In traditional fuel vehicles, 12V low-voltage batteries provide power to various low-voltage consuming loads inside the vehicle, such as wipers, headlights, or displays. These batteries tend to have small capacity and low discharge power, typically tens of AH and less than 1kW respectively. In new energy vehicles (EVs), however, the capacity of traction batteries tends to be tens of kWh. The Vehicle to Load (V2L) feature of bidirectional OBCs can provide external load equipment with the energy from the traction batteries. The inverter generates 220V (most national standards)/110V (North American standard) AC power of a few kW (depending on the inverter capacity of the OBC), which can power loads such as outdoor electric camping equipment. V2L can also be expanded to other application scenarios such as Vehicle to Grid (V2G) and Vehicle to Home (V2H), enabling new EV owners to sell the redundant power of their vehicles to the grid or supplement household electricity, improving energy resilience and emergency response.

To optimize space in new EVs, the V2L's AC discharge scocket shares a connector with the AC input charging interface. Since AC charging and V2L discharge cannot occur simultaneously, relays are used to diconnect the circuits and ensure independence between them. Given the possibility of direct contact between the discharge socket and the human body, the V2L circuit of the OBC must monitor the safety state of the output voltage, in addition to the structural design for protection against electric shock. Therefore, it is critical to detect whether the AC relay contacts on the V2L circuit are sticking, and the system needs to confirm that the AC discharge socket only outputs 220V/110VAC after the discharge initialization sequence is complete.