Transient stability of grid following inverters: The impacts of damping and fault ride‐through

Abstract

AbstractThe interaction of grid following inverters with a weak grid raises risks of transient instability. The effects of damping and fault‐ride through (FRT) make the transient dynamics more complicated. To investigate the impact of FRT on the transient stability of converters, this paper first employs the switch system theory to construct a mathematical model for the synchronous mechanism of inverters. Secondly, the method of semi‐algebraic system real root classification is comprehensively used to analyse the existence of equilibrium points (EPs) and provide necessary and sufficient conditions for their existence. Finally, based on the theory of differential geometry, a method for computing the stability domain of converters is proposed. Compared with traditional methods, the results obtained from this approach are precise and non‐conservative. The study in this paper indicates that the equivalent damping effect from the proportional control in a phase‐locked loop significantly enlarges the stability region, whereas the active current injection shrinks the stability region. The reactive current droop characteristic also has impacts on the stability region, especially with active current injection. The switchover between the droop mode and constant current mode requires extra precaution in the calculation of the EPs and critical fault clearing time.