Superconducting Wind Turbine Generators Research Articles

Technology Transition of Large Scale Wind Turbine System and Technology Status of High Temperature Superconducting Wind Turbine Generator

Technology Transition of Large Scale Wind Turbine System and Technology Status of High Temperature Superconducting Wind Turbine Generator

Electrical design and structure optimization of 10 MW fully superconducting wind turbine generators

In this paper, two types of conceptual structures of 10 MW fully superconducting offshore wind turbine generators (FSWTG) with an efficient electrical design method are presented. Four types of generator models, Gen. A - D, are compared according to different armature winding structures, and it's found that Gen. A is the preferable one. Optimization of the main generator parameters reveals that 36 poles with a pole pitch of 474 mm and electrical load of 6.0 kA/cm yields the best performance. The different design parameters of FSWTGs are compared to partially superconducting wind turbine generators (PWTG) with HTS field windings and copper armature windings and traditional wind turbine generators (WTG). Results show that FSWTGs are smaller in size, weigh 0.7 and 0.4 times less and are more efficient by 1.9–2.1% and 2.9–3.1% than PWTGs and WTGs, respectively. Lastly, the AC losses generated in the superconducting armature windings of the four types of FSWTGs are calculated and discussed.

Cooperative strategy of SMES device and modified control for cost-effective fault ride-through enhancement and power smoothing of 10 MW class superconducting wind turbine

Superconducting wind turbine generators (SWTGs) are an effective option of 10 MW class WTG units integrated into offshore wind farms, owing to their potential advantage of reduced size and weight compared with conventional generators. Reliable grid-connection of SWTGs faces two main challenges including fault ride through (FRT) and wind power smoothing. Traditional solutions consist mainly of device-based and control-based schemes. However, the device-based scheme causes a high-cost burden due to the introduction of additional devices, while the control-based scheme is not suitable for FRT enhancement under serious grid faults. To solve these problems, this paper presents a cooperative strategy integrated with one cost-effective superconducting magnetic energy storage (SMES) device and two modified WTG controls. The utilization of SMES devices can achieve a favorable wind power smoothing effect during normal operations and overvoltage suppressing effect in dc-link of WTG during grid faults. Moreover, two modified WTG controls of power decreasing control method and reactive power control provide effective assistance for suppressing dc overvoltage, offering adequate reactive current support and reducing the capital cost of SMES devices simultaneously. Several test cases are conducted to demonstrate the feasibility of the proposed strategy.

Performance Evaluation of Practical REBCO Coated Conductor Tapes for Superconducting Wind Power Coils

A Korean-type large scale floating offshore wind power system with a superconducting generator is the result of an innovative wind power project to develop high-temperature superconducting coils, a test facility, an offshore floating system, and network connection technologies. The 10 MW-class floating offshore wind power system utilizes a superconducting generator fully supported by Korea Electric Power Corporation. Large-scale applications of rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes, particularly in superconducting wind turbine generators, must encompass high generation efficiencies and low-weight designs; they can do so by utilizing the high performance of REBCO CC tapes at cryogenic temperatures and under magnetic fields. Performance evaluations of the CC tapes are carried out by investigating the stress and strain dependency of Ic including irreversible degradation region under an external magnetic field. Generally, under a magnetic field, the Ic degradation behavior may be different from the results obtained at self-field and dependent on the fabrication processes and materials of the practical CC tapes. In this study, electromechanical properties such as Ic degradation behavior and the irreversible limits of three commercially available REBCO CC tapes were examined using uniaxial tension tests at the expected operating conditions, 35 K and 2 T. Results were compared to those obtained at 77 K and in a self-field.

Performance of Multi-Layer and Stator-Shifting Fractional-Slot Concentrated Windings for Superconducting Wind Turbine Generators Under Normal and Short-Circuit Operation Conditions

High temperature superconducting (HTS) generators are being considered for large offshore direct-drive (DD) wind turbines as they are expected to be lightweight and compact. However, short circuit torques of an HTS generator with integral-slot distributed windings (ISDWs) are too high for wind turbine constructions, mainly due to the large magnetic air gap. Fractional-slot concentrated windings (FSCWs) can be considered to address this issue since their high leakage inductance can limit short circuit currents and torques. Unlike ISDWs, FSCWs produce great contents of space harmonics that induce excessive losses in rotor components. Multi-layer and stator-shifting windings have been proposed to effectively reduce such losses. Based on a conventional 12-slot 10-pole configuration, this paper evaluates the effects of multi-layer and stator-shifting FSCWs on torque production and loss reduction in a 10 MW DD HTS generator. The examined losses include eddy current losses in the rotor shields and AC losses in the HTS field winding. This paper also checks if these FSCW schemes maintain the advantage of achieving a low short circuit torque. The results show that a 6-phase stator-shifting winding is the best choice for applying FSCWs to HTS generators.

Ground Testing of the World's First MW-Class Direct-Drive Superconducting Wind Turbine Generator

The EU-funded EcoSwing project addresses the world's first full-scale direct-drive (DD) high temperature superconducting (HTS) wind turbine generator. Before the generator was installed on a commercial wind turbine, the generator had been tested on the ground at the Dynamic Nacelle Testing Laboratory (DyNaLab) in Fraunhofer Institute for Wind Energy Systems (IWES), serving as an experimental validation of the generator design. This article is centered on the ground testing of the EcoSwing HTS generator, which includes corresponding tests for validating the generator's cryogenic design and electromagnetic performance. Despite one HTS coil with a defect limiting the operating current significantly, partial power production up to 1 MW at 14.5 rpm was reached. The critical auxiliary systems, i.e., vacuum system and rotary helium coupling, behaved as expected or even better than anticipated. The work reported in the article successfully validates the generator design, and also provides firsthand information prior to installing and testing the HTS generator on the wind turbine.

Experimental Validation of a Full-Size Pole Pair Set-Up of an MW-Class Direct Drive Superconducting Wind Turbine Generator

The article presents a full-size pole pair set-up of an MW-class direct drive (DD) high temperature superconducting (HTS) wind turbine generator. The set-up serves as a precursor to the world's first full-scale DD HTS generator developed within the EU-funded EcoSwing project. The set-up built for de-risking employs an HTS field winding in the rotor and a conventional copper armature winding in the stator, representing a minimum independent unit of the corresponding full generator. Such a prototyping approach well reflects the performance of the full generator at a low cost. The article first explains the main design considerations of the full generator, followed by designing and construction details of the set-up. Afterward, a number of tests for determining the key performance of the set-up are reported. The testing results showed that the HTS field winding ran stably at its rated current of 480 A and was well maintained below 30 K. Moreover, the tangential force in the set-up reached 29.8 kN, projecting the 2 MW target output power of the full generator. The set-up developed effectively validated the design ideas and engineering feasibilities of the full generator, leading to successful kick-off of the EcoSwing project.

Designing and Basic Experimental Validation of the World's First MW-Class Direct-Drive Superconducting Wind Turbine Generator

High temperature superconducting (HTS) technologies are expected to be a key enabler for lightweight and cost-effective direct-drive (DD) trains for large wind turbines. This paper reports the designing and basic experimental validation of the world's first full-scale DD HTS generator demonstrated on a commercial wind turbine. The HTS generator has its rotor with an HTS field winding working below 30 K, which is achieved by using off-the-shelf Gifford-McMahon cryocoolers. The stator of the generator is essentially conventional, except that the armature winding has four segments to limit fault torques in case of sudden short circuits due to converter failures. Compared to an existing DD permanent magnet generator on the turbine, the air gap shearing stress of the HTS generator is doubled, and the weight is reduced by 24%. The overall design requirements from the turbine integration perspective, as well as the topological considerations, are first described in this paper. The electromagnetic and cryogenic designs are then presented, followed by performance testing of HTS coils. The basic experimental validation shows that the cryogenic design is satisfactory and the measured no-load voltage matches the finite element calculation very well.

Short-Circuit Characteristics of a High Temperature Superconducting Wind Turbine Generator Employing a Segmented Armature Winding

High temperature superconducting (HTS) wind turbine generators (WTGs) are expected to offer a compact and lightweight direct drive train for large offshore wind turbines. However, short circuits occurring at armature winding terminals can pose great challenges, such as high peak torques due to a large magnetic air gap in HTS generators, field current rise over the critical current that may cause a quench, and AC losses in HTS field windings that may cause local overheat. Segmentation of armature windings could be a solution to mitigate such challenges. In this paper, an optimized design of a 10-MW direct drive HTS generator using 2G HTS wires in the field winding is studied based on a well-verified generator topology. The generator design has two scenarios, i.e., without segmentation and with four segments in the armature winding. These two winding scenarios are compared through a phase-to-phase short circuit occurring at the terminals of the armature winding. The effects of segmentation are revealed on 1) electromagnetic torque, 2) current rise in the HTS field winding, and 3) AC losses in the HTS field winding after the short circuit occurs. The results show the great benefits of using segmented armature windings in an HTS WTG: the peak torque is reduced by a factor of 4, and the AC losses in the HTS field winding are nearly halved although the maximum field current is almost unchanged.

Investigation about the effects of metal-clad winding on the electromagnetic characteristics of the GdBCO racetrack coils in a time-varying magnetic field

Abstract In this study, the electromagnetic characteristics of the insulated (INS), non-insulated (NI), and metal-clad (MC) racetrack coils are examined in a time-varying magnetic field. The delay in the generation of induced current and the amount of induced current when the coils are exposed to the time-varying magnetic field have been thoroughly examined. Additionally, the electromagnetic stability of each test coil was investigated under an overcurrent condition in the presence of an external magnetic ripple field. We also performed an AC loss test to investigate the effects of an MC layer on the magnitude of the AC loss. Based on the test results, the feasibility of using an MC winding technique for developing a highly stable high-temperature superconducting wind turbine generator with an enhanced electromagnetic response was thoroughly examined

Design of a 20-MW Fully Superconducting Wind Turbine Generator to Minimize the Levelized Cost of Energy

Superconducting machines are promising candidates for direct-drive multimegawatt offshore wind turbines. Here, we designed a 20-MW fully superconducting synchronous wind turbine generator using magnesium diboride (MgB 2 ) superconductors for both rotor and stator windings. MgB 2 tapes operating at 10 K are used for the rotor windings in order to improve the packing factor. A Rutherford cable made of 91-filament MgB 2 wires operating at 20 K is used for the stator windings in order to limit the ac losses. Two separate cryostats are considered for the stator and the rotor to increase the system reliability. Besides, to reduce the machine's weight and to simplify the cryogenic system, a toothless magnetic circuit is adopted. The goal of the two-dimensional finite element method based optimization was to minimize the levelized cost of energy (LCOE). Numerical results show that the adopted topology is lightweight enabling to reduce the cost of the nacelle, tower, and foundation, and therefore, the LCOE in comparison to a conventional generator. But the ac losses are significant, requiring at this stage of the study an impractical number of cryocoolers.

Short Circuits of a 10-MW High-Temperature Superconducting Wind Turbine Generator

Direct Drive high-temperature superconducting (HTS) wind turbine generators have been proposed to tackle challenges for ever increasing wind turbine ratings. Due to smaller reactances in HTS generators, higher fault currents and larger transient torques could occur if sudden short circuits take place at generator terminals. In this paper, a finite element model that couples magnetic fields and the generator's equivalent circuits is developed to simulate short-circuit faults. Afterward, the model is used to study the transient performance of a 10-MW HTS wind turbine generator under four different short circuits, i.e., three-phase, phase-phase clear of earth, phase-phase-earth, and phase-earth. The stator current, fault torque, and field current under each short circuit scenario are examined. Also included are the forces experienced by the HTS field winding under short circuits. The results show that the short circuits pose great challenges to the generator, and careful consideration should be given to protect the generator. The findings presented in this paper would be beneficial to the design, operation and protection of an HTS wind turbine generator.

A Full-Size High-Temperature Superconducting Coil Employed in a Wind Turbine Generator Setup

A full-size stationary experimental setup, which is a pole pair segment of a 2 MW high-temperature superconducting (HTS) wind turbine generator, has been built and tested under the HTS-GEN project in Denmark. The performance of the HTS coil is crucial to the setup, and further to the development of the full generator. This paper deals with the HTS coil employed in the setup. The coil utilizing YBCO tapes is double-layered with 152 turns per layer and is wound on an FeNi9 iron core. Several sensors are installed to monitor the operating status of the coil, e.g., temperature, field, and voltage. The coil is tested in LN $_\text{2}$ first, and then tested in the setup so that the magnetic environment in a real generator is reflected. The experimental results are reported, followed by a finite-element simulation and a discussion on the deviation of the results. The tested and estimated I $_\text{c}$ in LN $_\text{2}$ are 148 A and 143 A, respectively. When tested in the setup, the maximum temperature of the coil is controlled at 77 K and 40 K, and the I–V curves under both conditions are presented. It is found that the lower half coil that is closer to the stator has a smaller I $_\text{c}$ due to a higher field level. The study is of significance to the development of HTS generators.

Effects of Armature Winding Segmentation With Multiple Converters on the Short Circuit Torque of 10-MW Superconducting Wind Turbine Generators

Superconducting synchronous generators (SCSGs) are drawing more attention in large direct-drive wind turbine applications. Despite low weight and compactness, the short circuit torque of an SCSG may be too high for wind turbine constructions due to a large magnetic air gap of an SCSG. This paper aims at assessing the effects of armature winding segmentation on reducing the short circuit torque of 10-MW SCSGs. A concept of armature winding segmentation with multiple power electronic converters is presented. Four SCSG designs using different topologies are examined. Results show that armature winding segmentation effectively reduce the short circuit torque in all the four SCSG designs when one segment is shorted at the terminal.

A novel no-insulation winding technique of high temperature-superconducting racetrack coil for rotating applications: A progress report in Korea university.

This paper presents our recent progress on core technology development for a megawatt-class superconducting wind turbine generator supported by the international collaborative R&D program of the Korea Institute of Energy Technology Evaluation and Planning. To outperform the current high-temperature-superconducting (HTS) magnet technology in the wind turbine industry, a novel no-insulation winding technique was first proposed to develop the second-generation HTS racetrack coil for rotating applications. Here, we briefly report our recent studies on no-insulation (NI) winding technique for GdBCO coated conductor racetrack coils in the following areas: (1) Charging-discharging characteristics of no-insulation GdBCO racetrack coils with respect to external pressures applied to straight sections; (2) thermal and electrical stabilities of no-insulation GdBCO racetrack coils encapsulated with various impregnating materials; (3) quench behaviors of no-insulation racetrack coils wound with GdBCO conductor possessing various lamination layers; (4) electromagnetic characteristics of no-insulation GdBCO racetrack coils under time-varying field conditions. Test results confirmed that this novel NI winding technique was highly promising. It could provide development of a compact, mechanically dense, and self-protecting GdBCO magnet for use in real-world superconducting wind turbine generators.

Superconducting Wind Turbine Generators

Wind energy is well known as a renewable energy because its clean and less polluted characteristic, which is the foundation of development modern wind electricity. To find more efficient wind turbine is the focus of scientists around the world. Compared from conventional wind turbines, superconducting wind turbine generators have advantages at zero resistance, smaller size and lighter weight. Superconducting wind turbine will inevitably become the main trends in this area. This paper intends to introduce the basic concept and principle of superconductivity, and compare form traditional wind turbine to obtain superiority, then to summary three proposed machine concept.While superconductivity have difficulty in modern technology and we also have proposed some challenges in achieving superconducting wind turbine finally.

Development of a cooling system for superconducting wind turbine generator

This paper deals with the cooling system for high-Tc superconducting (HTS) generators for large capacity wind turbines. We have proposed a cooling system with a heat exchanger and circulation pumps to cool HTS field windings designed for 10MW-class superconducting generators. In the cooling system, the refrigerants in the stationary and rotational systems are completely separated; heat between the two systems exchanges using a rotational-stationary heat exchanger. The refrigerant in rotational system is circulated by highly reliable pumps. We designed the rotational-stationary heat exchanger based on a conventional shell-and tube type heat exchanger. We also demonstrated that heat exchange in cryogenic temperature is possible with a commercially available heat exchanger. We devised a novel and highly reliable cryogenic helium circulation pump with magnetic reciprocating rotation system and verified its underlying principle with a small-scale model.

Design Study of Fully Superconducting Wind Turbine Generators

In this paper, two fully superconducting generators employing MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> armature winding, with YBCO and MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> field winding respectively, are presented and analyzed. The ac loss in armature winding is estimated, and a simple comparative study is carried out. The results show that both electromagnetic designs for fully superconducting generators are promising with respect to the power density. However, the cost of removing ac loss in armature winding is as high as $900 000. It is also noted that with the current price of YBCO tape, the generator employing MgB 2 field winding would have lower cost.

Design Cost and Scaling Model of Superconducting Wind Turbine Generator for Electricity Generation

This paper reports on the design cost and scaling model of a small scale superconducting wind turbine generator, where the levelized cost of energy (COE) was calculated. The proposed design of the wind turbine is based on the vertical axis wind turbine (VAWT) type that drives the superconducting generator. VAWT was chosen due to its ability to operate under low wind speed. Wind turbine using superconducting generator was proposed since it is able to enhance magnetic flux within the stator of the generator and consequently improve the performance of the generator. Once the design has been accomplished, all the cost of parts and components must be accounted and contributes to the overall cost of generating electrical energy from the superconducting wind turbine generator. The cost elements include the initial capital cost (ICC), balance of station (BOS), operation and maintenance (O&amp;M), levelized replacement cost (LRC) and annual energy production (AEP). The calculated levelized COE shows that the cost of generating electricity using superconducting wind turbine generator is lower than generating electricity from conventional sources.

Conceptual Design of the Cryogenic System for a 12 MW Superconducting Wind Turbine Generator

A direct drive 12-MW superconducting wind turbine generator has been designed. The rotor of the generator is made of low temperature superconductor (LTS) coils, which are wound from NbTi/Cu cable-in-conduit conductors (CICC) cooled with forced flow supercritical helium at 4 K. To ensure the stability of the generator rotor, it is necessary to design a reliable cryogenic system. With consideration of the radiation heat loads, ac loss, conduction heat leak by residual gas, current leads and torque tube, the heat load of the cryogenic system is analyzed. Aiming at decreasing the heat load of the cryogenic system and enhancing the overall efficiency of the generator, new structures of torque tube and thermal shields are proposed, and the main parameters of the cryogenic system are determined.