Controlled Rectifier Problems

[ozmongoose]

Hi
I got a problem with my experiment. The task is how to regulate a stable DC link voltage (620-640V) by controlling a Power Unit PU (Baumueller Bus623) with PWM on IGBTs. Voltage supply 400 VAC, Capaccitor on DC link: 970 microF, inductance at AC input of Power Unit : 3.625 mH (3 phase).
Imax of PU: 30 A; Power of PU: 8Kw. Power Unit will be controlled (Pulse enalbe, Ta,b,c of PWM..) via controllsystem based on dSpace.
First, Pulse inable signal if NULL, PU operates as a uncontrolled rectifier. The capacitor will be loaded until Udc= 560V. Then Pulseenable siganl will be 1, the controll system also works. With the present of the inductance, DC link voltage will be boosted to about 640V (something like boost control), but right after that, an overcurrent appeared and checking sysstem will block the PU.

Sampling time for control system is 400 microsecond.

Can any one explain the problem and give me some suggestions to pass over it?

the causes, as I thought may be: low sampling time of current controller.

Thanks for your ideas

Ozmongoose

 

[jbartos]

Suggestion: Please, would you clarify the appearance of the overcurrent? Is the PU loaded and at which load?

 

[ozmongoose]

Hi Jbartos
The Loading procedure is only on the capaccity. We have no load except the C. (of may be, we can add a resistance, parallel with C on DC link)-

Ovvercurrent as I found by the STATUS ERROR Signal, reading from the Communication Interface of PU. The checking subroutine works automaticaly and internal the PU.
Thanks for any helps
ozmongoose

 

[jbartos]

Suggestion: There may be a current limiting feature that is dependent on the magnitude of the dc link voltage. Once the DC reaches 640VDC i.e. maximum, than the current limiting features becomes "on" and the PU will be blocked.