Design And Analysis Of Permanent Magnet Linear Oscillation Machine For Stirling Power Generation System

With the current increasingly worsened energy situation,the development of the space energy attracts much attention from engineers around the world.The stirling power generation system is one of the techniques that are widely used in the space technology,solar energy applications,and heat energy recovery due to its wide fuel source,environmental friendly,and high efficiency.The stirling power generation system is mainly composed of a stirling engine and a linear generator,where the linear generator is connected to the stirling engine.In the working process,firstly,the thermal energy is converted into mechanical energy,which is converted into electrical energy by the linear generator,achieving the conversion process of thermal energy-mechanical energy-electrical energy.Therefore,the linear machine is one of the critical components of the system.Considering the unique structural characteristics of the linear machine(such as cogging effect,auxiliary tooth effect,end effect,etc.),this paper designs,analyzes and optimizes the cylindrical linear oscillator machine used in the space power generation systems based on the analytical and numerical methods,with the results verified by experiments.The main research works are as follows:1.Based on the traditional tubular linear permanent magnet oscillation generator(TLPMOG),the structure and operating principle of the linear machine are presented,as well as an established analytical calculation model,meanwhile,the problem in the existing electromagnetic analytical model are addressed.A two-dimensional analytical subdomain model based on the polar coordinate conversion method is proposed,which effectively considers the end effects of the primary and secondary of the linear machine.Firstly,the coordinate transformation method is used to establish a two-dimensional subdomain analysis model of the TLPMOG,based on which the linear machine is converted from the cylindrical coordinate system to the polar coordinate system,and therefore reduces the complexity of the solution.Secondly,the subdomain method is applied to calculate the general solution of Laplace equation and Poisson equation in each region.Based on the analysis model,the electromagnetic properties such as magnetic flux density and back electromotive force of the linear machine are obtained.Finally,the accuracy of the method is verified by finite element methods and experimental tests.The polar coordinate conversion model proposed in this paper has certain versatility and can be applied to any surface mount permanent magnet linear motor.2.The disconnection structure in the end leads to the end-effect problems of the tubular permanent magnet linear oscillation machine,while excessive end-effect affects the smooth operation of the machine.The traditional method to suppress the end-effects of linear machine is to introduce the auxiliary teeth structure.Meanwhile,finite element method(FEM)is usually used for the design of auxiliary tooth tubular linear permanent magnet oscillation generator(Aux-TLPMOG),due to its machine performance prediction accuracy,but FEM is a timeconsuming tool.This paper proposes a method based on the magnetic field reconstruction(MRFC)for this type of generator.With this method,the cogging effect,auxiliary teeth effect and end effect of the Aux-TLPMOG can be effectively considered.Firstly,the traditional calculation method for Aux-TLPMOG is described,with the advantages and disadvantages of the traditional methods compared and presented.Secondly,polar coordinate conversion method is used to establish the analytical model for Aux-TLPMOG with the end-effects of slotless magnetic field consideration.Thereafter,the two-step Schwarz-Christoffel transformation method is launched to account for auxiliary-teeth and slot effects.Subsequently,the MFRC technology is performed to integrate the above results and the forces are obtained.Finally,the accuracy of the presented method is validated with the results obtained from both the FEM model and the experimental tests on the Aux-TLPMOG prototype.The main contribution of this part in the paper is to present a hybrid method which has a good trade-off between the computation time and the accuracy.The analytical results using the MFRC method agree well with that of FEM model,which is in less than 7% deviation with the experimental results.Therefore,it is an efficient tool in the initial design procedures of Aux-TLPMOM.3.Detent force is an obvious drawback of permanent magnet linear machine(PMLM),as excessive detent force will cause machine vibration and affect the system positioning accuracy when the PMLM operate in electric state.This paper optimizes the detent force of this type of linear machine based on the aforementioned Aux-TLPMOG.An improved PMLM structure with arc-teeth and inner-ladder end teeth(AIL-teeth)is proposed in this paper to reduce the detent force.This structure is advantageous as it reduces the detent force while remaining the motor size.Firstly,the parameters that affect detent force are confirmed using Fourier analysis method.Secondly,a hybrid optimization method is adopted to obtain the structural parameters of the AIL-teeth PMLM,which is based on the flux-tube and Taguchi methods.The optimal structural parameters of the AIL-teeth PMLM are determined with the optimization method.Finally,two PMLMs with traditional and improved structures are validated with FEA analysis and experimental tests,which show that the improved AIL-teeth PMLM can reduce detent force effectively by 70% with the least sacrifice of electromagnetic performance.4.Considering the size and the quality of the linear oscillator machine limitation in the stirling power generation system,a hybrid laminated double stator tubular linear oscillating generator(HL-DSTLOG)is designed.Compared to the above-mentioned TLPMOG,the HLDSTLOG has a small volume,a compact structure,and a fast mover response,and can be well used in a deep space detection power generation system.The paper first introduces the basic structure of the HL-DSTLOG,analyzes and introduces the operation principle of the linear machine.Then the hybrid lamination technology is discussed,with the lamination methodology in the linear machine described,and the main lamination coefficient derived.Finally,the FEA method is used to analyze the electromagnetic field of the HL-DSTLOG,and the effects of the different structural parameters on the no-load electromotive force and the detent force of the HL-DSTLOG are discussed,for the final optimal structural parameters determination,and the electromagnetic output performance is investigated of the linear machine under load condition.5.The temperature field is required to secure a safe and reliable operation of the HLDSTLOG in the special operating environment of the stirling power generation system.Firstly,the thermal model techniques analyzing the temperature field in the machine are introduced and compared between the existing method.Lumped parameter thermal network(LPTN)method is selected to analyze the temperature field of the HL-DSTLOG,with its time effective characteristics.Based on the heat transfer path of the linear machine,an analytical model of thermal network is established.Secondly,the thermal parameters and heat sources of the machine in the analytical model are determined and solved,and the steady-state temperature distribution of the HL-DSTLOG after 2 hours of continuous operation is calculated with the model.Finally,sensitivity analysis is conducted on the factors that affect the temperature field distribution in the studied machine,and the effects of different processing techniques discussed.6.For the above Aux-TLPMOG and HL-DSTLOG design verification,two prototypes are manufactured and tested.Based on the existing implementation conditions of the laboratory,a TLPMOH test platform was built to test the detent force,electromagnetic performance of noload,load condition,and temperature of the above two prototypes.The results show that for the no-load condition of Aux-TLPMOG,the back-electromotive force(EMF),detent force results from the FEA and tests are similar,with the test results of the HL-DSTLOG slightly lower than the FEA results.The main reasons are the gap between the silicon steel sheets and the gap at the splicing place of the mixed laminated sheet due to the manufacturing errors of the lamination.For the loading condition,there is a slight phase deviation between the measured waveform of Aux-TLPMOG and the FEA result.The reason is that the crankshaft connecting rod device is connected with the linear motor through an iron block.When the generator reciprocates,the iron block itself will be subjected to reciprocating tension,resulting in a slight deviation in the movement speed of the crankshaft connecting rod device and the linear motor,causing the experimental platform to vibrate.The loading condition of the HL-DSTLOG matches well with the measured waveform,with some deviations due to the fact that the frequency converter cannot be accurately measured with manual controlling.