Study on the Stable Operating Region of Grid-forming PMSG Based on Impedance Analysis

Grid-forming direct-drive wind turbines, as pivotal power generation equipment in modern power systems, play a crucial role in providing voltage and frequency support. The control strategy based on the Virtual Synchronous Generator (VSG) significantly enhances system stability. However, the wideband oscillation stability of grid-forming direct-drive wind turbines poses a challenge due to their combined characteristics which resemble those of synchronous generators and the rapid control response of power electronics. This paper establishes a sequence impedance model that considers the generator, machine-side converter (MSC), and grid-side converter (GSC). By employing a zero-order optimization algorithm (ZOO) and the maximum peak Nyquist stability criterion, the dominant frequency bands of each control loop are identified. Furthermore, an evaluation method for the oscillation stability operating region based on the forbidden region radius is proposed, providing technical support for the safe and stable operation of power systems with a high proportion of renewable energy.