Detailed Dynamic DC Models of VSC Considering Controls for DC-Fault Simulations in Modernized Microgrid Protection

Abstract

Nowadays, emerging microgrids have been forming fully integrated power and energy systems using multi-infeed ac/dc (MIACDC) power architectures. An MIACDC power architecture easily integrates renewables, battery energy storage systems, fossil-fuel-based generating units, and various types of loads into one coherent microgrid. Therefore, in modernized microgrids (MMGs), time constants (or equivalently bandwidths) of system dynamics are broad; indeed, multiple controls in different parts of grid-connected voltage-sourced converters (GC-VSCs) create them. For the first time, this article takes into account the detailed dynamics of every GC-VSC's part. It also effectively incorporates their controls to propose “detailed” dynamic dc (DDDC) models for dc-fault simulations. The suggested models are able to simulate dc-fault currents in MMGs' MIACDC power systems more accurately. This research bridges the gap between VSCs' controls and their dynamic dc models, which can be used in dc-fault simulation studies associated with MMG protection. It derives DDDC models of GC-VSCs for two fundamental modes of operation, i.e., P/Q-controlled and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> /Q-controlled modes. To this end, detailed dynamics of VSCs considering those of ac- and dc-side filters are thoroughly employed using VSCs' space-phasor representation. After linearization, for creating the models mentioned above, relevant GC-VSCs' controls are considered. In order to show the validity of the detailed GC-VSC's dynamic dc models, experimental results are provided. Besides, for studying the models' response to dc faults, adequate comparisons of time-domain simulations of the proposed models and those of the accurate switching models are made. In this regard, an MMG with an MIACDC structure is simulated in PSCAD/EMTDC software; the MMG is implemented first by the proposed VSC's DDDC models and second by the switching ones to generate the simulation results with which one can compare. Moreover, in order to reveal the effectiveness of the DDDC models, comparative outputs are produced by simulating conventional models that do not consider dynamics induced by the controllers. Last but not least, comparison outcomes of the DDDC models and those of conventionally adopted models show that this research is able to fill in gaps in the needed models.