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Analysis of Several Frequency Converter Interference Types and Solutions

Posted by: Yoyokuo 2022-08-12 Comments Off on Analysis of Several Frequency Converter Interference Types and Solutions

Power processing production units have extremely high requirements for the working efficiency of mechanical equipment, so in order to make the working efficiency of mechanical equipment meet production needs, many power processing units will install and use frequency converters. Because there are many types and quantities of mechanical equipment used in the processing and production unit, the frequency converter is prone to interference during the production process. Once the frequency converter is disturbed, it will seriously affect its working efficiency.

Frequency converter interference solution

Power processing production units have extremely high requirements for the working efficiency of mechanical equipment, so in order to make the working efficiency of mechanical equipment meet production needs, many power processing units will install and use frequency converters. Because there are many types and quantities of mechanical equipment used in the processing and production unit, the frequency converter is prone to interference during the production process. Once the frequency converter is disturbed, it will seriously affect its working efficiency.

In the process of using the inverter, if it is found that the inverter is interfered by the signal, it is necessary to first determine the source of the interference signal, and take appropriate methods to block the signal interference according to the actual situation. interference, so that the state of the inverter is more stable during the working process.

Generally, the frequency converter is easily disturbed by radiation during the working process. If the frequency converter is interfered by the radiated signal in the production work, the interference signal needs to be propagated by radiation. The specific method is to weaken the interference signal by wiring and shielding the radiation source and the interfered line.

If the inverter is affected by the interference signal propagated by the line, it is necessary to install filters on the input and output sides of the inverter, and deal with it by means of reactors or magnetic damage. Specifically, the signal line and the power line may be vertically crossed to perform vertical crossover to divide the wiring. The shielded tube should be grounded as much as possible, and a continuous and reliable grounding should be maintained throughout its entire length.

The inverter is affected by the line propagation interference. It is necessary to keep the shielding layer grounded away from the inverter. At the same time, the distance between the inverter and the grounding point of the inverter should be maintained, which should be separated from the grounding point of the inverter. In order to prevent the inverter from being affected by the interference of the line propagation signal, the magnetic ring can be used on the input power line and the output line of the inverter. In the process of winding, the magnetic ring should be close to the inverter, so as to avoid the inverter being affected by the interference signal of the line.

Analysis of Several Frequency Converter Interference Types and Solutions

Inverter anti-interference measures

Due to the nonlinearity of the main loop (switching action), the inverter itself is a source of harmonic interference, while its peripheral control loop is a low-energy, weak-signal loop, which is extremely susceptible to interference from other devices, causing the inverter itself and its surrounding The device is not working properly. Therefore, when the inverter is installed and used, anti-interference measures must be taken for the control circuit.

1) The basic control loop of the inverter

There are two basic circuits for signal exchange with the outside, analog and digital:

① 4~20mA current signal loop (analog); 1~5V/0~5V voltage signal loop (analog).

②Switch signal loop, inverter’s start and stop commands, forward and reverse commands, etc. (digital).

The external control command signal is introduced into the inverter through the above-mentioned basic circuit, and the interference source also generates an interference potential on its circuit, and the control cable is used as the medium to invade the inverter.

2) Basic types of interference and anti-interference measures.

①Electrostatic coupling interference: refers to the potential generated in the cable due to the electrostatic capacitance coupling between the control cable and the surrounding electrical circuit.

Measures: Increase the distance from the interference source cable, when the diameter of the conductor is more than 40 times, the degree of interference is not obvious.

Install a shielded conductor between the two cables, and then ground the shielded conductor.

②Electrostatic induction interference: refers to the potential induced in the cable by the change of the magnetic flux generated by the surrounding electrical circuit. The size of the interference depends on the magnetic flux generated by the interference source cable, the closed-loop area formed by the control cable and the relative angle between the interference source cable and the control cable.

Measures: Generally, lay the control cable separately from the main circuit cable or other power cables. The separation distance is usually more than 30cm (minimum is 10cm). When the separation is difficult, lay the control cable through the iron pipe. Twist the control conductor, the smaller the twisting spacing, the shorter the laying route, and the better the anti-interference effect.

③ Radio wave interference: It means that the control cable becomes an antenna, and the electric potential is generated in the cable by the external electric wave.

Action: As described in 1 and 2. If necessary, put the inverter into an iron box for radio wave shielding, and the iron box used for shielding should be grounded.

④Poor contact interference: refers to the interference caused by poor contact between the electrical contacts and relay contacts of the inverter control cable and the change of resistance in the cable.

Measures: For poor contact of relay contacts, use parallel contacts or gold-plated contact relays or use sealed relays. The cable connection points should be tightened and strengthened regularly.

⑤ Power line conducted interference: refers to the fact that when various electrical equipment obtains power from the same power supply system, the potential is directly generated by other equipment in the power supply system.

Measures: The control power supply of the inverter is powered by another system, and a line filter is installed on the input side of the control power supply; an insulating transformer is installed, and the shield is grounded.

⑥ Grounding interference: refers to the body grounding and signal grounding. For various unexpected interferences that can be induced by weak voltage current loops and any unreasonable grounding, such as setting more than two grounding points, a potential difference will be generated at the grounding, resulting in interference.

Measures: The control cable for given speed is grounded at one point, and the ground wire is not used as a signal path. The grounding of the cable is carried out on the side of the inverter, and the specially designed grounding terminal is used, which is not shared with other grounding terminals, and the resistance of the lead point of the grounding terminal is minimized, generally not more than 100d.

3) Other precautions

① Control cabinets equipped with frequency converters should be kept away from large-capacity transformers and motors as far as possible. The control cable lines should also avoid these devices with large leakage flux.

②The weak voltage and current control cables should not be close to circuit breakers and contactors that are prone to arcing.

③It is recommended to use 1.25mm×2 or 2mm×2 shielded stranded insulated cable for control cable.

④The shielding of the shielded cable should be continuous to the same length as the cable conductor. When the cables are connected in the terminal box, the shield terminals are connected to each other.

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