Global Frequency Reference Tracking as an Oscillation Suppression Mechanism in VSM Primary Control: A Coupled-Oscillator Study

Abstract

Synchronization in power systems is traditionally achieved through physical network coupling, whereby inverter-based resources (IBRs) and synchronous machines converge to a common frequency via oscillatory swing dynamics. In conventional operation, secondary control acts on a slow time scale and is typically engaged only after the primary dynamics have largely settled. As a result, in the absence of an explicit global reference, disturbances can induce prolonged transients and large phase excursions. This work considers a setting in which the total active power balance is known and maintained at all times, and proposes a control architecture for virtual synchronous machine (VSM) based inverters in which all units track a broadcast global frequency reference. Under this assumption, synchronization is transformed from a mutual oscillator locking problem into a reference tracking problem. Using a second order swing network model, we show that embedding a simple proportional integral (PI) frequency controller can significantly improves transient behavior. A washout mechanism ensures that the additional control action vanishes in steady state, thereby preserving network determined power sharing. Simulations on a three oscillator network demonstrate reduced frequency overshoot, elimination of underdamped oscillations, and lower angular stress compared to conventional open loop synchronization, highlighting the effectiveness of a global frequency reference as a coordination mechanism for grid-forming inverter networks.