TransformerRHS:

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   Dynamical model of a transformer in the dq frame.  
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   Form:
   iDot = TransformerRHS( i, t, d )
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   ------
   Inputs
   ------
   i            (2,1) [iD;iQ]
   t            (1,1) Time (not used)
   d            (1,1) Data structure
                      .L     (1,1) Inductance (H)
                      .R     (1,1) Resistance (ohms)
                      .omega (1,1) Reference frequency (rad/s)
                      .u1    (2,1) [uD;uQ]
                      .u2    (2,1) [uD;uQ]

   -------
   Outputs
   -------
   i            (2,1) d[iD;iQ]/dt

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	References:	  T. Demiray, F. Milano and G. Andersson 
                 "Dynamic Phasor Modeling of the Doubly-fed 
                 Induction Generator under Unbalanced Conditions"
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