Learn common inverter harmonic interference phenomena and solutions

AC drive harmonic control reactive power compensation

The harmonic interference phenomenon of the inverter includes: after the inverter starts or runs, the motor overheats, whistles (including increased noise, etc.), and vibrates/vibrates. The motor often breaks down, it is found that the stator insulation of the motor is breakdown after disassembling the motor. The connecting wire between the motor and the inverter will overheat, burst, and even catch fire. The instrumentation, sensors, communications, etc. around the motor will have problems such as work disorder. The above-described phenomena are likely to be caused by the harmonics generated in the inverter inversion process, which must be paid great attention by everyone.

Variable speed drive harmonic interference phenomenon

When you encounter the following problems, if there is no problem with the inspection equipment itself, you should consider it from the perspective of the harmonic interference of the inverter:

1. Motor overheating

The harmonics generated during the inverter inversion process can cause the motor to overheat. If you use a thermometer to test the motor's casing, or accidentally touch the motor's casing, you will find this kind of The problem.

2. Motor vibration/vibration

During the operation of the inverter, you will obviously feel that the motor has obvious vibration/vibration, and the amplitude may even be relatively large. Because of the safety of the motor, you have to stop the operation of the inverter system, except In addition to the reason of the motor itself and the reason that the motor is not firmly fixed, it is likely to be caused by the harmonics of the inverter.

3. Motor whistle/noise increase

Another possibility of the influence of the inverter harmonics on the motor is to cause the motor to emit a harsh whistling sound, or the noise of the motor increases significantly. There is no doubt that this may also be caused by the inverter harmonics, at least the one of the possible factors.

4. Motor insulation is frequently damaged

Some customers who use frequency converters find that the motor is not durable, and it will break once in a few days, weeks or months. After replacing the motors of many manufacturers, the problem remains (all the stator insulation of the motor is broken down, showing a point-like shape). Breakdown), can not find the reason, in fact, it is very likely that you have ignored the harmonic interference of the inverter.

5. Motor bearings are frequently damaged

When the motor is disassembled, it is found that there are pitting, cracking and other problems on the bearing of the motor. After replacing the bearing, there is no effect. After a period of time, the bearing of the motor is broken again. In this case, you should consider that this is very likely to be The inverter harmonics are doing the trick.

6. Cable

When you use a thermometer or accidentally touch the connecting cable between the inverter and the motor, you will find that the temperature of the cable is obviously abnormal or high, or you can see the connecting cable between the inverter and the motor The cable has problems such as burst skin/burst. In addition to the quality problem of the cable itself and the age of the cable, there is also a possibility that the high-frequency harmonics generated during the inverter inverter process may be the culprit. .

7. Instrumentation, sensors, communication

The harmonics generated during the inverter inversion process may also propagate through space, which is the so-called radiated harmonics, which will cause abnormalities in instruments, sensors, communications, etc.: the values displayed by the instruments are inaccurate, or violent The value transmitted by the sensor is inaccurate, or there is no way to transmit data at all; the communication is intermittent, or the communication cannot be carried out normally at all, all of the above may also be caused by the harmonics of the inverter. .

AC drive harmonic interference cause analysis

In the operation process of the inverter, there is an indispensable link, that is, it is necessary to convert the DC power into the AC power we need. This link is the inverter. In the inverter's inverter process, it is the process of first chopping and then recovering. It is in this chopping process that conducted harmonics and radio frequency harmonics will be generated. This chopping is similar to our chopping vegetables, but chopping is much finer than our chopping. Typically, the inverter circuit will cut a complete waveform into thousands of segments, depending on the carrier frequency of the inverter, or switching frequency. If you have seen the inverter voltage waveform at the output of the inverter, you will find that this waveform is not only not a sine wave, but also has a lot of "burrs" on it. In fact, this is the root cause of the harmonic interference of the inverter. where.

AC frequency inverter harmonic interference solutions

When encountering the harmonic interference problem of the inverter, first determine whether it is caused by the harmonics of the inverter rectification, or the harmonics of the inverter, or the result of both. Then take corresponding countermeasures, so that you can get twice the result with half the effort, so that the harmonics of the inverter have nowhere to hide.

The solutions to the harmonic interference of the inverter are as follows:

1. Ground

Good grounding is the basis for the safe, stable, reliable and efficient operation of the frequency conversion system. Therefore, grounding is a very important part.

2. Cable

If your cable length is less than or equal to 50 meters, you can consider replacing the ordinary cable with a cable with a shielding layer, and grounding the shielding layer reliably through cable clips or U-clamps, which is also a solution. A method of frequency converter harmonic interference.

3. Devices

In addition to the above methods, the harmonics generated by the inverter can also be suppressed by installing a special harmonic suppression device for the inverter, which can also achieve the expected effect, or achieve a relatively good effect. The most widely used are the special output filter of MLAD-V-SC frequency converter, the special output reactor of MLAD-VR-SC frequency converter, MLAD-DW series Du/Dt filter, MLAD-SW sine wave filter and so on.