Coordinated charging control of plug-in electric vehicles at a distribution transformer level using the vTOU-DP approach

With the increasing public awareness of environmental issues, there is growing interest in plug-in electric vehicles (PEVs) which can be charged from the power grid. Consequently, the large numbers of PEVs could lead to considerable power demand from the power system, which poses a great threat to the power grid security (especially at the distribution level) if the PEV charging strategy is not properly regulated. In this paper, taking advantage of the vehicle to grid (V2G) service, the coordinated PEV charging control problem is studied at a distribution transformer level using the proposed virtual time of use rate dynamic programming (vTOU-DP) approach. For each PEV, the coordinated control problem is formulated as a constrained optimal control problem based on a self-defined concept of virtual time of use rate (vTOU), which reflects the distribution transformer load level. Then, the optimal charging rate is solved using the dynamic programming (DP) technique. The vTOU-DP, which is a plug-and-play control, can be implemented in real time. Simulation results show that the vTOU-DP provides better control performance than two commonly used baseline controllers in terms of transformer peak reduction and transformer load profile smoothness. Compared with the non-PEV base load, by charging PEVs at the transformer using the vTOU-DP, the transformer peak load is reduced by over 20%, and the variance of the transformer load profile is reduced from about 9 kW² to less than 0.01 kW².