This paper presents a new field-modulation double-stator electrical excitation synchronous machine (FM-DSEESM) and analyzes its harmonic components of double-layer air-gap magnetic field. The key is that both the types and sources of various harmonic-components of air-gap magnetic field are derived by taking into account the permeance components of both inner and outer stator teeth and modulation-ring rotor. The selection criteria of main working harmonic components of excitation field is clarified to achieve the armature-winding configuration. Then, the working harmonic components of air-gap magnetic field, which have the same pole pairs, rotating direction and rotating speed respectively, can be figured out by comparing the mathematical derivation and finite-element analysis results from the excitation field and armature reaction magnetic field. By analyzing the contributions of the air-gap flux density components to the electromagnetic torque, it is found that the electromagnetic torque of the proposed FM-DSEESM mainly consists of two parts, namely the reluctance torque components generated by the stationary working harmonic components and the armature reaction torque components provided by the rotating working harmonic components. A low-speed direct-drive FM-DSEESM prototype is fabricated to verify the validity of the proposed analysis approach.

This paper proposes to implement a segme-nted-rotor high-temperature superconducting (HTS) flux-switching generator with dual electrical ports for offshore wind power generation. The originality is both electrical ports, namely armature windings and field-excitation windings, are placed in the stator so that the stationary seal of the cryogenic cooling system can be achieved. The key lies in that the HTS field-excitation windings in the stator side provide high field excitation, and the sinusoidal electromotive force in armature windings is induced by the magnetic field modulation of the segmented rotor. A new kind of racetrack-shaped Dewar with vacuum-sandwich was proposed and fabricated to accommodate and cool the HTS coils. Based on this proposed racetrack-shaped Dewar, a cryogenic cooling system of the proposed generator was established to maintain the superconducting properties of HTS wires. Both finite element analysis and experiments were carried out to verify the validity of the proposed generator and its cryogenic cooling system.

This paper proposes a novel high-temperature super-conducting (HTS) claw-pole vernier machine, which combines the merits of stator HTS-excitation machine with the “magnetic gearing effect” designed for direct-drive applications. The key is to adopt claw-pole stator structure to realize the multi-pole pattern using single HTS-excitation unit with stationary seal, thus greatly simplifying the cooling Dewar architecture as well as improving the structural compactness. Moreover, the armature windings are wound around the split-teeth which are set on the surface of claw poles to achieve the physical separation from the HTS-excitation coil, thus reducing their space conflicts and impact with each other. The operation principle analysis and the initial machine design are conducted in details. By using the three-dimensional finite element analysis, the machine performances are evaluated, and its validity is verified.

TheSuperconducting (SC) machines have the merits of higher power and torque density due to the fact of higher electrical or magnetic loading. Especially, the field modulation SC machine (FMSCM) recently attracts more and more attention from scholars, since this kind of SC machines successfully overcome the drawbacks of the traditional SC synchronous machines, such as the rotating seal of the coolant and the electrical brush-slip-ring for current transfer. However, the research method of the FMSCM mainly adopts the finite element analysis (FEA). Although the FEA can provide accurate results, the time consumption is huge, particularly at the initial design of the large capacity FMSCM, the time cost will be unacceptable. Aiming at solving this problem, this paper attempts to establish the mathematical analysis model of a double-stator field modulation HTS machine (DSFM-SCM) using a new theory of electrical machine, i.e., general airgap field modulation theory, for the first time. Both the FEA and experiments are carried out on the DSFM-SCM, to verify the effectiveness of the proposed mathematical analysis model. Although there is discrepancy between the proposed analytical method and FEA, it can basically meet the requirement at the initial design, and sufficiently exhibit the modulation effect of geometric structure, reflecting the essential mechanism of the DSFM-SCM. In addition, it is worth noting that the establishment process of analytical model of the DSFM-SCM can provide reference for the other FMSCMs.

This paper proposes a high temperature superconducting (HTS) double stator machine (HTS-DSM), based on the magnetic field modulation principle. In the proposed HTS-DSM, the HTS field winding and the copper armature winding are separately located on the two stators, so that it overcomes the drawbacks caused by the coupling device for cryogenic transfer, the torque tube, the carbon brushes, and slip rings in the conventional HTS synchronous machines with the rotating field winding, bringing the merits of high reliability and low maintenance cost. Moreover, a method of amounting a ferromagnetic ring outside the HTS field winding is also proposed to reduce the negative effects of the armature reaction field on the HTS field winding, since the alternating current (AC) losses induced by the armature reaction field easily cause the quench of the HTS field winding. Totally four different topologies are proposed, and the operation principle of the HTS-DSMs is analyzed based on the magnetic field modulation principle. Then the design and optimization of the HTS-DSM is discussed in detail to present the main design parameters of the four topologies. Finally, the performance of the four different topologies are compared by the finite element analysis, the results reveal that the HTS-DSM with modular dewar and iron-teeth inner stator exhibits the merits of higher power density.