1. Introduction
In the recent years, the opening of the electricity side and the deepening of the concept of the energy Internet have further promoted the integration of various energy systems and the allocation of plug–in energy resources [
1]. A large number of distributed power generators, distributed energy storage systems, intelligent electrical equipments, and other players participate in the power market [
2]. Through smart grid technology, traditional subjects have transformed from mere energy consumers into ‘energy prosumers’ that integrate energy production and consumption. They are capable of generating new energy, responding to power demand and participating in active distribution network [
3]. Especially, in a diversified market structure, large–scale EVs with flexible charging–discharging characteristics will become an important component of smart grid construction [
4].
EVs can be regarded as load when they are being charged and can be used as distributed power sources when they are idle. EVs can be connected to the grid and send the energy back to the grid by V2G (vehicle–to–grid). Appropriate charging–discharging control cannot only restrain the adverse impact of EVs on the power grid but also support peak shifting, frequency modulation, rotary standby, and other services to coordinate the development of EVs and the power grid [
5]. Therefore, EV agent can act as a mediation between users and the power grid. It can facilitate centrally dispatch the charging–discharging resources of EVs on behalf of the huge and dispersed users. This will help EV users, agent, and the power grid realize potential benefits. For this system to work, the game competition among the three needs a safe, transparent, and secure trading mechanism [
6].
Due to the scattered load resources and high uncertainty of EVs, they need to enter the network through an agent. Flexible trading contracts can be signed between them to ensure the balance of interests. Accordingly, the agent also needs to sign the corresponding transaction contracts with the power grid company through the power dispatching center. However, at present, the traditional power transaction mode mostly adopts centralized configuration to dispatch resources. This leads to the following problems among market subjects [
7]: (a) transaction information is tampered with each other; (b) information between the parties can be asymmetric; (c) high transaction costs.
Blockchain technology has a decentralized accounting mechanism and a smart contract system for automatic and secure transactions, which can guarantee decentralization, verification, and integrity. Nowadays it is applicable to various fields, including smart grids and distributed energy trading [
8]. Therefore, the smart contract technology of blockchain can be introduced into the mechanism of EVs to the power grid, which achieves distributed decentralized scheduling and demand response. This mechanism can meet the users’ requirements of trustworthiness, fairness, privacy, and other aspects, making up the deficiency of traditional scheduling mechanism.
There are several existing works on power market by blockchain in the literature. For demand response with power trading, Ref. [
9] integrates the distributed ledger with smart contracts to ensure the balance demand–production and validate the timely adjustments of demand response based on Ethereum. Ref. [
10] presents a decentralized cooperative demand response framework to manage the energy exchanges within smart buildings, which benefits all the participants. Ref. [
11] proposes an energy trading platform to solve the security problem. It implements the point–to–point system that enhances the transparency and immutability under smart contracts.
For the specific application of EV energy transaction, Ref. [
12] proposes a novel EV participation charging scheme, to minimize the power fluctuation level in the grid and the total charging cost for EV users. Ref. [
13] proposes a real–time system that contains the concepts of prioritization and cryptocurrency. This can incentivize EV users to collectively charge with an energy–friendly schedule. Ref. [
14] approaches the problem of an agent bidding into electricity market with the objective of minimizing charging costs while satisfying the EV demand. Ref. [
15] proposes a multistage stochastic model of an EV agent to participate electricity market under several uncertainties such as the behaviour of users and electricity prices. The results of this model can effectively increase the agent’s profit.
Although the above literatures have established a relatively complete blockchain trading mechanism under the demand response to a certain extent, the research on the advantages of the demand resources for EVs especially in the economic market is less involved. Most of literatures are based on the deterministic electricity price model, which only realizes the charge–discharge energy interaction between EVs and other subjects. Moreover, most of the proposed bidding mechanisms only realize the win–win situation between users and agent or between agent and the power grid. There is a lack of bidding research involving discharging. Under the background of blockchain, there are few studies on achieving economic win–win among users, agent, and power grid by fully exploiting the demand response of charging–discharging resources of EVs. Therefore, how to use the blockchain smart contract technology to build a reasonable and effective bidding mechanism among the three parties is worth studying.
This paper combines the EV participating in bidding mechanism with the blockchain smart contract technology. Firstly, a bidding mechanism framework for EVs on and off the chain is built. The mechanism off the chain includes the design of cluster classification methods for EVs with different driving demands and the demand of unit commitment between generator sets and energy plans. The mechanism on the chain includes the design of the transaction under the smart contracts between the users, the agent, and the power dispatching center, which is divided into two aspects to establish a complete DRM: On the one hand, the smart contract model between the users and the agent can be achieved with the goal of minimum electricity purchase cost for the users and maximum revenue for the agent. On the other hand, the smart contract model between the agent and the power dispatching center is achieved with the aim of minimizing the load variance of the power grid and the cost of power economic dispatching. After that, the combination of particle swarm and genetic algorithm is used to realize the above two aspects of smart contract models. Then, the results are recorded in the blockchain distributed ledger. Finally, an example is given to verify the effectiveness of the bidding mechanism and DRM, which achieves economic win–win among several aspects.
The contributions and innovations of this paper are as follows:
- (a)
Different from the traditional blockchain trading architecture with a single chain, this paper innovatively proposes the on and off chain architecture considering the applicability and bottleneck of smart contract technology. The bidding relationship among market subject is only used as the logic of contract on the chain to realize distributed trading. Off the chain, EV cluster classification and unit commitment still adopt centralized dispatching.
- (b)
Different from the traditional centralized bidding of EVs, this paper classifies EVs with different driving characteristics in a unified cluster and adopts a different DRM. This method fully excavates the diverse charging–discharging demands of different users and provides a more real demand response for bidding in the market.
- (c)
Based on the literatures [
16,
17], the traditional user–side and grid–side DRM have been extended to introduce the concept of EV agent. The smart contract interaction between EV users and agent is taken as the user side in a broad sense. The smart contract interaction between EV agent and power dispatching center is taken as the power grid side in a broad sense. On the whole, this paper will achieve economic win–win results based on the demand response of the three parties.
- (d)
Based on the traditional EV charging bidding, the demand response and economic impact brought by discharging are considered. Moreover, a reasonable and effective bidding mechanism and algorithm are designed, which obtains better optimal scheduling and economic benefit than bidding only containing charging.
4. Conclusions and Future Work
This paper introduces the blockchain technology into the bidding mechanism of EVs. This paper combines the distributed transaction on the chain with the centralized dispatching off the chain. Then, a win–win bidding mechanism among EV users, agent, and power dispatching center is established: Off the chain, the EVs classification layer and unit commitment layer interact with the information through DRM; on the chain, smart contracts are reached among market subjects considering their respective demands and interests. On the premise of eliminating the risk of third–party data storage, this mechanism can fully allocate EV charging–discharging resources to participate in market bidding. The distributed ledger of the blockchain guarantees tamper–proof, transparent, and traceable data. An example analysis shows that the results of contract price and volume under bidding can be used as a way of DRM. The result of the contract charging price reduces the price excluding charging–discharging of EVs by about CNY 0.07/(kW·h). For the economic benefits, the economic dispatching cost is about CNY 36 ten thousand and CNY 84 ten thousand less than that under the orderly and disordered strategy; the cost of purchasing power for users is about CNY 5 ten thousand and CNY 49 ten thousand yuan less than that under the orderly and disordered strategy; compared with other strategies, the agent can gain an additional profit of about CNY 13 ten thousand. In all, the results not only provide flexible and effective optimal scheduling for power grid peak–cutting and valley–filling, but also achieve economic win–win for all market subjects.
In the simulation implementation of this paper, only an example is used to verify the smart contract mechanism among market subjects. The mechanism proposed in this paper is not built in the real blockchain environment. The verification of blockchain in transaction efficiency, security, applicability, and other aspects needs to be further explored. Therefore, in the future work, it is worthwhile to further study the bidding and trading mechanism including V2G in the blockchain Ethereum, so as to expand the applicability of this mechanism.