## 1 Introduction  
With the development of the world economy, the number of automobiles is increasing rapidly, which has brought about a series of environmental and traffic problems such as exhaust gas pollution, accelerated consumption of fossil energy, traffic congestion and parking difficulty. People's quality of life and the development of the city are greatly restricted. As a green travel tool, replacing fuel vehicles, electric vehicles will become the main means of transportation in the future, which has become a trend of the times [1]. Meanwhile, the emergence of the sharing economy has made resource utilization more rational. According to statistics, each shared car can replace 6-10 private cars on average [2]. Once it is applied on a larger scale in transportation, it will greatly improve the current traffic situation, relieve the pressure of infrastructure and improve the efficiency of resource utilization [3]. For consumers, car sharing services can save the cost of car purchase, maintenance, insurance, parking and so on while meeting travel demand [4]. What cannot be ignored is that electric vehicles not only can be regarded as mobile loads but also flexible energy storage units, which will provide high quality auxiliary services for the power grid, such as peak shaving, frequency modulation and spinning reserve [5; 6]. Moreover, the application of the sharing mode makes electric vehicles (EVs) belong to one or more interests, when dispatching the shared electric vehicles to participate in grid auxiliary services, the interests are more easily coordinated and the efficiency will be significantly improved. Therefore, promoting the development of shared electric vehicles is of strategic significance for alleviating environmental and traffic pressure, promoting the effective allocation of resources and ensuring the safe operation of the power grid. At present, there are some existing literatures about electric vehicle sharing, mainly focused on market forecasting, network planning, operational mode, and pricing mechanism analysis. [PERSON] [7] predicted the future car sharing market in Australia, Malaysia, Indonesia and Thailand based on expert opinions. [PERSON] [8] and [PERSON] [9] predicted the demand for electric vehicle sharing and determined the most preferred address based on mobile edge computing and the analytic hierarchy process, respectively. [PERSON], [PERSON], et al. [10; 11; 12] studied the influence of ownership rate of fuel vehicles on the application of electric vehicle sharing and came to the conclusion that electric vehicle sharing has greater competitiveness under the guidance of reasonable price. These studies point out that shared electric vehicles have great demand potential in cities. In the research of operational mode and pricing mechanism analysis, [PERSON] [13] considered the maximization of operator profit, and established a mixed integer nonlinear programming model to optimize fleet size and prices. Aiming at the shared autonomous electric vehicles, [PERSON] [14] analyzed the impact of pricing strategies on its market share and operational effectiveness. However, neither of the two papers considers the role of government subsidies. Some cities such as Seoul, Dublin and Paris have implemented electric vehicle sharing programs and explored their operating models and pricing mechanisms. The program in Seoul achieved good customer satisfaction, but a survey conducted by [PERSON] [15] shows that respondents tend to be less satisfied with charging because the charging standard is based on taxi pricing. With the support of the government, Dublin accomplished a test area for electric vehicle sharing. However, the operational efficiency of the project has not achieved satisfactory results, due to high operating costs and sustained financial support from the government [16].