Sequence impedance and equivalent circuit of a converter system

The author describes a means of deriving the sequence impedance and equivalent circuit of a power converter at fundamental frequency. The technique used is based on modulation theory, and the results can be used in the analysis of converter systems under unbalanced operation. The effect of commutation overlap is represented by a modified switching function so that an accurate calculation can be carried out. The method proposed provides a simple model for power converters which can be used in the steady-state analysis of unbalanced power systems containing several converters. Case studies using a simple converter system and a realistic power supply system have been carried out, and the results obtained confirm the validity of the method proposed.