According to the basic principles of electromagnetics, the formation of electromagnetic interference ( EMI ) requires three elements: electromagnetic interference source, electromagnetic interference path, and system sensitive to electromagnetic interference. To prevent interference, hardware and software anti-interference measures can be adopted. Among them, hardware anti-interference is the most basic and important anti-interference measure. Generally, interference is suppressed from two aspects: resistance and prevention. The general principle is to suppress and eliminate the interference source, cut off the coupling channel of interference to the system, and reduce the sensitivity of the system to interference signals. Specific measures in engineering can be isolation, filtering, shielding, grounding and other methods.
1. Isolation
The so-called interference isolation refers to isolating the interference source and the part susceptible to interference from the circuit so that they do not have electrical contact. In the variable frequency speed drive system, an isolation transformer is usually used on the power line between the power supply and the amplifier circuit to avoid conducted interference. The power isolation transformer can be a noise isolation transformer. In actual engineering, when arranging equipment, the inverter should be arranged separately as much as possible to eliminate the electromagnetic interference generated by the inverter. Often due to the limitation of the room area, it is impossible to arrange it separately. The weak current control equipment that is susceptible to interference should be separated from the inverter as much as possible, such as placing the power distribution cabinet between the inverter and the control equipment to reduce interference.
2. Filtering
The high-order harmonics generated by the inverter during operation will affect the power grid, causing serious distortion of the grid waveform, which may cause a large voltage drop in the grid and a low power factor. Special attention should be paid to high-power inverters. The general solution is to use a power-free compensation device to adjust the power factor. At the same time, according to the specific situation, an inductive filter is installed at the power supply line end and the load side to minimize the impact on the grid.
3. Shielding
Shielding interference sources is the most effective way to suppress interference. The inverter should be fully enclosed in a metal shell and the metal shell should be reliably grounded to reduce the electromagnetic waves radiated through space and reduce interference to other equipment, especially electronic circuits and equipment. On the other hand, the inverter uses high-performance microprocessors and other integrated circuits, which are sensitive to external electromagnetic interference and may cause errors due to the influence of electromagnetic interference, causing adverse effects on operation. External interference invades through the inverter control cable as a medium, so sufficient anti-interference measures must be taken when laying cables. The measures usually taken are: the analog control line must use shielded wires and shielding layers. The end close to the inverter should be connected to the common end of the control circuit. ( COM ) Instead of being connected to the inverter ground ( E ) or the earth, the other end of the shielding layer is suspended.
4. Grounding
Practice has proved that grounding is often an important means to suppress noise and prevent interference. A good grounding method can greatly suppress the coupling of internal noise, prevent the intrusion of external interference, and improve the anti-interference ability of the system. There are several forms of grounding for frequency converters, such as multi-point grounding, single-point grounding, and busbar grounding. They should be adopted according to the specific situation. Be careful not to interfere with the equipment due to poor grounding. The grounding terminal E of the frequency converter should be well connected to the earth. When the frequency converter and other equipment or multiple frequency converters are grounded together, each device should be connected to the ground separately, and it is not allowed to connect the grounding terminal of one device to the grounding terminal of another device before grounding, so as to reduce the radiation in the space and the mutual interference between the equipment, so as to make the equipment operate normally.
Post time: Nov-28-2024