Residual current sensor for electric vehicles

With the increasing adoption of electric vehicles, residual current detection (RCD) is becoming critical for complying with international safety regulations and protecting end users. The FG-R series from YAGEO Group is a current-controlled AC and DC residual current sensor optimized for Mode 2 and Mode 3 electric vehicle charging systems and suitable for on-board charger (OBC) applications. It combines precision, robustness, and compliance with standards in a compact, modular package.

Technical Overview

The FG Series is an open-loop current-controlled ground fault sensor that provides analog monitoring of ground fault currents and independent digital alarms for AC and DC thresholds. Its architecture enables fast response times, a wide frequency range, and compliance with global standards, including:

IEC 62752:2016/A1:2018
IEC 62955:2018 (RDC-MD)
UL 2231-2
Use of AEC-Q-certified components for automotive-grade quality
ASIL B-capable, RoHS-compliant

With selectable residual current thresholds (AC: 20/30 mA, DC: 6 mA), the sensor supports the trip points required by global EVSE regulations and minimizes false trips through precise phase detection and self-test routines.

Functional details

Rated for up to 22 kW / 32 A AC charging
Single-phase: up to 80 A
Three-phase: up to 40 A
Analog output for real-time monitoring of fault currents (AC and DC combined)
Alarm outputs with open-drain logic for direct integration into the charge controller
Operating temperature: up to 105 °C
Frequency response: optimized for 50/60 Hz fault current detection, stable up to 2 kHz
Trip current profile: Compliant with pulsating DC detection at 0°, 90°, and 180° phase angles

Mechanical Integration

Available in several mechanical variants, including the vertical busbar variant FG-R04/FG-R14, the sensor is designed for efficient installation in compact power electronics systems and supports the natural flow of current:

Supports cables up to 4 x 6 mm² or busbars for up to 40 A
Modular, integrated design minimizes EMI exposure
Simplified system integration through clear pin assignment for analog and digital outputs

Technical Unique Selling Points

The FG series stands out from conventional RCD modules due to:

A custom-designed driver IC for improved oscillator stability and current-controlled duty cycle modulation
Improved phase angle response to minimize false tripping
Self-test pin enables system-initiated diagnostic cycles without interrupting the load
Multi-standard certification for use in European and North American systems with a single hardware platform

Expansion to in-vehicle applications

The importance of residual current detection extends beyond the charging infrastructure to the vehicle itself, as electric vehicles are becoming mobile power stations:

Vehicle-to-Load (V2L): Modern electric vehicles are equipped with AC outlets that allow devices such as laptops, scooters, or coffee makers to be powered directly from the vehicle. Each AC outlet requires dedicated RCD protection to ensure safety in the event of a potential ground fault.
Vehicle-to-Grid (V2G): When feeding energy back into residential or industrial grids, three-phase power transfer is common. In such cases, three-phase fault current detection is required to meet regulatory requirements and safely control discharge operations.

The current FG-R series delivers solid performance for many traditional applications, but a new series will overcome previous limitations by offering full three-phase RCD detection and improved performance for in-vehicle power systems. This forward-looking design will better meet the growing demands of V2L and V2G functions while maintaining the high reliability and compliance that YAGEO Group customers have come to expect.

Application Note – IEC 62955 Compliance

Design engineers implementing the IEC 62955 RDC-MD requirements should note that the DC and AC alarm outputs are independent. However, in the event of a high AC fault current (>60 mA), the DC alarm may also trigger due to shifts in the BH curve. It is recommended to add a timing control logic to the EVSE controller to delay the DC response under high AC conditions, ensuring that shutdown times remain within the specified tolerances. The new FGR1 series, featuring a newly developed ASIC, resolves this issue by ensuring that alarms operate independently without delay.