Electromagnetic Compatibility Simulation Test Design of New Energy Vehicles

“Electromagnetic Compatibility (Electromagnetic Compatibility, EMC). Refers to the ability of a device or system to work normally in its electromagnetic environment without causing unacceptable electromagnetic interference to anything in the environment.

“

1. The necessity of electromagnetic compatibility testing in new energy vehicles

Electromagnetic Compatibility (Electromagnetic Compatibility, EMC). Refers to the ability of a device or system to work normally in its electromagnetic environment without causing unacceptable electromagnetic interference to anything in the environment.

EMC includes two requirements: On the one hand, it means that the electromagnetic interference generated by the equipment to the environment in the normal operation process cannot exceed a certain limit, that is, the so-called Electromagnetic Interference (EMI).

On the other hand, it means that the equipment has a certain degree of immunity to the electromagnetic interference existing in the environment, that is, the so-called Electro Magnetic Susceptibility (EMS).

Compared with traditional vehicles, the EMC problem of new energy vehicles is more prominent. The power of new energy vehicles directly uses the electric drive system, and the use of high-voltage accessories will make the problem of electromagnetic interference more serious. The power system will emit strong radiation and electromagnetic interference due to the beating of current in a very short time and the rapid movement of high-power semiconductor switches.

In addition, Electronic and electrical components occupy a large proportion, and the electromagnetic compatibility problem is closely related to the safety of the whole vehicle. Various controllers in the car, DCDC and DCAC are strong sources of interference, and the wiring harness is many and long, and the radiation interference is very serious. With the release of CISPR25-2016, the EMC requirements of high-voltage systems have become more and more stringent, and EMC testing has become one of the most severe challenges for automotive manufacturers.
　

　　

A typical DCDC topology

In order to reduce electromagnetic interference, we must strengthen electromagnetic compatibility testing.

2. Analysis principle of EMC

Traditional EMC design generally follows: product design – sample production – EMC test – test failure – rectification – change design – sample production – test pass.

Difficulty positioning, repetitive work.

EMC simulation is a forward electromagnetic compatibility design method based on software analysis, including 3D simulation, PCB simulation and system and circuit simulation.

There are analytical methods and numerical methods for analyzing electromagnetic fields. EMC simulation software is based on numerical method.

Commonly used numerical methods
　　

The basis of all algorithms in EMI, Maxwell’s equation:
　

Integral form of Maxwell’s equation
　　

Differential Form of Maxwell’s Equation

Now the more mainstream EMC simulation software has ANSYS series and CST series

EMC simulation yields accurate results
　　

3. Three elements of EMC

In order to solve the electromagnetic compatibility problem, we need to start from three points. The three elements of the EMC problem are inseparable:

A source of interference, a circuit or device that causes interference.

Optimize the electrical structure of the equipment, select appropriate electronic components, and reduce the power of the equipment.

Transmission path (coupling path), the path that can transfer the interference energy generated by the interference to the sensitive source.

Shield interference source equipment and related wiring harnesses, increase wiring harness filtering, and rationally plan wiring harnesses.

Sensitive equipment, disturbed circuits or equipment. In high-voltage systems, every high-voltage electrical appliance that relies on waveform control may output wrong control signals if subjected to electromagnetic interference. Low-voltage systems, such as vehicle controller VCU, CAN communication system, battery management system BMS (especially switch trigger circuits and sensors), energy management units, brake controllers, etc., almost every electrical appliance with control and regulation functions is sensitive. source.

Reduce the area where the device receives interference and increase the distance between the device and the source of interference. Choose a suitable ground and ground it nearby. Enhanced filter design for sensitive frequency bands.

Interference source, propagation path and sensitive source, any one of the three elements is controlled, and the anti-electromagnetic interference performance of the system will be improved.

Electromagnetic Compatibility Simulation Test Design of New Energy Vehicles

There are three types of interference suppression methods: shielding, filtering and grounding

Shielding mainly solves radiation interference and prevents the interference source from spreading interference to the surrounding environment or being interfered by electromagnetic signals in the environment. The effect of shielding is related to the material of the shielding layer, the thickness of the shielding layer, the type of signal in the environment, the signal strength, the integrity of the shielding layer and other factors.

Filtering mainly solves the conducted interference. The interference conducted through the circuit cannot be avoided by means of shielding. Only a filtering device is installed in the circuit. The parameter setting of the filter is directly related to the frequency of the protected circuit and the interference source, and the filter type and parameters can be selected according to the gap between the two. The wires in the power system have strong antenna characteristics, which can not only receive external interference signals, but also transmit interference signals to the environment.

Grounding is a suppression measure against common-mode interference. Connecting the interference source and the system ground can reduce the current or voltage of the interference signal. However, it is not possible to use wire connection directly to completely play the role of anti-interference. The effect of grounding is closely related to the grounding mode. Inappropriate grounding will instead transmit the interference signal in the car’s grounding system to the original system with perfect shielding measures.

Shielding, to achieve the purpose of blocking the propagation channel and eliminating the interference source or sensitive source at the same time; filtering, based on the theory of blocking the propagation channel; grounding, based on the theory of eliminating the interference source.

4. EMC testing and new standards

For the electromagnetic compatibility of electric vehicles, strict industry standards have been formulated internationally. Automotive EMC standards, including EMC standards for complete vehicles, components, and ICs.

Vehicle EMC tests and standards include:

External interference of the whole vehicle, radiation interference of the whole vehicle; anti-interference of the whole vehicle, anti-interference of the whole vehicle radiation.

Electromagnetic Compatibility Simulation Test Design of New Energy Vehicles

Parts EMC test:

External interference of components, anti-interference of components,

Electromagnetic Compatibility Simulation Test Design of New Energy Vehicles

Auxiliary inverter EMC test

Chip EMC test standard

Conducted emissions and conducted interference injection (DPI) in chips are the more common tests for ICs.

Each OEM has its own standards, the test items are similar, but the test limits are slightly different The need for technological progress. At present, basically all power components related to new energy vehicles in China are tested for conduction and radiation in accordance with GB/T 18655-2010.

This new standard includes radiated emission (divided into broadband and narrowband tests, refer to GB/T 18655), radiation immunity (divided into BCI high current injection and ALSE anechoic chamber method, refer to ISO 11452-4 and ISO 11452- 2), Power Line Transient Conducted Immunity (refer to ISO 7637-2) and Electrostatic Discharge Immunity (refer to ISO 10605).

This standard is different from the previous standards for automotive electronics. This standard extracts the content proposed by multiple standards such as radiation, high current injection, radiation immunity, pulse immunity, and static electricity, and aims at driving The system is merged into a standard, so it is a product standard.

The release of the new standard will greatly accelerate the improvement and improvement of the EMC testing level of the existing domestic electric vehicle drive components, and give EMC practitioners in this field a clearer direction for their efforts. This is a challenge and an opportunity for new energy practitioners.