas for realizing V2G peak shaving
applications. Based on the peak shaving needs and the V2G statistical
information of each charging station, the power grid formulates a V2G charging
and discharging plan through relevant strategies and sends it to each charging
station; after receiving the plan, each charging and discharging station will
pass the relevant Strategies and algorithms rationally select vehicles, allocate
charging and discharging power, and ensure reasonable execution of charging and
discharging plans. 4. Prediction of available capacity and available time. From
the perspective of grid security, V2G, as a large number of distributed power
generation units with user participation, connected to the system will
inevitably have a certain impact on the operation of the grid. Therefore,
accurate prediction of V2G in the dispatch process Various parameters in the
grid will definitely become one of the issues that the power grid dispatching
and operating agencies pay attention to. Precisely because V2G has two-way
interaction with user energy, its available capacity prediction problem is more
complex than traditional load prediction. From a technical analysis, the
available capacity of V2G energy storage can be obtained in the following two
ways. (1) The user setting method means that the user sets the plan for the
vehicle to participate in V2G for the next week on a weekend. The V2G operator
and the backend management center use this as a standard to calculate the V2G
available capacity for the next week, and give priority to the planned part in
the actual charging and discharging execution. This model is similar to the
contract market and real-time market models in the power market, and has good
promotion prospects. (2) Using historical data for prediction, V2G capacity is
closely related to weather, holidays, prices, temperatures, seasons, economic
development, and the number of electric vehicles participating in V2G services.
In the early stages of V2G service implementation, since there are relatively
few participating vehicles, a peak-hour discharge model can be adopted. As the
technology and market mature, the number of participating vehicles will
gradually increase, and the historical data of V2G will gradually accumulate, so
that various prediction methods can be used to predict available capacity, such
as the regression analysis method, time series method, etc. commonly used in the
current power system. Exponential smoothing method, gray model method, Kalman
filter method and some artificial intelligence methods such as expert system,
artificial neural network, fuzzy prediction and other methods. The main
components of the V2G system are: battery management system (BMS), charger and
discharger, V2G background management system and V2G control center. Its various
functions and control relationships are as follows: (1) The V2G control center
formulates V2G charging and discharging plans based on load forecast, V2G
forecast and new energy power generation forecast and publishes them to each V2G
background management system; the V2G control center bases on the real-time
frequency of the power grid, The real-time power of new energy power generation
forms real-time frequency modulation power commands and disturbance suppression
commands and is sent to each V2G background management system; (2) BMS provides
the maximum charge and discharge current, real-time battery power and voltage,
battery charge, and battery charge to the V2G background management system
through the charge and discharge machine. Discharge permission and other
information; (3) The user inputs the SOC lower limit and available time
information on the human-machine interface on the charger and discharger, and
sends it to the V2G background management system; (4) After obtaining the above
information, the V2G background management system will use the charging and
discharging strategy according to the Select the charging and discharging
vehicle and charging and discharging power, and control the execution of the
charging and discharging machine. At the same time, the V2G background
management system monitors the information of the entire charging and
discharging station and feeds it back to the V2G control center. The above
various information and command transmissions are completed through the
communication network. 6 Conclusion With the development of the scale of
electric vehicles, the development of electric vehicle charging and discharging
technology and networking, and the development of smart charging station
technology and management models, electric vehicles will increasingly reflect
the need for clean and energy-saving transportation. The role of the power grid
in providing reliable and high-quality power supply.
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