3 phase inverter for AC induction and servo motors


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Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 642
Posted: 12:02pm 05 Jan 2021      

Just as an example, I have a 24DC bore pump its one of those screw types, helical rotor or something.
First thing it will do when connected, is check there is high enough voltage from the solar panel, in this case there is the usual 60 cell 250w 34V or 37 VOC not sure last time I looked, (I put 5 panels on it and it still runs with a light cloudy day) it will rev up to its running speed and the input voltage will drop a bit.
When the voltage gets low the pump will also slow down, but still plenty fast enough for it to pump the pressure and distance needed.
If the voltage lowers anymore it will stop altogether then check the voltage and try again after a set time.
However it will not try to start at all if the voltage is too low, even though the voltage was slightly higher than the voltage it would stop at.
Can't check this ATM, no water here, all still dry as buggery.

I think there are some off grid solar air conditioners that work this way.  


For the 3 phase induction pump motor, this is something I thought I might have to try, with a trimpot just to find the sweet spot where its no longer worthwhile for the pump to continue running, previously I just took a guess at 40hz for the frequency and the cutout voltage from the solar panels would have to be determined later or percentage of panel working voltage......Not sure about this yet.


So it looks like using the transformers, we may be limited to a frequency range which should be plenty to play with.

When I had the VFD running I was sure I had a 3 phase motor running at very low hz and the power consumption was very low, there was some videos of people running a drill press at very low rpm, I will have to check this next time when the Vfd is connected to 1HP motor.


I would be interested to try this, one using the transformers (still have to see whats available there) and the other one could be without any transformer, just high voltage solar input, perhaps if the MPPT works.
The 3 phase bore pump here, I'm sure its star configuration, other above ground pump motors, (direct couple or belt driven) can be either star or delta, usually not hard to change if needed.

Most of these pumps are only running to transfer water into a tank or a turkeys nest so some variation in speed or shutdown due to cloud cover wouldn't mater.


  Quote  A change to the code to have output voltage drop as the frequency drops
now prevents saturation. I maintain the voltage/frequency ratio as a constant
over the 40 to 60 Hz.

It all looks good,  I will read it all a few more times later, when I get my brains back into gear.