A New Transform Method for Modeling Unbalanced Electric Power Systems

R. McCann and M. Daniels (USA)


Symmetrical components, unbalanced systems, active filters.


This paper develops a new analysis technique for modeling the dynamics of unbalanced three-phase electric power systems. This method extends time-domain sym metrical component theory by defining a new transformation that expresses the sequence component variables in state-space form. This transformation relies upon a decomposition of the instantaneous sequence components (DISC transformation). Unlike previous analysis techniques, this method models the dynamics of positive and negative sequence components for systems with arbitrary resistance, inductance, and capacitance imbalances in a systematic manner. Harmonics are also included in the analysis in a straightforward manner. Dynamic models derived using the DISC transformation are well suited for active power filter applications. This paper develops the theory of the DISC transformation and gives an application to the analysis of a static inverter supplying an unbalanced permanent magnet synchronous motor load. Experimental measurements from a laboratory inverter are compared to analytical results obtained from DISC transformation analysis.

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