Sampling of quadrature-phase quantities

When discrete-time control and/or monitoring of an electric machine or a power system is performed in the synchronously rotating d-q reference frame, some issues need to be addressed properly. In this paper, it is shown that the obtained samples may be severely corrupted by the phase shift of the antialiasing prefilter, and how this can be corrected by slightly modifying the d-q transformation, provided that the prefilter has approximately linear phase in the passband. Design of suitable prefilters is discussed. It is finally shown how d-q frame sampled-data system models can be obtained