Research On Tubular Staggered-Teeth Transverse-Flux Permanent-Magnet Linear Machine

The free-piston Stirling power generation system composed of a free-piston Stirling engine and a linear machine, can make use of a variety of energy sources and has promising applications for renewable energy generation, aerospace power supply and ship propulsion. The linear machine is one of the challenges in the power generation system, whose structure and performance are influential factors for the overall system efficiency of energy conversion. Aiming at the requirement of free-piston Stirling power generation system, this paper proposes a novel tubular staggered-teeth transverse-flux permanent-magnet linear machine(TST-TFPMLM). This scheme can provide a new idea to resolve the problems of complex structure, low productivity, large flux leakage and low power factor of conventional TFPMLMs. This paper makes an intensive study of the TST-TFPMLM, which mainly consists of the following parts:Firstly, the mathematical model and performance analysis under variable velocity trajectory of TST-TFPMLM have been researched to simplify the analysis and design process. Considering the characteristics of complex three-dimensional magnetic circuit of TST-TFPMLM, the simplified equivalent magnetic circuit model is established to calculate the equivalent magnetic resistances of critical areas. As the simulation of three-dimensional finite element is time-consuming and inefficient, the simplified model is adopted and investigated for higher efficiency. A solution for deducing data under variable velocity using calculated data under constant velocity is proposed for the variable motion problem of TST-TFPMLM in the power generation system, which can largely reduce calculation time under the same accuracy limit.Secondly, with the flux leakage, back EMF and thrust of TST-TFPMLM taken as a highly considered target, the determination method of main structure parameters is investigated, and the calculation method of main electromagnetic parameters is also provided. Aiming at the complicated flux-leakage characteristic, the forms and evaluation method of flux leakage are investigated. Then the distribution law of flux leakage and the selection principle of main structure parameters under condition of low flux leakage are further obtained. At the initial design stage of TST-TFPMLM, with back EMF and thrust taken as a highly concerned target, the determination method of main structure parameters like the axial length of stator core, the width and thickness of tooth tip, is provided to obtain the high back EMF and thrust. With the accurate control problem of the TST-TFPMLM system considered, the calculation method of inductance is also investigated.Thirdly, the key performances of TST-TFPMLM, including power factor, detent force, efficiency and thrust density, are deeply analyzed and optimized. In order to improve the power factor, the influence factors of TST-TFPMLM power factor are analyzed through analytic method. Optimizing methods are proposed from the aspects of PM dimensions, winding turns and current amplitude, inner power factor angle and structure parameters of tooth top. Aiming at the problems of detent force influencing the operating characteristic of the machine system, the methods of reducing detent force are discussed. On this basis, the methods of calculating loss and efficiency are given. The optimal design of TST-TFPMLM considering magnetic performance and machining process is determined by comparing the electromagnetic performance of two different design schemes.Afterwards, thermal field calculation and influence factors on cooling effect are researched to garantee the safty operation of TST-TFPMLM under high temperature, high pressure and confined space. The simplified three-dimensional finite-element thermal field model is established to determine relavant thermal parameters, considering machine actual structure, heat transfer characteristics and cooling condition. On this basis, the temperature distributions of machine winding, insulation materials, permanent magnets and other key areas are determined. Furthermore, the influences of slot filling factor, material properties and air flow velocity on cooling effect are analyzed.Lastly, a prototype machine of the TST-TFPMLM is manufactured to verify the accuracy of theoretical analysis and discuss manufacturing process. An experimental bench is established to test the electrical parameters, no-load characteristics, motoring and generating performances, which can provide the theoretical and experimental reference for further improvement and engineering application of the TST-TFPMLM.