At present, Level 2 conductive AC charging (SAE J1772) is limited to a maximum of 11.5 kW (48 amperes (A) at 240 VAC). As the use of Electric Vehicles (EVs) increases, the benefits of faster charging will create a demand for greater charging power than is available with the existing coupler hardware and J1772 standard. This demand will also be driven by the move toward drive systems that integrate the on-board charging electronics with the propulsion inverter and motor, because such systems are inherently capable of higher power charging.

AC Propulsion, has demonstrated a Level 2-style wall box system that accommodates delivery of 19.2 kW of AC power to on-board vehicle chargers. The design is compatible with existing vehicles that use on-board chargers and those using both on-board Level 2 chargers and off-board Level 3 chargers. This document describes the higher-power "Level 2+" system and proposes that SAE J1772 be amended to include it.

The fundamental concept of Level 2+ is to enable the Electric Vehicle Supply Equipment (EVSE) to deliver high-current AC power to compatible vehicles through the Level 3 contacts of the Avcon connector. These contacts are rated for 400 A DC, and can just as readily transfer AC current. As proposed, Level 2+ retains full compatibility with vehicles that are equipped for conductive charging under the present J1772 standard. Vehicle presence detection, GFI operation, and Level 2 confirmation values remain unchanged.

Note: Level 1 equipment is not affected

Level 2+ EVSE uses modified oscillator voltages and pulse-width scaling, and an additional confirmation value (for high power charge request). As with existing Level 2 equipment, all charge control functions are managed on the vehicle, so no digital J1850/J2293 communication is necessary. The compatibility of vehicle/EVSE combinations is shown in Table I.

System Description

The present Level 2 charging system is shown in Figure 1. In this configuration, contacts 3 and 4 are not used by the EVSE, but they can be wired on the vehicle side for off-board Level 3 DC charging.

Figure 1. Level 2 Charging Schematic/ Basic System

Figure 2 shows a schematic for the proposed Level 2+ configuration. The EVSE includes a high-current circuit through the Level 3 contacts of the charging coupler. The vehicle shown in Figure 2 is configured to accept low-current AC from contacts 1 and 2, or high current AC from contacts 3 and 4, but not from an off-board Level 3 charger. Level 3 compatibility could be provided in a Level 2+ vehicle, but would require an additional contactor in the vehicle.

To maintain compatibility with standard Level 2 EVSE, the low-current AC contacts 1 and 2 are wired in parallel with the high-current contacts 3 and 4 respectively, on the vehicle side. The vehicle's charge control can request either Level 2 or Level 2+ AC power, and determines the available line current from the pilot signal. This current capacity is encoded on the safety pilot signal by the EVSE as described below (Encoding of Level 2+ Capability). The Level 2+ EVSE opens the low-current contactor when the high current contactor is closed to prevent a parallel current path.

Figure 2. Proposed Level 2+ Charging Schematic

Figure 3 shows the proposed Level 2+ EVSE charging a vehicle equipped for Level 2 charging (e.g. Honda EV Plus). In this case, the vehicle determines the available current for the low-current AC contacts through the safety pilot pulse width. The vehicle is not equipped to request Level 2+ power, so the EVSE will only close the standard Level 2 contactor. AC voltage will not be present on contacts 3 and 4 because the high-current contactor of the EVSE will not close.

Figure 3. Charging a vehicle configured for Level 2 only.

Figure 4 shows the Level 2+ EVSE charging a vehicle equipped for both regular Level 2 charging and Level 3 off-board DC fast charging (e.g. fast-charge Ford Ranger). Since the vehicle only requests Level 2 power, the EVSE will close only the low-current AC contactor. The vehicle will recognize the connection as a standard Level 2 EVSE, and will charge accordingly.

Figure 4. Charging a vehicle configured for Level 2 and Level 3. Both sets of contactors for the Level 3 pins remain open.

Figure 5 shows how a vehicle equipped for Level 2+ can be charged from a current Level 2 EVSE wall box. In this case, the vehicle does not detect the coding on the safety pilot signal which indicates Level 2+ EVSE, so it charges based on the low-current pulse width scale of the safety pilot according to the existing standard.

Figure 5. Charging a vehicle configured for Level 2+ from standard Level 2 EVSE.

Figure 6 shows the Level 2+ EVSE system connected to a vehicle capable of Level 3 DC charging only (e.g. Chrysler EPIC). In this case, the vehicle cannot use AC power, so no connection is made, and no charging occurs. All vehicles with off-board DC chargers must establish J1850/J2293 communications before the vehicle contactors can be closed. Since the Level 2+ EVSE has no digital communication for off-board charging, the vehicle will not attempt to charge.

Figure 6. Connecting a Level 3 only vehicle to a Level 2+ EVSE. All contactors remain open.

Encoding of Level 2+ Capability and Current Rating

The high-current contacts, pins 3 and 4, are capable of a 400 A rating. Not all Level 2+ EVSE applications will need or utilize this much current, so a new pulse width (PW) scale is proposed, providing a scaled current limit of 20 through 500 amps continuous, compared to the 5-48 amp current limit of the existing standard. The proposed high-current pulse width scale is:

I (current limit) = (600) x (pulse width) - (40)

In order to distinguish Level 2 and Level 2+ charging modes, Level 2+ EVSE will use a modified oscillator voltage of +12/-9vdc. A connected vehicle can then request either a Level 2 charge, or a Level 2+ charge (based on the returned pilot signal voltage). Resulting pilot voltages of +9/-3 correspond to a Level 2+ charge request, and voltages of +6/-9 (no ventilation) or +3/-9 (ventilation) correspond to Level 2 charge requests. During Level 2+ charging, the EVSE and the EV use the new high current pulse-width scale to designate line current capacity. During Level 2 charging, the existing low-current pulse-width scale is used. Because no pure resistance across the pilot signal can result in a valid charge request, power will only be applied to a properly functioning EV.

Figure 7. Pilot circuit for Level 2+ EVSE.

NEC 625-14 specifies that EV loads be considered continuous, meaning that the maximum allowable demand is 80% of the circuit and over-current device rating. Common service equipment ratings include 100, 200 and 400 amps. Therefore a 100 amp EVSE will use a 100 A circuit and circuit breaker, and provide an available capacity, as conveyed by the pilot signal pulse width, of 80 A. Separate over-current protection is required when a low-current AC circuit is provided.

Level 2+ requires revisions to SAE J1772. The changes below refer to the existing J1772 tables, and are backward compatible with vehicles and EVSE:

State H Standard Level 2 request

State I Level 2+ charge request

Level 2+ EVSE

Output voltage lowóo.c. -9 V (+-5%)

Input voltage lowóState H -9 V (+-5%)

Input voltage lowóState I -3 V (+-5%)

EV requirements (for vehicles using Level 2+ system)