BOBC (Bi-directional on-board charger) is a power conversion system component for AC charging and discharging of new energy vehicles. It has two working modes: AC charging mode and AC discharge mode. In the two working modes, the BOBC belongs to both the controller and the actuator.
In some extreme cases such as communication and control failure of the AC charging mode, new energy vehicles have the risk of high-voltage battery overcharging and overheating, which will lead to high-voltage battery fire or even explosion. In the AC discharge mode, it involves the actual operation of the users on electricity, and the risk of short circuit and open circuit may happen in the process, which endangers the safety of the users. Based on the risks brought by the two working modes, it should pay more attention to the safety of the BOBC. ISO26262 provides the corresponding guiding analysis method and quantitative index for the hazard caused by the failure of automobile electronics and electrical appliances. It is necessary for BOBC to carry out functional safety design according to ISO26262.
This paper focuses on the functional safety development process of new energy vehicle AC charging system and BOBC, including item definition, HARA (hazard analysis and risk assessment), functional safety concept and technical safety concept.
The boundary range, system functions and vehicle operating conditions of the AC charging system of new energy vehicles will be described in item definition. They will be provided as input conditions for HARA in the next step. During HARA, functional safety goals and ASIL levels of the AC charging system will be determined by identifying severity, exposure and controllability. The functional safety requirements related to BOBC will be determined according to the functional safety goals, and then we will use the FTA method to give out the technical safety requirements of BOBC according to the functional safety requirements of BOBC.