Small-signal stability and fault performance of mixed grid forming and grid following offshore wind power plants connected to a HVDC-diode rectifier

Abstract

[EN] This study aims at validating the simultaneous operation of grid following and grid forming wind power plants when connected to a common diode rectifier-based HVDC link. The controllers for both grid forming and grid following wind turbines include fault-ride-through capability with soft restoration of the off-shore AC-grid. Current and voltage controllers are developed in the stationary alpha beta reference frame. The presented control and soft restoration strategies are based on local measurements only and do not require communication between wind turbine generators. The small-signal stability analysis of the mixed system in multiple d-q axis using detailed string models is carried out in order to show the sensitivity to grid following phase-locked-loop gains and to grid forming droop gains. Interoperability between grid forming and grid following wind turbines during transients is shown by means of detailed simulation during symmetric faults in different locations of the off-shore grid.