Dynamic model and control of AC-DC-AC voltage-sourced converter system for distributed resources

This paper introduces a dynamic model of the AC-DC-AC voltage-sourced converter (VSC) system which provides a linear relationship between the input and output variables. The model is developed in two steps. First, the exact abc frame switched model of a VSC is transformed to a Switching Reference Frame (SRF). Then, the SRF model is transformed to an appropriate dqO reference frame. The fundamental-frequency dynamic model of the VSC is deduced from the dqO model and provides a set of single-input single-output controls for the VSC system. The fundamental-frequency steady-state model of the VSC system is deduced from the dynamic model and provides a closed-form solution to the VSC system. The developed models are used to design controllers and define steady-state settings, e.g. modulation indices, for electronically-coupled distributed resources. The developed models are applied to a test system and the results are validated based on time-domain simulation studies in the PSCAD/EMTDC environment.