Integration and Safety of electric vehicles in a residential electrical installation for V2H services

Vehicle-to-Home (V2H) supposes that electric vehicle (EV) chargers are bidirectionnal. It is necessary to find the best solution to use a bidirectionnal EV charger in a residential installation in terms of safety, availability and cost. This paper shows a method to determine if a residential installation can be supplied by an EV in stand-alone mode, without risk for person safety or availability in case of insulation faults, compared to the grid-connected mode. The used method is the event-tree analysis: an event tree for the "insulation fault" event is proposed to determine the consequences in function of success or failure of intermediate events. Here, two configurations are considered: first, a TT-earthing installation supplied by the utility grid and secondly the same installation without change in stand-alone mode and only supplied by an EV (corresponding to an IT-earthing system). The last configuration is studied because energy supply is not the main function of an EV, so the extra cost and the system complexity due to a bidirectionnal charger must be avoided as far as possible. After the weighting of intermediate event success and failure for each configuration, the event tree analysis reveals that the IT-earthing in stand-alone mode configuration is not an issue for person safety but that there is a decrease of the supply availability compared to the grid-connected mode. The parameters, which causes these decrease, depends primarily on the installation architecture, connected loads and the sizing of EV charger components. The method proposed here can be applied to other configurations in grid-connected or stand-alone mode to verify if there is any risk for safety or availability and to verify the robustness of the architecture in case of failure in the installation (for example, an appliance which is not connected to the protective conductor).