Electronics > Projects, Designs, and Technical Stuff

3-phase "equalisation" transformer?

<< < (3/4) > >>

filssavi:
What I think is happening is simply the OP is hitting the speed limit given by the combination of motor back EMF,  and maximum drive voltage.

if that is the case, usually two different routes are viable:
1)  usually with native three phase inverters flux weakening is used, where a part of the driving current is used to counteract (and thus lower) the rotor magnetic field, this allows to widen the operating speed range, of course thermal limits still apply and since the part of the current employed to lower the back emf  can't generate torque, the higher the speed in the FW region the lower the torque. However I'm not sure that with your setup (driving just 2 phases and not all three) its doable
2)  use a higher voltage to begin with (in this case higher transformer turn ratio or higher starting voltage)


in any case I strongly doubt the problem is a phase imbalance, also be aware of the mechanical speed limits of bearings, couplers, the rotor itself etc, as you are already 6 times higher than rated spead, and going higher the machine could suffer a rapid unsheduled disassembly

ogden:

--- Quote from: Circlotron on July 30, 2019, 12:38:56 am ---Is there some kind of three phase transformer that could perform the function of making the voltage of all three phases equal?

--- End quote ---

It is called active load balancing and is done using solid state technologies, not transformers. Just few examples of search results:

http://www.elcopower.com.my/ALB.html
https://www.schneider-electric.com/en/product-range-presentation/63426-accusine-pcs%2B/

duak:
Soldar, you are correct that a more complicated arrangement is probably needed.  A few years ago I had looked into using a Zig-Zag Grounding Bank for a possible solution for an ungrounded delta circuit but never tried it out.  If my understanding of the zig-zag connection is correct, it wil also try to coerce a three phase circuit into balance because it has a different impedance to imbalance currents.   I wasn't sure that my idea would solve Circlotron's problem and said so.  The more complex circuit, as shown in the Wikipedia article, generates a better balanced set of phases rather than trying to coerce them into balance.


Kleinstein:
The zig-zag transformer might improve the balance a little, but it is not 100% coupling.

Anyway the problem with the motor should have nothing todo with imbalance, more with insufficient voltage. Usually one needs to increase the voltage if a higher frequency is used - often a voltage about proportional to frequency is used.

If a higher speed is wanted, I would not start with a rare 1000 U/min motor, but with a more normal 2900 U/min (at 50Hz) motor, so already 3 times the speed. A US motor for the lower 208 V and 60 Hz could also be a good idea. There are also special motors for higher frequencies: something like 200 V at 300 Hz is sometimes used.

NiHaoMike:
There are a lot of BLDC motors that will operate that those range of speeds.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod