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Application of Impedance-Based Stability Criterion in Power Systems with Multiple STATCOMs in Proximity

Image of IEEE 14-bus system with 4 STATCOMS
Fig. 1. IEEE 14-bus system with four STATCOMs
Ever since it was derived from Nyquist stability criterion and first developed in dc-dc power electronics converter systems, impedance-based stability criterion has been proven to be a powerful tool for small-signal stability analysis and design. It requires less knowledge than state-space modeling and is design-oriented. Recently it has been extended to ac systems to address the issues and challenges that come with more and more power electronics based converters that connect to existing ac power grids, either in at a transmission or distribution level. With that, only terminal information is necessary to judge small-signal stability and thus online detection and tuning is feasible. A case study with multiple STATCOMs in an IEEE 14-bus system is shown as an example. It is the first time that the impedance-based method has been used to demonstrate the interactions between STATCOMs at the transmission system level.

Bode plots of D-D, D-Q, Q-D, Q-Q impedance measured at PCC of STATCOM1
Fig. 2 Impedance measurements at PCC of STATCOM 1 with different bandwidths of ac voltage loop

Graph of Loci of return ration L(s) with different bandwidth of AC voltage loop
Fig. 3 Characteristic loci of the return ration L(s) with dif-ferent bandwidths of ac voltage loop
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