Frequency-Domain Stability Criteria for Converter-Based Power Systems

Frequency-domain stability criteria are developed for converter-based power systems with any number of converters. The converters may be grid following or forming, and the can an ac hybrid ac-dc network. network all modeled in a common (stationary) reference frame based on small-signal sequence immittances. Coupling over frequency coupling considered most general form. For each type systems, frequency-domain model is first by nodal analysis then reformulated to fit form feedback loop open-loop guaranteed practical conditions. System determined Nyquist-like criterion without need check right-half-plane poles. Further simplification system models made possible a) generalized $n$-port equivalent circuits that include both types coupling, b) equivalence at internal external nodes, c) relationship between dynamics perturbation frequency. Reduction into separate single-input-single-output presented several special along their applications. Quantitative experimental results verify theories.