Why NACS Inlet Compatible For Both AC and DC Charging

In the evolving landscape of electric vehicles (EVs), the North American Charging Standard (NACS) inlet has emerged as a significant development, offering compatibility for both AC and DC charging. This compatibility is achieved through a combination of carefully designed features and protocols.

1. Pinout and Contact Function Definitions

NACS Inlet Pinout

The NACS charge inlet has a specific pinout with defined contact functions that support both AC and DC charging.

• DC+/L1 and DC−/L2: In DC charging, these are the positive and negative terminals for the DC voltage feed respectively. In AC charging, DC+/L1 serves as Line 1 in split-phase or sole line in single-phase, and DC−/L2 serves as Line 2 in split-phase or neutral in single-phase.
• Ground (G): It provides a connection to earth and acts as a reference point for control signals in both AC and DC charging.
• Control Pilot (CP): This contact enables digital communication between the charging system and vehicle. In DC charging, it transmits a pulse-width-modulated signal. In AC charging, it uses the same pulse-width-modulation (PWM) scheme as in J1772 AC charging systems for safety-related functions and to advertise the available power level from the charging station. It can also transmit a 5% pulse width signal to indicate the need for High Level Communication (HLC).
• Proximity Pilot (PP): Detects the status of the vehicle connector using a low-voltage signal and disables power delivery when the charging plug is unlocked, applicable in both AC and DC charging scenarios.

2. Communication Protocols

The NACS standard utilizes two primary communication protocols that facilitate AC and DC charging compatibility.

• Basic Signaling (BS): This protocol uses the same pulse-width-modulation (PWM) scheme transmitted over the CP contact as used in J1772 AC charging systems. It is primarily for safety-related functions and, in the case of AC charging, to advertise the available power level from the charging station. It can also transmit a signal to indicate the need for the more advanced High Level Communication (HLC).
• High Level Communication (HLC): A more advanced protocol based on the DIN SPEC 70121 and ISO/IEC 15118 standards. It transmits modulated high-frequency signals over the CP contact (power-line communication or PLC). This protocol enables the transmission of digital commands and information for more complex charging scenarios, applicable in both AC and DC charging when needed.

3. Charging Sequence and Safety Mechanisms

NACS Charging Interlocks Charging Sequence and Safety Mechanism

The charging process for NACS, which varies slightly between AC and DC charging, incorporates safety mechanisms and a defined sequence that supports compatibility.

• Vehicle and Charging Station Connection: The EV is physically connected to the charging station using the NACS connector.
• Communication and Authentication: The EV and charging station establish a communication link and authenticate each other to ensure compatibility and security.
• Charging Mode Selection: The charging system determines whether AC or DC charging is appropriate based on the vehicle's capabilities and the available charging infrastructure.
• Power Negotiation: The vehicle and charging station negotiate the maximum charging power and voltage.
• Charging Initiation: The charging process begins, with power flowing from the charging station to the EV's battery.
• Monitoring and Control: The system continuously monitors charging parameters (e.g., voltage, current, temperature) and adjusts the charging rate as needed.
• Charging Completion: Once the battery reaches its target state of charge or the charging session is manually terminated, the charging session concludes.
• Disconnection: The EV and charging station safely disconnect.

Throughout the charging process, various safety mechanisms are in place to prevent hazards such as overheating, overcurrent, or electrical faults. These safety features, along with the defined charging sequence, ensure that the NACS inlet can handle both AC and DC charging effectively and safely.

In conclusion, the NACS inlet's compatibility for both AC and DC charging is a result of its well-defined pinout, communication protocols, and a carefully structured charging sequence with built-in safety mechanisms. This makes it a crucial component in the development of a more unified and efficient EV charging infrastructure.