Investigation Into a Frequency Coupling Matrix of an Adjustable Speed Drive for System-Level Harmonic Studies in Sequence Domain

Adjustable speed drives are widely used in the industry and, in view of costs, frequently have a diode bridge interface to the grid. While it is well-known that this causes current harmonics, the nature of the response to harmonics in the grid voltage waveforms, in particular, if they are unbalanced, is not well-explored. This work develops a model for the input performance of the drive as a frequency coupling matrix, which is suitable for system-level studies in the frequency domain. A sequence-domain description is introduced to simplify and improve the modeling of the drive, especially in the presence of unbalanced harmonics in supply voltage. The model shows a high sensitivity to even-order harmonics and significant coupling between positive and negative sequences. The model is validated using hardware and simulation approaches. A case study is also presented to illustrate the use of this model in system-level studies and thus the application of this modeling approach.