Noise from AC frequency drive ......

[jit_singh_tara]

Dear Friends ,

I am driving a circuit i nwhich in which i am using delta ac drive to control speed of 3 phase motor.The drive converts the single phase to 3 phase voltages .

The problem is the moment ac drive rotates the motor , I see noise in the 5V linear power supply or smps(meanwell) power supply .
The noise disrupts the adc reading as well as sometimes disables the usb communication.

I tried to use ferrite bead to reduce the noise in the out put of 7805 , as well as in the input 9-0-9 transformer wires . But the noise persists . Please suggest how to proceed in such kind of an application where motor is used and on the same L-N AC MAINS another circuit is operating which is using high precision adc like adc1230 .Though the adc is of a weighing scale pcb( used a ready made card).

I need to operate tensile testing machine which is plotting graph on laptop via usb communication. The moment it turns on the motor adc counts drift and sometimes usb communication disables.

 

[ud23]

For that it is advisable to use ground isolation for your communication rx,tx pins and other board ground. use opto isolator for this two pins and possible then use ground isolation ICs from maxim. for adc noise use good filtering circuit at your analog signal pins.

You can use snubber circuit at your AC drive mains supply you need to calculate the snubber value.

 

[jit_singh_tara]

The motor is turned on from the ac drive , there is no contactor switching the motor .I guess RC snubber is used on contacts like relays or contactors to suppress the arcing that creates noise in the ac mains line....
This is a high freq noise generated from the ac drive or motor or both .

 

[ud23]

The motor is turned on from the ac drive , there is no contactor switching the motor .I guess RC snubber is used on contacts like relays or contactors to suppress the arcing that creates noise in the ac mains line....
This is a high freq noise generated from the ac drive or motor or both .

yes you are right.

http://www05.abb.com/global/scot/scot239.nsf/veritydisplay/a05e87eeb064df20c12571b600587bff/$file/SOUND.pdf

you can look at the above link

 

[FvM]

A usual VFD installation manual requires screened motor cables and emc cable glands connecting the screen directly to the inverter and motor case. An input filter may be required for conformance with emc regulations.

Ignoring these requirements won't cause VFD operation failure, but makes life hard for sensitive circuits in the vicinity. It would be appropriate to tackle the basic problem of usiuitable motor wiring.

 

[chuckey]

As above but also with a look at the PWM pulses traveling "backwards" out on the AC power leads. So really good high frequency decoupling on the DC bus could help. Often VFDs offer a high performance mains filter as an option.
Frank

 

[jit_singh_tara]

I was talking about electrically induced noise not the audible noise , However the pdf was informative ....

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Please explain why ferrite beads was not able to suppress the noise.......?

 

[chuckey]

Ferrite beads have an appreciable effect in the VHF and UHF region, I doubt if your PWM has an appreciable energy content at this sort of frequency.
Frank

 

[mtwieg]

Please explain why ferrite beads was not able to suppress the noise.......?

The effectiveness of a given method will depend on how the interference is being coupled to your measurement in the first place. If the interference is coupled via radiation directly to the point of measurement, then ferrite beads will not help (they will only help with conducted interference). Radiated interference must be eliminated at the source, or shielded. A detailed diagram of the system would help a lot with specific recommendations.