High Temperature Superconducting Motor Research Articles

Thermal quench modeling of REBCO racetrack coils under either alternating current or short-circuit voltage

Abstract Racetrack coils in REBCO High-Temperature Superconductor (HTS) motors help to increase the power-over-weight ratio by raising the magnetic flux density and output power. Nevertheless, HTS motors face thermal quench due to self-heating effects when subjected to alternating or short-circuit onset DC voltage. Additionally, thermal events have been observed due to screening currents when motors operate at high frequencies. Therefore, for the safe operation of HTS motors, quench research is crucial. To accurately simulate and analyze quench events in different scenarios, it is imperative to employ fast and precise software to numerically model the electrothermal behavior in racetrack coils. Our contribution involves the development of a novel and efficient model implemented in C++ that takes screening currents into account. This model is designed to conduct coupled electromagnetic and electrothermal analyses, utilizing variational methods. Specifically, the model incorporates both Minimum Electro-Magnetic Entropy Production and the Finite Difference Method. In this article, we explore the phenomenon of temperature rise within a racetrack coil subjected to either alternating or DC voltages of magnitudes ranging from 0.1 V to 1000 V. The study encompasses conditions of adiabatic operation and heat exchange with liquid nitrogen (LN2). Among other results, we found that in moderate DC voltages like 10 V, non-uniformity in the AC loss causes highly localized quench at the central turns. Then, screening currents play a key role also for DC voltages. The developed model exhibits the potential to comprehensively and swiftly analyze the electromagnetic and electrothermal characteristics of real-world superconducting applications, including high-field rotating machines, such as motors for aviation.

Multi-Objective Optimization Design of 40 MW High-Temperature Superconducting Motor

Abstract To reduce the length of the superconducting wire of the superconducting motor, the no-load back EMF E and the magnetic field component perpendicular to the wire B⊥ were selected as the optimization goals. Therefore, a multi-objective optimization method based on the Response Surface Method (RSM) and Genetic Algorithm (GA) was proposed by taking a high-temperature superconducting motor (HTSM) with a rated power of 40 MW as the research object. Firstly, the overall structure, mathematical model, and output characteristics of HTSM were introduced. Secondly, the sample points required for constructing the RSM equation were obtained by Finite Element Analysis (FEA), and the multi-objective optimization of the RSM equations was performed by applying GA to obtain the Pareto optimal frontier. Finally, the calculated optimal design was simulated and verified. Compared with the initial design, the E of the optimized HTSM was increased by 4.47%, and the B⊥ was reduced by 4.83%. Based on the motor parameters obtained by multi-objective optimization, the final optimized design of HTSM was obtained. The length of the superconducting wire used in the motor has been reduced by 10.2%, which greatly reduces the cost.

Liquid hydrogen storage and transfer-control system for integrated zero emission aviation (IZEA)

The growth in the aviation sector has highlighted the need to decrease carbon emissions, a significant factor in climate change. Hydrogen is a potential alternative clean fuel due to its high energy density. As a collaborative effort in developing integrated zero emission aviation (IZEA, a NASA ULI), we present the design concept for a liquid hydrogen storage system for short-range aircraft with a gravimetric index greater than 0.6. Our design leverages the cryogenic cooling power of liquid hydrogen to support the temperature and heat loads of various power system components, such as the high-temperature superconducting (HTS) generator, HTS motor, DC power distribution cable network, and power electronic converters. By controlling the pressure in the storage tank, we demonstrate that it is feasible to deliver the desired mass flow rate of hydrogen while effectively cooling the power system components using practical heat exchangers. Also, since heat exchangers are an integral part of our hydrogen storage and flow system, their design also impacts the overall system storage density. The entire system is designed considering the space and weight factors of an aircraft. This work represents a significant advancement towards developing the complete IZEA thermal management system for a given airplane and flight profile.

Optimization Study of Cooling Channel for the Oil Cooling Air Gap Armature in a High-Temperature Superconducting Motor

With the continuous advancement of science and technology, the application of high-temperature superconductivity has developed rapidly. The high-temperature superconducting (HTS) motor replacing the copper coil in the traditional motor with HTS winding is increasingly used in power equipment, and the effective thermal management of HTS winding is vital in ensuring the life and effective operation of the HTS motor. In this study, five enhancement structures of indirect oil cooling channels were designed to improve the heat dissipation capacity of the HTS motor winding, and the enhancement effects of the different structures were comprehensively evaluated through numerical simulation using Fluent software 2022R1. The best enhancement structure was selected through structural optimization. The results showed that the Nusselt number of the gap-type enhanced structure was higher than that of the V- and staggered-type structures at the same flow velocity and 68% higher than that of the bare pipe. At the same inlet flow velocity and with a pressure drop limit of 30 kPa, the performance evaluation criterion value of the gap-type structure was 39% and 63% higher than that of the staggered- and V-type structures, respectively. The gap type is the optimal enhancement structure and can effectively improve the heat dissipation of the HTS winding coil.

Numerical analysis of 40 MW HTS motor electromagnetic characteristics for ship electric propulsion

In recent years, with the development of ship electric propulsion system, High Temperature Superconducting (HTS) motors have gained attention as a promising potential resolution due to their high-power density and the progression of cryogenic refrigeration technology. We present an electromagnetic characteristics numerical analysis of 40 MW, 120 rpm, HTS synchronous motor which is a semi-superconducting motor: in fact, it has a superconducting rotor composed of YBCO material and a conventional stator. Combining electric resistivity variation of rotor copper shielding sleeve in low temperature environment and YBCO coil critical current, the electromagnetic behavior of the 40 MW HTS synchronous motor is analyzed with non-ferromagnetic stator support structure. To assess the effects of varying stator winding currents and thickness on eddy current losses of the copper shielding sleeve, calculations were done, and a preliminary discussion was initiated. This study has certain reference significance for electromagnetic design and optimization of multi-ten MW HTS motors, especially used in ship electric propulsion system.

Analysis of the Experimental Test Results of Laboratory-Scale HTS DC Motor for High-Torque Electric Propulsion

A laboratory-scale direct current (DC) rotating machine with a high-temperature superconducting (HTS) magnets was conceptually designed to obtain 500 W output power under a liquid nitrogen cooling method to verify the operation characteristics of the HTS DC motor. The experimental test results of the HTS motor for high-torque electric propulsion are analyzed and presented in this paper. The two HTS magnets were fabricated and assembled using a dynamo system to demonstrate the operation. The excitation current for the two HTS magnets connected in series was kept within 0–40 A using the DC power supplier. The rotational speed of the motor could be kept at 100–600 rpm, and the torque was measured during real-time operation. These test results can be used to design a large HTS DC rotating machine for an electric propulsion system.

Influence of Interturn Contact Stress on the Quench Behavior of Insulated YBCO Pancake Magnets: A Study Based on Numerical Simulations

Insulated high temperature superconducting (HTS) magnets are still widely used in low field applications, such as HTS motors and generators. In this paper, a two-dimensional/three-dimensional (2D/3D) mixed electrothermal model and a homogeneous 3D electrothermal model are employed to study the influence of inter-turn contact stress on the minimum quench energy (MQE), longitudinal and transverse normal zone propagation velocity (NZPV) of insulated YBCO magnets for the temperature range 30 K – 60 K. This temperature range is of interest usually in applications, such as HTS motors, generators and transformers, because it allows the use of low cost cooling system. It is found that MQE increases significantly with increasing inter-turn contact stress. The inter-turn contact stress has small influence on the longitudinal NZPV of insulated YBCO pancake magnet. However, the transverse NZPV rises significantly with the increase of inter-turn contact stress. The transverse NZPV is nearly proportional to the inter-turn contact stress. The 3D homogeneous model gives results that are in agreement with those of 2D/3D mixed model, especially for the temperature range 45 K – 60 K; however, the MQE and transverse NZPV given by the two models are different for the temperature range 30 K – 45 K. That means for insulated HTS YBCO pancake magnets operating at the temperature range 45 K – 60 K, the 3D homogeneous electro-thermal model can be a good replacement of the 2D/3D mixed model to study the quench behavior, which can achieve better computational efficiency without significant loss of accuracy.

Design and Characteristic Analysis of an Axial Flux High-Temperature Superconducting Motor for Aircraft Propulsion.

In line with global environmental regulations, the demand for eco-friendly and highly efficient aircraft propulsion systems is increasing. The combination of axial flux motors and superconductors could be a key technology used to address these needs. In this paper, an axial flux high temperature superconducting (HTS) motor for aircraft propulsion was designed and its characteristics were analyzed. A 2G HTS wire with high magnetic flux characteristic was used for the field winding of the 120 kW axial flux HTS motor, and the rotational speed and rated voltage of the motor were 2000 rpm and 220 V, respectively. The axial flux HTS motor implements a revolving armature type for solid cooling of the HTS field coil. The electromagnetic and thermal features of the motor were analyzed and designed utilizing a 3D finite element method program. The HTS coil was maintained at the target temperature by effectively designing the current lead and cooling system to minimize heat loss. These results can be effectively used in the design of propulsion systems for large commercial aircraft in the future as well as for the design of small aircraft with less than 4 seats.

Operational characteristics of active rotating-type contactless superconducting field exciter for high-temperature superconducting synchronous machines

The operational characteristics of a contactless superconducting field exciter (CSFE) for operating rare-earth barium copper oxide (REBCO) field windings in high-temperature superconducting (HTS) synchronous machines are investigated, and its performance is evaluated. The CSFE based on permanent magnets (PMs) is a promising candidate as a direct-current power supply for energizing superconducting coils in a noncontact manner, which can enhance the thermal stability, system efficiency, and operational reliability for superconducting applications by significantly reducing the thermal loads of cryogenic cooling systems. However, the limited or passive control performances in our previous demonstration of a 1-kW-class HTS synchronous generator, which depend only on the rotational speed of the HTS synchronous machine, make it difficult to control the field winding during the operation of the HTS synchronous machine. Therefore, in this study, we develop an improved CSFE that is operated independently using active rotating-type PMs to improve the controllability of the field winding operated by the CSFE. Thus, an active rotating-type CSFE is developed to excite and control a 15-kW-class HTS motor, and no-insulation REBCO field magnets are fabricated to utilize the charging loads. Through hardware implementations, we experimentally analyze the operational characteristics of contactless excitation in various operation modes of the HTS synchronous machine, such as initial field excitation at rotor stop, current increase/decrease control, current holding control (i.e., permanent current control), and current control corresponding to the rotation speed and direction of the rotor. The current to the four-pole REBCO field winding is charged to 143.74 A in a noncontact manner, which is 2.87 times the rated field current and close to the critical currents of the REBCO field windings. The qualitative effects of the new function on the active control of noncontact charging current are experimentally verified, and these results can facilitate the application of CSFEs in electric propulsion systems using superconducting motors.

Design and Analysis of Cryogenic Cooling System for Electric Propulsion System Using Liquid Hydrogen

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.

Investigation on Time-Varying Behavior of NI HTS Field Coil for Synchronous Motors Considering Armature Reaction and Slotting Effect

This paper presents calculation results of time-varying behavior of no-insulation (NI) high temperature superconductor (HTS) field coil for synchronous motor considering armature reaction and slotting effect. We selected four NI HTS motor models having different stator topologies for confirmation of armature reaction and slotting effect. Also, before NI behavior analysis, we proposed a wound field synchronous motor (WFSM) dq-equivalent circuit which can be considered as a circuit model of insulated (INS) HTS motor. The circuit model used in this paper contains parameters varying with the position of rotor and dq-axes cross-coupling inductance for describing the armature reaction and slotting effect of practical motor. Next, to investigate time-varying behavior of NI field coil during steady-state operation, simulations of a new circuit model combining proposed dq-equivalent circuit and NI lumped circuit were implemented. Turn to turn radial leak current values of selected models were calculated at different armature current density. Also, torque ripple values of the NI and the INS case were obtained by circuit simulations. It can be confirmed that peak to peak radial current occurs by largest value at the topology having the greatest flux linkage harmonics and torque ripple value of NI motor is smaller than that of INS HTS motor.

Design, Performance Analysis, and Testing of Composite Components for the Oil-Cooling Air-Core Stator of a High Temperature Superconducting Motor

To form the stator slots and isolate the stator and rotor, composite components for the oil-cooling air-core stator of a high temperature superconducting motor (HTSM) were designed based on a process that could be summarized as follows. First, the computational fluid dynamics analysis of the oil-cooling air-core stator was conducted. From the results, the load of temperature and oil pressure that apply on the composite cylinder were chosen to be 50 °C and 0.1 MPa, respectively. Second, the structure of the composite components was designed according to the forming technology, and the performance of that was obtained from the finite element method. The results show that the composite teeth were chosen to be a combination of GFRP block and 1Cr18Ni9Ti sheet. And the stresses of the composite cylinder with the thickness of 11 mm in all directions were lower and without buckling at 0.1 MPa. Third, the full-scale composite cylinder was designed and manufactured, and a full-scale simplified performance test platform was also developed to verify the strength of the cylinder. The test results show that the maximum strain of measuring point on the cylinder under 0.1 MPa is 325.1 με, which meets the design requirements of the HTSM.

Design and test results of a novel quench protection circuit for a HTS ship propulsion motor

This paper describes a novel configuration of a quench protection circuit for a high-temperature superconducting (HTS) ship propulsion motor that can protect the HTS coils from an unexpected outage in its cryogenic cooling system. The quench protection circuit consists of conductor parts placed adjacent to the HTS coils and dump resistors and diodes placed in the cryogenic-temperature and normal-temperature areas, respectively. The conductor parts are shaped and arranged such that the magnetic coupling with the HTS coil is extremely large. Thereby, the current of the HTS coils can be instantaneously attenuated immediately after the quench protection is activated. With this configuration, the electromagnetic energy of the HTS coils can be absorbed in the dispersed parts. This can make the dump resistors smaller and make it easier to install them on a HTS ship propulsion motor. By analysing the equivalent electric circuit model of the protection circuit, we derived the conditions under which instantaneous current attenuation of the HTS coil occurs. In accordance with the conditions, we have fabricated a quench protection circuit that protects one HTS field pole of the 3 MW HTS motor developed by Kawasaki Heavy Industries. The fabricated circuit was empirically evaluated and proved to be highly effective in quench protection. The present quench protection circuit technology contributes to the practical application of HTS ship propulsion motors.

Investigation on Key Parameters of NI HTS Field Coils for High Power Density Synchronous Motors

As global environment regulations are gradually strengthened, active research has been conducted on electric propulsion applications. High power density is one of the major research interests, as well as a machine's efficiency for a high-performance propulsion system. Among various electric propulsion technologies under development, a motor incorporating the no-insulation (NI) high-temperature superconducting (HTS) winding has the advantages of high current density and robustness to external disturbances, which are suitable for high specific power. However, still, there is little research on the motor with NI HTS coil. Therefore, as basic research, we investigated the potential application of the NI HTS motor, then derived required machine parameters and NI HTS coil designs in this paper. For that, first, basic parameters of the existing propulsion motors were investigated, then the target application and performance of the NI HTS motor were determined. Based on the target performance, conceptual designs of a motor with NI HTS coil were obtained by changing key design parameters including rated power, main dimensions, operating temperature, and width of air-gap. Calculated parameters were numerically compared, and expected design requirements and challenges were suggested.

Improvement of trapped magnetic field in GdBCO by waveform control pulse magnetization at 70 K

We attempted to trap a strong magnetic field with a single pulsed magnetic field by applying waveform control pulse magnetization (WCPM) method to a high-temperature superconductor (HTS) bulk sandwiched between two vortex-type copper coils at less than 77 K. The GM cryocooler conductively cooled the GdBCO bulk to 70 K in an arrangement similar to the internal structure of our axial gap type HTS motor. The HTS bulk showed no flux jump, while the duty ratio of WCPM was small. When we increased the duty ratio, we found a flux jump without looking at any prior signs and the trapped magnetic flux density increased twice. Hence we attempted a negative feedback WCPM with the control target at the highest trapped magnetic flux density while no flux jump was found. After trial and error of control conditions, the HTS bulk sample trapped a maximum magnetic flux density of 1.79 T by a single pulse magnetic field. If the WCPM technique is used, a single pulse magnetic field will cause the HTS bulk to obtain a higher trapped field at lower temperatures.

Design and Test of a High-Speed Double-Winding High Temperature Superconducting Synchronous Motor

The current carrying ability of the high temperature superconducting (HTS) material would be seriously influenced by the additional complex magnetic field. Because of this effect, the HTS material cannot be adapted in the field of high speed motors that work with high frequency current and strong magnetic field density. Therefore, this paper presents a novel HTS high speed motor system with high efficiency, high power density and high speed that could be adopted in the field of flywheel energy storage and high efficiency propulsion system. The one armature winding of the novel HTS high speed motor system is the superconducting coils, and the other armature winding is copper winding. Under this configuration, the motor with two armature windings is the doubly-fed motor. The two kinds of windings should operate in synchronous state. In this paper, a 2kW, 12000r/min high speed flywheel energy storage motor is designed. Surface magnetic field distribution of the superconducting winding and the characteristic of this type motor are detailed analyzed based on the current carrying ability of the HTS material. The new configuration of our novel HTS motor broaden the application of HTS materials in various electrical fields.

Research on AC losses of racetrack superconducting coils applied to high-temperature superconducting motors

Aiming to address the computational difficulties caused by the large width ratio of superconducting tapes, especially in calculating the AC losses of 3D superconducting coils, this paper proposes to study the AC loss laws of a 3D model of racetrack superconducting coil using the T–A equation group model. Firstly, the critical current of the superconducting coil is estimated based on the structure of the coil and the technical parameters of superconducting materials used in high-temperature superconducting (HTS) motors. The transmission AC losses of the superconducting coil under different n values, different transmission currents, different frequencies and different coil structure sizes are studied using T–A equations. Finally, the critical current test system and AC loss test system for HTS tapes and coils are set up. The critical current test and AC loss test for HTS tapes and coils are carried out, and the results are compared with those calculated by finite element method. The test results show the reliability of the T–A mathematical model, which can be used as a pre-valuation in engineering applications.

Design and Study of a 2G HTS Synchronous Motor With Brushless HTS Flux Pump Exciters

A high temperature superconducting (HTS) synchronous motor with brushless HTS flux pump exciters was designed and is under construction. This HTS synchronous motor is composed of copper armature windings, HTS field windings, HTS flux pump exciters, vacuum chamber, rotary gas seal, etc. The double racetrack-type HTS field coils are wound with second-generation (2G) YBCO tapes and cooled directly by the cold heads. The designed operation temperature is about 30 K. An HTS flux pump was designed to be used as DC power supply to inject large currents into the HTS field coils, which eliminates the slip ring in the motor and avoids thermal load from current leads. The novel design of multiple sources enables us to control the excitation current of the HTS field winding for each pole separately and to prevent all the series field coils from stopping at the same time due to the quench of one coil. To describe the performance characteristics of the HTS motor, an electromagnetic design was carried out with 2-D finite-element method models. Finally, the total losses of HTS synchronous motor are calculated. The next step is to manufacture and install the HTS exciters, HTS field windings, etc. into the HTS synchronous motor.

A Novel Hybrid Magnet Made of HTS Tape Stacks and Permanent Magnets for Motor Applications

High-temperature superconducting (HTS) tape stacks could be used in motors as a substitute for permanent magnets (PMs) to improve the power density. However, the magnetization difficulty and safety concern limit its wider application. A novel hybrid magnet made of HTS tape stacks and PMs is proposed in this paper and investigated in experimental and numerical modeling methods. A hybrid magnet sample is manufactured and tested using pulsed field magnetization (PFM) at 77.3 K. Then, a 3-D electromagnetic-thermal coupled model is built and verified to simulate the field performance at lower temperatures. After the optimization process of the thickness ratio, an optimal 5-mm hybrid magnet of 0.5-mm tape stack +4.5 mm PM is obtained. Compared with the PM, the optimal hybrid magnet could enhance the magnetic field by 114%. Compared with the pure tape stack of the same size, the hybrid magnet could be magnetized with relatively small pulsed field, could reduce the consumption of the HTS tapes, and could enhance the operation safety especially encountering a cooling system failure. The results offer a novel perspective to introduce the HTS material into the conventional motor applications and provide a possible reference to the future study of HTS motors.

Rotor Flexible Support Components Design of a High Temperature Superconducting Motor

A high-temperature superconducting (HTS) motor was designed, which employs the HTS wires in the rotor. To support the HTS magnet, the novel flexible support components are designed, and the design process is summarized as follows. First, the structure of flexible support components was designed, and the structural size and piece number of the leaf spring were obtained by means of theoretical calculation and test. Second, the structure of the whole rotor with its support components was conducted by the finite element method. The results show that the cold mass has a slight vibration in the radial direction and the resonance is avoided. Last, a full-scale simplified rotor low-temperature test platform was developed to verify the strength and the stiffness of the support. The low temperature test results show that the maximum radial displacement and the maximal strain of leaf spring under test condition are 0.54 mm and -459.7 μe, which are far below the yield strength of the spring steel and satisfy of the design requirements of the HTS motor.