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Topic Title: Drive DC Bus undervoltage
Topic Summary: Due to weak supply from small generator - what could help?
Created On: 12 March 2010 12:27 PM
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 12 March 2010 12:27 PM
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Joined: 01 April 2004

Any ideas on the following problem are welcomed as several things have been tried already without success.
The system is a motor yacht with a 28kW single phase generator outputting 230V at 60Hz. There are many loads connected but for the purposes of identifying the fault, the only load is a 10hp 3-phase 230V motor connected via a ABB ACS550 variable speed drive. The purpose of the drive is to allow for soft starting of the relatively large motor (for the capacity of the supply) and of course to provide the availability of three phase power from a single phase supply.
The application is a hydraulic system in which the motor is connected to a variable-displacement hydraulic pump. Due to the nature of the system, the torque on the motor can increase significantly in a short space of time.
It is under these conditions that the drive will shut down due to its DC bus being undervoltage.
This situation occurs because the generator output voltage will dip due to the rapid change in current demand - there are two issues as far as I understand:
1) the response time of the generator (AVR-Governor-Engine Inertia)
2) the high source impedence due to the relatively small generator alternator
We have tried some things - mainly the settings within the drive (it has an undervoltage control feature and a DC stabiliser) and ensured that all of the basic settings match the motor 230V, 24.8A, 60Hz, 1760RPM, 10HP.
I was hoping that anyone may have some practical suggestions for what measurements and tests we could carry out that could lead to an eventual solution.
Your thoughts are greatly appreciated.
 12 March 2010 05:24 PM
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Joined: 10 October 2007

Obviously check the d.c. joints/connections as Alan says because they can easily effect lower d.c. voltages.

Personally I think you need to get a good approximation of how long the d.c. bus dips for, and to what level, and contact ABB and ask them if their drive should be able to cope with that with adjustment. If they say yes and you set the drive accordingly and it still faults out you may have a faulty drive but if they say no then you will either have to look at the motor/shaft/starting arrangement or ask ABB what the options are, if at all, for adding some extra storage/smoothing onto their drive/bus. However the d.c. bus may be faulting out, because it is more sensitive, but the drive may actually be correct because if the supply dips then obviously its own supplies will dip and thus you may have to resolve the cause at it's source! Check also any contactor/switch tips/connections back to where the drive gets its supplies.

 12 March 2010 09:28 PM
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Both previous posts are spot on.
I would guess that the ABB drive is running a PWM output section run from as you say a DC bus.
I am guessing you are changing parameter 0107 with regard to the DC bus voltage?
Have you ever had this system running?
If it is a new start up have the DC bus capacitors been reformed according to ABB docs if the drive has been in storage?
When I was doing applications for an ABB competitor, if we have serious sudden shock loads for very short periods where we believed that the DC bus voltage would decay for very short periods and possibly on trials experienced this sort of error, we would fit additional capacitance to the DC bus in the form of one of our special capacitor modules, this added an energy store to prevent the dip and allowed the drive to overcome such short duration events.
Have you tried optimising the PID loop in the drive via the software or the built in optimisation routine if this is possible?
Another option is to redesign the hydraulics (we had both divisions, Westonpa knows who I worked for) and add a full unloader for the pump which then loads the pump up softly too.
Can you change the response time of the pump by optimisation of the pump control loop?
You don't say whether it is a piston or vane type.
Either of these will give you the results you require.
I don't have the tech info on the ABB to give any accurate values, however, it is a common solution with VSD & other PWM drives to add DC bus capacitance, according to manuf' instructions mind!
Also you will need to add a bus discharge system as the caps can hold the bus up for minutes.
We had one application where after the machine was e-stopped and all power to the drives was killed the bus cap and drives were configured to move over 100kg's of machine without the mains energised!

 13 March 2010 07:23 AM
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Pat Lucey

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Joined: 18 May 2006

Hi Andy, is this a new install. ? Good thoughts from others but is your Generator sized right and working correctly. Could be a clogged fuel filter or air cleaner. ?? Also nearly all generators are sized larger than the the power that the engine can drive. Check what you have. The engine will load down and trip under freq rather than melting the generator if its loaded too much. Load the generator up with other loads and see it pulls its max. Take the load off and dump it all back on again..
Your AVR could have settings that will make the voltage dip less if the engine is up to it.... Governer can be an issue ..
Any more info on the enigne governer, AVR etc...

I will get my coat....

 10 April 2010 05:37 PM
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very fine

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