Equivalent Circuit Analysis of Open-Loop Modal Resonance

The theory of open-loop oscillation mode resonance has been widely used in the field of broadband oscillation analysis of power system. However, the related work focuses on the validation of the power system after an accident, and lacks the simulation and validation on the typical circuit model. In order to verify the open-loop mode resonance, this study constructs a closed-loop circuit model consisting of two second-order circuits combined by an adder, and the feedback is realized by a third second-order circuit. Then, it is verified by time-domain simulation that when the open-loop oscillation modes of the two open-loop subsystems are close to each other, the open-loop oscillation modes repel each other in the complex plane and peak at the two closest open-loop modes. Then, the open-loop mode resonance theory is used to predict the open-loop gain thresholds for system stability and instability, and the correctness of the computational results is verified by time-domain simulations. This study helps to provide a theoretical basis for the application of open-loop mode resonance in practice.