Line Commutated Converter Response during Total and Partial De-Blocking of a Bipolar MTDC System

This paper focuses on the fault blocking analysis and operational issues associated with MTDC systems incorporated in an AC network. The dynamic modelling of a line-commutated converter based bipolar multi-terminal direct current (LCC MTDC) system are shown, and the dynamic response of the converter during a DC converter fault is discussed. The converter controller design for both rectifiers and the inverters system was modelled for a realistic active power and extinction angle (γ) control with consideration to the VI characteristics of all the converter stations. An overall power controller was modelled for both converter pole. Two operational scenarios of converter fault were simulated using PSCAD EMTDC. The converter firing angle and extinction angle, as well as the voltage-dependent current order limiter, was monitored and plotted on a graph. Results show that the MTDC link became unstable during the full deblocking stage with a continuous occurrence of commutation failure. Furthermore, the results presented in this paper show that during partial converter de-blocking showed a favourable performance, as the power system remains stable and commutation failure of the MTDC system is prevented.

Factive islands from necessary blocking

Oshima (2007) and Schwarz & Simonenko (2018a) credit the unacceptabilityof so-called factive islands to necessary infelicity – the violation of someor other felicity condition on (wh-)questions in all accessible contexts. We applythis analysis to new types of factive islands – in wh-questions with if any and inmultiple wh-questions – and argue that they pose challenges for an analysis in termsof necessary infelicity. We propose that factive islandhood can be understood asdue to necessary blocking: in all accessible contexts where such a question wouldotherwise be felicitous, the speaker would have had to use a different, more suitable,question instead. We show that the necessary blocking analysis applies correctly toboth classic factive islands and to the new types that we have identified.