VVVF Drive Electrical Noise

[vudu]

Hi,

can a VVVF drive radiate noise back onto the mains line?
What are the typical frequencies that are emitted?
If not into the mains, where else can this noise be radiated?

Cheers,

Vudu

 

[aolalde]

Contamination of the power lines has been a problem developed by VFDs; harmonic currents are the result of non-sinusoidal current, which is characteristic of diodes or SCRs.
Some of the problems that could arise are:
Communications interference, overheating of transformers, increased heating of motor lamination and conductors, resonance with power capacitors.
The magnitude and frequency of harmonics changes from system to system, then a specific analysis or measurement should be conducted for each application.
To reduce these negative effects, several techniques have been developed, such as: DC Link choke/inductor, line reactors, drive isolation transformers, multipulse method converters, harmonic filters, etc.

 

[Marke]

Hello Vudu

Yes, VVVF do create many frequencies which radiate from the motor, the cable between the inverter and the motor, the inverter itself, and the incoming supply lines.
The input circuit of the inverter is a rectifier which converts the AC current into DC current. This generates low frequency harmonic currents in the supply. These harmonics can be reduced by the use of DC Bus chokes and AC line reactors.
The output stage of the inverter comprises 6 switching elements that are operated at a high speed following a form of PWM pattern to regenerate the three phase current to the motor. These switching elements are FETs on low voltage low current inverters, and IGBTs on higher voltage (400 - 600) higher current inverters.
The switching time of these switching elements is very fast (much less than 1 uS) and this results in considerable high frequency energy which is difficult to filter completely.
Most VVVF manufacturers can supply/recomend filters to reduce this interference and there are regulations (EMC) in many parts of the world now covering the acceptable levels of electromagnetic interference from these devices.

The use of AC line reactors, DC Bus chokes and output filters all help to reduce the level of interference.

Best regards,

Mark Empson

http://www.lmphotonics.com