Comparative small-signal stability analysis of voltage-controlled and enhanced current-controlled virtual synchronous generators under weak and stiff grid conditions

Abstract

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.