During this time, there are always customers who come to inquire about whether the inverter has a built-in filter, whether it still needs a special input filter for the pre-inverter,LCL harmonic filter、Active harmonic filterProblems with harmonic suppression devices of equi VFD. Let’s put it this way, in the more than 20 years that Yifan has worked in Green Bojie Neng, he has participated in at least 100 similar cases. In other words, even if the inverter already has a built-in filter, there will still be customers who need to add MLAD-V-SR inverter special input filter, LCL harmonic filter, active harmonic filter and other inverter harmonic suppression devices.

1. What exactly is the built-in filter of the VFD?

The built-in filter of the VFDis actually what we often sayEMI filter, or simple EMI filter, its main component, is also the filter inductor, filter capacitor and discharge resistor, its main function is to suppress the high-frequency harmonics of 150KHz~30MHz generated by the VFD in the rectification process, and its harmonic suppression efficiency is generally ≤ 30%.

2. Why do VFD have built-in filters?

According to Yifan’s understanding, the purpose of the built-in filter of the VFD is mainly derived from two aspects: one aspect is that the VFD manufacturer knows that the VFD will produce harmonics when running, and these harmonics may interfere with the electrical equipment and motors around it and the VFD using the same power supply, etc., in order to solve this problem, the VFD built-in filter is undoubtedly a helpless move; Another aspect is that when the inverter is exported, it also needs to do CE, UL and other certifications, which will undoubtedly includeEMC testIt is unlikely that the inverter itself will pass the EMC test, so in order to pass the EMC test, the inverter manufacturer has to have a built-in filter to determine that the inverter can pass the EMC test.

3. Why can’t the built-in filter of the VFD work?

If the VFD already has a built-in filter, it also needs a pre-VFD special input filter, LCL harmonic filter, active harmonic filter and other VFD harmonic suppression devices, then it means that theVFD has a built-in filter, or it is not good, in fact, it cannot be so simple to understand this problem.

1. Cost, volume and other elements

From the perspective of VFD manufacturers, the built-in filter of the VFD will not only increase the cost, but also increase the volume of the VFD, but now there are many brands in the VFD market, and the involution is very powerful, increasing the cost, which means reducing its competitiveness; In addition, customers require that the smaller the inverter, the better, which can reduce the cost of the inverter cabinet and make it more convenient to install…… Seeing this, you may understand that the component configuration of the inverter’s built-in filter can basically be said to be the component configuration of the inverter pre-filter, and there is no comparison.

2. Efficiency elements

If the number and parameters of the components of the inverter built-in filter do not reach the inverter pre-filter, naturally, its filtering efficiency will not be the same as that of the MLAD-V-SR inverter special input filter,MLAD-GFC seriesLCL Harmonic Filter,MLAD-APFActive harmonic filters and other inverter pre-harmonic suppression devices are compared.

3. Functional elements

In fact, you also need to know one thing, in the harmonics generated by the VFD in the rectification process, not only high-frequency harmonics, but also 5, 7, 11, 13 times and other high harmonics, but the built-in filter of the VFD for 5, 7, 11, 13 times and other high harmonics, it can be said that it is helpless, and can only watch these high harmonics flow wantonly through its body.

3. Under what circumstances does the VFD with built-in filter need a pre-filter

Since the built-in filter of the VFD cannot be said to be a pure decoration, when necessary, it is still necessary to install the optional MLAD-V-SR inverter special input filter, MLAD-GFC series LCL harmonic filter, MLAD-APF active harmonic filter and other inverter pre-harmonic suppression devices, then, when do you need to install the optional MLAD-V-SR inverter special input filter, MLAD-GFC series LCL harmonic filter, What about MLAD-APF active harmonic filters and other inverter pre-harmonic suppression devices? Next, Yifan will talk to you about this issue.

1. When it is impossible to resist high-frequency harmonics

As mentioned earlier, although the built-in filter of the VFD can resist some high-frequency harmonics, due to the limitations of volume, cost and other aspects, its filtering ability is still very limited, but when the content of high-frequency harmonics is relatively high, the built-in filter of the VFD can not better cope with these high-frequency harmonics, or it is necessary to install these high-frequency harmonic suppression devices such as the special input filter of theVFD.

2. When it is necessary to suppress higher harmonics

As mentioned earlier, in the process of inverter rectification, not only will there be high-frequency harmonics injected into the power grid, but also 5, 7, 11, 13 times and other high harmonics will be injected into the power grid, at this time, the built-in filter of the VFD can be said to have no way to these high harmonics, at this time, it is necessary to rely on the inverter special input reactor, the inverter special DC reactor, LCL harmonic filter, active harmonic filter and other inverter pre-harmonic suppression devices.

3. When the system-level EMC test cannot be passed

Although the inverter has a built-in filter, but when we do the EMC test of the inverter system, it may not be able to pass the EMC test smoothly, and it can even be said that in many cases, it is not possible to successfully pass the EMC test of the inverter system.

4. When the harmonics of the VFD system exceed the standard

There are some times, there are occasions, it is not only required that your frequency conversion system does not interfere with other power equipment, other power equipment can not interfere with your frequency conversion system is so simple, but to clamp the harmonics of the frequency conversion system to ≤ 5%, 10%, 20%, 30% and other limits, at this time, the VFD with built-in filter, basically has no hope of reaching these limits, at this time, you may have to choose a special input reactor for the VFD, a special DC reactor for the VFD, an LCL harmonic filter, Active harmonic filters and other VFD pre-harmonic suppression devices.