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• An enhanced CC-VSG control is proposed for the application in weak and stiff grids. • Small-signal models of conventional VC-VSG and enhanced CC-VSG are compared. • A detailed analysis is provided to assess CC-VSG operation in weak and stiff grids. • The analysis is verified via EMT simulations. Currently, the academic and industrial community have considerable expectations for the modern power converter control strategy – a grid-forming control. Within this strategy, the most promising and effective is considered one based on the voltage-controlled virtual synchronous generator (VC-VSG). However, such control system is characterized by challenges in ensuring small-signal stability under continuously changing conditions of the grid strength. The major cause is associated with the emergence of the power coupling problem. Therefore, this paper proposes an enhanced control structure based on a current-controlled virtual synchronous generator (CC-VSG). Additionally, in this paper theoretical analysis, analysis of small-signal models in Matlab and experimental studies of detailed nonlinear models via PSCAD™/EMTDC™ for the conventional structure of VC-VSG and the proposed CC-VSG were performed. As a result, it has been proved that in the enhanced CC-VSG model the power coupling problem is practically excluded due to which small-signal stability is ensured in a wide range of short-circuit current ratio changes from 1 to 100. At the same time, a fast dynamic performance and a high damping level that provide an appropriate inertial response have been achieved. It is also proved that the improvement of damping by tuning the virtual damper winding allows to reduce the rise time and has a favorable impact on the inertial response of the CC-VSG model over the entire considered range of grid strength variation, which cannot be obtained for the conventional VC-VSG. [ABSTRACT FROM AUTHOR]

• Novel approach for relays tuning using detailed mathematical model. • Hybrid Real-Time Power System Simulator is used as a source of necessary data. • Proposed approach allows to adapt protection settings to practical conditions. The correct operation of relay protection (RP) devices largely determines the security of electric power systems (EPS). The key point that in turn determines the behavior of protection in various emergency modes is a determination of their settings. The existing methodologies and tools often do not allow to provide RP settings adequate to the practical conditions of their functioning. This statement is confirmed by the statistics of faults in EPSs. The main reason for this issue is the inability to reliably reproduce transients in EPS via the software programs used in practice to calculate the RP settings. The Hybrid Real-Time Power System Simulator (HRTSim), developed by the authors, allows to reliably reproduce the entire range of normal and emergency modes and processes in EPS of any scale, topology and configuration by using detailed three-phase models of all power system components. Taking into account this possibility and features of the HRTSim, the task of detailed modeling of RP devices, including instrument current and voltage transformers, becomes relevant. The implemented special tools for RP modeling and the HRTSim in general allow to develop a new methodology for RP tuning. At the same time, the typical elements – relays – can be identified for each type of RP that determine their operation algorithm. This paper presents an analysis of the main relays of the most modern microprocessor-based RP devices and proposed principles of their tuning. The developed approach allows to adapt the RP settings to the practical conditions of their functioning in EPSs and to minimize the probability of RP maloperation. [ABSTRACT FROM AUTHOR]