Main electromagnetic interference sources and ways of frequency conversion speed control system
2.1 Main sources of electromagnetic interference
Electromagnetic interference, also known as electromagnetic disturbance (EMI), is the electromagnetic interference caused by external noise and unwanted signals in the reception, usually through circuit conduction and in the form of field. The rectifier bridge of the frequency converter is a non-linear load to the power grid, and the harmonics generated by it will cause harmonic interference to other electronic and electrical equipment of the same power grid. In addition, most of the inverters of the inverter use PWM technology. When they work in the switching mode and switch at high speed, a large amount of coupling noise is generated. Therefore, the inverter is an electromagnetic interference source for other electronic and electrical equipment in the system. On the other hand, harmonic interference in the power grid mainly interferes with the frequency converter through the power supply of the frequency converter. There are a large number of harmonic sources in the power grid, such as various rectifier equipment, AC and DC interchange equipment, electronic voltage adjustment equipment, non-linear loads and lighting equipment. These loads cause waveforms and voltages in the power grid to be distorted, which can cause harmful interference to other equipment in the power grid. After the power supply of the inverter is disturbed by the contaminated AC grid, if it is not processed, the grid noise will interfere with the inverter through the grid power supply circuit. The mains interference of the power supply to the inverter is overvoltage, undervoltage, instantaneous power loss; surge, drop; spike voltage pulse; radio frequency interference. Secondly, the 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 inverter can generate harmonics with higher power and is more intrusive to other devices in the system. The interference path is consistent with the general electromagnetic interference approach, mainly divided into electromagnetic radiation, conduction, and inductive coupling. Specifically: 1 generates electromagnetic radiation to surrounding electronic and electrical equipment; 2 generates electromagnetic noise to the directly driven motor, so that the iron loss and copper consumption of the motor increase, and conducts interference to the power source, and is transmitted to other equipment of the system through the power distribution network; 3 The inverter inductively couples adjacent lines to induce interference voltage or current. Similarly, the interfering signals in the system interfere with the normal operation of the frequency converter by the same way.
