ABC2SRF:

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   Transformation from abc to the switching reference frame.
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   Form: 
   SRF = ABC2SRF(ABC,S)
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   ------
   Inputs
   ------
   ABC         (3,1)  Voltage or current in ABC reference frame
   S           (3,3)  Switching function matrix

   -------
   Outputs
   -------
   SRF         (3,1)  Voltage or current in SRF reference frame

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   Reference: Nikkhajoei et al "Dynamic Model of a Matrix Converter for
              Controller Design and System Studies", IEEE Transactions
              on Power Delivery, vol 21, no. 2, April 2006, pp 744-754
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