1 Department of Mathematics, Technical University of Denmark2 Department of Applied Mathematics and Computer Science, Technical University of Denmark3 VESTAS Wind Systems A/S4 Vestas Technology R&D
The idea of introducing a superconducting generator for offshore wind turbine applications has received increasing support. It has been proposed as a way to meet energy market requirements and policies demanding clean energy sources in the near future. However, design considerations have to take into account hysteresis losses in the superconducting windings during transient responses. Modeling and simulation of these transients is a challenging task. It requires considering a system that spans spatially 5 (or 6) orders of magnitude: from the 1 µm thick superconducting layers in the windings, to the actual generators in the KW (MW) class with an expected cross section in the order of decimeters (meters). This thesis work presents cumulative results intended to create a bottom-up model of a synchronous generator with superconducting rotor windings. In a first approach, multiscale meshes with large aspect ratio elements are used to simulate the electromagnetic properties of superconducting thin films. This provided a computational speedup of two to three orders of magnitude without compromising accuracy. A second approach used a homogeneous-medium anisotropic bulk with a power law E - J relationship to model stacks of superconducting tapes. This method provided an additional speedup of about two orders of magnitude when calculating AC losses in superconducting stacks. The anisotropic bulk was latter used to model a generator with superconducting rotor windings. Transient response of the generator including ramp-up of rotor coils, load connection and change was simulated. Hence, transient hysteresis losses in the superconducting coils were computed. This allowed addressing several important design and performance issues such as critical current of the superconducting coils, electric load change rate, cryostat design and identification of quench-prone regions.
Superconducting generator; AC losses; Finite Element Simulation; Homogenization; HTS coils