Conference Agenda

Phasor models have been widely used inshort-circuit simulations, in which system operators verify thebehaviour of the grid over thousands of different contingencies.However, it is still unclear if phasor models can still be usedin fault studies in modern or future power grids dominated byrenewable generation with power electronics and converters.Therefore, this paper analyses the suitability of phasor modelsto simulate short-circuit transients in grids with grid-following(GFL) and grid-forming (GFM) voltage-source converters (VSC).Phasor models of GFL and GFM were developed and tested intwo test systems, one with 50% of converters in the generationmix and another powered 100% by converters. Asymmetricaland symmetrical faults were applied at different points of thesystems and key variables were used to compare the phasormodels against EMT models during the transients. The resultsshowed that, despite neglecting transients in the grid, phasormodels could be used in a preliminary stage of short-circuitstudies as it was capable of tracking the steady-state valueof almost all variables analysed. In this case, detailed EMTsimulations, although necessary, would be used only at moreadvanced stages of the studies.

The rising renewable energy in-feed in power systems entails wider presence of power electronic devices (PEDs). Consequently, adverse dynamic phenomena can be observed in power systems, as a result of the interaction between different controllers or between controllers and existing power grid equipment in the close vicinity. This paper aims to outline the key contributing factors of controller interactions with focus on HVDC-connected offshore wind farms (OWF) by proposing a comprehensive methodology to identify system topologies and conditions that can instigate interactions in the onshore system. In this regard, a benchmark model has been developed in an EMT-type tool comprising three generic HVDC-connected OWFs, a fourth OWF connected through an AC cable and a STATCOM. Moreover, two different versions of the control system of the HVDC links were developed to study interactions between controllers from different manufacturers. Parametric EMT-type simulations were performed for various system conditions and topologies to provide a wider view on the risk of interaction between multi-infeed HVDC links and OWF systems. Harmonic stability is also studied to illustrate the risk of resonance between two HVDC links connected in the network.

The solid-state transformer (SST) is being presented as a technology that enables the construction of new power systems due to its many advantages. These benefits include reduced weight and volume compared to traditional transformers, power factor compensation, accurate output voltage regulation, harmonic mitigation, short-circuit current limitation, and voltage dip immunity, under certain conditions. Unlike other studies that only demonstrated the effectiveness of Model Predictive Control (MPC) in individual parts of the SST, this study shows the control of an entire SST using the MPC strategy. The performance of the SST during power system transients is evaluated to showcase the features of the SST by predictive control.

Transient simulations are usually carried out to analyze the behavior of control and protection systems when performing switching action in power transformers. For this reason, the saturation curve and/or the hysteresis curve of the transformer must be properly modelled. However, in most of the cases the real saturation/hysteresis curve of a transformer is not known, because such measurements are not carried out as part of the factory tests of a transformer. This article describes a method to measure the hysteresis- and saturation curve with a portable measuring system on-site. The added value of the measured saturation curve is illustrated through an example, in which a
single-phase low voltage transformer is modelled. This example shows the added value of a measurement-based modelling. An additional example illustrates measurement of the hysteresis curve of 350 MVA, 420/110 kV power transformers.