Electric vehicle network technology: supporting electric grid with electric vehicles

With the intelligentization of power grid operation and the popularity of electric vehicles, it has become possible to solve the inherent problems of large-scale power grids through the exchange of information between electric vehicles and the electric grid and the use of electric vehicle power storage functions.

The technology used here is called electric vehicle networking technology.

One, the soft underbelly of the power grid

Under the appearance of a huge transmission grid, the regulation of the grid is a very fragile task.

In simple terms, the parameters of a normally operating grid are almost stable. In a particular grid, all generators entering the grid should have the same speed, and the electricity generated should be equal to the power required by the user. Power generation and power supply are like a balance and they must be as close as possible to balance. In terms of professional terms, it is necessary to perform peak shaving on the grid at any time to ensure the balance of the grid.

However, as a huge number of users in the power grid, their power consumption changes rapidly, showing a close to a sleek curve change compared to the capacity of the power grid. However, a limited number of power plants in the power grid, whether they are listed or decommissioned, are presented. Make a step change. This kind of change will have a certain impact on the power grid itself, and when it is severe, it will cause the power grid to lose its oscillation.

When this out-of-step shock is strong enough to a certain extent, it may cause the power plant to trip. The tripping, in turn, caused the power supply gap to increase, causing more severe oscillations, such as the collapse of a series of dominoes, the continuous increase in power supply losses, the rapid increase in the extent of power outages, and eventually the possibility of being too large to control.

The large-scale power outages that occurred in the United States and Canada in 2003 were caused by out-of-step shocks caused by accidents at individual power plants. The large-scale power outage that occurred in the United States on April 7, 2015 may have also been caused by the destabilization of small-scale fires in power plants.

On the other hand, the mainstream mainstream forms of power generation (coal power, hydropower, nuclear power) are all very time-consuming and labor-intensive. For example, thermal power plants are composed of boilers, steam turbines and generators. The boiler generates steam to propel the turbine to generate electricity. From boiler heating and boosting to the turbine speed reaching rated, the final operation of the generator set meets the voltage frequency requirement of the network, which is a long process. The reverse process (stopping power generation) is also quite time consuming. Therefore, relative to the rapidly changing state of the power grid, the correspondence between the power generation units governed by the power grid is very slow. Even in some extreme situations, the shutdown of the power generation unit even needs the support of the power grid, otherwise a major accident may occur.

The familiar accident of the Fukushima nuclear power plant in Japan was like this: When the great earthquake struck, the Fukushima nuclear power plant immediately stopped generating electricity, and was shut down. The cooling process after the nuclear power station was stopped also needed electricity! It was precisely because of the earthquake that the towers that supplied power to the nuclear power plant collapsed and this part of the electricity could not be supplied; the tsunami after the earthquake destroyed the remaining power supply of the nuclear power plant, and the internal heat of the reactor could not be distributed. Produce a large amount of water vapor, cause explosion and cause the nuclear reactor to overheat and melt, and then the worst nuclear power plant accident has occurred since Chernobyl.

Second, the so-called electric car network technology

The electric vehicle network access technology is based on the vehicle's power storage function and supports an application of smart grid work.

There are three parts that smart grids expect from electric vehicles.

1. Absorb surplus power generated by non-mainstream forms of power generation (power generation other than thermal power, hydropower, and nuclear power), that is, as a grid-to-vehicle (G2V) grid capacity.

This function is mainly used to ease the fluctuations caused by peaks and troughs in the power grid, and to ease the pressure of power grid mediation and dispatching;

2. Power supply from the vehicle to the grid, which means that the capacity of the grid to support the grid is insufficient (V2G, Vehicle to Grid)

3. As a home-powered power supply during a power outage (V2H, Vehicle to Home)

This function is mainly used to deal with large-scale disasters such as floods, earthquakes and fires. When the public power supply system is damaged and cannot provide normal power, the vehicle battery is used to supply power to the household so as to maintain the normal life of the family;

The above functions can be summarized into the following table:

Third, use electric vehicles to support the power grid

As a "mobile large battery", electric vehicles can contribute to the stability and normal operation of the power grid.

Research shows that small vehicles used by individuals (including pure electric vehicles and hybrid vehicles) travel only about 10% of the total time (which can be understood as 24 hours a day), and the time before and after 90% is the stop time. If this 90% of the time is connected to the power grid, the battery resources of the vehicle can be fully utilized, and the burden on the vehicle owner can also be reduced.

Take the example of LEAF, a Japanese Nissan Motor Co.'s electric vehicle, with a battery capacity of 24kWh. According to the average user's average travel time of 30 kilometers, about 4kWh is consumed. If such an electric vehicle is networked, this extra 20 kWh can be used as a buffer for the grid.

According to reports, as of the end of 2014, the number of vehicles in China was 154 million. If 1% of them were electric vehicles, their capacity reached 3.08 million kWh, which is equivalent to the capacity of three of China's largest thermal power generating units.

Fourth, the problem of electric vehicle network technology

At present, the following problems exist in the technology of electric vehicle network access:

1. Connect the electric vehicle to the power grid and implement the above-mentioned functions to support the power grid. It requires certain hardware conditions. In essence, there is no visible benefit to the owner of the grid to support the operation of the grid. Therefore, how to resolve the cost of importing such hardware and how to mobilize the enthusiasm of vehicle owners to invest in hardware access through policies (such as economic benefits, etc.) is what the government departments that hold public grid resources need to do.

2. When an electric vehicle (more accurately, an on-board battery) supports a power grid, it must generate a higher number of charge and discharge times than usual. As we all know, the number of times the battery is charged and discharged is limited. If the life of the battery is shortened due to network access, how to make economic compensation to the owner is also a problem to be considered.

3. From a technical point of view, since the electric vehicles entering the network are used as a buffer device of the grid capacity, under extreme conditions, there may be a case where the battery is insufficiently charged to affect the use of the vehicle.

V. Conclusion

The electric vehicle network technology is a systematic project that requires long-term research, planning and adjustment. It not only covers the representative industries of the two modern worlds of the automotive industry and the electric power industry. At the same time, because it involves a large number of information transmission processes, it is valued by the IT industry.

Countries around the world are also formulating economic policies and industrial policies that are in line with their own national conditions based on their own industrial characteristics and economic development. At present, the technology of electric vehicle network access has gone through preparatory studies such as concept studies and gradually studies the integration of electric vehicles and electric vehicles. European countries that have moved faster (especially Germany) have started to make proposals for international standards. Competition for the dominance of international standards is beginning to show dramatic trends.

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