Wenfeng Zhang

The flywheel energy storage system (FESS) is a high-performance physical energy storage device that can be used for peak shaving and frequency regulation in power grids, effectively improving grid operational reliability. To address the heating issues of permanent magnet machines in existing FESS devices, a brushless superconducting-field claw-pole machine (BSCM) is proposed to enhance the energy-to-volume ratio of the FESS and solve the heating problem of permanent magnet machines in FESS. Three topologies of brushless electrically-excited claw-pole machines were designed and their performances analyzed and compared. The results show that the 18/20-pole BSCM exhibits the optimal design characteristics. A prototype of the 18/20-pole machine was further developed and experimentally validated, confirming the accuracy of its simulation design. This machine topology was applied to the FESS, and an integrated design was implemented, addressing the heat dissipation while eliminating the use of brushes. Magneto-thermal coupling simulations indicate that the superconducting-machine-based FESS reaches a long-term temperature rise of 59.184 °C with a reasonable temperature distribution. This study provides a feasible technical reference for the application of superconducting machines in FESS.

Compared with the traditional brushless doubly-fed generator (BDFG), the BDFG with double stator (BDFG-DS) architecture achieves enhanced configurability by physically decoupling the power and control windings onto independent stator assemblies. The design offers benefits such as expanded slot dimensions and enhanced power density, yet it remains constrained by inherent asymmetry in three phases, which causes large harmonics and torque ripples. In this paper, the working mechanism of the BDFG-DS is introduced. Then the root cause of the asymmetric phenomena is discussed. And based on the analysis, an optimization method with complementary skewed stators is developed to enhance the performance of the BDFG-DS. By adopting the appropriate combination of pole slot and skewing slot angles of the two stators, the asymmetry and performance, including harmonics and torque ripples, are improved. Meanwhile, unlike the traditional skewing slot method, the torque density and power density are not decreased. Finally, a finite element analysis model is built and simulations are conducted to demonstrate the electromagnetic optimization efficacy of the proposed skewed-stator topology.

In the traditional control scheme of a 12/8-pole bearingless switched reluctance motor (BSRM), radial force and torque are usually controlled as a compromise due to the conflict between their effective output areas. Additionally, each phase requires individual power circuits and is excited in turn to produce a continuous levitation force, resulting in high power device requirements and high controller costs. This paper discusses a 12/8-pole single-winding hybrid-rotor bearingless switched reluctance motor (HBSRM) with a hybrid rotor consisting of cylindrical and salient-pole lamination segments. The asymmetric rotor of the HBSRM slightly increases the complexity of its structure and magnetic circuit, but makes it possible to generate the desired radial force at any rotor angular position. A control scheme for the HBSRM is developed to utilize the independent excitation of the four windings in one phase to generate the desired levitation force at any rotor angular position, and it requires only half the number of power circuits used in the conventional control scheme of a 12/8-pole single-winding BSRM. Different from the average torque chosen to be controlled in traditional methods, this scheme directly regulates the instantaneous total torque produced by all excited phases together and presents a current algorithm to optimize the torque contribution of each phase so as to reduce torque pulsation, and the improved performance of this bearingless motor is finally validated by simulation analysis.

The optimized design of a new high-temperature superconducting rotating pole machine is presented. Its main structural feature is the use of a double stator core which separates the synchronous machine pole shoe from the pole body to rotate separately as the machine rotor, allowing the superconducting coil to operate in a stationary state. The inner stator core, the stationary dewar and the rotor core together form the excitation system of the machine. The excitation coil windings adopt a rectangular cross-section, with flux divertor strategically placed between the high-temperature superconducting coils. This configuration aims to modulate the background magnetic field, specifically reducing the perpendicular magnetic field component. This mitigation minimizes the impact of ambient magnetic fields on the superconducting coil’s current carrying capacity, ensuring an optimized magnetic field environment for its operation. Through the integration of these modifications, the technical and economic parameters of the enhanced high-temperature superconducting machine have been significantly improved. The optimization of design, coupled with detailed calculations of the 3D electromagnetic field, was achieved utilizing the commercial software Ansys EM module.

Damping and shielding system (DSS) is one of the key structures in the superconducting machines, which is used to provide damping for the machine to reduce the influence of the prime mover torque and electromagnetic torque fluctuation on the operation, and to shield harmonic magnetic field of the armature side to reduce the ac loss generated in the superconducting field winding. The method based on the traditional electromagnetic DSS will affect the damping performance when ensuring the shielding effect. At the same time, the size of the support structure needs to be increased in order to cope with the large failure torque, which would further increase the effective air gap of the machine, thus affecting the increase in power density. This paper proposes a superconducting machine hybrid damping and shielding system that combines mechanical damping and electromagnetic damping shielding system, which can provide sufficient damping for the machine on the one hand, and ensure good shielding performance on the other hand. The shielding performance analysis model of the DSS, the seventh-order state equation and Simulink analysis model of the machine when the mechanical damping is considered are established, and the transient fault response of the machine before and after the mechanical damping is compared. The result shows that the hybrid DSS can provide better shielding and damping effect for the superconducting machine.

In order to cope with the grid fluctuation caused by large‐scale wind power connected to the grid, the wind thermal power generation system has been proposed and extensively studied. The wind thermal power generation system uses a wind turbine to drive a heat generation device to heat the heat storage medium, which is further exchanged to drive a turbine to generate electricity. A superconducting magnetic eddy current heater (SMH) is proposed for the characteristics of wind thermal power generation system, which uses non‐resistive, large current‐carrying superconducting coils for excitation, and has high output efficiency and power density. The working principle of magnetic eddy current heating is analysed, and the structure of SMH with no ferromagnetic material and two heating screens inside and outside is proposed according to the characteristics of SMH. An analytical model of the SMH is established, and the influence of the structure and materials of the SMH on the magnetic field distribution is analysed. Based on this, a 22‐pole SMH was designed and analysed for output power at 10–20 rpm. A three‐dimensional magnetism‐stress combined analysis model of SMH is established, and the strain and stress characteristics of SMH are simulated under the condition of maximum output power, which verifies the feasibility of the mechanical properties of existing superconducting materials for application in SMH.

As a kind of high-power density machine, superconducting machines have important application prospects in the fields of aerospace, ship propulsion and wind power generation. The existing semisuperconducting-type machines have great difficulties in design and application because of the need to use complicated structures such as brushes and rotating dewars. A rotating-pole-shoe-type high-temperature superconducting machine is proposed in this paper. The machine separates the pole shoe from the magnetic pole and generates a magnetic field synchronized with the armature side by rotating the pole shoe. The excitation system of the machine consists of a rotating rotor and a stationary inner stator. The superconducting coil is placed on the inner stator, avoiding the use of complex structures such as brushes and rotary seals. Aiming at the special structure of the rotating-pole-shoe-type superconducting machine, a three-dimensional magnetic field analysis of the superconducting machine is performed to improve the machine structure. The output performance of the machine is calculated and compared with that of the semisuperconducting-type machine.

Junction temperature is a key parameter that influences both the performance and the reliability of the insulated gate bipolar transistor (IGBT) module, while solder fatigue has a significant effect on the accuracy of junction temperature estimates using the electro-thermal model. In this paper, an improved electro-thermal model, which is independent of solder fatigue, is proposed to accurately estimate the junction temperature of IGBT module. Firstly, solder fatigue conditions are monitored in real time with the information of the case temperatures. Secondly, when solder fatigue is found, the update process of the electro-thermal model parameters is performed to match the model parameters with the fatigue device. With the above two-step process, the influence of solder fatigue on the accuracy of temperature estimates can be removed in good time. Experimental results are provided to validate the effectiveness of the proposed method.