REESS — Rechargeable Energy Storage System for EV EMC Testing

What Is REESS?

REESS stands for Rechargeable Energy Storage System. In the context of automotive EMC regulations, REESS refers to the rechargeable energy storage device that provides electric energy for vehicle propulsion. This includes high-voltage battery packs used in battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs), as well as other rechargeable storage technologies such as supercapacitors or flywheel systems used in electrified drivetrains.

The term REESS is used extensively in UNECE Regulation No. 10 (ECE R10) to define specific EMC test requirements for vehicles that derive propulsive power from a rechargeable energy storage source. As electric vehicles have become a major segment of the global automotive market, the REESS-related provisions in ECE R10 have grown in scope and importance, particularly with Revision 7.

Why REESS Matters for EMC Testing

Electric vehicles present unique electromagnetic compatibility challenges compared to conventional internal combustion engine (ICE) vehicles. The high-voltage power electronics that manage energy flow between the REESS and the electric motor generate significant electromagnetic emissions across a broad frequency spectrum. Key EMC-relevant subsystems associated with REESS include:

• High-voltage battery pack: The REESS itself, including cell modules, busbars, and internal wiring, can act as an antenna or coupling path for conducted and radiated emissions.
• Battery Management System (BMS): The electronic control unit that monitors cell voltages, temperatures, and state of charge. The BMS communicates over digital buses and can be both a source and a victim of electromagnetic interference.
• DC-DC converter: Converts the high-voltage REESS output (typically 400V or 800V) to the 12V auxiliary bus. Switching power converters are well-known sources of broadband electromagnetic emissions.
• Onboard charger (OBC): Converts AC mains power to DC for charging the REESS. The OBC operates at high power levels with significant switching noise.
• Inverter/motor drive: Controls the electric traction motor using pulse-width modulation (PWM) at high voltage and high current levels. The fast switching edges produce emissions from kilohertz through hundreds of megahertz.
• Wireless power transfer (WPT) system: Inductive charging systems that couple energy magnetically from a ground pad to the vehicle. WPT systems operate at specific frequencies (typically 85 kHz) and require careful EMC management.

REESS in ECE R10: Applicable Annexes

ECE R10 addresses REESS-equipped vehicles through several annexes that define specific test procedures and requirements:

Annex 7 — Vehicle Broadband Electromagnetic Emissions

For vehicles with REESS, broadband emission testing must be conducted with the electric drivetrain operating under defined conditions. The vehicle must be tested in electric drive mode (if applicable) with the REESS at a specified state of charge (SoC). The regulation defines the SoC range that must be maintained during testing to ensure representative emission levels.

Annex 8 — Vehicle Narrowband Electromagnetic Emissions

Narrowband emission testing follows similar REESS operating mode requirements. The DUT (vehicle) must be operated in modes that activate all relevant high-voltage power electronic systems, including the inverter, DC-DC converter, and any active thermal management systems for the REESS.

Annex 9 — Vehicle Immunity to Electromagnetic Radiation

Immunity testing of REESS-equipped vehicles verifies that the vehicle’s electronic systems, including the BMS and motor controller, continue to operate safely when exposed to external electromagnetic fields. The test must demonstrate that the vehicle does not exhibit any safety-critical malfunctions such as unintended acceleration, loss of braking, or uncontrolled REESS discharge.

ESA-Level Annexes

Individual components associated with the REESS (such as the BMS, OBC, DC-DC converter, and inverter) can also be tested as Electronic Sub-Assemblies (ESAs) under the relevant ECE R10 annexes. Component-level testing requires appropriate test setups that replicate the high-voltage environment and operating conditions of the vehicle.

Test Configurations for REESS Vehicles

State of Charge Requirements

The REESS state of charge during EMC testing must be controlled and documented. ECE R10 specifies that the REESS should be at a state of charge that allows the vehicle to operate in its normal driving mode for the duration of the test. Typical requirements include:

Parameter	Requirement
Minimum SoC at test start	Sufficient for sustained electric driving
SoC range during test	Maintained within manufacturer-specified normal operating range
Charging state testing	Separate tests with OBC active (AC charging)
Discharging state testing	Vehicle operating in electric drive mode

Operating Modes to Be Tested

REESS-equipped vehicles must be tested in multiple operating modes to capture all relevant emission and immunity scenarios:

1. Electric drive mode: The vehicle is driven by the electric motor with energy supplied by the REESS. The inverter, DC-DC converter, and BMS are all active.
2. Charging mode (AC): The onboard charger is actively charging the REESS from an AC supply. This mode generates emissions associated with power factor correction circuits and AC-DC conversion.
3. Charging mode (DC): If the vehicle supports DC fast charging, emissions during DC charging may also be assessed, though the off-board charger typically has its own EMC requirements.
4. Regenerative braking mode: The electric motor operates as a generator, feeding energy back into the REESS. This mode can produce different emission characteristics compared to motoring mode.
5. Standby/key-on mode: The vehicle is powered on but not moving. The BMS, thermal management, and auxiliary systems are active.

High-Voltage Safety During Testing

EMC testing of REESS-equipped vehicles requires strict adherence to high-voltage safety procedures. Test personnel must be trained in high-voltage safety, and the test facility must be equipped with appropriate safety equipment including insulated tools, personal protective equipment (PPE), and emergency disconnect procedures. The REESS must be properly isolated and monitored throughout the test.

Challenges in REESS EMC Testing

Electromagnetic Emissions from Power Electronics

The high-voltage power electronics in REESS-equipped vehicles generate broadband emissions that can extend from tens of kilohertz to several hundred megahertz. The fast switching transitions in the inverter and DC-DC converter produce harmonics that can couple into the vehicle’s wiring harness and radiate from cable runs and body panel gaps. Effective EMC design requires careful attention to filtering, shielding, and grounding of high-voltage components.

Battery Pack as an EMC Element

The REESS battery pack itself is a large conductive structure that can influence the vehicle’s electromagnetic behavior. The pack housing can act as a shield or as a resonant cavity, depending on its construction and grounding. Internal wiring and cell interconnections can create coupling paths for high-frequency noise. Proper bonding of the REESS enclosure to the vehicle chassis is critical for EMC performance.

Reproducibility of Test Results

Maintaining consistent REESS operating conditions during EMC testing is essential for reproducible results. Variations in state of charge, battery temperature, and load conditions can all affect emission levels. Test procedures must define these parameters precisely and monitor them throughout the measurement.

How TESTUPS Can Help

TESTUPS has invested in specialized test infrastructure for REESS-equipped vehicle EMC testing, including high-voltage capable test chambers, programmable AC and DC power supplies for charge mode testing, and dynamometer systems for drive mode emissions and immunity testing. Our engineers are trained in high-voltage safety procedures and experienced in the specific requirements of ECE R10 Annexes 7, 8, and 9 for electric vehicles. We support testing across all REESS operating modes and provide detailed reports suitable for type approval submission.

Contact TESTUPS to discuss your electric vehicle EMC testing requirements.