  Electric Vehicles (EVs) are becoming more and more popular in our daily life,
which replaces traditional fuel vehicles to reduce carbon emissions and protect
the environment. EVs need to be charged, but the number of charging piles in a
Charging Station (CS) is limited and charging is usually more time-consuming
than fueling. According to this scenario, we propose a secure and efficient
charging scheduling system based on a Directed Acyclic Graph (DAG)-blockchain
and double auction mechanism. In a smart area, it attempts to assign EVs to the
available CSs in the light of their submitted charging requests and status
information. First, we design a lightweight charging scheduling framework that
integrates DAG-blockchain and modern cryptography technology to ensure security
and scalability during performing scheduling and completing tradings. In this
process, a constrained multi-item double auction problem is formulated because
of the limited charging resources in a CS, which motivates EVs and CSs in this
area to participate in the market based on their preferences and statuses. Due
to this constraint, our problem is more complicated and harder to achieve
truthfulness as well as system efficiency compared to the existing double
auction model. To adapt to it, we propose two algorithms, namely Truthful
Mechanism for Charging (TMC) and Efficient Mechanism for Charging (EMC), to
determine an assignment between EVs and CSs and pricing strategies. Then, both
theoretical analysis and numerical simulations show the correctness and
effectiveness of our proposed algorithms.
