Frequency-Domain Large-Signal Modeling and Stability Analysis for Dispatchable Virtual Oscillator Controlled Grid- Connected Converters

Abstract

Dispatchable virtual oscillator control (dVOC) is a time-domain method for implementing nonlinear control of grid-forming, grid-connected voltage-source converters (VSCs). The large-signal stability assessment of the dVOC-based VSC-grid system under large disturbances is crucial to ensuring secure and resilient system operation. In this work, a comprehensive frequency-domain large-signal modeling and stability analysis approach is developed to ensure global asymptotic large-signal stability under large disturbances. We utilize the small-gain theorem to analyze large-signal stability by separating the linear and nonlinear gains of the dVOC-based VSC-grid system in the frequency domain. A symmetric linear gain matrix is obtained, and a bounded nonlinear gain is derived, accounting for the limited current capacity of VSCs. Moreover, it has been mathematically proven that the large-signal stability condition is independent of grid voltage disturbances. As long as the overall system gain, as the product of the linear and nonlinear gains, is less than one, the dVOC-based VSC can always synchronize with the grid under large disturbances. A sufficient condition for global asymptotic large-signal stability is derived, and the theoretical analysis is validated through experimental tests.