Abstract
A significant challenge in the design of fully superconducting (SC) machines is managing ac losses in the SC armature. Recent developments in MgB 2 superconducting conductors promise low ac loss conductors suitable for fully SC machines. This paper presents an optimized design targeting low losses and low weight for a 10-MW fully SC generator suitable for offshore wind turbine applications. An outer rotor air-core machine topology is investigated to optimize the design with low weight and low losses. An active shielding concept is used to minimize the pole count without adding excessive weight. This enables a reduction in the electrical frequency for a practical design by a factor of 4 to 5 over current designs, driving ac losses and active components weight lower by an order of magnitude. In this study, armature current is varied to control electrical and magnetic loading in order to minimize losses. A pole count study is conducted to identify the design space suitable for MW scale machines. A comparison is made between active shield, passive shield and a hybrid topology to address the benefits of an active shield for weight reduction. Results suggest that low-pole-count designs with MgB 2 conductors will enable machines with less than 1 kW of ac losses.
Highlights
O FFSHORE wind turbines are becoming an integral part of future large-scale renewable generation initiatives
This paper explores a novel high field, air-core fully superconducting machine topology which borrows and adapts a technique utilized in the MRI industry: that of an active magnetic shield comprised of SC coils to contain the flux within the machine [9]–[11]
Initial optimization results shows that low pole count machine design with ac losses lower than 1 kW can be achieved
Summary
O FFSHORE wind turbines are becoming an integral part of future large-scale renewable generation initiatives. Several partial and fully SC machine designs have been proposed and demonstrated for offshore direct-drive wind turbines. A key challenge to be addressed is high ac losses generated in the armature winding. These losses pose a significant barrier for high-speed applications. Due to the low operating frequency of direct-drive wind turbines and the availability of mature, low-loss MgB2 filaments, it is expected that ac losses will be low enough for practical extraction at cryogenic temperatures. Most fully SC machines proposed in the literature [3]–[8] are primarily focused on electromagnetic (EM) design and validation of electrical performance; none are optimized for minimal armature ac loss. A rigorous ac loss calculation along various paths within the armature coils utilizes finite element analysis in tandem with analytical ac loss models available in the literature
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