Impedance modeling and analysis of VSC-based HVDC system considering frequency coupling effects

This paper develops an impedance-based small-signal model for the two-terminal VSC-based HVDC system. At first, the recent developments of impedance models of the converters involving mirrored frequency coupling effects are presented. Then, the small-signal perturbation-response characteristics of HVDC system are investigated, considering the frequency coupling effects of both the rectifier and inverter, as well as the dynamics of the DC-link. Based on that, a new sequence impedance model that consists of eight transfer functions is proposed for the whole HVDC system, which can not only represent the perturbation-response characteristics at each terminal, but also the transfer characteristics between the two terminals. Finally, the application of the new model for the modeling of complex multi-converter system is discussed.