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Scalar VFD Unbalanced Current in Induction Machine

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I am working on a Scalar VFD, to drive a 2 pole, 400V, 50Hz machine (110kW) with machine parameters taken directly from a pre-existing MATLAB model (Image 1)

When measuring the phase currents within the stator windings of the IM I am encountering imbalance between each phase. There is both a DC offset and change in Amplitude between each phase. In a no load condition (mechanical connection of IM is attached directly to the rotational reference) there is an electromagnetic torque produced by the motor (Image 2)

Any guidance in solving this problem would be greatly appreciated!
asked Oct 31, 2022 by Cirros (17 points)

1 Answer

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Best answer

The problem appears to be with the generation of the three-phase reference signals. You should use a Sine Wave block to generate the reference or use the wrapping feature of the Integrator, rather than the Memory block for this purpose (which can have unintended effects). Please find attached a modified version of your circuit with balanced phase currents.


answered Nov 9, 2022 by Kris Eberle (1,511 points)
selected Nov 9, 2022 by Cirros
Thank you for getting back to me on this. Its good to know this for future designs!