Novel grid-forming control of PMSG-based wind turbine for integrating weak AC grid without sacrificing maximum power point tracking

Abstract

Traditional permanent magnet synchronous generator (PMSG)-based wind turbine (WT) normally utilises phase lock loop (PLL) for obtaining accurate phase angle of AC grid to make sure of maximum power point tracking (MPPT). However, a weak AC system with a low short circuit ratio (SCR) and high control bandwidth of PLL might have impaired effects on the stability of the system. To overcome these, a novel power synchronous control of PMSG-based WT with grid forming ability of PMSG for integrating very weak AC system is first proposed in this study. Grid-side converter (GSC) of PMSG emulates the inertia response of synchronous generator (SG) by artificially coupling the DC-link voltage with the grid frequency based on the certain droop property, while the converter voltage magnitude is regulated according to DC-link voltage deviation by controlling the modulation index of GSC. This novel scheme can realise the grid synchronisation without PLL by mimicking the natural characteristic of SG. Small-signal analysis of the proposed scheme indicates the DC-link capacitor energy can be exerted for system inertia support during system disturbances, while the system damping can be provided by spontaneously alternating converter voltage magnitude. More importantly, MPPT property of PMSG is not compromised while providing inertia and damping for the system, and the related inertia and damping coefficient of WT with the proposed control can be easily tuned for satisfying the system requirement. Non-linear simulations of one PMSG connected with one large SG considering a sudden change of active power reference and variable wind speeds have been studied to verify the effectiveness of the proposed grid-forming control.