Honghui Wen

Aiming to extend the speed range of E-core outer-rotor permanent magnet flux-switching (OR-PMFS) machine, two derived structures are proposed in this article from the perspective of winding reconfiguration. Distinguished by the characteristics of introduced winding, the mechanism of winding reconfiguration is investigated, and outer-rotor dual-armature flux-switching (OR-DAFS) machine and outer-rotor hybrid-excitation flux-switching (OR-HEFS) machine are developed, respectively. With the aid of general air-gap field modulation theory, the speed range extension principles are revealed for two derived topologies. On this basis, a thorough comparison is put forward among the initial OR-PMFS machine, the proposed OR-DAFS machine, and the OR-HEFS machine. Particular emphasis is placed on the output torque and the speed range extension capabilities, and advantages and disadvantages are summarized in this process. Compared to the initial OR-PMFS machine, the proposed OR-DAFS machine could achieve a great balance between output torque and speed range, while the speed regulation capability of the OR-HEFS machine is more remarkable, and its speed range is much wider. The prototype experiment is carried out for both the OR-DAFS machine and the OR-HEFS machine, and the overall performance is concluded to visualize the outcome of this article.

Aiming to improve torque characteristics, a rotor salient-pole modulator design method is proposed for flux-switching permanent magnet (FSPM) machines by considering both pole number and configuration. With the aid of general air-gap field modulation theory, the influence of rotor pole number is analyzed, and a reliable selection method is proposed to enhance average torque and reduce torque ripple. The result indicates that the rotor modulator with an odd pole number possesses better torque characteristics. Thereafter, the configuration of the rotor salient-pole modulator is investigated and modeled mathematically by the design parameters. Utilizing the proposed design method, an FSPM machine is designed and manufactured. Through the performance comparison and prototype experiment, the proposed design method is verified to be effective in improving the torque characteristics. Without increasing the PM amount, the average torque is enhanced by 14.8%, and the torque ripple is reduced by 93.1%.

This paper designs a tubular linear permanent magnet machine for a free-piston Stirling generator. Considering the high coaxiality requirement of the free-piston Stirling generator for short stroke and high-speed reciprocating operation, the power piston is nested within the mover, which has a full pitch ironless toroidal winding, shortening the axial length and enhancing integration. The operating and magnetic field characteristics of the proposed machine are further analyzed to reveal the generation principle of cosine induced electromotive force. Given the dual role of the proposed machine in providing oscillating force for the free-piston Stirling generator startup and damping force during power generation, the optimization targets both generator and motor operation states, leading to a multiplied cost for the calculation. To mitigate this, a gradient boosting regression tree model with Bayesian optimized hyper-parameters is introduced. It can capture the high-dimensional nonlinear relationship between high sensitivity design variables and optimization objectives on the basis of targeted search for the best hyper-parameters. Utilizing the proposed model, the optimization cycle is shortened by 80% and the output power and thrust are significantly enhanced. In addition, the impact of the segmented permanent magnet process on performance as well as its feasibility are analyzed from the perspective of manufacturing friendliness. Finally, the prototype experiment is launched to evaluate the design and optimization results.

This paper proposed, optimized and compared two dual–rotor axial–flux permanent magnet machines for all–electric aircraft (AEA) propulsion. Firstly, the design requirements are determined and the initial structures of the yokeless and segmented armature (YASA) machine and the axial–flux vernier permanent magnet (AFVPM) machine are designed with identical outer radius, inner radius and axial length. Several features, including the Halbach array and PM skewing, are introduced to improve power density and efficiency. Then, to reduce the computational burden of finite element analysis, the surrogate models of machines are constructed by Box–Behnken design. The electromagnetic performances, such as induced voltage, torque characters and efficiency of the proposed machines are simulated. Subsequently, the discussions are carried out, where the strength and weakness of the two machines are evaluated. Finally, it is concluded that the YASA machine is a superior choice for AEA propulsion due to its higher output torque, power density, torque density and efficiency when compared to the AFVPM machine.

Given its high torque density, robust structure, and efficient heat dissipation, the in-wheel flux-switching machine has garnered significant interest in e-bike applications. This paper introduces an in-wheel hybrid-excitation flux-switching (IW-HEFS) machine to reduce the reliance on the costly PM materials. Specifically designed for in-wheel applications, the optimization issue for the IW-HEFS machine involves six variables, six objectives, and two primary constraints. To streamline the optimization process, three principles are proposed to improve the solving efficiency by means of the Kriging model, sensitivity analysis, and dimensionality reduction strategies. On this basis, the electromagnetic performance of the IW-HEFS machine is significantly enhanced, particularly in terms of the torque and efficiency characteristics. Moreover, the optimization results are compared, along with the analysis of their strengths and weaknesses. Additionally, an evaluation of the proposed IW-HEFS machine is conducted to further reveal its potential in in-wheel applications by comparing with an existing outer-rotor flux-switching permanent magnet machine. Finally, the prototype experiment is launched with the consideration of manufacturing friendliness to estimate the analytical discussion.

Stirling generator is considered as the most promising solution for energy conversion on the plateau. In order to meet the requirement of the free-piston Stirling engine, a moving-magnet single-phase tubular linear oscillating permanent magnet machine (MM-STLOPM) for Stirling generators is introduced in this paper. Compared with traditional flat linear machines, the sealing process is more convenient and the net radial forces can be eliminated theoretically. On the basis of developed multi-objective particle swarm algorithm (MOPSO), the structure parameters evaluated and identified as highly sensitive through the sensitivity analysis are optimized to maximize rated power, maximize rated force, minimize total voltage harmonic distortion, and minimize total force harmonic distortion. However, the substantial radial force of the MM-STLOPM in the eccentric state poses significant challenges of testing. Therefore, a moving-coil candidate (MC-STLOPM) without eccentric forces is further designed and optimized. For the sake of convenience and cost savings, segmented parallel magnetization was employed for PM manufacturing. Static force and power generation tests in combination with the Stirling engine were conducted on the manufactured MC-STLOPM. The results indicate that segmented parallel magnetization has minimal impact on performance and validate the consistency between simulation and experimental results, confirming the effectiveness of the theoretical analysis.

In this article, an asymmetrical composite rotor featuring flux barrier and short-circuited coil magductance is proposed for the brushless doubly fed machine (BDFM). A qualified magnetic field modulation effect, cross-coupling capability, and reduction of unproductive high-order summation modulated harmonics under asynchronous modulations are provided by the design. First, compensation for the phase shift caused by the magductance of short-circuited coils from the rotor is achieved through an asymmetrical configuration based on the newly proposed vector magnetic circuit theory. On this basis, the operating principle, modulation operator, and modulation capability of the proposed composite rotor are evaluated. Analytical investigation such as various airgap field harmonics prediction is accomplished. In addition, torque contributions of effective airgap harmonics and torque component composition are achieved based on the theoretical evolution. For further improvement of modulation airgap field and cross-coupling efficiency, as well as reduction of output torque ripple, parameter adjustments are considered globally. Thus, a typical 4/2 pole pair BDFM featuring asymmetrical composite flux barrier/magductance rotor is subjected to multiobjective optimization based on sensitivity analysis. A proof-of-concept prototype of the optimized BDFM is fabricated, and the corresponding experimental results are provided to verify the effectiveness of theoretical analyses.

The brushless doubly‐fed machine (BDFM) utilizes an asymmetric composite rotor featuring salient pole reluctance and magductance to effectively compensate for the phase shift in space, as well as enhance magnetic field modulation effects, and is therefore used as a modulator. This paper evaluates the modulation capability of the modulator from the perspective of the magnetic field conversion mechanism. The theoretical evolutions of the average magnetic field conversion factors and torque contributions of various airgap field harmonics are accomplished. Additionally, multi‐objective optimization is conducted for better performance, using stratified sensitivity analysis on typical 4/2 pole pair BDFMs featuring symmetrical and asymmetric composite rotors. As a result, further improved modulation of the air gap magnetic field is expected, the cross‐coupling efficiency of the rotor is improved, and a lower output torque ripple is also achieved compared to the conventional symmetrical counterpart. Theoretical investigation of the optimized BDFM, including its effectiveness in enhancing performance metrics such as coupling factor, airgap flux density, and phase shift mechanism, is verified through 2D finite element analysis. Furthermore, a proof‐of‐concept prototype for experimentation was manufactured, which achieved good agreement with the theoretical predictions.