Frequency Domain Model of a Three-Phase Power Electronics Interface for Unbalanced Harmonic Studies

This paper proposes a frequency domain model that can be applied to any three-phase three-wire power electronic (PE) interface (no neutral connection). The model is obtained using a phase domain frequency coupling matrix and can be used to estimate the response of the PE interface under unbalanced harmonic conditions in low-voltage applications. The frequency coupling matrix is developed by linearizing the three-phase PE interface under small signal conditions in the frequency domain. The model is exemplarily parameterized for a variable frequency drive (VFD). The obtained model is tested for different distorted and unbalanced voltage waveforms obtained from actual field measurements. For validation, the response of the frequency domain model is compared with the response of a time-domain model developed in MATLAB. The applicability of the model is demonstrated using a case study of a network comprising linear and nonlinear loads.