Impedance-based Stability Analysis for HVDC Diode-Rectifier Connected Off-shore Wind Farms

This paper includes a stability study of a HVDC diode rectifier connected off-shore wind power plant. Usually, the internal control strategy of commercial wind turbines are not completely known, so stability studies based on transfer functions or eigenvalue analysis are of limited use. However, the frequency behaviour of both wind turbine grid side converters and HVDC diode rectifier station can be obtained without a detailed knowledge of the control internals of the wind turbines. This paper includes the validation of impedance-based stability analysis for HVDC diode-rectfier connected off-shore wind farms. The frequency dependent impedance of the wind turbine converters and of the diode rectifier HVDC station are developed both analytically from their respective analytical models and also by using signal injection. It is shown that the stability analysis using the identified impedance frequency response and that from analytic calculation lead the same results, thus validating the use of the impedance method for the stability analysis of grid-forming Diode-rectifier connected wind power plants.