1. How to determine the interference problem of the inverter The interference problem of the inverter is mainly reflected in the operation of the motor. For example, the motor suddenly stops during the running process, the motor runs fast and slow, and the running speed is unstable. The motor can't stop, the button doesn't work, and so on. These are the manifestations of the inverter being disturbed.
2. The third way to deal with the grounding interference problem is to ensure good grounding. The general requirements for the grounding terminal are: grounding terminal is grounded in "third way" (separate grounding), the shorter the grounding wire, the better, and It must be well grounded; the control circuit line uses shielded wire, and the shield wire at the far end of the shield wire is suspended and the ground is grounded at the near end; according to the product requirements, reasonable wiring, strong and weak electricity are separated, keep a certain distance, and avoid the parallel power line and signal line of the inverter. Wiring, should be distributed wiring; increase anti-radio interference filter, inverter input and output anti-interference filter or reactor; take shielding measures to prevent electromagnetic induction, and even shield the inverter with metal iron box; properly reduce the carrier frequency; If the communication function is used, the RS485 communication line uses twisted pair. Below, I will do a specific analysis for different interference situations in actual use.
3. Three-phase five-wire power supply has encountered such a situation, the inverter has been running, pressing the stop button does not work, after inspection, the ground wire of the inverter is only connected with the neutral line of the transformer, and the transformer The neutral line is not connected to the earth. After the neutral line of the transformer is grounded, the inverter returns to normal. Many small factories today generally do not pay attention to the connection of the ground wire. When the machine tool leaves the factory, the ground and neutral lines are strictly separated according to the standards stipulated by the National Electrical Code. The neutral line of the power distribution cabinet has dedicated terminal blocks, and the ground wire has special grounding screws. Since the user came from the transformer three phase lines and one neutral line, only the neutral line was connected to the "N" terminal, and the ground line was not connected to the neutral line. Although the control line used shielded lines, the shielding layer was also The grounding screw was received, but it was not connected to the earth, and it could not be shielded. As a result, the inverter could not stop due to interference and the motor could not stop. After connecting the neutral line and the ground line in the power distribution cabinet, it will return to normal. You can also connect the ground wire in the power distribution cabinet directly to the earth. Many users adopt the method of connecting the ground line to the neutral line. However, the disadvantage of using this method is that if the neutral line is disconnected, starting a certain action of the machine tool may cause the machine to be charged, posing a safety hazard to the person. This type of interference is the type of interference that the frequency converter itself has.
4. Case of interference from external equipment to the inverter (1) Phenomenon. The motor can't stop occasionally. After checking that the shield is properly grounded, reducing the carrier frequency does not work. The magnetic loop filter on the input side and output side of the inverter does not work.
(2) Analysis. The power distribution cabinet in which the inverter is installed is too close to the power distribution room. The power distribution cabinet in the power distribution room has a large current flowing through it. There is a strong magnetic field around the current, which interferes with the normal operation of the inverter and keeps the power distribution cabinet away from the power distribution. After the room, it will return to normal, which belongs to the interference of the external equipment to the inverter.
5. Case of interference from the inverter to external equipment (1) Phenomenon. The motor does not operate after the inverter is started.
(2) Analysis. The inverter is given the running frequency by the external 4-20ma, and the DC signal of 4-20MA is sent by the transmitter. Looking at the display panel, the frequency is displayed as 0.00. The output of the transmitter was measured with an ammeter and found to have no output. After the output terminal of the transmitter is connected with a capacitor of 102, it is restarted and the device returns to normal, indicating that the signal source is disturbed. A simple signal line shunt capacitor solves the big problem in engineering practice and is a practical method that is often effective. This is the interference of the inverter to external devices.
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