GPF-based method for evaluating EVs' free charging impacts in distribution system
Conventional electric vehicles' (EVs) free charging impacts evaluation in a separate distribution system may result in an “optimistic” result. Therefore, a new method based on global power flow (GPF) with transmission and distribution grids included, defined as GPF-based method, was proposed in this paper. With EVs' free charging loads model, the power injected into the distribution system was obtained. Then, supposing global system is a master-slave-typed system, GPF-based evaluation was performed with master-slave-solver where transmission and distribution power flow were iteratively calculated. When global power flow came to convergence, the iterative relations of transmission and distribution systems were fully reflected and a more realistic evaluation result was achieved. A global power system was constructed and the simulation results of different evaluation methods were compared. GPF-based method obtained a more reliable evaluation result. Therefore, it is necessary to adopt GPF-based method to evaluate EVs' charging impacts, especially when they are largely integrated in smart grid.