Three-phase unbalance may occur in distribution networks with large-scale charging loads of electric vehicles (EVs) plugged in

which significantly threatens the operation of power networks. Most coordinated EVs charging strategies are based on the assumption of single-phase power networks to the neglect of three-phase unbalance problems. A coordinated charging strategy for EVs considering three-phase load balance is proposed. In the outer layer of the proposed strategy

the three-phase backward/forward sweep load flow algorithm is used to iteratively update the node voltages. In the inner layer of the proposed strategy

a three-phase coordinated EV charging optimal model is created and solved based on the updated node voltages. By optimizing the charging power and charging periods of EVs

the objectives of the optimal model

power loss reduction and the three-phase load balance

are achieved. Simulation results show that the proposed strategy can eliminate the three-phase unbalance problems

reduce power losses and flatten the load curve

guaranteeing the economics and security of operation of the power network. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2011AA05A110).