Jiangtao Yang

Wavelet-based multiresolution algorithm for integral and boundary element equations in electric and magnetic field computations

Summary form only given. The wavelet algorithm for integral equations was first studied by Beylkin et al.(1991). When applied to electric and magnetic field problems formulated in terms of the method of moments (MoM) or the boundary element method (BEM), it was recognized that the wavelet transform (WT) yielded a sparse algebraic equation matrix. However, when the domain was discretized with regular basis functions, for example piecewise constant or piecewise linear, it was necessary to allocate extra memory for the transformed matrix. Moreover, the transformed matrix did not appear to have a better condition number than that of the original one. We use wavelet functions as both basis and weight functions to obtain a reasonable trade-off between the entire domain and subsectional basis functions. The whole domain may be divided into several subsections. In each subsection, the higher resolution basis is incorporated, thus preserving the merits of entire domain basis functions while yielding a sparse matrix. The wavelet-based multiresolution algorithm is described in the full paper and numerical examples are presented to illustrate its flexibility.

Application of a wavelet transform in eigenvalue problems for electromagnetic field computations

In this paper, we present the wavelet transform (WT) method to reduce the dimension of a matrix without sacrificing too much precision on eigenvalues. By using the WT, the original matrix is split into two matrices, with each being a quarter the size of the original one. One of the derived matrices contains the smaller eigenvalues, while the other has larger ones. Moreover, this procedure can be taken successively, one can have a series of reduced order matrices.

A Novel Multi-Unit Out-Rotor Homopolar Inductor Machine for Flywheel Energy Storage System

Homopolar inductor machine (HIM) has been widely applied in the field of flywheel energy storage system (FESS). However, conventional HIM suffers from the low power and torque density due to its unipolar air-gap flux density. To solve this problem, a novel multi-unit out-rotor HIM (MOHIM) with bipolar air-gap flux density is proposed. First, the structure and operation principle of MOHIM are illustrated. To simplify analysis, MOHIM is divided into unit machines (UMs) based on the equivalent magnetic circuit. The back-EMF, flux density and output torque of MOHIM and UM are respectively compared, which proves the effectiveness of UM. Finally, the performance of MOHIM is investigated by three-dimension finite element analysis (3-D FEA), which indicates that this machine is a good candidate for the application of FESS. Keywords-Homopolar inductor machine (HIM); multi-unit out-rotor HIM (MOHIM); bipolar air-gap flux density; unit machine (UM).

Research of an Axial Flux Stator Partition Hybrid Excitation Brushless Synchronous Generator

A vehicular generator has stringent requirements on its weight and volume. As a combination of permanent magnet and electric excitation motor, hybrid excitation machine could meet the requirements of vehicular generator, with small size, light weight, adjustable output voltage. In this paper, an axial flux stator partition hybrid excitation brushless synchronous generator (ASHG) is proposed. First, the structure and operation principle of ASHM is illustrated. Afterwards, the shape of the magnetic pole is optimized to obtain the air-gap flux density with low harmonic content. Moreover, the regulation performance of the magnetic field and output voltage are investigated by three dimensional finite element analysis (3D FEA). The result indicates that ASHG has a high performance of adjusting terminal voltage. It can improve the generator efficiency, power density and stability comparing with the conventional vehicular generator.

Comparison research of a novel brushless hybrid-excitation axial flux machine

A novel brushless hybrid-excitation axial flux machine (BHAFM) is investigated in this paper. It is designed for electric vehicle which requires the ability of wide speed range and high starting torque of machine. Adopting the special structure of claw poles, BHAFM realizes the function of hybrid-excitation without brush and slip ring. Meanwhile, contrasted with traditional permanent magnet synchronous motor (PMSM), it has the merits of less demagnetization to permanent magnet (PM) and more flexible design. The comparison research mainly focus on the ability in the condition of flux weaken control, and the working principle of traditional PMSM and BHAFM in that condition is introduced.

The Control Strategy and Experiment Research of Integrated Energy Storage Pulsed Alternator

The pulsed high-power supplies in this paper employs a homopolar inductor alternator (HIA) as the motor/generator integrated energy storage pulsed alternator. Lumped parameter design equations are developed, which is used to establish the mathematical model of the HIA, and the analytic calculation method of inductance matrix is derived. Prototype flywheel energy storage was built, and the basic structure of HIA is analyzed by using finite-element method (FEM). This paper proposes a simplified equivalent 2-D salient-pole synchronous generator model to simplify the 3-D FEM of HIA and investigates the motor control method of HIA based on the simplified 2-D equivalent model. The experiments were conducted for speed up to 8000 rpm and the six-step inverter drive strategy presented in this paper achieves the motor/generator integrated control on inductor energy storage pulsed alternator (IESPA). Most experimental results were in line with designed value.

Design and Research of a High-Speed and High-Frequency Pulsed Alternator

Pulsed alternators have the merits of high energy and power densities, which are applied to a wide range of applications, such as the electromagnetic launch, the pulsed laser, and the pulsed high magnetic field. A new type of high-speed and high-frequency pulsed alternator integrating an alternator and a motor, is proposed in this paper. A solid rotor which is made of high-strength alloy steel with high yield strength is used in the pulsed alternator, so it can work at a high tip speed. This machine consists of two alternators and a motor which share one rotor and one field winding. According to different voltage levels and operation frequencies, the motor and the alternators with different stack lengths and pole-pairs are designed, respectively. Therefore, it has the abilities of being driven by low-frequency current and discharging high-frequency pulses. In this paper, the basic structure and fundamental of the pulsed alternator are introduced, the specific parameters of the prototype are given, and the performances are verified by the simulation. The results show that the machine proposed in this paper is suitable for the applications that require high-frequency pulsed discharge.

Research on the No-Load Rotor Eddy Loss of a High-Speed Pulsed Alternator

Homopolar inductor alternator (HIA) has been widely used as a high-speed pulsed alternator in the electromagnetic launch field due to its merits of high-speed operation, power density, and reliability. To achieve the above-mentioned merits, a high-strength and high-stiffness solid rotor is usually adopted in the HIA. However, the solid rotor would be subject to high eddy current loss. Some works have been done to analyze the rotor eddy current of the HIA, while the research on analytic calculation and reduction of rotor eddy current loss is relatively few. In this paper, an analytic calculation method is established to calculate no-load rotor eddy current loss for HIA, which is validated by the finite-element analysis and corresponding experiments. Besides, to minimize the rotor eddy current loss, a simple method, by slitting the rotor tooth, is proposed. Moreover, the influence of circumferential and axial slits on the rotor eddy current loss and air friction loss is comparatively studied. Finally, the influence of the width, depth, and number of slits on the eddy current loss is investigated. It is shown that the circumferential slits have better performance than that of axial slits to reduce the eddy current loss.

Multiresolution algorithm for integral and boundary element equations in magnetic field computations

Wavelet algorithm far integral equations was first studied in [I] . In magwetic field computations, previously plblished p a p utilized the standard scheme to gel a dense ma& and then applied the fast wavelet vansfonii to appvimate it to a sparse one. Therefore, one have to allccate extra metnon for the transformed matrix. Mnmver, the t r d d mabix did not appear to have beuer condition number lhan the original one. In this paper, we use wavelet functions as bath basis functions and weight funnions. It is a reasonable trade-olf between tbe entire domain and subsstiM basis functions. The whole dornais may be divided iiib several subsections, while in each subsection the higher resolution basis is incorporated, whsch preserve the merits of entire domain basis functions. A sparse matrix thus is derived

Wavelet-galerkin Method In Solving Dynamic Electromagnetic Field Problems

This paper presents a wavelet-Galerkin method to solve dynamic electromagnetic field problems. It differs from some former methods which discretize the whole space domain using wavelet functions; however it discretizes the space domain with finite element, because of its flexibility to the boundary. At the same time, it introduces the scaling function as trial functions for time domain, which are space orthogonal along the real line but have poor ability to adapt complex boundaries. Thus, it incorporates the merits of both techniques. The results are better without too much calculation time.