NACS Charge Inlet: AC and DC Compatibility Explained

The electric vehicle (EV) landscape is rapidly evolving, with charging infrastructure playing a crucial role in its growth. While various charging standards exist, harmonization remains a key challenge. The North American Charging Standard (NACS), also known as SAE J3400, aims to address this by introducing a single port capable of handling both AC and DC charging. This article delves into the inner workings of the NACS inlet.

The NACS Charge Inlet Pinout

NACS Charge Port Contacts Function Definition:

DC+/L1:
DC Charging: Positive terminal for the DC voltage feed.
AC Charging: Line 1 in split-phase or sole line in single-phase.
DC−/L2:
DC Charging: Negative terminal for the DC voltage feed.
AC Charging: Line 2 in split-phase or neutral in single-phase.
Ground (G): Provides a connection to earth and serves as a reference point for control signals.
Control Pilot (CP): Enables digital communication between the charging system and vehicle using the IEC 618516 standard. Transmits a pulse-width-modulated signal during DC charging.
Proximity Pilot (PP): Detects the status of the vehicle connector using a low-voltage signal. Disables power delivery when the charging plug is unlocked.

Two Primary Communication Protocols for NACS Charging:

The NACS standard utilizes two primary communication protocols: Basic Signaling (BS) and High Level Communication (HLC).
Basic Signaling (BS):
Uses the same pulse-width-modulation (PWM) scheme transmitted over the CP contact as used in J1772 AC charging systems.
Primarily for safety-related functions and, in the case of AC charging, to advertise the available power level from the charging station.
Can also transmit a 5% pulse width signal to indicate the need for HLC.

High Level Communication (HLC):
A more advanced protocol based on the DIN SPEC 70121 and ISO/IEC 15118 standards.
Transmits modulated high-frequency signals over the CP contact (power-line communication or PLC).
Enables the transmission of digital commands and information for more complex charging scenarios.
In essence, BS provides a basic level of communication for safety and power level indication, while HLC offers a more sophisticated means of data exchange for advanced charging features.

Electric Vehicle Charging Event Sequence Overview

Additional Considerations:

Safety Features: Throughout the charging process, various safety mechanisms are in place to prevent hazards such as overheating, overcurrent, or electrical faults.
Communication Protocols: The specific communication protocols used between the EV and charging station may vary, but they generally involve standardized methods for exchanging information and commands.

NACS DC Charging Sequence Steps Explained

• t < t0: The operator initiates a charging request. After the vehicle is ready, the mechanical interlock allows the connection.
• t0 - t1: After the vehicle connector is inserted into the vehicle, it is locked. The initial charging parameters are exchanged and compatibility is verified through control pilot communication. The lock and digital communication remain throughout the charging process.
• t1 - t2: An optional internal isolation test on VCHG can be performed.
• t2 - t3: Relays K1 and K2 close, and an isolation test is performed between VCHG and VFCLINK. At this point, power transfer is still inhibited.
• t3 - t4: The voltages of VCHG and VFCLINK are adjusted to match VBAT.
• t4 - t5: Relays K3 and K4 close, enabling the energy transfer from the DC power source to the vehicle battery.
• t5 - t6: When VBAT approaches the desired level, S1 is opened momentarily or for a sustained period, or indicates that the charging session should be stopped and ICHG is turned off.
• t6 - t7: The connection is disconnected. K1, K2, K3, and K4 are opened, and VFCLINK is removed.
• t > t7: After the electrical disconnection is verified, the mechanical lock is disengaged, allowing the vehicle connector to be removed, thus completing the charging session.

NACS AC Charging Sequence Steps Explained:

Based on above information we can see that, the NACS inlet includes interlocks and safety protocols to ensure only one power-delivery path is active at a time. The NACS and SAE J3400 connector support vehicle-charger communications using the dual-mode powerline communication (PLC) protocol defined in the IEC 61851 standard. The NACS shared pin charging + safety control system has two modes. The first mode, Basic Signaling (BS), is the same pulse-width-modulation (PWM) scheme transmitted over the CP contact used by J1772 ac charging systems for safety-related functions and to advertise power level for ac charging. The station can transmit a 5% pulse width to indicate the use of High Level Communication (HLC) protocol. The HLC protocol involves transmitting a modulated high-frequency signal over the CP contact (also known as power-line communication or PLC) based on DIN SPEC 70121 and the ISO/IEC 15118 standard and can be used to transmit digital commands and information. This is how the NACS Charge inlet combines AC and DC charging by using these different communication modes and protocols.