Virtual Oscillator Grid-Forming Inverters: State of the Art, Modeling, and Stability
Minghui Lu
Abstract
Grid-forming (GFM) inverters are dc–ac converters that regulate their ac terminal voltage and frequency in response to real-time measurements. Recent developments on GFM controls have focused on a particular dispatchable virtual oscillator control whose implementation features a nonlinear Andronov–Hopf oscillator at its core. In this article, we systematically model and study this controller, its synchronization dynamics, as well as its stability. We show that system voltages and frequency are regulated in a decentralized and autonomous manner while exhibiting nonlinear droop-like behavior. Small-signal models are formulated for an individual inverter connected to an infinite voltage bus in addition to systems of interconnected GFM inverters. These models allow us to characterize dynamical stability and synchronization. Robustness is shown after sweeping key system parameters under the aforementioned models that capture system performance. Numerical simulations and experimental results validate the analytical developments.