We present a simplified 2-D analytical subdomain model to predict the open-circuit magnetic field of a tubular linear permanent magnet oscillation generator (T-LPMOG) to account for its primary and secondary end effects. At present, the magnetic field calculations of the T-LPMOG are typically analysed in cylindrical coordinates, and the end effect is neglected accordingly to apply the periodic boundary. In this paper, a simplified 2-D analytical subdomain model in polar coordinates is proposed to consider the end effect. First, a coordinate transformation method is adopted to establish the 2-D subdomain analytical model, the cylindrical coordinates are converted into polar coordinates, and the T-LPMOG is analysed under this new coordinate system. Next, the subdomain method is used to analyse the analytical model by solving Laplace's equation and the Poisson equation. Based on the simplified analytical model, the flux density and back-electromotive force (back-EMF) are obtained. The analytical results are verified using the finite element analysis (FEA) method, and the computational times compared with the FEA method are provided. Finally, a T-LPMOG prototype is manufactured and tested, and the results show that the proposed analytical model can be useful in the initial design and optimization of the T-LPMOG.

A field-modulated tubular linear generator with quasi-Halbach magnetization (FMTLG) is proposed for ocean wave energy conversion. The FMTLG equipped with field-modulated technology and quasi-Halbach arrays can overcome the disadvantages of heavy weight and inefficiency caused by the low speed ocean waves to some extent. In order to design and optimize FMTLG in a short time, the open-circuit magnetic field distribution is established with analytical method. The finite elements method (FEM) results show that the back-EMF of FMTLG is 43% higher than that of quasi-Halbach magnetization linear generator (TLPMG). A novel assistant tooth of FMTLG makes the cogging force 8 times smaller than the TLPMG. Finally, a prototype is manufactured to verify the simulation results by the experiments.

The tubular linear permanent magnet oscillator (TLPMO) has been widely used in the industrial field as an energy conversion machine. Detent force is an obvious drawback of TLPMO and one of efficiency way to minimize this phenomenon is adding auxiliary-teeth. In this paper, a magnetic field reconstruction (MFRC) method is proposed to analyze the TLPMO comprehensively, which the auxiliary-teeth, slot, and end effects are included. Firstly, the subdomain conversion model is used to consider the end effects of slotless magnetic field under no-load condition. 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, the forces are obtained. Finally, the accuracy of the presented method is validated by comparing the results from FEA model and experiment of TLPMO prototype. The main contribution of this paper is presenting a hybrid method which has a good trade-off between the computation time and the accuracy. The analytical results using the MFRC method closely agree with that of FEA model and it has less than 7% deviation compared with the experimental measurement. Hence, it can be regarded as an efficient tool in the initial design procedures of TLPMO.

Litz wires are widely used in electrical machines with reduced AC losses, compared to traditional random winding. The reduced AC losses can improve both electrical machines electromagnetic performance, such as efficiency and thermal performance. Thermal aspect is identified as a key enabler for next generation high power density electrical machines, where thermal modelling plays a critical role. Equivalent slot thermal conductivity is one of the most challenging parameters to be determined in the process of thermal model development, due to various components, such as copper, insulation, and impregnation resin. There are extensive literatures where the litz wire thermal conductivity in the radial direction are reported. However, the thermal conductivity in the axial direction is not well studied, which is critical to determine the heat transfer, such as for electrical machines with end winding spray-cooling system. In this paper, the axial thermal conductivity is investigated with analytical calculations and experimental validation. Firstly, 9 litz wire samples are selected with various types, such as rectangular and circular shapes, with varnish process and without. Two different analytical methods are then introduced and presented to calculate the litz wire thermal conductivity in axial direction, based on equivalent length theory and equivalent medium theory, respectively. Finally, experimental tests are conducted, and results are compared to those obtained from the proposed analytical methods. Guidelines are also provided to predict the litz wire axial thermal conductivity in this field.

To improve the power density and reliability of radial (RS-TLPMG) and quasi-Halbach (QH-TLPMG) magnetization tubular linear surface-mounted permanent magnet generators under realistic sea-state conditions, a novel tubular linear generator with multilayer interior permanent magnets (MI-TLPMG) for wave energy conversion is proposed and analyzed in this paper. Using finite element analysis (FEA), a comprehensive comparison of air gap flux density, flux linkage, back electromotive force (back-EMF), load, and no-load performance is investigated to verify the advantages of the proposed machine. The FEA results indicate that MI-LTPMG with a flux-concentrating effect has higher back-EMF, air gap magnetic flux density, flux linkage, and output power than do the other two machines. Finally, a prototype is manufactured and measured on the test platform and wave tank. The experiment and simulation results show a great agreement with each other.

This paper presents a developed 2-D analytical subdomain model for design and analysis of the double-stator permanent magnet linear synchronous machine (DS-PMLSM) to account for both the primary and secondary end effects. First, considering the time constraint, polar transformed method is adopted to establish the 2-D subdomain analytical model, the DS-PMLSM is deformed into a ring-segment PMLSM, and the analytical model is calculated in polar coordinates instead of Cartesian coordinates. Then, the subdomain method is adopted to analyze the analytical model by solving Laplace's equation and Poisson's equation, and 2-D relative permeance function is used to consider the slot effect. The flux density and back electromotive force are calculated based on the developed analytical model. Finally, the analytical results are verified by the finite-element method and experiment. The results show that the proposed analytical model can accurately predict the electromagnetic performance, which is useful for the initial design of the DS-PMLSM.