The frequency converter has been applied to various fields of industrial control due to its power-saving, energy-saving, reliable and high-efficiency characteristics, but it also brings some interference problems. The on-site power supply and electrical equipment will affect the inverter, and the high-order harmonics generated during the operation of the inverter will also interfere with the operation of the surrounding equipment. There are three main types of interference caused by frequency converters: interference to electronic equipment, interference to communication equipment, and interference to radio. The interference to electronic equipment such as computers and automatic control devices is mainly inductive interference; the interference to communication equipment and radios is radiation interference. If the inverter's interference problem is not solved properly, not only the system cannot operate reliably, but also the normal operation of other electronic and electrical equipment. 2 Main electromagnetic interference sources and ways of frequency conversion speed regulation system 2.1 Main sources of electromagnetic interference Electromagnetic interference, also known as electromagnetic interference (EMI), is electromagnetic interference caused by external noise and unwanted signals in the reception, usually conducted through circuits and spread in the form of fields. The rectifier bridge of the frequency converter is a non-linear load to the power grid, and the harmonics it generates will cause harmonic interference to other electronic and electrical equipment on the same power grid. In addition, the inverters of frequency converters mostly use PWM technology. When they work in switch mode and perform high-speed switching, a large amount of coupling noise is generated. Therefore, the frequency converter is a source of electromagnetic interference to other electronic and electrical equipment in the system. On the other hand, the harmonic interference in the power grid mainly interferes with the inverter through the power supply of the inverter. There are a large number of harmonic sources in the power grid, such as various rectifier equipment, AC/DC interchange equipment, electronic voltage adjustment equipment, non-linear loads, and lighting equipment. These loads all cause the voltage and current in the power grid to produce waveform distortion, thereby causing harmful interference to other equipment in the power grid. After the power supply of the inverter is interfered by the polluted AC power grid, if it is not dealt with, the power grid noise will interfere with the inverter through the power supply circuit of the power grid. The main interferences of the power supply to the inverter include overvoltage, undervoltage, and instantaneous power failure; surges and drops; spike voltage pulses; radio frequency interference. Secondly, common mode interference through the control signal line of the inverter will also interfere with the normal operation of the inverter. 2.2 Ways of electromagnetic interference The frequency converter can generate high-power harmonics, which has strong interference to other equipment in the system. The interference path is the same as the general electromagnetic interference path, mainly divided into electromagnetic radiation, conduction, and inductive coupling. Specifically: ① Generate electromagnetic radiation to the surrounding electronic and electrical equipment; ② Generate electromagnetic noise to the directly driven motor, which increases the iron and copper loss of the motor, and conducts interference to the power supply, and conducts it to other equipment in the system through the power distribution network; ③The inverter generates inductive coupling to other adjacent lines, and induces interference voltage or current. Similarly, the interference signal in the system interferes with the normal operation of the inverter through the same way. Let's analyze them separately.
