SAE J1772, which is a standard for electrical connectors for electric vehicles, describes the use of an electrical signal referred to as the pilot signal that is sourced by the Electric Vehicle Supply Equipment (EVSE) (sometimes referred herein as an “electric vehicle charging station”) that can perform one or more of the following functions: verifies that the electric vehicle is present and connected to the EVSE, permits energization/de-energization of the supply, transmits available supply current to the electric vehicle, monitors the presence of the equipment ground, and specifies vehicle ventilation requirements.
SAE J1772 also describes detecting the presence of the connector in the vehicle inlet (referred to as “proximity detection”). SAE J1772 also describes that the proximity detection circuit may be used to provide a signal in the vehicle charge control strategy to help reduce electrical arcing of the coupler during disconnect. Arcing causes cumulative negative impacts such as the pitting of the contacts leading to greater contact resistance, which in turn raises the heating in the connector which can lead to the connector shell melting. The arc itself can also lead to heat that can cause damage to the connector shell. Also, a previously pitted connector can cause damage to an otherwise pristine mating connector when operating under normal conditions.
Such use of a proximity detection circuit is not mandatory to be compliant with SAE J1772. Thus, electric vehicle on-board charging systems can be designed to be compliant with SAE J1772 without implementing such a feature.
Traditionally, on-board charging systems are able to turn off current flow before the connector is removed from the vehicle inlet in one of two ways. The first is to turn off the Insulated Gate Bipolar Transistors (IGBTs) in the on-board charging system thereby halting the flow of current. The second way is to raise the voltage level of the pilot signal's positive phase from 6V to 9V, which signals the EVSE to open its contactor to de-energize the connection. Although SAE J1772 suggests that a proximity detection circuit can be used to provide a signal in the vehicle charge control strategy to help reduce electrical arcing of the connector during disconnect, SAE J1772 does not describe how this is implemented.