{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/393818"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/393818","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Investigation of High-Temperature Superconducting Trapped Field Magnets in a Superconducting Motor","abstract":"This doctoral research presents a systematic investigation of magnetisation and cross-field demagnetisation in high-temperature superconducting (HTS) trapped field stacks (TFSs) within a partially superconducting machine, employing a finite element method (FEM)-based modelling approach. The key innovations presented in this work are: (1) a systematic methodology to investigate TFS demagnetisation by extracting the airgap cross-fields in a real motor environment; (2) systematic strategies for enhancing magnetisation performance via optimisation of TFS architecture and machine stator; (3) a comprehensive iron loss analysis for magnetisation process optimisation; (4) a systematic evaluation of operational harmonic interactions; and (5) a demagnetisation assessment employing multilayer modelling of HTS TFSs over a large frequency range. Notably, the research reveals the critical influence of high-frequency harmonics on demagnetisation dynamics. This dissertation begins with a thorough review of trapped field magnets (TFMs) for superconducting machines, examining simulation techniques, experimental methods, fabrication processes, applications, and challenges like cross-field demagnetisation. The insights gained from this review informed key design and operational strategies for superconducting motors, enhancing their robustness and reliability. The TFM configuration in this dissertation, utilising TFSs, leverages the distinct advantages of TFSs over trapped field bulks (TFBs) (outlined in section 2.2.1). These characteristics position TFSs as a more viable solution for practical superconducting machine implementation, addressing critical limitations of conventional approaches while maintaining operational reliability. The actual research work commenced with the validation of a superconducting machine model, which coupled the electromagnetic and thermal characteristics of HTS coated conductors (CCs), through experimental results, ensuring the accuracy and reliability of the model. The validated model was then utilised to examine the electro-mechanical performance of the studied HTS machine, employing TFSs as rotor magnets. A novel analytical approach significantly improved simulation efficiency by reducing degrees of freedom while maintaining accuracy. Optimisation strategies were proposed to achieve optimal trapped magnetic fields by pulsed field magnetisation (PFM) in superconducting machines while minimising energy losses. A computational method was devised to determine the optimal combination of layer number and magnetisation current amplitude for achieving the maximum magnetisation field in superconducting machines. Additionally, innovative superconducting machine structures were designed to enhance the magnetisation efficiency of pulsed field magnetisation by optimising several stator parameters, including winding configuration and slotting. Based on the original machine layout, a new concept was developed that produces smoother trapped field waveforms, which can minimise the introduction of harmonics during the magnetisation phase, contributing to improved performance and stability. Subsequently, a detailed loss assessment was performed on the non-superconducting components of the HTS machine during pulsed field magnetisation. This analysis specifically quantified: (1) copper losses in the stator magnetisation windings and (2) iron losses in the core materials across varying pulsed current amplitudes. The research introduces: (1) an innovative linear interpolation technique based on steel grade characteristics for precise iron loss estimation, and (2) two practical motor configurations with corresponding calculation methodologies. These approaches, employing steel grade-based linear interpolation (specifically for M270-35A material), enable accurate iron loss prediction while maintaining computational efficiency. Finally, this study presents a systematic investigation of cross-field demagnetisation effects in HTS TFSs, analysing the influence of critical parameters including field amplitude and frequency. The demagnetisation analysis incorporates cross-field components extracted from the motor airgap during operation, revealing average tangential flux densities of 25 mT (fundamental harmonic) and 1.75 mT (fifth harmonic) acting on the TFSs, for the 462 mT peak value of the magnetic flux density in the air gap. The investigation further characterises magnetisation losses across all constituent layers of the HTS tapes. The trapped field exhibits accelerated demagnetisation when subjected to cross fields surpassing the penetration threshold, with the decay rate and magnetisation losses demonstrating a strong positive correlation to both the frequency and amplitude of the applied cross field. This research establishes a framework for optimising HTS TFSs in superconducting machines, advancing sustainable propulsion aligned with net-zero goals. By integrating theoretical and computational methods, it provides critical tools for developing superconducting machine technology. As energy systems demand higher efficiency, these innovations position HTS TFS machines as viable solutions for high-performance applications, bridging fundamental research with practical engineering implementation.","abstract_html":"This doctoral research presents a systematic investigation of magnetisation and cross-field demagnetisation in high-temperature superconducting (HTS) trapped field stacks (TFSs) within a partially superconducting machine, employing a finite element method (FEM)-based modelling approach. The key innovations presented in this work are: (1) a systematic methodology to investigate TFS demagnetisation by extracting the airgap cross-fields in a real motor environment; (2) systematic strategies for enhancing magnetisation performance via optimisation of TFS architecture and machine stator; (3) a comprehensive iron loss analysis for magnetisation process optimisation; (4) a systematic evaluation of operational harmonic interactions; and (5) a demagnetisation assessment employing multilayer modelling of HTS TFSs over a large frequency range. Notably, the research reveals the critical influence of high-frequency harmonics on demagnetisation dynamics. This dissertation begins with a thorough review of trapped field magnets (TFMs) for superconducting machines, examining simulation techniques, experimental methods, fabrication processes, applications, and challenges like cross-field demagnetisation. The insights gained from this review informed key design and operational strategies for superconducting motors, enhancing their robustness and reliability. The TFM configuration in this dissertation, utilising TFSs, leverages the distinct advantages of TFSs over trapped field bulks (TFBs) (outlined in section 2.2.1). These characteristics position TFSs as a more viable solution for practical superconducting machine implementation, addressing critical limitations of conventional approaches while maintaining operational reliability. The actual research work commenced with the validation of a superconducting machine model, which coupled the electromagnetic and thermal characteristics of HTS coated conductors (CCs), through experimental results, ensuring the accuracy and reliability of the model. The validated model was then utilised to examine the electro-mechanical performance of the studied HTS machine, employing TFSs as rotor magnets. A novel analytical approach significantly improved simulation efficiency by reducing degrees of freedom while maintaining accuracy. Optimisation strategies were proposed to achieve optimal trapped magnetic fields by pulsed field magnetisation (PFM) in superconducting machines while minimising energy losses. A computational method was devised to determine the optimal combination of layer number and magnetisation current amplitude for achieving the maximum magnetisation field in superconducting machines. Additionally, innovative superconducting machine structures were designed to enhance the magnetisation efficiency of pulsed field magnetisation by optimising several stator parameters, including winding configuration and slotting. Based on the original machine layout, a new concept was developed that produces smoother trapped field waveforms, which can minimise the introduction of harmonics during the magnetisation phase, contributing to improved performance and stability. Subsequently, a detailed loss assessment was performed on the non-superconducting components of the HTS machine during pulsed field magnetisation. This analysis specifically quantified: (1) copper losses in the stator magnetisation windings and (2) iron losses in the core materials across varying pulsed current amplitudes. The research introduces: (1) an innovative linear interpolation technique based on steel grade characteristics for precise iron loss estimation, and (2) two practical motor configurations with corresponding calculation methodologies. These approaches, employing steel grade-based linear interpolation (specifically for M270-35A material), enable accurate iron loss prediction while maintaining computational efficiency. Finally, this study presents a systematic investigation of cross-field demagnetisation effects in HTS TFSs, analysing the influence of critical parameters including field amplitude and frequency. The demagnetisation analysis incorporates cross-field components extracted from the motor airgap during operation, revealing average tangential flux densities of 25 mT (fundamental harmonic) and 1.75 mT (fifth harmonic) acting on the TFSs, for the 462 mT peak value of the magnetic flux density in the air gap. The investigation further characterises magnetisation losses across all constituent layers of the HTS tapes. The trapped field exhibits accelerated demagnetisation when subjected to cross fields surpassing the penetration threshold, with the decay rate and magnetisation losses demonstrating a strong positive correlation to both the frequency and amplitude of the applied cross field. This research establishes a framework for optimising HTS TFSs in superconducting machines, advancing sustainable propulsion aligned with net-zero goals. By integrating theoretical and computational methods, it provides critical tools for developing superconducting machine technology. As energy systems demand higher efficiency, these innovations position HTS TFS machines as viable solutions for high-performance applications, bridging fundamental research with practical engineering implementation.","abstract_has_math":false,"creators":["Wang, Qi"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Coombs, Timothy"],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-04-27","date_published":"2025-04-27","updated_at":"2026-07-24T01:33:30Z","subjects":["Applied Superconductivity","High Temperature Superconductor","Superconducting Motor","Trapped Field Magnets"],"languages":["eng"],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/5eaea0c1-2bf9-4cb1-93b9-91ca4b868892/download","https://creativecommons.org/licenses/by/4.0/"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.123988","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Coombs, Timothy"]},{"key":"dc:creator","label":"Author","values":["Wang, Qi"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2025-04-27"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/393818"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Applied Superconductivity","High Temperature Superconductor","Superconducting Motor","Trapped Field Magnets"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/5eaea0c1-2bf9-4cb1-93b9-91ca4b868892/download","https://creativecommons.org/licenses/by/4.0/"]},{"key":"dc:rights.embargodate","label":"Dc Rights Embargodate","values":["2026-12-15"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["embargo"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.123988"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/58de60c2-f074-4550-9fb1-b52d4bdb21e2/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["This doctoral research presents a systematic investigation of magnetisation and cross-field demagnetisation in high-temperature superconducting (HTS) trapped field stacks (TFSs) within a partially superconducting machine, employing a finite element method (FEM)-based modelling approach. The key innovations presented in this work are: (1) a systematic methodology to investigate TFS demagnetisation by extracting the airgap cross-fields in a real motor environment; (2) systematic strategies for enhancing magnetisation performance via optimisation of TFS architecture and machine stator; (3) a comprehensive iron loss analysis for magnetisation process optimisation; (4) a systematic evaluation of operational harmonic interactions; and (5) a demagnetisation assessment employing multilayer modelling of HTS TFSs over a large frequency range. Notably, the research reveals the critical influence of high-frequency harmonics on demagnetisation dynamics. This dissertation begins with a thorough review of trapped field magnets (TFMs) for superconducting machines, examining simulation techniques, experimental methods, fabrication processes, applications, and challenges like cross-field demagnetisation. The insights gained from this review informed key design and operational strategies for superconducting motors, enhancing their robustness and reliability. The TFM configuration in this dissertation, utilising TFSs, leverages the distinct advantages of TFSs over trapped field bulks (TFBs) (outlined in section 2.2.1). These characteristics position TFSs as a more viable solution for practical superconducting machine implementation, addressing critical limitations of conventional approaches while maintaining operational reliability. The actual research work commenced with the validation of a superconducting machine model, which coupled the electromagnetic and thermal characteristics of HTS coated conductors (CCs), through experimental results, ensuring the accuracy and reliability of the model. The validated model was then utilised to examine the electro-mechanical performance of the studied HTS machine, employing TFSs as rotor magnets. A novel analytical approach significantly improved simulation efficiency by reducing degrees of freedom while maintaining accuracy. Optimisation strategies were proposed to achieve optimal trapped magnetic fields by pulsed field magnetisation (PFM) in superconducting machines while minimising energy losses. A computational method was devised to determine the optimal combination of layer number and magnetisation current amplitude for achieving the maximum magnetisation field in superconducting machines. Additionally, innovative superconducting machine structures were designed to enhance the magnetisation efficiency of pulsed field magnetisation by optimising several stator parameters, including winding configuration and slotting. Based on the original machine layout, a new concept was developed that produces smoother trapped field waveforms, which can minimise the introduction of harmonics during the magnetisation phase, contributing to improved performance and stability. Subsequently, a detailed loss assessment was performed on the non-superconducting components of the HTS machine during pulsed field magnetisation. This analysis specifically quantified: (1) copper losses in the stator magnetisation windings and (2) iron losses in the core materials across varying pulsed current amplitudes. The research introduces: (1) an innovative linear interpolation technique based on steel grade characteristics for precise iron loss estimation, and (2) two practical motor configurations with corresponding calculation methodologies. These approaches, employing steel grade-based linear interpolation (specifically for M270-35A material), enable accurate iron loss prediction while maintaining computational efficiency. Finally, this study presents a systematic investigation of cross-field demagnetisation effects in HTS TFSs, analysing the influence of critical parameters including field amplitude and frequency. The demagnetisation analysis incorporates cross-field components extracted from the motor airgap during operation, revealing average tangential flux densities of 25 mT (fundamental harmonic) and 1.75 mT (fifth harmonic) acting on the TFSs, for the 462 mT peak value of the magnetic flux density in the air gap. The investigation further characterises magnetisation losses across all constituent layers of the HTS tapes. The trapped field exhibits accelerated demagnetisation when subjected to cross fields surpassing the penetration threshold, with the decay rate and magnetisation losses demonstrating a strong positive correlation to both the frequency and amplitude of the applied cross field. This research establishes a framework for optimising HTS TFSs in superconducting machines, advancing sustainable propulsion aligned with net-zero goals. By integrating theoretical and computational methods, it provides critical tools for developing superconducting machine technology. As energy systems demand higher efficiency, these innovations position HTS TFS machines as viable solutions for high-performance applications, bridging fundamental research with practical engineering implementation."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["7a94ef7511e8a9aa770ece4bdd4b4249","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Investigation of High-Temperature Superconducting Trapped Field Magnets in a Superconducting Motor"]}]}],"canonical_facts":{"dc:contributor.advisor":["Coombs, Timothy"],"dc:creator":["Wang, Qi"],"dc:date.issued":["2025-04-27"],"dc:description.abstract":["This doctoral research presents a systematic investigation of magnetisation and cross-field demagnetisation in high-temperature superconducting (HTS) trapped field stacks (TFSs) within a partially superconducting machine, employing a finite element method (FEM)-based modelling approach. The key innovations presented in this work are: (1) a systematic methodology to investigate TFS demagnetisation by extracting the airgap cross-fields in a real motor environment; (2) systematic strategies for enhancing magnetisation performance via optimisation of TFS architecture and machine stator; (3) a comprehensive iron loss analysis for magnetisation process optimisation; (4) a systematic evaluation of operational harmonic interactions; and (5) a demagnetisation assessment employing multilayer modelling of HTS TFSs over a large frequency range. Notably, the research reveals the critical influence of high-frequency harmonics on demagnetisation dynamics. This dissertation begins with a thorough review of trapped field magnets (TFMs) for superconducting machines, examining simulation techniques, experimental methods, fabrication processes, applications, and challenges like cross-field demagnetisation. The insights gained from this review informed key design and operational strategies for superconducting motors, enhancing their robustness and reliability. The TFM configuration in this dissertation, utilising TFSs, leverages the distinct advantages of TFSs over trapped field bulks (TFBs) (outlined in section 2.2.1). These characteristics position TFSs as a more viable solution for practical superconducting machine implementation, addressing critical limitations of conventional approaches while maintaining operational reliability. The actual research work commenced with the validation of a superconducting machine model, which coupled the electromagnetic and thermal characteristics of HTS coated conductors (CCs), through experimental results, ensuring the accuracy and reliability of the model. The validated model was then utilised to examine the electro-mechanical performance of the studied HTS machine, employing TFSs as rotor magnets. A novel analytical approach significantly improved simulation efficiency by reducing degrees of freedom while maintaining accuracy. Optimisation strategies were proposed to achieve optimal trapped magnetic fields by pulsed field magnetisation (PFM) in superconducting machines while minimising energy losses. A computational method was devised to determine the optimal combination of layer number and magnetisation current amplitude for achieving the maximum magnetisation field in superconducting machines. Additionally, innovative superconducting machine structures were designed to enhance the magnetisation efficiency of pulsed field magnetisation by optimising several stator parameters, including winding configuration and slotting. Based on the original machine layout, a new concept was developed that produces smoother trapped field waveforms, which can minimise the introduction of harmonics during the magnetisation phase, contributing to improved performance and stability. Subsequently, a detailed loss assessment was performed on the non-superconducting components of the HTS machine during pulsed field magnetisation. This analysis specifically quantified: (1) copper losses in the stator magnetisation windings and (2) iron losses in the core materials across varying pulsed current amplitudes. The research introduces: (1) an innovative linear interpolation technique based on steel grade characteristics for precise iron loss estimation, and (2) two practical motor configurations with corresponding calculation methodologies. These approaches, employing steel grade-based linear interpolation (specifically for M270-35A material), enable accurate iron loss prediction while maintaining computational efficiency. Finally, this study presents a systematic investigation of cross-field demagnetisation effects in HTS TFSs, analysing the influence of critical parameters including field amplitude and frequency. The demagnetisation analysis incorporates cross-field components extracted from the motor airgap during operation, revealing average tangential flux densities of 25 mT (fundamental harmonic) and 1.75 mT (fifth harmonic) acting on the TFSs, for the 462 mT peak value of the magnetic flux density in the air gap. The investigation further characterises magnetisation losses across all constituent layers of the HTS tapes. The trapped field exhibits accelerated demagnetisation when subjected to cross fields surpassing the penetration threshold, with the decay rate and magnetisation losses demonstrating a strong positive correlation to both the frequency and amplitude of the applied cross field. This research establishes a framework for optimising HTS TFSs in superconducting machines, advancing sustainable propulsion aligned with net-zero goals. By integrating theoretical and computational methods, it provides critical tools for developing superconducting machine technology. As energy systems demand higher efficiency, these innovations position HTS TFS machines as viable solutions for high-performance applications, bridging fundamental research with practical engineering implementation."],"dc:format.checksum.md5":["7a94ef7511e8a9aa770ece4bdd4b4249","87eda9de84448d1f82354d60eee3eb5f"],"dc:identifier.doi":["https://doi.org/10.17863/CAM.123988"],"dc:identifier.uri":["https://www.repository.cam.ac.uk/bitstreams/58de60c2-f074-4550-9fb1-b52d4bdb21e2/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/393818"],"dc:rights":["https://www.repository.cam.ac.uk/bitstreams/5eaea0c1-2bf9-4cb1-93b9-91ca4b868892/download","https://creativecommons.org/licenses/by/4.0/"],"dc:rights.embargodate":["2026-12-15"],"dc:rights.embargotype":["embargo"],"dc:subject":["Applied Superconductivity","High Temperature Superconductor","Superconducting Motor","Trapped Field Magnets"],"dc:title":["Investigation of High-Temperature Superconducting Trapped Field Magnets in a Superconducting Motor"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T01:33:30Z"}