Power-synchronization control for ultra-weak AC networks: comprehensive stability and dynamic performance assessment

Power-synchronization control (PSC) is a promising control strategy to improve the stability and performance of voltage-source converters (VSCs) in ultra-weak AC grids. However, evaluation of PSC to date has investigated performance only at single controller operating points, rather than holistically varying multiple controller gains. This paper develops a new methodology, based on small-signal eigenvalue analysis, to comprehensively analyze PSC-VSC stability. The maximum active power transfer of PSC is established across a broad range of controller tunings and the two-way and three-way couplings between the power-synchronization control, AC voltage control and high-pass current filter gains are quantified. A new stable tuning region is introduced, which represents the controller parameter space for stable operation. It is shown that PSC can achieve rated power transfer into an AC grid (short circuit ratio(SCR)=1) at multiple controller operating points, but dynamic performance varies significantly within this region. The robustness of this operating region to SCR changes is also investigated. The stability boundary and dynamic performance are validated using control hardware-in-the-loop experiments with a real-time digital simulator. Practical recommendations arising from this work are a set of controller gains that provide stability and good dynamic performance at high power transfer for ultra-weak grid-connected VSCs employing PSC.