This paper proposes an analytical model for the prediction of airgap magnetic field distribution for axial flux permanent magnet (AFPM) machine with partial magnet demagnetization. The AFPM machine geometry is first converted to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then current sheet representation of PM is derived to consider the partial demagnetization using superposition principle. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the results of proposed approach agrees with that of finite-element method. The model is further validated by experiments under both healthy and demagnetized conditions, which can validate the proposed approach. Main contribution of the work is to consider the partial irreversible demagnetization. Moreover, the proposed method is applicable for both AFPM and radial flux permanent magnet machine.

This paper investigates the surface-mounted permanent-magnet (SPM) and the interior permanent-magnet (IPM) motors for high-speed applications. An SPM motor and an IPM motor are designed with the same power/speed rate and the same key dimensions. Finite-element analysis is used to compare the mechanical, electromagnetic, and antidemagnetization performances of the two motors, and lumped parameter thermal networks are involved to compare their thermal performances. It can be concluded from the comparisons that the IPM motor has comparable electromagnetic performances with the SPM motor in high-speed operations, and its costs and torque per PM weight are superior to those of the SPM motor. However, its rotor structure is not as robust and is prone to irreversible demagnetization.

In recent years, axial flux permanent magnet (AFPM) machines with pancake shape, compact construction, high efficiency and high power density have gained increasing interests of many researchers. Extensive literatures which involving a variety of AFPM machines topologies in different areas have appeared. This paper describes various conventional stator and rotor structures and several special ones of the AFPM machines, compares performance characteristics of the AFPM machines and the traditional radial flux permanent magnet (RFPM) machines, analyses the AFPM machine design and analysis methods and discusses the AFPM machines for different areas researches and applications. Finally, development trends of the AFPM machine related technologies are summarized and prospected.

Wind power generation has increased rapidly in China over the last decade. In this paper the authors present an extensive survey on the status and development of wind power generation in China. The wind resource distributions in China are presented and assessed, and the 10 GW-scale wind power generation bases are introduced in details. The domestic research status of main components of WP system is then elaborated, followed by an evaluation of the wind power equipment manufacturers. Finally, the outlook for the development of the wind power utilization in China is presented.

This paper deals with stator winding design of induction motors for high efficiency. The stator winding type is an important factor to decide stator copper loss and stray loss of induction motors. After analyzing the effect of stator winding type and connection form on the losses of induction motors, some measures to improve stator winding design are proposed in order to reduce the losses of three-phase induction motors and therefore increase the efficiency, including the use of concentric low harmonic windings and Y-Δ mixed windings.

This paper presents a detailed magnetic equivalent circuit (MEC) method for predicting the torque performance of axial flux permanent magnet machines. The MEC model takes into account the magnetic saturation, armature reaction, leakage flux and the relative motion, provides a tradeoff between finite element method and analytical methods in terms of simulation times and accuracy. The investigated machine structure and feature are introduced, and then further analysis of the average torque and torque density are calculated with the proposed method and verified by 3D-FEM with a good agreement achieved. Sensitive parameters effects on the machine torque density are discussed, and finally an axial flux permanent magnet machine with yokeless and segment armature is optimally designed.

This paper presents the design, analysis and verification of a 150 kW, 24 krpm high speed permanent magnet motor (HSPMM). The HSPMM is a two-pole motor with Gramme ring windings, which can shorten the end winding length and improve the rotor stiffness. The design procedure based on analytical methods, including the rotor mechanical design, magnetic design and cooling design is described. Then a prototype designed by the proposed design techniques is further verified by numerical methods including finite element analysis (FEA) and computational fluid dynamics (CFD) and experiments.

This paper presents a detailed magnetic equivalent circuit (MEC) to improve the analysis accuracy and reduce computation time in modeling of axial flux permanent magnet machines. In the proposed MEC model, the magnetic saturation, armature reaction, leakage flux, and rotor rotation are considered to calculate the machine's static characteristics. The investigated machine structure and feature are first introduced. Then, the air-gap flux density distribution, back electromotive force waveform, and the average torque are calculated with the proposed method. Finally, the accuracy of the proposed method is verified by the 3-D finite-element method, and good agreements are achieved.

This paper investigates the electromagnetic and thermal performances of the open-circuit air cooled high-speed permanent magnet motor (HSPMM) with Gramme ring windings. Take a 36 kr/min, 75 kW HSPMM as an example, the electromagnetic losses, in particular the rotor eddy current loss and the stator iron loss of the motor are calculated. The influences of switching frequency and air gap length on these losses are studied. Then, a computational fluid dynamics (CFD) model is composed to calculate its coolant flow parameters and the temperature distribution. Based on the CFD results, a lumped-parameter thermal network (LPTN) is created and verified. Then, a 24 kr/min, 140 kW prototype with the same structure and cooling configuration is designed using the LPTN. Experiments show that the calculated results are with reasonable accuracy. Finally, a sensitivity analysis is applied to the 140 kW prototype based on the LPTN to disclose the influences of different parameters on the rotor permanent magnet temperature rise.

This paper investigates the losses of a high-speed permanent magnet motor. The iron losses are calculated by a model that can consider the skin effect and rotational loss. The rotor eddy current losses are estimated by a fast hybrid method that can consider the end effect. Pulse-width modulation (PWM) harmonics brought by the voltage source inverter (VSI) are considered in the loss calculations. Then the temperature distribution of the motor is evaluated by using the calculated loss results and computational fluid dynamic (CFD) modeling. Finally, based on the CFD results, the motor structure is optimized to achieve better rotor cooling. The outer slots are closed to force the cooling air flow through the rotor surface. Calculated temperature distributions and optimization results are verified by measurements.

This paper presents a novel switched-flux memory motor (SFMM) by artfully incorporating the flux-mnemonic concept into the conventional switched-flux permanent magnet machine. The magnetic susceptibility of AlNiCo PM provides the flexible online controllability of air-gap flux by imposing a transient current pulse. To uniformize magnetization levels of PMs, a time-divisional magnetization strategy (TDMS) is proposed. Due to the uniqueness of hysteresis nonlinearity and instability regarding AlNiCo PM operating point, the time-stepping finite element method (TSFEM) dynamically coupled with a nonlinearity-involved parallelogram hysteresis model (NIPHM) of AlNiCo PM is performed to investigate the electromagnetic performance of the proposed SFMM. The results derived from the combinative algorithm verifies the flux-adjustable capability of the proposed motor equipped with TDMS and the validity of the proposed NIPHM.

High speed permanent magnet machines (HSPMMs) have a promising future in applications such as aeronautics and astronautics, energy and ultra-precision manufacturing. This paper enumerates various stator and rotor structures and materials of the HSPMM in literature. Then different losses in the HSPMM are summarized in aspects of stator iron loss, copper loss, rotor eddy current loss and air friction loss. Various motor temperature rise calculation methods and three kinds of high speed rotor bearings are compared, followed by an overview of the problems linked to the rotor strength and dynamics analysis. Finally, development trends of the HSPMM related technologies are summarized and prospected.

An analytical method is presented to predict the magnetic field of the axial magnetized tubular ironless permanent magnet linear motor (TIPMLM) based on the magnetic charge method in the cylindrical coordinate system. The no-load magnetic field distribution is analyzed, the expressions of the axial and radial components of which are derived. By combining the motor parameters, the back electromotive force (EMF) and thrust force are derived. Then the no-load field distribution, back EMF and thrust force of a TIPMLM are calculated by using the proposed method and the finite element method (FEM), separately. Finally, the effect of load current on the magnetic field of the motor is analyzed by FEM. It is shown that the results of the proposed analytical method and FEM are very close to each other, which verifies the proposed analytical method. The effect of load current on the magnetic field distribution on the surface of the permanent magnets is negligible, which is one of the merits of the investigated motor structure.

A three-dimensional analytical modeling of the magnetic field of the stator-ironless axial flux permanent magnet (AFPM) machine under open-circuit condition is presented in this paper. It involves the analytical solution of the governing field equations in the region between back-irons in the cylindrical coordinate, in which the magnets are assumed to be axially magnetized and have constant relative recoil permeability. The proposed modeling method is applied to a specific AFPM machine, and the analytical results are in good agreement with those of three-dimensional finite element analysis (FEA).

Core-loss prediction is an important issue in design and analysis of permanent-magnet (PM) motors. Because of the diverse structure, flux distribution, and rotational variation of flux, it is difficult to predict the core loss in a machine exactly. In this paper, a core-loss model for the PM motor is introduced in which flux variation loci in different parts of the motor are predicted by carrying out a finite-element transient analysis. Since the flux variation pattern is complicated, an improved equation based on the conventional three-term expression is used for core-loss calculation. The core-loss model is developed totally in ANSYS parametric design language as a parametric model and it can be used easily for different types of PM motors. Calculation and experiments on a high-speed PM motor have shown that the model can produce results that agree with the experimental ones.