Modified VSG Control for Enhancing its Numerical Stability and Reducing the Impact on ULFO of System

Virtual synchronous generator (VSG) has gained interest due to its capability of contributing in equivalent inertia of the system. However, it has been observed in this work that 1) higher penetration of VSG and 2) an increase in inertia coefficient and consequent decrease in undamped natural frequency (UNF) of active power loop (APL) of VSG, the ultra-low frequency oscillations (ULFOs) of system is negatively influenced and its magnitude increases. Such undamped ULFO poses serious threat to operational security of system. To rectify this, integrated adaptable inertia (IAI) coefficient is proposed which also contributes in maintaining the numerical stability of VSG. Further, for practical implementation of IAI and to analytically verify its efficacy, a novel real-time computation index i.e. Ambient Sensitivity Index (ASI) is formulated. It evaluates the characteristics and sensitivity of dominant modes corresponding to ULFO and thus the IAI of VSGs can be properly tuned. Also, the effectiveness of IAI is validated at real-time simulation level on the modified two-area system.