Abstract
With the rapid expansion of the electric vehicle (EV) industry and the implementation of GB/T 40428-2021, the demand for electromagnetic compatibility (EMC) testing has surged. This paper details the development of a low-electromagnetic interference (EMI) intelligent CP signal generator, addressing the inaccuracies in EMC testing caused by CP signal interference from charging equipment. The generator features a signal output range of -15 to 15 V, 0-100% duty cycle adjustment, and a stable 1000 Hz frequency, with EMI emissions exceeding standard limits by over 15 dB. Experimental results validate its effectiveness in enhancing testing accuracy and efficiency for various EV models.
1. Introduction
1.1 Research Background
The EV market has witnessed exponential growth, with China’s production and sales of new energy vehicles reaching 11.345 million and 11.262 million units by November 2024, representing year-on-year increases of 34.6% and 35.6%, respectively . Concurrently, the proliferation of charging infrastructure has amplified EMC-related challenges, necessitating rigorous testing compliant with GB/T 40428-2021. This standard mandates EMC testing for charging modes 2, 3, and 4, exposing inconsistencies in test outcomes due to CP signal interference from external charging equipment .
1.2 Problem Analysis
In practical EMC testing, CP signals from third-party charging devices often induce significant interference, leading to failed conduction/radial emission tests and charging interruptions during immunity testing. These issues obscure fault source identification, highlighting the need for a standardized, low-EMI CP signal solution .
1.3 Research Significance
The developed intelligent CP signal generator offers:
- A unified, stable CP signal source to mitigate external interference.
- Precise control over signal parameters via innovative circuit design.
- Compliance with strict EMI limits, enabling reliable EMC testing and supporting EV industry standards .
2. System Design and Implementation
2.1 Overall System Architecture
The system adopts a modular design, comprising:
- Power Module: 12V lithium battery with DC-DC conversion for stable power supply.
- Signal Processing Module: Generates and modulates CP signals.
- Control Module: 32-bit MCU for system coordination.
- Human-Machine Interface Module: LCD display and keypad for parameter configuration .
Table 1: System Module Specifications
| Module | Functionality | Key Components |
|---|---|---|
| Power Module | Converts 12V battery power to stable voltages for other modules | DC-DC converters, voltage regulators |
| Signal Processing | Generates CP signals with adjustable amplitude and duty cycle | DAC chips, operational amplifiers |
| Control Module | Manages signal generation and system operations based on user inputs | 32-bit MCU, memory units |
| HMI Module | Enables user interaction for parameter setting and status monitoring | LCD screen, pushbuttons |
2.2 Low-EMI Design
2.2.1 Reference Voltage Generation Circuit
The circuit employs a 16-bit high-precision DAC (AD5761R) for voltage stability, paired with a low-offset operational amplifier (AD8610, input offset voltage ≤ 50 μV, temperature drift 0.3 μV/°C). A temperature compensation network further suppresses amplitude variations due to thermal fluctuations .
The reference voltage \(V_{ref}\) is expressed as:\(V_{ref} = V_{DAC} \times \frac{R_f}{R_i}\) where \(V_{DAC}\) is the DAC output, and \(R_f/R_i\) is the feedback ratio of the op-amp circuit.
2.2.2 Signal Control Design
CP signal quality is critical for EMC testing accuracy. The design uses pulse-width modulation (PWM) with a high-speed comparator (LT1719, 8 ns propagation delay) for precise duty cycle control. A dead-time control circuit (200 ns via RC delay and Schmitt trigger) prevents shoot-through in the half-bridge driver (IR2110), while overcurrent and under-voltage protection ensure safety .
The duty cycle D is defined as:\(D = \frac{t_{on}}{T} \times 100\%\) where \(t_{on}\) is the on-time and T is the period (1 ms for 1000 Hz frequency).
2.2.3 PCB Design Optimization
A four-layer PCB structure enhances EMC performance:
- Layer 1: Analog and control signals
- Layer 2: Ground plane (low-impedance return path)
- Layer 3: Power plane
- Layer 4: Digital circuits
Key design principles include:
- Analog-digital partitioning with isolated ground planes.
- Star-topology power distribution to minimize crosstalk.
- Fan-out layout for high-speed components to reduce signal reflections.
- Multi-parallel filter capacitors to lower equivalent series inductance .
3. Experimental Validation
3.1 Test Protocol
Tests were conducted in an EMC laboratory per GB/T 40428-2021, comprising:
- Functional testing of technical specifications.
- EMI emission and immunity testing.
- In-vehicle validation for real-world performance .
3.2 Functional Performance Verification
Table 2: Key Technical Specifications and Test Results
| Parameter | Design Requirement | Test Result | Tolerance |
|---|---|---|---|
| Output Voltage | -15 to 15 V | -15.02 to 14.98 V | ±0.02 V |
| Duty Cycle Adjustment | 0-100% continuous | 0-100% with 0.1% step | ±0.1% |
| Frequency | 1000 Hz ±1% | 1000.3 Hz | +0.03% |
| Power Supply | 12 V DC | 12 V ±0.5 V | ±4.17% |
All parameters met design targets, demonstrating stable adjustability for various charging modes .
3.3 EMC Testing Results
EMI emissions were measured across the standard frequency range, with results exceeding the limit by 15 dB or more. For example, at 30 MHz, the measured emission was 42 dBμV/m, 18 dB below the 60 dBμV/m limit .
The suppression ratio S is calculated as:\(S = 20 \log_{10}\left(\frac{E_{limit}}{E_{measured}}\right)\) where \(E_{limit}\) is the standard limit and \(E_{measured}\) is the measured emission.
3.4 In-Vehicle Application
Field tests on multiple EV models showed:
- Reliable CP signal communication and vehicle recognition.
- Stable signal transmission during charging, eliminating interference-induced interruptions.
- 42.6% reduction in average testing time compared to conventional methods .
4. Conclusions
4.1 Technical Innovations
- Multi-stage EMI filtering design achieving emissions 18 dB below standards.
- High-precision CP signal control with -15 to 15 V output and 0-100% duty cycle adjustment.
- Intelligent software for automated charging mode control .
4.2 Engineering Value
- Successful deployment in vehicle manufacturers and testing institutions.
- Enhanced testing efficiency, reducing time consumption by 42.6%.
- Robust support for GB/T 40428-2021 implementation .
4.3 Future Directions
- Optimize electromagnetic shielding for higher immunity.
- Expand compatibility with additional charging protocols.
- Develop networked remote monitoring and data analysis capabilities.
- Integrate intelligent diagnostic algorithms for fault localization .