# An EV Charging Scheduling Mechanism Based on Price Negotiation
## 2 EV Charging System Framework Based on Price Negotiation  
In this section, an EV charging system framework based on price negotiation, as shown in Figure 1, is discussed. As the name suggests, the main participants of this system are the charging station operator and EV user. Both parties want the EV to be charged at a price that is accepted through negotiation between them. When an EV needs to be charged, the EV user sends a charging request by using a mobile device that installs the charging price negotiation software (APP) through the cellular communication network. Once the operator of the specific charging station receives the charging request through the same kind of charging price negotiation using APP, the operator will form the initial expected charging price according to the state of charging station, such as the current idle ratio of charging piles, load of power grid, power generation of renewable energy resources, and so on. When both of the two participants desire to reach an acceptable charging price by negotiating with each other, the price negotiation will be started according to their own strategies of price negotiation. Once the price negotiation is successfully formed after several rounds of price bidding, comparing and negotiating, the EV can be charged. The renewable energy resources will be given priority to be used. When the renewable energy resources cannot meet the demand of charging power, the charging station operator can send a power request to the power grid to purchase additional power that is needed by the EV user. The renewable energy resources can be operated by a charging station operator or Electricity Services Operator (if the policy of Electricity Services Operator allow). The difference is the cost of the charging station operator. For the first mode, the power generated by renewable energy sources is free, but the charging station operator needs to invest in probleme fixed infrastructure. For the second mode, no additional investment in fixed infrastructure is required, but the charging station operator needs to purchase power from the Electricity Services Operator. Of course, the price must be lower than that purchasing power from power grid. Thus, our technique is not only limited to the application in a self-consumption system. Both \"Direct\" (this is the sale made on the Power Exchange or through bilateral contracts stipulated with wholesalers) and \"Indirect\" (form of sale through the stipulation of a simple agreement with the Electricity Services Operator (GSE), which acts as a commercial intermediary between the producers and the electricity system) ways of sale to the electricity network produced by a plant can be chosen depending on the organization of the power infrastructure. In this mode, the charging station can not only fully use the renewable energy resources and reduce greenhouse gas emissions, but can also reduce the cost and balance load of power grid. An EV  
Figure 1: EV charging system framework based on price negotiation. charged at a negotiated price will bring operator more profit, which can attract more operators to invest in the construction and operation of charging stations of EVs. Most EV users undoubtedly charge their EVs at a relatively lower price through price negotiation, which not only saves the charging cost but also improves customer satisfaction. Due to the real-time price and changing load of the power grid and the changing arrival rate of EV users, we set 15 min as the basic time slot of a charging price negotiation. During one basic time slot, all of the above factors are assumed to be constant. Thus, each day 24 h are divided into 96 time slots of a charging price negotiation. If the charging price negotiation is successfully formed in a certain time slot, the EV can be charged in the time slot. In the next time slot, if both the operator and EV user agree that it is not necessary to launch another round of price negotiation the EV can be charged at the last round at the negotiated charging price.