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Driving 3-phase motor from 2 amplifier phases
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Benta:
It will work, but your control scheme needs refining.
Running one phase at ground and the other two phases at -60 and +60 degrees is fine, this will in fact give you 3 x 120 degrees at the motor leads.

But a characteristic of PMSMs is that they have no feedback, and you need a concept of starting it. This is usually done by increasing voltage and frequency from zero up to running speed. You also need to place the motor in a certain starting position first, this is normally done by energizing one pair of phases to get it positioned.

soldar:

--- Quote from: Benta on December 27, 2018, 07:29:22 pm --- Running one phase at ground and the other two phases at -60 and +60 degrees is fine, this will in fact give you 3 x 120 degrees at the motor leads.
--- End quote ---
Taking one phase as reference that means the other one is at 120º. If you make that -120º then the rotation of the phases changes direction and the motor will rotate in the opposite direction. It is the same as just electrically switching both phases.
Benta:

--- Quote from: soldar on December 27, 2018, 07:42:48 pm ---
--- Quote from: Benta on December 27, 2018, 07:29:22 pm --- Running one phase at ground and the other two phases at -60 and +60 degrees is fine, this will in fact give you 3 x 120 degrees at the motor leads.
--- End quote ---
Taking one phase as reference that means the other one is at 120º. If you make that -120º then the rotation of the phases changes direction and the motor will rotate in the opposite direction. It is the same as just electrically switching both phases.

--- End quote ---

This is semantics and we mean the same thing.
One option is running one amplifier directly with no phase shift and the other at 120 degrees.
The other is running one at -60 and the other at +60 degrees, which is easier to do.
The end result is the same.
soldar:

--- Quote from: Benta on December 27, 2018, 07:49:44 pm --- This is semantics and we mean the same thing.
One option is running one amplifier directly with no phase shift and the other at 120 degrees.
--- End quote ---
No phase shift with respect to what? What is your reference? I am using one phase as reference. Using a point equidistant from two phases is ... strange. I have never seen it done in a three phase system to say one phase is -60º, another is +60º, and the third is 180º.  I suppose you could do that but it just seems unusual. Normally you would take one phase as reference.
Circlotron:

--- Quote from: Benta on December 27, 2018, 07:29:22 pm ---Running one phase at ground and the other two phases at -60 and +60 degrees is fine, this will in fact give you 3 x 120 degrees at the motor leads.

--- End quote ---
That’s exactly what I thought initially too. But if we are speaking with reference to the first driven phase then the second has to be 60 deg different. If it is 120 deg different then the voltages across the windings are unequal for one thing. I know 60 deg sounds ridiculous. Had to sim a three phase source and earth one corner and measure around it. Hard to get ones head around it. I’ll post the sim later on.
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