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Currently, there is a large-scale penetration of renewable energy sources (RES) in power systems around the world, most of which are based on the power converter technology. The result of such penetration is the emergence of frequency and voltage regulation problems in power systems with RESs. An effective way to solve the mentioned problems is the use of energy storage systems (ESS), among which hydrogen ESSs are promising. However, the quality of such solution mainly depends on the approach to the power converters control. One of the most effective is a grid-forming power converter control strategy. Within this strategy, many scientific groups have proposed the concept of a virtual synchronous generator (VSG). However, the existing VSG models use a series structure with a stiff direction of signals, which completely mimics conventional synchronous generators. In this regard, the fundamental problems inherent in such a structure arise, e.g., a coupling between active and reactive power control. This paper describes a freely configurable VSG model (FC-VSG), in which the structural control blocks can be transferred from one level to another, and the levels themselves can be installed not only in series, but also in parallel. The case studies carried out made it possible to identify the configuration of the FC-VSG, which excludes the fundamental problems inherent in the conventional VSG structures. At the same time, the most efficient and reliable frequency and voltage regulation is provided, which has been proved by qualitative and quantitative comparison, including with the conventional VSG structure. [ABSTRACT FROM AUTHOR]

• 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]

• The synthesis of the modern VSG models into generic structures is performed. • The comprehensive assessment of the generic VSG structures is carried out. • The most reliable VSG structure for grid-connected operation is highlighted. The large-scale penetration of renewable energy sources has a significant impact on the steady-state operation and emergency control of modern electric power systems (EPS). Moreover, as a rule, the mentioned impact is negative. Therefore, the challenge associated with the development of a 'comprehensive' control strategy for renewables becomes extremely relevant. Such a strategy should ensure the same reliable operation of EPSs, as in the case of conventional synchronous generation. Among the existing directions, the concept of a virtual synchronous generator (VSG) is the most preferable. Within this paper, the synthesis and combination of the state-of-the-art concepts of VSG into generic structures has been performed. For the obtained structures, a comprehensive assessment and an experimental comparison were performed. On the basis of the results obtained, the benefits and drawbacks of the generic structures are highlighted, and a conclusion is made about the VSG structure, demonstrating the most effective and reliable operation. [ABSTRACT FROM AUTHOR]