Analysis Report on the Necessity of Vehicle OBC Electromagnetic Compatibility Testing

International Level

• CISPR 25 serves as the core standard, specifying limits and measurement methods for vehicle radio disturbance characteristics, forming the foundation for global market access.
• ECE R10 proposes the latest electromagnetic compatibility requirements for plug-in vehicles (including on-board charging modules), with some content related to the SAE J1772 standard.
• ISO 6469-3, ISO 5474 series specify requirements for vehicle high-voltage components (such as OBC) from an electrical safety perspective.

Regional Level

• GB/T 18655 is the core basis for EMC testing of vehicle electronic components in China and is clearly regarded as the "ticket to the domestic market".
• GB 14023-2022 (equivalent to CISPR 12:2009), as a mandatory standard, imposes strict requirements on vehicle electromagnetic radiation emission.
• Standards such as GB 18384 and GB/T 31498 supplement the testing requirements for OBCs from an electrical safety perspective.

Safety Risks

• Direct safety risks such as electric shock and burns.
• Interference with the stable operation of vehicle positioning systems (GPS) or emergency call functions.
• OBC internal temperature exceeding limits may send error codes and trigger fire risks.

Brand Impact

• Electromagnetic interference issues may cause vehicle function failures, reducing user experience.
• Large-scale product recalls due to EMC issues generate high costs.
• OBC products that pass EMC compliance testing can enhance the brand's competitiveness in the market.

Core Changes Between 2016 and 2021 Versions

• Frequency Range Extension: The 2016 version covers 150kHz to 2.5GHz, while the 2021 version extends the upper limit to 5.925GHz.
• Technical Content Adjustment: The 2021 version removes the TEM cell-related test methods from the original standard and adds an appendix for measurement uncertainty assessment.
• Refinement of Applicable Scenarios: The 2016 version first included test requirements for charging modes of electric vehicles (EV) and plug-in hybrid electric vehicles (PHEV).

Challenges for OBC Design from Added Frequency Bands

The compatibility requirements for the newly added 5.9GHz V2X communication band pose higher demands on OBC design, requiring optimization at three levels:

1. Reduce high-frequency noise source intensity by optimizing topology (e.g., using soft switching technology).
2. Strengthen EMI suppression design in PCB layout.
3. Adopt high-performance shielding materials and filtering components.

Standard System Comparison

International standards, national standards, and enterprise standards exhibit hierarchical complementary characteristics in technical requirements. In the field of emission testing, GB/T 18655 and CISPR 25 are basically equivalent. Both testing methods use ALSE/TEM cells, and limit requirements are divided into levels 1-5. However, domestic standards may have additional requirements for transient pulses (such as ISO 7637).

Compliance Strategy Implementation

1. Build a Three-Tier Compliance Path: Use international standards as the basic framework, add national standard special requirements, and meet the enhanced clauses of enterprise standards.
2. Design and Testing Optimization: Reduce electromagnetic interference risks from the source by using shielded cables, integrated filter circuits, and electromagnetic simulation analysis.
3. Application of Parallel Testing for Export EU Models: Utilize the equivalence between GB/T 18655 and CISPR 25, adopting the sequence of "International first, then National Standard".

Test Methods

• Voltage Method: Implemented through a Line Impedance Stabilization Network (LISN), frequency coverage typically 150kHz~108MHz.
• Current Method: Uses a current probe directly clamped on the harness to measure common-mode current in the harness, with a wider frequency range (150kHz~245MHz).

Interference Characteristics Under Different Operating Conditions

According to GB/T 18655 standard, it is necessary to scan the disturbance level in the frequency range of 150kHz to 108MHz under different load conditions:

• Under full load, the interference amplitude corresponding to the switching frequency and harmonics of power devices is usually higher than under light load conditions.
• In LLC resonant topology, if the resonant frequency shifts to 200kHz, significant harmonic peaks may appear in the 220kHz to 500kHz frequency band.

Test Environment

This test is usually conducted in an Anechoic Chamber (ALSE). It is necessary to simulate the actual installed state of the OBC to arrange the harness (length 1.7m~2m), and select according to different frequency bands:

• Biconical Antenna (30MHz~200MHz)
• Log-Periodic Antenna (200MHz~1GHz)
• Horn Antenna (1GHz~6GHz)

Standard Limit Differences

GB/T 18655 limits the test frequency band for component electromagnetic radiation emission to 150kHz～6GHz; the CISPR 25 standard clearly covers the 150kHz~6GHz frequency band, requiring radiated emission testing for high-frequency bands above 2.5GHz.

Test Methods

• Anechoic Chamber Method: Simulates the space electromagnetic field through a transmitting antenna in a shielded environment. Typical test frequency range is 80MHz~6GHz, field strength covers 20V/m~200V/m.
• Bulk Current Injection (BCI) Method: Injects interference signals into the cable through a current probe. Frequency range is 0.1MHz~400MHz, injection current level is 60mA~200mA.

Impact of RF Field on PFC Circuit

The space RF field enters the PFC circuit through radiation coupling or cable conduction, interfering with sensitive units in the control loop:

• May cause distortion of the output signal from the voltage sampling circuit.
• Causes the PFC controller to misjudge the input voltage status.
• Affects the current feedback loop through electromagnetic coupling.

Test Standards

According to the international standard ISO 7637-2, this standard defines various transient pulse waveforms for vehicle 12V/24V electrical systems:

• Pulse 1: Simulates power supply and inductive load disconnection transients.
• Pulse 2a: Simulates transient phenomena caused by sudden interruption of current in a device parallel to the module due to harness inductance.
• Pulse 2b: Simulates transient phenomena when a DC motor acts as a generator and the ignition switch is turned off.
• Pulse 3a/3b: Simulates transient phenomena caused by switching processes.

Test Environment

To ensure the accuracy and safety of the test, a dedicated isolation platform needs to be set up to achieve accurate measurement of common-mode current and injection testing of differential-mode voltage.

High Voltage Load Dump Test

As a key project of voltage abnormality testing, it mainly verifies the resistance ability of the electric drive system to transient voltage pulses when the high-voltage battery is suddenly disconnected during power generation or charging.

Core Instruments

• EMI Receiver
• Must meet the CISPR 16-1-1 standard requirements for 6dB bandwidth and peak detector.

Antenna System

• 1m Monopole Antenna (150kHz~30MHz)
• Biconical Antenna (30MHz~200MHz)
• Log-Periodic Antenna (200MHz~1GHz)
• Horn Antenna (1GHz~6GHz)

Core Instruments

• Signal Generator and Power Amplifier
• Conducted Transient Immunity System

Coupling/Decoupling Network (CDN)

As a key component of the EMS testing system, it undertakes the important function of coupling the disturbance signal to the Equipment Under Test (EUT) and isolating auxiliary equipment.

Layout Design

• Six-sided box structure, internally covered with absorbing material.
• The floor is a conductive ground plane (copper/aluminum plate with thickness ≥0.5mm).
• The harness is fixed (50±5)mm above the ground plane.

Performance Indicators

• Field Uniformity (FU) must reach ±3dB (over 75% of the test volume area).
• Normalized Site Attenuation (NSA) must comply with the CISPR 16-1-4 standard requirements.

Grounding System

• The ground plane uses copper or aluminum plates with a thickness not less than 0.5mm.
• Minimum width is 1000mm or the test arrangement width plus 200mm (whichever is larger).
• Minimum length is 2000mm or the test arrangement length plus 200mm (whichever is larger).

Auxiliary Facilities

• Tooling Fixtures and Special Testing Equipment
• Simulated Battery Load Box
• Fiber Optic Isolation Measurement System

Standard Tracking

• Systematically organize EMC standard requirements at international, domestic, and enterprise levels.
• At the international level, comply with general standards such as CISPR 25.
• At the enterprise level, meet specific specifications such as GM GMW3097.

Simulation Prediction

• Use simulation software like CST to perform electromagnetic compatibility simulations on PCB layout, shielding structure, and key circuits.
• Combine rectification solutions such as multi-stage LC filter optimization, low-impedance magnetic material selection, and soft switching technology upgrades.

Standard Development Direction

• The application of high-frequency communication technologies such as V2X and 5G promotes the expansion of test frequency bands.
• The development of 6G communication technology will further push frequency bands into the millimeter wave range.
• The deepening of electrification technology (such as the popularization of 800V high-voltage platforms) increases high-frequency interference risks.

Testing Capability Building

• Coexistence interference testing capability between vehicle millimeter-wave radar and OBC.
• Construction of automated and intelligent testing systems.
• Deep integration of EMC design and testing.