Frequency Stability Analysis of Grid-Forming PMSG Based on Virtual Synchronous Control

Abstract

A small-signal model of a virtual synchronous generator (VSG) control system for wind turbines, which considers the rotor speed regulation characteristics, has been established in this paper. Additionally, the damping torque coefficient expression of the VSG based permanent magnet synchronous generator (PMSG) was derived. The critical factors affecting the frequency stability of the wind turbine system in the maximum power point tracking (MPPT) mode were analyzed. Furthermore, it has been clarified that when the DC voltage is controlled by the generator-side-converter, the mechanical characteristics of the generator can weaken the wind turbine’s capability to damp the power oscillation. The minimum damping value of the VSG control system has been determined, which can provide a reference for the deployment of grid-forming PMSGs in industry. Finally, a typical VSG based PMSG system was established in the RT-LAB platform, and the correctness of the conclusions drawn in this paper was verified.

Keywords

• Source dynamics of wind turbines
• virtual synchronous control
• damping torque coefficient
• frequency stability