Modeling, control, and dynamic stability analysis of two-stage dc collector grids in offshore wind park clusters

Sidik, Yohan Fajar; de Doncker, Rik W. (Thesis advisor); Thiringer, Torbjörn (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2022)
Book, Dissertation / PhD Thesis

In: E.ON Energy Research Center ; Ausgabe : PGS, Power Generation and Storage Systems 107
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

The development of power electronic technologies makes it possible to build electrical transmission and distribution system based on a direct current (dc) technology. The standard solution for long submarine transmission of offshore wind parks uses high voltage direct current (HVDC). However, the existing dc collector grid connecting the offshore wind park and the HVDC is still based on medium voltage alternating current (MVAC). The offshore wind park system efficiency can be further increased by using medium voltage direct current (MVDC) as the collector grid. So far, research on the dc collector grid for the offshore wind park investigated configurations, efficiencies, and main components. The promising configuration is a two-stage dc collector grid, which requires an additional platform to step up dc voltages. This work investigates the dynamic system stability of the two-stage dc collector grid for an offshore wind park. A complete circuit based on components/switching models is built to conduct simulations in the time domain under various operating conditions. In addition, frequency-domain simulations by means of impedance-based analysis are developed as a tool for analyzing the system stability. In the first part, a description of the offshore wind park based on dc technology is introduced. Next, components of the two-stage dc collector grid are modelled. Those are a wind turbine, a generator, a machine side converter (MSC), a cable, and an offshore platform converter(OPC). The modelling method is a component-based modelling. For power converters, the MSC and the OPC, this component-based modelling is also called a switching model. Controller strategies of converters are also presented. In the second part, impedance models are developed for frequency-domain simulations by means of impedance-based analysis. Finally, both time domain and frequency domain simulations assess the system stability under various operating conditions. Both simulation results are compared to get insight into the dynamic behaviour of the offshore wind park based on the two-stage dc collector grid. The agreements between both approaches show that the (linearized) impedance-based analysis can be used to analyze the stability of a two-stage dc collector grid for a large wind park.