This paper reviews the trends in wind turbine generator systems. After discussing some important requirements and basic relations, it describes the currently used systems: the constant speed system with squirrel-cage induction generator, and the three variable speed systems with doubly fed induction generator (DFIG), with gearbox and fully rated converter, and direct drive (DD). Then, possible future generator systems are reviewed. Hydraulic transmissions are significantly lighter than gearboxes and enable continuously variable transmission, but their efficiency is lower. A brushless DFIG is a medium speed generator without brushes and with improved low-voltage ride-through characteristics compared with the DFIG. Magnetic pseudo DDs are smaller and lighter than DD generators, but need a sufficiently low and stable magnet price to be successful. In addition, superconducting generators can be smaller and lighter than normal DD generators, but both cost and reliability need experimental demonstration. In power electronics, there is a trend toward reliable modular multilevel topologies.

Trends in Wind Turbine Generator Systems

Superconducting magnetic energy storage (SMES) is known to be a very good energy storage device. This article provides an overview and potential applications of the SMES technology in electrical power and energy systems. SMES is categorized into three main groups depending on its power conditioning system, namely, the thyristor-based SMES, voltage-source- converter-based SMES, and current-source-converter-based SMES. An extensive bibliography is presented on the applications of these three types of SMES. Also, a comparison is made among these three types of SMES. This study provides a basic guideline to investigate further technological development and new applications of SMES, and thus benefits the readers, researchers, engineers, and academicians who deal with the research works in the area of SMES.

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An Overview of SMES Applications in Power and Energy Systems

Superconducting technology applications in electric machines have long been pursued due to their significant advantages of higher efficiency and power density over conventional technology. However, in spite of many successful technology demonstrations, commercial adoption has been slow, presumably because the threshold for value versus cost and technology risk has not yet been crossed. One likely path for disruptive superconducting technology in commercial products could be in applications where its advantages become key enablers for systems which are not practical with conventional technology. To help systems engineers assess the viability of such future solutions, we present a technology roadmap for superconducting machines. The timeline considered was ten years to attain a Technology Readiness Level of 6+, with systems demonstrated in a relevant environment. Future projections, by definition, are based on the judgment of specialists, and can be subjective. Attempts have been made to obtain input from a broad set of organizations for an inclusive opinion. This document was generated Superconductor Science and Technology Supercond. Sci. Technol. 30 (2017) 123002 (41pp) https://doi.org/10.1088/1361-6668/aa833e Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 0953-2048/17/123002+41$33.00 © 2017 IOP Publishing Ltd Printed in the UK 1 through a series of teleconferences and in-person meetings, including meetings at the 2015 IEEE PES General meeting in Denver, CO, the 2015 ECCE in Montreal, Canada, and a final workshop in April 2016 at the University of Illinois, Urbana-Champaign that brought together a broad group of technical experts spanning the industry, government and academia.

https://iopscience.iop.org/article/10.1088/1361-6668/aa833e/pdf

High power density superconducting rotating machines—development status and technology roadmap

Ever since the Wright brothers’ first powered flight in 1903, commercial aircraft have relied on liquid hydrocarbon fuels. However, the need for greenhouse gas emission reductions along with recent progress in battery technology for automobiles has generated strong interest in electric propulsion in aviation. This Analysis provides a first-order assessment of the energy, economic and environmental implications of all-electric aircraft. We show that batteries with significantly higher specific energy and lower cost, coupled with further reductions of costs and CO2 intensity of electricity, are necessary for exploiting the full range of economic and environmental benefits provided by all-electric aircraft. A global fleet of all-electric aircraft serving all flights up to a distance of 400–600 nautical miles (741–1,111 km) would demand an equivalent of 0.6–1.7% of worldwide electricity consumption in 2015. Although lifecycle CO2 emissions of all-electric aircraft depend on the power generation mix, all direct combustion emissions and thus direct air pollutants and direct non-CO2 warming impacts would be eliminated. Electric aircraft offer an aviation decarbonization pathway and attract increasing attention owing to the rapid development of batteries. Here Andreas Schafer and colleagues analyse the potential technological, economic and environmental viability of battery-electric commercial aircraft.

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Technological, economic and environmental prospects of all-electric aircraft

High temperature superconductor (HTS) technology enables generators with one third the weight and one half the losses of conventional machines. These technologies enable a significant reduction in the size and weight of 10 MW-class generators for direct-drive wind turbine systems and reduce the cost of clean energy relative to conventional copper and permanent-magnet-based generators and gearboxes. With compact and light-weight 10 MW-class HTS generators, installation and low maintenance operation of high power wind turbine systems becomes practical and enable cost-effective access to wind resources. Under a program funded by the NIST-Advanced Technology Program, key generator technologies for a 10 MW class generator have been developed. This paper summarizes work under the NIST and internal programs.

10 MW Class Superconductor Wind Turbine Generators

PREFACE. ACKNOWLEDGEMENTS. Abbreviations. CHAPTER 1 Introduction. CHAPTER 2 HTS Superconductors. 2.1 Introduction. 2.2 HTS Background and Nomenclature. 2.2.1 Background. 2.2.2 Nomenclature. 2.3 BSCCO-2212 Conductors. 2.4 BSCCO-2223 OPIT Wires. 2.4.1 Manufacturing Process. 2.4.2 Characteristics - Electrical and Mechanical. 2.5 YBCO-123 Coated Conductors. 2.6 Magnesium Diboride (MgB2). 2.7 State-of-the-art of Various HTS Conductors. 2.8 Superconducting Magnet Design. 2.9 Summary. References. CHAPTER 3 Cooling and Thermal Insulation Systems. 3.1 Introduction. 3.2 Anatomy of a Cryostat. 3.3 Cryogenic Fluids for Cooling HTS Magnets. 3.4 Direct Cooling with Cryogens. 3.5 Indirect or Conduction Cooling. 3.6 Refrigeration Systems. 3.6.1 Gifford-McMahon (G-M) Cryocoolers. 3.6.2 Stirling Coolers. 3.6.3 Pulse Tube Coolers. 3.7 Open Loop Cooling with Liquid Nitrogen. 3.8 Magnet Materials. 3.9 Current Leads. 3.9.1 Design of Conduction Cooled Leads. 3.10 Example Cryostat Design. 3.10.1 Configuration. 3.10.2 Thermal Load Calculations. 3.10.2.1 Radiation Thermal Load Through MLI. 3.10.3 Current Leads. 3.10.4 Conduction. 3.10.5 Selection of Refrigerator. 3.11 Summary. References. CHAPTER 4 Rotating AC Machines. 4.1 Introduction. 4.2 Topology. 4.3 Analysis and Parameter Calculations. 4.3.1 Magnetic Circuit and Harmonic Components. 4.3.2 Parameter Calculations. 4.3.3 Machine Terminal Parameters. 4.4 Design. 4.4.1 Stator Winding Design Issues. 4.4.2 Field Winding Design Issues. 4.4.3 Electromagnetic (EM) Shield Design Issues. 4.4.4 Loss and Efficiency Calculations. 4.4.5 Example Design. 4.5 Manufacturing Issues. 4.5.1 Superconducting Field Winding and Its Cooling Systems. 4.5.2 Torque Transfer from Col Field Winding to Warm Shaft. 4.5.3 Stator Winding. 4.6 Simulation. 4.7 Generators. 4.7.1 High Speed Generators. 4.7.2 Low Speed Generators. 4.8 Motors. 4.8.1 High Speed Motors. 4.8.2 Low Speed Motors. 4.9 Summary. References. CHAPTER 5 Rotating DC Homoploar Machines. 5.1 Introduction. 5.5 Principle. 5.3 Configuration. 5.4 Design Challenges. 5.5 Prototypes. 5.6 Summary. References. CHAPTER 6 Synchronous AC Homoploar Machines. 6.1 Introduction. 6.2 Principle. 6.3 Design. 6.4 Design Challenges. 6.5 Prototypes. 6.6 Summary. References. CHAPTER 7 Transformers. 7.1 Introduction. 7.2 Configuration. 7.3 Design Analysis. 7.3.1 50MVA Example Design. 7.4 Challenges. 7.5 Manufacturing Issues. 7.6 Prototypes. 7.7 Summary. References. CHAPTER 8 Fault Current Limiters. 8.1 Introduction. 8.2 Principle and Configuration. 8.2.1 Resistive Fault Current Limiters (R-FCL). 8.2.2 Inductive FCL with Shielded Iron Core. 8.2.3 Inductive FCL with Saturated Iron Core. 8.3 Design Analysis. 8.3.1 Example Design - Resistive FCL. 8.3.2 Example Design - Saturated Core FCL. 8.4 Challenges. 8.4.1 Challenges of Resistive FCL. 8.4.2 Challenges of Inductive FCL. 8.5 Manufacturing Issues. 8.6 Prototypes. 8.6.1 AMSC s Fault Current Limiter. 8.6.2 Superpower s Fault Current Limiter. 8.6.3 Zenergy Power s Fault Current Limiter. 8.6.4 Nexans s Fault Current Limiter. 8.7 Summary. References. CHAPTER 9 Power Cables. 9.1 Introduction. 9.2 Configurations. 9.2.1 Resistive Cryogenic Cable. 9.2.2 HTS Cables. 9.3 Design Analysis. 9.3.1 Cryogenic Cable Analysis. 9.3.2 HTS Cable Analysis. 9.3.2.1 HTS Coaxial Cable - High Voltage. 9.3.2.2 HTS Coaxial Cable - Medium Voltage. 9.3.2.3 TriaxTM HTS Cable - Medium Voltage. 9.4 Challenges. 9.4.1 Resistive Cryogenic Cable. 9.4.2 HTS Cable. 9.5 Manufacturing Issues. 9.5.1 Resistive Cryogenic Cable. 9.5.2 HTS Cable. 9.6 Prototypes. 9.6.1 Resistive Cryogenic Cable. 9.6.2 HTS Cable - High Voltage. 9.6.3 HTS Cable - Medium Voltage. 9.6.4 TriaxTM HTS Cable - Medium Voltage. 9.7 Summary. References. CHAPTER 10 Maglev Transport. 10.1 Introduction. 10.2 Configuration. 10.2.1 Electro-dynamic Suspension (EDS). 10.2.2 Electro-magnetic Suspension (EMS) . 10.3 Design Analysis. 10.3.1 Electro-dynamic Suspension Maglev. 10.3.2 Electro-magnetic Suspension Maglev. 10.4 Challenges (Technical/Economic). 10.4.1 EDS System Challenges. 10.4.2 EMS System Challenges. 10.5 Manufacturing Issues. 10.6 Prototypes. 10.6.1 Northrop Grumman Concept. 10.7 Summary. References. CHAPTER 11 Other Applications of HTS. 11.1 Introduction. 11.2 Air-Core Magnets. 11.2.1 High Field Magnets. 11.2.2 Low Field Magnets. 11.3 Iron-Core Magnets. 11.3.1 Beam Bending. 11.3.2 Induction Heating. 11.3.3 Synchrotron. 11.4 Challenges. 11.5 Summary. About the Author. INDEX.

Applications of High Temperature Superconductors to Electric Power Equipment

A 5 MW, 230 RPM, 6-pole high temperature superconductor (HTS) ship propulsion motor is presently under test at the Center for Advance Power Systems (CAPS). This paper provides a summary of the key design features of the motor, predicted performance, factory test results and extended test results to date at CAPS. This motor was designed and built under the U.S. Navy's Office of Naval Research (ONR) funding (Contract #N00014-02-C-0190) to address the next generation of electric ship propulsion systems. HTS motors are characterized by high power density, quiet operation and high efficiency. HTS air-core motors have unique electrical characteristics and therefore require dynamic testing to validate all modes of operation. The test program at CAPS is designed to address dynamic performance and simulation of this class of propulsion motor. The motor has been operated at 5 MW load for over 3 hours at CAPS.

The performance of a 5 MW high temperature superconductor ship propulsion motor

Compact and lightweight direct-drive generators in large rating are desired for offshore wind farm applications. A key goal for such generators is that they be manufactured and tested in a factory and shipped to the site as fully assembled units. A possible approach to achieving this goal is to construct both rotor and stator windings with high-temperature superconducting (HTS) materials. The magnesium diboride (MgB2) superconductor wire currently becoming available with properties suitable for application in large rotating machines appears to be the most cost-effective option for such machines. This paper presents a design concept for a 10-MW 10-r/min generator using MgB2 wire for both rotor and stator coils. The concept design includes ambient-temperature magnetic iron on both the rotor and the stator. The field winding on the rotor employs race-track-shaped excitation coils operating at 20 K. The armature winding on the stator also uses race track coils operating at 20 K. All coils employ round cables build with commercially available MgB2 wire. Coils are cooled with available off-the-shelf cryocoolers. The concept the 10-MW generator is expected to be less than 5 m in diameter, less than 2 m in axial length, weigh around 52 000 kg, and cost about $3.2 million (including the cost of power electronics).

Superconducting Wind Turbine Generator Employing $ \hbox{MgB}_{2}$ Windings Both on Rotor and Stator

A superconducting rotating machine includes a direct current field excitation source and an alternating current armature winding mounted on a stationary support member, at least one of which includes a superconducting material, a core member formed of a magnetic permeable material and rotatable around the static support member, and a refrigerator unit which cryogenically cools at least one of the field excitation source and the armature winding. The superconducting rotating machine may have a construction for providing polyphase (e.g., three-phase) power.

Swarn S. Kalsi

Papers

High power density superconducting rotating machines—development status and technology roadmap

Applications of High Temperature Superconductors to Electric Power Equipment

The performance of a 5 MW high temperature superconductor ship propulsion motor

Superconducting Wind Turbine Generator Employing $ \hbox{MgB}_{2}$ Windings Both on Rotor and Stator

A rotating machine having superconducting windings