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Superconductor technology has recently attracted increasing attention in power-generation- and electrical-propulsion-related domains, as it provides a solution to the limited power density seen by the core component, electrical machines. Superconducting machines, characterized by both high power density and high efficiency, can effectively reduce the size and mass compared to conventional machine designs. This opens the way to large-scale purely electrical applications, e.g., all-electrical aircrafts. The alternating current (AC) loss of superconductors caused by time-varying transport currents or magnetic fields (or both) has impaired the efficiency and reliability of superconducting machines, bringing severe challenges to the cryogenic systems, too. Although much research has been conducted in terms of the qualitative and quantitative analysis of AC loss and its reduction methods, AC loss remains a crucial problem for the design of highly efficient superconducting machines, especially for those operating at high speeds for future aviation. Given that a critical review on the research advancement regarding the AC loss of superconductors has not been reported during the last dozen years, especially combined with electrical machines, this paper aims to clarify its research status and provide a useful reference for researchers working on superconducting machines. The adopted superconducting materials, analytical formulae, modelling methods, measurement approaches, as well as reduction techniques for AC loss of low-temperature superconductors (LTSs) and high-temperature superconductors (HTSs) in both low- and high-frequency fields have been systematically analyzed and summarized. Based on the authors’ previous research on the AC loss characteristics of HTS coated conductors (CCs), stacks, and coils at high frequencies, the challenges for the existing AC loss quantification methods have been elucidated, and multiple suggestions with respect to the AC loss reduction in superconducting machines have been put forward. This article systematically reviews the qualitative and quantitative analysis methods of AC loss as well as its reduction techniques in superconductors applied to electrical machines for the first time. It is believed to help deepen the understanding of AC loss and deliver a helpful guideline for the future development of superconducting machines and applied superconductivity.
Hongye Zhang; Zezhao Wen; Francesco Grilli; Konstantinos Gyftakis; Markus Mueller. Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines. Energies 2021, 14, 2234 .
AMA StyleHongye Zhang, Zezhao Wen, Francesco Grilli, Konstantinos Gyftakis, Markus Mueller. Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines. Energies. 2021; 14 (8):2234.
Chicago/Turabian StyleHongye Zhang; Zezhao Wen; Francesco Grilli; Konstantinos Gyftakis; Markus Mueller. 2021. "Alternating Current Loss of Superconductors Applied to Superconducting Electrical Machines." Energies 14, no. 8: 2234.
Maglev technologies have been extensively studied for modern transport systems; however, their main applications are limited to transportation systems with fixed tracks. On-road vehicles could have a broader outlook if combined with maglev technologies, for which electrodynamic wheels (EDWs) have provided a possible solution. Conventional EDWs are designed based on permanent magnets (PMs), which generate limited thrust and lift forces while having a low power density. In order to enhance the feasibility of EDWs in maglev vehicles, a novel design of EDWs based on high-temperature superconducting (HTS) Halbach array magnets (HAMs) has been proposed in this paper. The suggested design is made of the second generation (2G) superconducting coils, which have been modeled with the A -formulation and T -formulation based finite element methods. Simulation results show that the proposed HTS HAM EDW can generate higher thrust and lift forces, improve the magnetic flux density distribution in the airgap, and greatly reduce the weight of the magnets compared with the conventional design. This paper provides a possibility for future on-road maglev vehicles.
Hongye Zhang; Kevin Kails; Philip Machura; Markus Mueller. Conceptual Design of Electrodynamic Wheels Based on HTS Halbach Array Magnets. IEEE Transactions on Applied Superconductivity 2021, 31, 1 -6.
AMA StyleHongye Zhang, Kevin Kails, Philip Machura, Markus Mueller. Conceptual Design of Electrodynamic Wheels Based on HTS Halbach Array Magnets. IEEE Transactions on Applied Superconductivity. 2021; 31 (5):1-6.
Chicago/Turabian StyleHongye Zhang; Kevin Kails; Philip Machura; Markus Mueller. 2021. "Conceptual Design of Electrodynamic Wheels Based on HTS Halbach Array Magnets." IEEE Transactions on Applied Superconductivity 31, no. 5: 1-6.
Air-cored electrical machines have attracted increasing attention in applications related to aircraft and wind power because they can eliminate core losses and decrease the total mass. However, the limited magnetic flux in air-cored machines has restricted their power level. In order to improve the power density and efficiency while further reducing the weight of air-cored electrical machines, a novel field winding topology composed of high temperature superconducting (HTS) Halbach Array magnets (HAM) has been proposed in this paper. C-GEN is an innovative multi-stage air-cored generator technology with permanent magnets, which has been demonstrated at laboratory scale. Taking a 1 MW C-GEN generator prototype as the example machine, an H -formulation founded HTSHAM model has been built in COMSOL Multiphysics with the homogenization method. Simulation results show that the proposed HTSHAM C-GEN generator can achieve a power density more than 4 times higher than the conventional design with permanent magnets (PM), with a reduced magnet weight of around half of the previous prototype. The proposed HTSHAM represents a generic approach for the design of fully air-cored superconducting synchronous machines, eliminating heavy ferromagnetic material, and thus provides a useful reference for the design of low-weight air-cored electrical machines with a high power density.
Hongye Zhang; Quan Li; Okechukwu Ubani; Markus Mueller. High Temperature Superconducting Halbach Array Topology for Air-cored Electrical Machines. Journal of Physics: Conference Series 2020, 1559, 012140 .
AMA StyleHongye Zhang, Quan Li, Okechukwu Ubani, Markus Mueller. High Temperature Superconducting Halbach Array Topology for Air-cored Electrical Machines. Journal of Physics: Conference Series. 2020; 1559 (1):012140.
Chicago/Turabian StyleHongye Zhang; Quan Li; Okechukwu Ubani; Markus Mueller. 2020. "High Temperature Superconducting Halbach Array Topology for Air-cored Electrical Machines." Journal of Physics: Conference Series 1559, no. 1: 012140.
Dynamic resistance is essential to evaluate the performance of high temperature superconducting (HTS) coated conductors (CC), especially when applied in synchronous electric machines, and HTS flux pumps. The analytical expression of dynamic resistance has been proposed and verified in many cases, and it appears that dynamic resistance, Rdyn, is in a linear correlation with transport current, It, and the amplitude of external AC magnetic field, Bext. However, some experimental data has shown that, the linearity of Rdyn(It) and Rdyn(Bext) curves only exists within a certain range. To quantitatively describe this interval, the lower demarcation current, Idl, the upper demarcation current, Idu, and the corner field, Bcor, have been defined in this paper, with explicit formulas. The proposed demarcation currents and corner field used to characterize the non-linearity of dynamic resistance have been validated by simulation and experimental measurements. This paper further adds upon the existing knowledge regarding the interaction of dynamic resistance with transport current and magnetic field, which is particularly significant for accurate loss controlling in HTS magnets, rotating machines, and flux pumps.
Hongye Zhang; Chuantong Hao; Ying Xin; Markus Mueller. Demarcation Currents and Corner Field for Dynamic Resistance of HTS-Coated Conductors. IEEE Transactions on Applied Superconductivity 2020, 30, 1 -5.
AMA StyleHongye Zhang, Chuantong Hao, Ying Xin, Markus Mueller. Demarcation Currents and Corner Field for Dynamic Resistance of HTS-Coated Conductors. IEEE Transactions on Applied Superconductivity. 2020; 30 (8):1-5.
Chicago/Turabian StyleHongye Zhang; Chuantong Hao; Ying Xin; Markus Mueller. 2020. "Demarcation Currents and Corner Field for Dynamic Resistance of HTS-Coated Conductors." IEEE Transactions on Applied Superconductivity 30, no. 8: 1-5.
Stackable power generators enable very compact electric machines with high power density. How to identify an effective way of stacking is necessary and requires new knowledge for future guidance. In this study, both possibilities of stacking modules concentrically and axially are explored and compared. An axial flux generator based on the existing double claw pole design is used as a case study. The claw pole generator, which is modular and stackable, significantly benefits on-site installation due to its flexible small modules that can be easily transported. This is particularly important to the installation of offshore wind turbines. Superconducting field windings are applied instead of copper in such power generators, which greatly increases their power density. In order to further increase their power density and reduce mass, the authors improved the modularity of 5 MW generators and stacked them in both ways. Results show that the power density versus mass as well as volume can be improved through stacking the modules both concentrically and axially, while the former approach is much more effective. Stacking two modules of 5 MW concentrically results in a 12.1 MW power generator with a more compact structure and higher power density than the original 10 MW generator.
Kevin Kails; Quan Li; Markus Mueller. Modular and stackable power generators for efficient renewable power generation. IET Renewable Power Generation 2019, 13, 2774 -2782.
AMA StyleKevin Kails, Quan Li, Markus Mueller. Modular and stackable power generators for efficient renewable power generation. IET Renewable Power Generation. 2019; 13 (15):2774-2782.
Chicago/Turabian StyleKevin Kails; Quan Li; Markus Mueller. 2019. "Modular and stackable power generators for efficient renewable power generation." IET Renewable Power Generation 13, no. 15: 2774-2782.
Air-cored machines offer benefits in terms the elimination of magnetic attraction forces between stator and rotor. With no iron in the stator there is not a good thermal conduction path for heat generated by Joule losses in the stator winding. Results from both models and experimental tests are provided in this paper to investigate different methods of cooling air-cored windings, including natural air-cooling, direct liquid cooling and the use of heat pipes.
Markus A. Mueller; Joseph Burchell; Yew Chuan Chong; Ozan Keysan; Alasdair McDonald; Mike Galbraith; Estanislao Juan Pablo Echenique Subiabre. Improving the Thermal Performance of Rotary and Linear Air-Cored Permanent Magnet Machines for Direct Drive Wind and Wave Energy Applications. IEEE Transactions on Energy Conversion 2018, 34, 773 -781.
AMA StyleMarkus A. Mueller, Joseph Burchell, Yew Chuan Chong, Ozan Keysan, Alasdair McDonald, Mike Galbraith, Estanislao Juan Pablo Echenique Subiabre. Improving the Thermal Performance of Rotary and Linear Air-Cored Permanent Magnet Machines for Direct Drive Wind and Wave Energy Applications. IEEE Transactions on Energy Conversion. 2018; 34 (2):773-781.
Chicago/Turabian StyleMarkus A. Mueller; Joseph Burchell; Yew Chuan Chong; Ozan Keysan; Alasdair McDonald; Mike Galbraith; Estanislao Juan Pablo Echenique Subiabre. 2018. "Improving the Thermal Performance of Rotary and Linear Air-Cored Permanent Magnet Machines for Direct Drive Wind and Wave Energy Applications." IEEE Transactions on Energy Conversion 34, no. 2: 773-781.
This paper discusses the development of linear Vernier Hybrid Machines for use in wave energy converters. A number of topology options are explored to reduce magnet usage and improve performance for use as a linear generator. Consequent pole, V-shape and Halbach arrays are designed for a target 25kW specification. A discussion of overall cost of energy produced is used to justify using efficiency and power factor to asses fixed magnet mass topology variants. A power factor improvement from 0.38 to 0.72 is presented. Physical integration of the electrical machine into wave energy converters is considered including flooded experimental results of thermal behavior and polymer bearing wear.
Nick J. Baker; Mohammad A. H. Raihan; Ahmed A. Almoraya; Joseph Burchell; Markus A. Mueller. Evaluating Alternative Linear Vernier Hybrid Machine Topologies for Integration Into Wave Energy Converters. IEEE Transactions on Energy Conversion 2018, 33, 2007 -2017.
AMA StyleNick J. Baker, Mohammad A. H. Raihan, Ahmed A. Almoraya, Joseph Burchell, Markus A. Mueller. Evaluating Alternative Linear Vernier Hybrid Machine Topologies for Integration Into Wave Energy Converters. IEEE Transactions on Energy Conversion. 2018; 33 (4):2007-2017.
Chicago/Turabian StyleNick J. Baker; Mohammad A. H. Raihan; Ahmed A. Almoraya; Joseph Burchell; Markus A. Mueller. 2018. "Evaluating Alternative Linear Vernier Hybrid Machine Topologies for Integration Into Wave Energy Converters." IEEE Transactions on Energy Conversion 33, no. 4: 2007-2017.
Ben McGilton; Richard Crozier; Alasdair McDonald; Markus Mueller. Review of magnetic gear technologies and their applications in marine energy. IET Renewable Power Generation 2017, 12, 174 -181.
AMA StyleBen McGilton, Richard Crozier, Alasdair McDonald, Markus Mueller. Review of magnetic gear technologies and their applications in marine energy. IET Renewable Power Generation. 2017; 12 (2):174-181.
Chicago/Turabian StyleBen McGilton; Richard Crozier; Alasdair McDonald; Markus Mueller. 2017. "Review of magnetic gear technologies and their applications in marine energy." IET Renewable Power Generation 12, no. 2: 174-181.
To optimise a tidal energy conversion system, the operation, maintenance and power generation aspects have to be taken into account. As a result the key focus of this study is to propose and investigate an alternative method of implementing a tidal energy conversion system using a pitch-regulated turbine and a variable-speed squirrel cage induction generator with long distance converters. The generator power output can be optimised by utilising variable-speed control strategies allowing the system to operate at maximum power coefficient while availability can be increased by reducing the components installed offshore by using long three-phase cables between the generator and onshore voltage source converters. The tidal current energy conversion system is investigated by developing a full resource-to-grid model in MATLAB/SIMULINK and by performing system analysis regarding the effects of harmonics in the long subsea cables. Simulation results show that optimised filter design and the choice of suitable operating frequency for the generator controller can minimise the overvoltages associated with the harmonics and the reflecting voltage waves in the cables.
Marios Charilaos Sousounis; Jonathan K.H. Shek; Markus A. Mueller. Modelling, control and frequency domain analysis of a tidal current conversion system with onshore converters. IET Renewable Power Generation 2016, 10, 158 -165.
AMA StyleMarios Charilaos Sousounis, Jonathan K.H. Shek, Markus A. Mueller. Modelling, control and frequency domain analysis of a tidal current conversion system with onshore converters. IET Renewable Power Generation. 2016; 10 (2):158-165.
Chicago/Turabian StyleMarios Charilaos Sousounis; Jonathan K.H. Shek; Markus A. Mueller. 2016. "Modelling, control and frequency domain analysis of a tidal current conversion system with onshore converters." IET Renewable Power Generation 10, no. 2: 158-165.
More effective energy production requires a greater penetration of storage technologies. This paper takes a looks at and compares the landscape of energy storage devices. Solutions across four categories of storage, namely: mechanical, chemical, electromagnetic and thermal storage are compared on the basis of energy/power density, specific energy/power, efficiency, lifespan, cycle life, self-discharge rates, capital energy/power costs, scale, application, technical maturity as well as environmental impact. It’s noted that virtually every storage technology is seeing improvements. This paper provides an overview of some of the problems with existing storage systems and identifies some key technologies that hold promise.
Siraj Sabihuddin; Aristides E. Kiprakis; Markus Mueller. A Numerical and Graphical Review of Energy Storage Technologies. Energies 2014, 8, 172 -216.
AMA StyleSiraj Sabihuddin, Aristides E. Kiprakis, Markus Mueller. A Numerical and Graphical Review of Energy Storage Technologies. Energies. 2014; 8 (1):172-216.
Chicago/Turabian StyleSiraj Sabihuddin; Aristides E. Kiprakis; Markus Mueller. 2014. "A Numerical and Graphical Review of Energy Storage Technologies." Energies 8, no. 1: 172-216.
Ozan Keysan; Markus A. Mueller. A Transverse Flux High-Temperature Superconducting Generator Topology for Large Direct Drive Wind Turbines. Physics Procedia 2012, 36, 759 -764.
AMA StyleOzan Keysan, Markus A. Mueller. A Transverse Flux High-Temperature Superconducting Generator Topology for Large Direct Drive Wind Turbines. Physics Procedia. 2012; 36 ():759-764.
Chicago/Turabian StyleOzan Keysan; Markus A. Mueller. 2012. "A Transverse Flux High-Temperature Superconducting Generator Topology for Large Direct Drive Wind Turbines." Physics Procedia 36, no. : 759-764.
This paper describes some of the key challenges to be met in the development of marine renewable energy technology, from its present prototype form to being a widely deployed contributor to future energy supply. Since 2000, a number of large-scale wave and tidal current prototypes have been demonstrated around the world, but marine renewable energy technology is still 10–15 years behind that of wind energy. UK-based developers are leading the way, with Pelamis from Pelamis Wave Power demonstrated in the open sea, generating electricity into the UK network and securing orders from Portugal. However, having started later, the developing technology can make use of more advanced science and engineering, and it is therefore reasonable to expect rapid progress. Although progress is underway through deployment and testing, there are still key scientific challenges to be addressed in areas including resource assessment and predictability, engineering design and manufacturability, installation, operation and maintenance, survivability, reliability and cost reduction. The research priorities required to meet these challenges are suggested in this paper and have been drawn from current roadmaps and vision documents, including more recent consultations within the community by the UK Energy Research Centre Marine Research Network. Many scientific advances are required to meet these challenges, and their likelihood is explored based on current and future capabilities.
Markus Mueller; Robin Wallace. Enabling science and technology for marine renewable energy. Energy Policy 2008, 36, 4376 -4382.
AMA StyleMarkus Mueller, Robin Wallace. Enabling science and technology for marine renewable energy. Energy Policy. 2008; 36 (12):4376-4382.
Chicago/Turabian StyleMarkus Mueller; Robin Wallace. 2008. "Enabling science and technology for marine renewable energy." Energy Policy 36, no. 12: 4376-4382.
Avernier hybrid machine has been developed for use as a linear generator in awave energy converter. Accurate predictions for power capture require testing this machine in a nonsinusoidal manner. A dynamic model capable of predicting the machine’s behavior for this kind of mechanical excitation is presented. Simple equivalent circuit models have been found to be unsuitable for these machines and a flux-linkage map approach is instead used. Experimental results are used to verify this approach and the functioning of a unity power factor controller.
M. A. Mueller; J. Xiang; N. J. Baker; P.R.M. Brooking. DYNAMIC MODELING OF A LINEAR VERNIER HYBRID PERMANENT MAGNET MACHINE COUPLED TO A WAVE ENERGY EMULATOR TEST RIG. Recent Developments of Electrical Drives 2007, 39 -49.
AMA StyleM. A. Mueller, J. Xiang, N. J. Baker, P.R.M. Brooking. DYNAMIC MODELING OF A LINEAR VERNIER HYBRID PERMANENT MAGNET MACHINE COUPLED TO A WAVE ENERGY EMULATOR TEST RIG. Recent Developments of Electrical Drives. 2007; ():39-49.
Chicago/Turabian StyleM. A. Mueller; J. Xiang; N. J. Baker; P.R.M. Brooking. 2007. "DYNAMIC MODELING OF A LINEAR VERNIER HYBRID PERMANENT MAGNET MACHINE COUPLED TO A WAVE ENERGY EMULATOR TEST RIG." Recent Developments of Electrical Drives , no. : 39-49.