PLC Transformers Help EVs and Chargers Communicate

Würth Elektronik has released a series of WE-PLC transformers designed to provide high voltage isolation in power line communication (PLC) systems commonly used for electric vehicle charging and grid communication applications.  

The isolation transformers can handle data signals from 500 kHz up to 30 MHz and offer 4500 VRMS of isolation in a compact 13.6 mm x 9.9 mm surface mountable package.  

When used in communication systems between EVs and charging stations, the WE-PLC series transformers comply with EN ISO 15118 standards for public charging infrastructure.       

WC-PLC signal isolation transformers. Image used courtesy of  Würth Elektronik

PLC Communication for EV Charging

When an EV is being charged at a charging station, the charging infrastructure (EVSE) and EV battery management system (BMS) must communicate in real-time to ensure the EV battery pack is charged safely and properly.

Power Line Communication (PLC) is a technique by which data can be communicated across power lines, and in the case of EVs, it allows for communication between the charger and EV battery system through the charging cable. A main advantage of PLC communications is that it eliminates the need for separate wiring for data communications, simplifying system design.  

PLC protocols for AC and DC charging stations are governed according to ISO 15118-3 standards.  

Isolation Requirements

When high-voltage AC or DC power is transmitted across the charging cable during an EV charge, board-level isolation must be provided at the charger and EV battery management system to protect the low-voltage digital control and communication systems.  

For EV charging applications, a PLC transformer with a 1:1:1 turns ratio is used on the EV supply equipment (EVSE) to interface with and isolate both the receive (RX) and transmit (TX) channels of the communication circuits. 

AC Type 2 EV charging PLC application. Image used courtesy of  Würth Elektronik

With an AC Type 2 plug, the Control Pilot (CP) pin and Protective Earth (PE) pin are used for the control signal exchange between the EV and EVSE, typically via a pulse width modulation scheme.

The WE-PLC series has a 1:1:1 turns ratio for EV charging and a 1:4:3 ratio for grid communications.  

Signal Quality

In addition to protecting communication circuits from high voltage, PLC transformers must maintain signal quality. PLC transformers can offer impedance matching within the communication network to reduce signal reflection and help maintain a high signal-to-noise ratio. This minimizes lost bits and other communication errors that could impact the EV charge operation’s reliability.

The WE-PLC series offers a low leakage inductance of just 0.2 µH max, ensuring good magnetic coupling across the transformer to minimize signal loss.

The signal isolation transformers can handle operating voltages up to 250 VAC.