Control strategies for permanent magnet synchronous generator-based wind turbine with independent grid-forming capability in stand-alone operation mode

This paper proposed two strategies for permanent magnet synchronous generator-based wind turbine (PMSG-based WT) with independent grid-forming ability considering the coordination of two-end converters of WT and the demand response in stand-alone operation mode (SAOM). In Strategy I, the grid side converter (GSC) of WT is controlled as an ideal voltage source with the fixed modulation index and frequency, while the rotor side converter (RSC) of WT regulates active power by stabilizing DC-link voltage through one PI controller. In Strategy II, the GSC of WT achieves grid-synchronization and inertia response utilizing the dynamic of DC-link voltage, while the RSC adjusts active power based on the DC-link voltage deviations to mimic the primary frequency control. Both proposed strategies are easy to implement with reduced controller complexity, which can effectively ensure the independent operation of WT without phase-locked loop (PLL) and external power supplies. Particularly, Strategy II stands out by the energy-efficient property by using the reserved energy in DC capacitor for system support and the load demand response to decrease the risks of WT tripping off. In addition, to stabilize the point of common coupling (PCC) voltage during system dynamics in Strategy II, an improved GSC control is further proposed. Furthermore, nonlinear simulations of one PMSG connected to several local loads have been conducted to verify the effectiveness of the proposed strategies under various power system contingencies.