Diode-Rectifier HVDC link to onshore power systems: Dynamic performance of wind turbine generators and Reliability of liquid immersed HVDC Diode Rectifier Units

摘要

The high potential of wind power far offshore calls for cost-effective solutions for grid connection. HVDC is the preferred grid access technology when large scale offshore wind power generation has to be connected to the energy system. The study investigates in the first part the interoperability of the offshore wind turbines with HVDC systems using diode rectifiers (DR) and voltage source converters (VSC). The wind turbines are assumed to be of type 4, which is the most commonly used wind turbine type in offshore wind power plants. Stable operation in AC and DC mode as well as a smooth transition between operational modes is achieved by implementation of the newly developed wind turbine grid side converter controller functions. In addition the dynamic behaviour including successful FRT test of entire DRU based DC grid access solution is demonstrated by comprehensive simulations. In the second part of this study aspects of product requirements, design elements, operation behaviour and reliability of the HVDC Diode-Rectifier Unit are discussed. State of the art HVDC converters are configured as air insulated systems with related limitations in optimization of required space. The approach of the newly arranged offshore rectifier solution called "HVDC Diode-Rectifier Unit" is to combine on the one hand side transformer, rectifier and smoothing reactor functionalities and on the other hand to be handled practically comparable to a conventional power transformer in an offshore substation. Selected novelties and challenges in product design, usage of materials and components, production and test to meet the high requirements in installation, reliable operation and defined appropriate maintenance activities during the whole lifetime are presented in more detail.