Modeling the Aggregated Response of Variable Frequency Drives (VFDs) for Power System Dynamic Studies

Accurate representation of system loads is critical for performing power system dynamic studies. As of date, in positive sequence bulk power system dynamic studies, the WECC composite load model is the state-of-the-art model for representing the aggregated behavior of loads at the substation bus. Although used widely, this model is continuously undergoing improvements to ensure that a reasonable representation of different load components can be obtained. One such refinement is the development of a model for representing the aggregated response of VFDs. This paper proposed a generic positive sequence model used to capture the aggregated response of a large number of VFDs connected at a load bus for bulk system dynamic studies. The model was developed and validated using laboratory test measurements of response different VFDs to voltage sags.