High Field, Fully Superconducting 'Air-Core' Generators for Ultra-large Wind-turbines

摘要：近年来，随着小型电机和电力电子等邻近领域的巨大进步，兆瓦级电机技术的进步步伐并没有跟上。快速发展的支持技术和令人兴奋的新应用为潜在的变革性电机设计提供了机会。例如，与传统设计相比，超导机器可以导致功率密度和效率的阶跃变化，使其在从可再生能源发电到交通运输的各种应用中具有吸引力。迄今为止开发的大多数超导机器都是部分超导的，定子或转子由传统的（铜或铝）导体制成。如果能够适应低温下增加的损耗，完全超导的机器可以进一步提高比功率。在完全超导的机器中引入的损耗是电频率的强烈函数，并且特别难以管理。这个项目的重点是一个机器概念，可以在相对较低的频率下保持高功率密度，使完全超导设计更加实用。一种轻量级的直接驱动发电机将被设计出来，它可以帮助降低海上风力发电的成本，降低风险。该项目还有望帮助重振美国学校对大型电机的研究，并培养下一代电机专家，以支持该行业日益增长的“电气化”趋势。将研究一种采用主动屏蔽的全超导发电机，以遏制和增强磁场。现在可以在气隙中获得显着更高的电磁剪切力，从而导致显着更高的扭矩重量比。主动屏蔽概念已应用于相对高速，高频的航空航天机器，具有显著的重量减轻。在航空航天应用中遇到的频率，电枢绕组中的“交流”损耗将非常大，因此到目前为止，仅考虑了部分超导机器与“直流”超导激励线圈。在本项目中，超导线圈也将用于电枢绕组。铁芯在过去已经被用于这样的机器中，超导体的磁通密度相对较小，导致可控的“交流”损耗。保持屏蔽“空芯”拓扑结构所能获得的高磁通密度并适应由此产生的“交流”损耗将是具有挑战性的，但这是实现承诺的减小发电机尺寸和重量的关键。初步研究表明，超低频率的缓解效果可以补偿增加的场，使塔顶重量显著减少（与最先进的重量相比，减少了5-10倍）。详细的多物理模型结合了部分超导机器项目中使用的电磁、低温、机械和材料相互作用，将扩展到包括超导绕组中基于物理的“交流”损耗计算。然后将设计一个可扩展的（10-50兆瓦）全超导机器并用于系统级评估。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Abstract: The pace of advancement in electric machine technology in the multi-megawatt scale has not kept up in recent years with the large strides made in smaller machines and in adjacent areas like power electronics. Rapidly advancing enabling technologies and exciting new applications offer the opportunity for potentially transformational electric machine designs. Superconducting machines, for example, can lead to a step change in power density and efficiency over conventional designs, making them attractive for applications ranging from renewable energy generation to transportation. Most superconducting machines developed to-date are partially superconducting, with either the stator or the rotor made with conventional (copper or aluminum) conductors. Fully superconducting machines can further improve specific power if the increased losses at cryogenic temperatures can be accommodated. The losses introduced in fully superconducting machines are a strong function of the electrical frequency, and are particularly difficult to manage. This project is focused on a machine concept that can retain high power density at relatively low frequencies, making fully superconducting designs more practical. A lightweight direct-drive generator that can help reduce the cost of electricity from offshore wind will be designed and risk reduced. The project is also expected to help reinvigorate research on large electrical machines in US schools, and train the next generation of electrical machine experts to support the growing 'electrification' trend in the industry.A fully superconducting generator employing active shielding for field containment and enhancement will be pursued. Significantly higher electromagnetic shear force can now be obtained in the airgap, leading to substantially higher torque to weight ratio. The active shielding concept has been applied to relatively high speed, high frequency aerospace machines, with significant weight reduction. At the frequencies encountered in the aerospace application, 'ac' losses in the armature winding would be prohibitively large, and thus only partially superconducting machines with just 'dc' superconducting excitation coils have been considered thus far. In this project, superconducting coils will be utilized in the armature winding as well. An iron core has been employed in such machines in the past, with relatively modest flux densities experienced by the superconductor, leading to manageable 'ac' losses. Maintaining the high flux densities that can be obtained with the shielded 'air-core' topology and accommodating the resulting 'ac' losses will be challenging, but key to obtaining the promised reduction in size and weight of the generators. Preliminary studies indicate that the mitigating effects of the ultra-low frequency can compensate for the increased field, enabling a significant reduction in tower top weight (5-10X compared to state-of-the-art). Detailed multi-physics models incorporating electromagnetic, cryogenic, mechanical and materials interactions used in the partially superconducting machine projects will be extended to include physics-based 'ac' loss computations in the superconducting windings. A scalable (10-50 MW) fully superconducting machine will then be designed and used in system level assessment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.