Electromagnetic design of light weight and high power density superconducting synchronous machines for 10 MW class wind turbine generators

This thesis focuses on the electromagnetic design of light weight and high power density superconducting synchronous machines for 10 MW class wind turbine generators. Wind energy is well known as a clean energy source, and the installation of wind energy turbines is increasing annually worldwide. The size of wind turbines has also increased from an economical point of view. Direct-drive, low speed, and high torque systems are often adopted for multi-MW class wind turbines because higher efficiency and lower maintenance are expected. There are several proposals for generators that deliver over 10 MW of power. However, a generator’s weight and tower cost increase with its power generating capacity. It is important to develop lightweight and high power density generators for large capacity wind turbine generators. High-temperature superconducting (HTS) technology is one of the key solutions. Superconducting wind turbine generators have the potential to realize compact and high power density generators, and have been actively studied throughout the world. In general, these generator structures are made of superconducting field coils and copper armature windings. Fully superconducting generators that have superconducting field and armature windings have the potential to be more compact, and have higher output density generators than other machines owing to air gap reduction. However, fully superconducting generators have the technically challenging issue of how to reduce AC loss at the superconducting armature windings. If multifilament MgB2 superconducting wires are applied to the superconducting generators, it is possible to reduce the AC losses. This research has three main purposes, namely (1) to develop the world’s first fully superconducting generator that has YBCO field coils and MgB2 armature windings, (2) to develop the electromagnetic design of three types of superconducting generator and a permanent magnet-type wind turbine generator and (3) to investigate the electromagnetic characteristics of 10 MW class direct-drive wind turbine generators by using generator size, weight, HTS wire length, generator losses, and so on.The four wind turbine generators that we focused on were investigated using finite-element method (FEM) analysis, a conventional permanent magnet generator, a salient pole superconducting generator, non-salient pole superconducting generator, and a fully superconducting generator. In Chapter 1, we present the introduction of this study. First, the current status of global wind energy installation and large-scale wind turbine generator systems is described. Next, superconducting wind turbine generators are introduced as a solution to the issues after explaining the challenging technical issues associated with generators in the over 10 MW class. Chapter 2 refers to design conditions for 10 MW class wind turbine generators. First, we present initial design conditions such as output power and current voltage. Next, four generator structures and their cooling system design schemes are described. Then, the design concepts for generator components are explained. Chapter 3 describes the electromagnetic design of a permanent magnet type synchronous generator (PMSG). The PMSG characteristics were investigated with 2D finite element method analysis (FEM). The calculation results showed that there are many technical challenges to realizing 10 MW class PMSGs from the perspectives of generator efficiency, weight, and cost. Chapter 4 shows the electromagnetic design of salient pole-type superconducting generators (S-SCG) with 2D FEM. Two types of generators with different pole numbers and outer diameters were designed and investigated. The results showed that S-SCG can reduce by over 30% of the generator diameter when compared to PMSG. Also, S-SCG was found to be suitable for the design of multiple and larger diameter structures. Chapter 5 explains the electromagnetic design of non-salient pole-type superconducting generators (NS-SCG) with 2D FEM. Two types of NS-SCG having different diameters were designed. The generator characteristics showed that both NS-SCG structures require over 1000 km of YBCO wires because of its air-cored structure. Their generator characteristics showed that both NS-SCG structures had many technical challenges. Chapter 6 focuses on the electromagnetic design of fully superconducting generators (FSCG), which is the original work of this study. Electromagnetic design and characteristics of the FSCG have been investigated using 2D FEM. Two types of FSCG were designed. Because of the air gap length reduction, the required length of HTS wire was reduced in spite of its air-cored structure. While the required length of the HTS wire was less than 200 km, the generator diameter was 4.0 m. FSCG is therefore considered to be a good candidate for the 10 MW class wind turbine generator system. In Chapter 7, we compare the electromagnetic characteristics of four designed wind turbine generators in terms of generator diameter, weight, HTS wire length, generator loss, and so on. The results show that the FSCG and the S-SCG are the best candidates for 10 MW class offshore wind turbine generators from the size and cost perspective. In Chapter 8, we conclude this paper and discussed future works of this study.報告番号: ; 学位授与年月日: 2013-03-25 ; 学位の種別: 課程博士 ; 学位の種類: 博士(工学) ; 学位記番号: ; 研究科・専攻: 工学系研究科電気系工学専