Modelling of Multi-terminal VSC-HVDC Links for Power Flows and Dynamic Simulations of AC/DC Power Networks
|Kustantaja||Tampere University of Technology|
|Tila||Julkaistu - 5 joulukuuta 2016|
|Nimi||Tampere University of Technology. Publication|
It is in this context that this thesis contributes new knowledge to the modelling of VSC-based equipment and systems for the assessment of steady-state and transient stability analyses of AC/DC power networks. The STATCOM, the back-to -back VSC-HVDC link, the point-to-point VSC-HVDC link and the multi-terminal VSC- HVDC link, all receive research attention in this work. The new models emanating from this research capture all the key steady-state and dynamic characteristics of the equipment and network. This has required a paradigm shift in which the VSC equipment has been modelled, here-to-fore, assuming that a voltage-sourced converter behaves like an idealised voltage source. In contrast, the models developed in this research resort to an array of basic power systems elements, such as a phase-shifting transformer and an equivalent shunt susceptance, giving rise to a two-port circuit where the AC and DC sides of the VSCs are explicitly represented. The ensuing VSC model is fundamentally different from the voltage source model; it represents, in an aggregated manner, the array of semiconductor switches in the converter and its PWM control. The VSC model was used as the basic building block with which to develop all the VSC-base d devices put forward in this thesis. The ultimate device is the multiterminal VSC-HVDC system, which may comprise an arbitrary number of VSC units commensurate with the number of otherwise independent AC sub-networks and a DC network of an arbitrary topology. The steady -state and dynamic simulations of the AC/DC systems are carried out using a unified frame-of-reference which is amenable to the Newton-Raphson algorithm. This framework accommodates, quite naturally, the set of discretised differential equations arising from the synchronous generators, HVDC and FACTS equipment, and the algebraic equations describing the conventional transmission lines, transformers and loads of the AC sub-networks. The application areas covered in this work are: power-flow studies and dynamic simulations.