How to do electromagnetic compatibility of power electronic equipment?

With the rapid development of electronic technology, modern electronic devices have been widely used in various fields of human life. Currently, electronic devices are in a period of rapid development, and this development process continues at an increasing rate. The widespread use and development of electronic devices inevitably leads to an increase in the level of electromagnetic fields they generate in their surrounding space. That is to say, electronic devices inevitably work in an electromagnetic environment (EME). Therefore, the adaptability of electronic equipment in an electromagnetic environment must be solved. Electromagnetic compatibility (EMC) is a science about the effects of electromagnetic interference (EMI).

Classification of electromagnetic interference sources

Various forms of electromagnetic interference are the main factors affecting the electromagnetic compatibility of electronic equipment. Therefore, it is an important part of the research that needs to be studied in electromagnetic compatibility design. Electromagnetic interference sources can be classified into internal interference and external interference. Internal interference refers to the mutual interference between the components inside the electronic device, including the interference caused by the leakage of the working power through the line and the insulation resistance (related to the operating frequency); the impedance of the signal through the ground, the power supply and the transmission line Mutual coupling, or interference caused by mutual inductance; some components inside the device or system generate heat, affecting the interference caused by the stability of the component itself or other components; the magnetic field and electric field generated by high-power and high-voltage components affect other through coupling Interference caused by components. External interference refers to interference from a line, device or system by factors other than electronic equipment or systems, including external high voltage, power supply interfering with electronic circuits, equipment or systems through insulation leakage; external high-power equipment generates strong space Magnetic field, interference with electronic circuits, equipment or systems through mutual inductance coupling; interference from space electromagnetic waves to electronic circuits or systems; unstable working temperature, causing interference caused by changes in internal components of electronic circuits, equipment or systems; The equipment and the interference generated by the power supply voltage through the power transformer.

Interference pathway

When the frequency of the interference source is high, the wavelength of the interference signal is smaller than the structure size of the interfered object, or the distance between the interference source and the victim is r 》 λ/2π, the interference signal can be regarded as a radiation field. It enters the path of the interfered object by the outward side of the electromagnetic field energy in the form of a plane electromagnetic wave.

Interference signals, in the form of leakage and coupling, are coupled to the interfered line, device or system via a common impedance coupling through an insulating support (including air). If the frequency of the interference source is low, the wavelength λ of the interference signal is longer than the structural size of the interfered object, or the distance r between the interference source and the interference object is “λ/2π, the interference source can be considered to be a stable field, Access to the interfered object in the form of an inductive field.

Interference signals can be introduced into a line, device, or system by direct conduction.

Basic principles of electromagnetic compatibility design

The first is grounding. The purpose of grounding includes: ensuring that the circuit system can work stably; preventing interference from external electromagnetic fields; ensuring safe operation. Followed by shielding. Shielding is the separation of metal between two spatial regions to control the induction and radiation of electric, magnetic and electromagnetic waves from one region to another. The principle of shielding material selection is: when the frequency of the interference electromagnetic field is high, the metal material with low resistivity is used; when the frequency of the electromagnetic wave is low, the material with high magnetic permeability is used; in some cases, if required When both high-frequency and low-frequency electromagnetic fields have good shielding effects, different metal materials are often used to form a multilayer shielding body.

There are other methods of suppressing interference, including filtering, proper selection of passive components, and circuit technology. Filtering is an important measure to suppress and prevent interference. The filter can significantly reduce the level of conducted interference, and a high-frequency circuit can use a CLCMÏ€-type filter composed of two capacitors and an inductor (high-frequency choke). There are many types of filters, and choosing the right filter eliminates unwanted coupling. Practical passive components are not "ideal" and their characteristics are different from the ideal ones. Practical components themselves can be a source of interference, so the correct choice of passive components is very important. Sometimes it is also possible to use the characteristics of the component to suppress and prevent interference. Sometimes, after shielding, the requirements for suppression and interference prevention cannot be met, and circuit technology such as balancing measures can be combined with shielding. A balanced circuit is one in which two wires in a two-wire circuit and all circuits connected to the two wires have the same impedance to ground or to other wires.

Specifications and standards for electromagnetic compatibility issues

The Interference Special Committee (CISPR), which focuses on the measurement of interference noise in radio systems. In 1976, CISPR began to develop EMI standards for electromagnetic interference. In October 1900, the reprinting standards were announced on the basis of several revisions. The committee then reviewed with the International Wireless Communications Advisory Committee to develop data requirements and specific methods for the detection of electromagnetic compatibility of electronic products. "Permissible values ​​of interference characteristics of industrial, scientific and medical radio instruments and their measurement methods" (Standard No. 11) for the noise of information technology devices; "The radio interference characteristics of vehicles, motor boats and spark ignition engines" Measurement method and permissible value" (Standard No. 12); "Measurement method and allowable value of radio interference characteristics of radio and television receivers" (Standard No. 13). Until the middle of 1992, the international EMI standard was finally improved. The tolerances recommended by CISPR have been adopted by many countries around the world and serve as the basis for their national regulations.

Some typical electromagnetic compatibility problems are solved

Due to the wide application of electronic technology in various industries, the space of human activities is ubiquitous with electromagnetic waves. Therefore, electronic devices cannot be compatible with electromagnetic wave interference problems. In practical applications, people have accumulated a lot of experience in researching anti-jamming technology, and constantly researched many practical methods to eliminate electromagnetic interference. The software anti-jamming of microcomputer equipment is mainly to stabilize the memory data and guarantee the program pointer. The microcomputer is a programmable control device, and the software can support and enhance the anti-interference ability of the hardware.

Ensuring electromagnetic compatibility of equipment is a complex technical task, and there is no one-size-fits-all solution to this problem. Electromagnetic compatibility technology involves a wide range of fields, and the field of electromagnetic compatibility is also developing. It is important to master the basic principles of electromagnetic compatibility, and to carefully analyze and test, you can choose the appropriate method to solve the problem.

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