Output voltage of VFD

[PAP]

Hello all
Have anyone ever seen the DC output voltage(Line-Ground) of an 3 phase inverter when we supply with 380Vac(L-L),but don't send any starting command and speed reference is still 0 HZ?
I 've measure this DC output voltage for all 3 phase,and it show 230Vdc(L-G) and 0 Vdc(L-L) ,but no any AC voltage appear at the output both L-L and L-G. Anyone please help me explain this phenomenon. (Inverter is ABB,ACS400)


Thank you in advance.
Psit P.

 

[ozmosis]

Either there is something seriously wrong with the ACS400 or you are measuring wrongly. The ACS400 is a PWM drive with a fixed DC Link voltage. You will get a DC link volts measurement of about 540Vdc (at 380Vac in) when you measure between the +/- of the DC link terminals. This voltage will vary slightly as you apply a load (drop). Are you checking the terminals U2, V2, W2? If the drive is not running then there should be no voltage DC or AC here at all. One possibility is that you could have activated a DC injection brake or something and you are measuring this. I don't work for ABB (their main competitor actually)so I would check with them first. If there was a fault somewhere, I would expect the drive to show a fault code. The ACS 400 are pretty well protected for things like this.

 

[PAP]

Hi Sed2developer
As I informed above,I measure the voltage at terminal U2,V2 and W2 .Only (-)230V DC appear between line to ground.From the principle of inverter,if one polarity of DC bus is connected to ground,should the voltage appear when IGBT output were fail or leakage occur?

In addition,there are no any faults occur on the display of ACS400.

Further comments,please suggest.

Regards
Psit P.

 

[cbarn24050]

Hi, the dc link is not connected to ground. If you measure between dc link and ground you get =230 and +230. The output voltage you are measuring is not unusuall.

 

[ozmosis]

cbarn24050, I agree with your comments but this is not how PAP is describing where he is measuring. It appears he is measuring the output phase (U2,V2 or W2) to ground and getting (-)230Vdc. This doesn't make sense

 

[jbartos]

Suggestion: It depends on the grounding. The ungrounded DC may experience common-mode voltages that may be high. Question is how much of DC current that voltage source can supply, which is in turn linked to DC power in Watts.

 

[cbarn24050]

Hi sed, yes it does make sence. Draw out the power circuit and you will see why.

 

[jbartos]

Comment: There are different DC-AC conversion (inverter) architectures available, e.g. bridge inverters, multi-step inverters, etc. The original posting does not address this aspect.

 

[cbarn24050]

I think you'll find that the op specified the inverter type

 

[jbartos]

Comment to the previous posting: I do not see it addressed specifically. The only item mentioned somewhat pertaining to the architecture is the IGBT; however, no specific IGBT circuits are outlined.