Yulong Shao

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.

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.