PM Machines Research Articles

A Novel Analytical Model for No-Load, Slotted, Surface-Mounted PM Machines: Air Gap Flux Density and Cogging Torque

An analytical model for prediction of air gap flux density and cogging torque in slotted surface-mounted permanent magnet (SPM) machines is presented in this paper. The proposed method is based on superposition theorem, the concept of equivalent magnetization currents (EMCs), and analytically solving of Poisson's equation. To solve Poisson's equation easily, the air gap flux density of the slotted SPM machine is stated as superposition of the air gap flux density functions of two slotless machines. The first slotless machine is excited by PMs, while the second one is excited by surface EMCs. Therefore, the concept of EMC is used in an iterative algorithm which converges quickly with a negligible computation time. Using the obtained analytical model and Maxwell's stress tensor, cogging torque of the slotted SPM machine is predicted. This analytical model provides a quick tool to study the effect of leading design parameters on the machine cogging torque. Finally, the validity of the proposed model and the obtained results are verified with finite element analysis.

Inductance calculation of high-speed slotless permanent magnet machines

Purpose – The purpose of this paper is to give a simple, fast and universal inductance calculation approach of slotless-winding machines and comparison of inductances of toroidal, concentrated and helical-winding machines, since these winding types are widely used among low-power PM machines. Design/methodology/approach – Harmonic modeling approach is applied to model the magnetic field of the windings in order to calculate the synchronous inductances. The method is based on distinction between electromagnetic properties of different regions in the machine where each region is represented by its own governing equation describing the magnetic field. The governing equations are obtained from Maxwell’s equations by introducing vector potential in order to simplify the calculations. Findings – Results of the inductances of toroidal, concentrated and helical-winding slotless PM machines, which have the same torque and dimensions, obtained by the proposed analytical method are in good agreement with 3D FEM, where the relative difference is smaller than 15 percent. However, the calculation time of the analytical method is significantly less than in 3D FEM: seconds vs hours. Additionally, from the results it is concluded that the toroidal-winding machine has the highest inductance and DC resistance values among considered machines. Helical-winding machine has lowest inductance and DC resistance values. Inductance of concentrated-winding machine is between inductance of helical and toroidal windings; however, DC resistance of the concentrated windings is comparable with resistance toroidal windings. Originality/value – In this paper the inductance calculation based on harmonic modeling approach is extended for toroidal and helical-winding machines which makes the method applicable for most of the slotless machine types.

Loss Calculation and Software Design Based on the Combination of Electric Circuit and Electromagnetic Field Solution in High Speed Permanent Magnet Machine

Mathematics model of loss for high speed machine is discussed. Calculation method of core loss and high-frequency additional copper loss of winding based on finite element analysis is introduced. Experiment results of losses are presented. In order to realize calculation and analysis, a method of PM machine by calling ANSYS and MATLAB based on VB of the combination of electric circuit and electromagnetic field solution is presented in this paper. The design and feature analysis of high speed PM machine takes an example to validate the accuracy and advantage.

Novel Carrier Signal Injection Method Using Zero Sequence Voltage for Sensorless Control of PMSM Drives

In this paper, a novel pulsating carrier signal injection strategy utilizing zero-sequence voltage is proposed for sensorless control of permanent-magnet synchronous machine (PMSM) drives. Different from the conventional zero-sequence carrier voltage sensing method using rotating signal injection in the stationary reference frame, the proposed pulsating injection is based on the estimated reference frame, which rotates anticlockwise at twice estimated rotor electrical angular speed. Then, the rotor position estimation is fulfilled via enabling the zero-sequence carrier voltage to zero. Compared with conventional rotating injection using zero-sequence voltage, the proposed strategy is simpler for signal demodulation and more robust to signal processing delays due to the fact that it is amplitude modulated by machine saliency and phase shifts of saliency position due to signal processing delays are intrinsically cancelled, which is the same as the classical pulsating injection in the estimated synchronous reference frame with carrier current sensing. Therefore, the proposed method can combine the synergies of zero-sequence method (i.e., high bandwidth and stability) and pulsating injection (i.e., increased accuracy and fast dynamic response). Furthermore, the cross-coupling magnetic saturation effects on zero-sequence voltage sensing-based sensorless control are discussed in detail. All the theoretical analyses are validated by experiments on a laboratory surface-mounted PM (SPM) machine.

Efficiency Improvement of Switched Flux PM Memory Machine Over Interior PM Machine for EV/HEV Applications

In this paper, a novel switched flux permanent-magnet (SFPM) memory machine, which consists of changeable magnetized permanent magnets (CMPMs) in the stator, is developed and investigated. By changing the magnetization directions of CMPMs, the PM flux linkage can be either enhanced or weakened. When PM flux linkage is weakened at high speed, the flux density in the lamination as well as iron loss can be reduced. Thus, higher efficiency can be obtained. To evaluate the efficiency improvement of SFPM memory machine, the efficiency map is calculated and compared with that of interior PM machine by taking Toyota/Prius 2010 as benchmark. It shows that several step changes of PM flux linkage can enlarge the high-efficiency region, and also reduce the back-EMF at high speed.

Permanent Magnet Machine Can Be a Vibration Sensor for Itself

This article presents a new vibration diagnostic method designed to (PM) machines with permanent magnets. Those devices are commonly used in small wind and water systems or vehicles drives. The author’s method is very innovative and unique. Specific structural properties of PM machines are used in this method electromotive force (EMF) generated due to vibrations. There was analysed number of publications which describe vibration diagnostic methods and tests of electrical PM machines and there was no method found to determine the technical condition of such machine basing on their own signals. In this article will be discussed: the method genesis, the similarity of machines with permanent magnet to vibration sensor and simulation and laboratory tests results. The method of determination the technical condition of electrical machine with permanent magnets basing on its own signals is the subject of patent application and it is the main thesis of author’s doctoral dissertation. Keywords—Electrical vehicle, generator, permanent magnet, traction drive, vibrations.

Permanent Magnet Machine Can Be a Vibration Sensor for Itself

This article presents a new vibration diagnostic method designed to (PM) machines with permanent magnets. Those devices are commonly used in small wind and water systems or vehicles drives. The author’s method is very innovative and unique. Specific structural properties of PM machines are used in this method electromotive force (EMF) generated due to vibrations. There was analysed number of publications which describe vibration diagnostic methods and tests of electrical PM machines and there was no method found to determine the technical condition of such machine basing on their own signals. In this article will be discussed: the method genesis, the similarity of machines with permanent magnet to vibration sensor and simulation and laboratory tests results. The method of determination the technical condition of electrical machine with permanent magnets basing on its own signals is the subject of patent application and it is the main thesis of author’s doctoral dissertation. Keywords—Electrical vehicle, generator, permanent magnet, traction drive, vibrations.

Reduction of Rotor Eddy-Current Losses for Surface PM Machines With Fractional Slot Concentrated Windings and Retaining Sleeve

High strength nonmagnetic metallic retaining sleeve is widely used in surface permanent magnet (SPM) machines for mechanical reliability, especially to high speed machines. Rotor eddy-current losses would be significantly increased in fractional slot concentrated winding (FSCW) SPM machines using sleeve. In this paper, the novel structure with copper damping rings inserted in rotor lamination is proposed. A current will be induced in the damping rings in reaction to the nonsynchronous harmonics field in the rotor, therefore, the eddy-current losses in sleeve and magnet will be reduced. FSCW SPM machines with common slot and pole combination such as 9-slot/8-pole, 12-slot/10-pole, and 24-slot/22-pole are investigated by the finite element analysis tools, and simulation results indicate that the eddy-current loss in sleeve, particularly on the single layer windings, is significantly reduced using the proposed structure.

Performance Analysis of Novel Fractional-Slot Concentrated-Winding Permanent Magnet Machine with Different Pole and Slot Matching

In order to analyze the possibility of the fractional-slot concentrated-winding for wind generation, this paper states the merits of fractional-slot concentrated-winding permanent magnet machines, and then analyzes the electromagnetic design rules of fractional-slot concentrated-winding. The fractional-slot concentrated-winding permanent magnet machine is modeled and designed in electromagnetic, and its performance is analyzed, some conclusions can be obtained, which will provide reference for further analysis and application of fractional-slot concentrated-winding PM machine.

Design and Analysis of Fractional-Slot Concentrated-Winding Permanent Magnet Machine for Wind Power Generation

In order to obtain the low synchronous speed, fractional-slot concentrated-winding PM machine is adopted to wind power generation system. This paper analyzed the pole slot combination rule, and then studied the electromagnetic design method by taking 12-slot and 10-pole machine. By using the finite element software, the characteristics is analyzed for this fractional-slot concentrated-winding permanent magnet generator, the research results show that this generator has good performance, thus prove that fractional-slot concentrated-winding scheme is feasible and effective.

Analysis and Tests of the Sensorless Rotor Position Detection of Ringed-Pole Permanent-Magnet Motor

To the aim of creating a high-frequency (HF) anisotropy in a surface-mounted PM machine conductive rings are placed around each pole such rings modify the d-axis HF impedance of the machine. A novel strategy is adopted to evaluate the HF signal injection response of such a ringed-pole electrical machine. The self-sensing capability of the machine is evaluated by means of a small-signal model of the machine in the d-q reference frame and finite-element simulations. The impact of the rings on the HF signals achieved in the analysis is validated by the comparison with experimental results.

Influence of Flux Gaps on Electromagnetic Performance of Novel Modular PM Machines

In order to simplify manufacture processes and improve fault-tolerant capabilities, modular electrical machines, especially the ones with segmented stators, are increasingly employed. However, flux gaps between segments are often inevitable. In this paper, to take advantage of these flux gaps to enhance the machine performance, novel modular permanent magnet machines with different slot/pole combinations have been proposed. The influence of these flux gaps on the electromagnetic performance of modular PM machines, such as winding factor, open-circuit air-gap flux densities, back-EMFs, cogging torque, on-load torque, inductances, magnetic saturation and copper losses, are comprehensively investigated and general rules have been established. It is found that for modular machines having slot number higher than pole number, the flux gaps between stator segments degrade the electromagnetic performance due to the lower winding factor and the flux defocusing effect. However, for modular machines having slot number lower than pole number, the electromagnetic performances can be significantly improved using proper flux gap width due to the higher winding factor and the flux focusing effect. The finite element results are validated by experiments using two prototype modular machines.

Online Estimation of Double-Star IPM Machine Parameters Using RLS Algorithm

Accurate and updated knowledge of the electric machine parameters provides benefits in many applications, such as model-based control methods. This paper presents an online parameter estimation method for double-star interior permanent-magnet (IPM) machines supplied with voltage-source inverters (VSI). The estimation method is based on a decoupled D-Q model of the machine and a recursive least-squares (RLS) algorithm. Initial machine parameters are estimated at a standstill. Then, in the rotating operating state, the inductances and the flux linkage produced by the PMs are updated. The estimation in the operating state is performed with a flux-linkage-based approach. The experimental results are compared with the corresponding values obtained from finite-element analyses. The results show an acceptable agreement and demonstrate the feasibility of the estimation scheme to estimate the parameters of double-star PM machines. The parameters are validated by comparing experimental and simulated open-loop responses and steady-state torques.

Slot Harmonic Effect on Magnetic Forces and Vibration in Low-Speed Permanent-Magnet Machine With Concentrated Windings

In this paper, the influence of slot harmonics on magnetic forces and vibration is studied in a 120-slot/116-pole low-speed PM machine at no-load. It is shown how the lowest mode of vibration is produced at no-load due to slotting. Comparing the cases of open slots, semi-closed slots and magnetic wedges, the effect of slot closure on radial forces and torque production capability is discussed. Magnetic flux distribution in the airgap is computed using finite element analysis. Spatial harmonics due to slotting are investigated in different cases. Maxwell's stress tensor is employed to calculate radial and tangential components of the force density in the airgap. Spatial distribution of the total forces on the teeth and also time-dependent force waveform on one tooth are analyzed and discussed for different cases. It is shown how the magnitude of the lowest mode of vibration is reduced in the case of using semi-closed slots and magnetic wedges. Tangential force density distribution and torque production capability are also discussed. Structural analysis is presented to compute the maximum amplitude of the stator deformations due to the radial forces. Experimental results of the prototype generator are presented verifying the existence of the lowest mode of vibration at no-load because of the slot harmonics.

On the investigation of the magnetic forces of CWPMM

Purpose– The purpose of this paper is to investigate the magnetic forces generated by a 12 slot/10 pole concentrated winding PM machines, considering a comparative study between two topologies: a surface mounted permanent magnet (SPM) machine and an interior PM (IPM) machine.Design/methodology/approach– Following a description of the main characteristics of the concentrated winding permanent magnet machines (CWPMMs) under comparison, an investigation of the magnetic forces developed by both machines under study is carried out using finite element analysis (FEA).Findings– A 2D FEA-based investigation has highlighted that the SPM machine develops higher magnetic forces than the IPM one. However, and following a 3D FEA, it has been found that the distribution of the magnetic forces along the air gap of the SPM machine is almost homogenous while it is concentrated in two opposite positions in the air gap of the IPM machine.Research limitations/implications– This work has treated almost all features of the machines under comparison, except the power losses. These should be investigated with emphasis on the PM eddy current losses is so far as the harmonic content of the armature air gap MMF is high.Practical implications– The list of the selection criteria of CWPMMs should be extended to the magnetic force cancellation in order to fulfill the requirements of many applications such as the automotive ones.Originality/value– The paper proposes a combined electromagnetic-mechanical approach to investigate the magnetic forces generated by CWPMMs using 2D and 3D FEA.

Air gap MMF based prediction of eddy current loss in the PMs of concentrated winding brushless machines

Purpose – The purpose of this paper is to an analytical approach-based prediction of the eddy current loss in the PMs of a concentrated winding machine equipped with 12 slots in the stator and ten poles in the rotor. Design/methodology/approach – The investigation of the PM eddy current loss has been carried out using an analytical model and a 2D time-stepped transient finite element analysis (FEA). Findings – It has been found, in the case of the treated machine, that just the subharmonic of rank 1 and the harmonic of rank 7 have significant contributions to the eddy current loss in the PMs. Research limitations/implications – A shift between the results yielded by the developed analytical model and those computed by FEA has been noticed. This limitation is mainly due to the slotting effect which has been omitted in the analytical model. Practical implications – Fractional slot PM machines are currently given an increasing attention in automotive applications. The prediction of their iron loss in an attempt to rethink their design represents a crucial efficiency benefit. Originality/value – The analytical prediction of the eddy current loss in each PM then in all PMs and their validation by FEA represent the major contribution of this work.

영구자석 동기발전기의 설계 및 시제품 특성 분석에 관한 연구

The small wind turbines has the merits of setting up with low costs by individuals, and get the energy saving effects that, it has the secured, separate markets from the big range systems, and the developing of it is continuously proceeding.<BR> The objective of this paper is to provide the design characteristics analysis of a permanent magnet synchronous generator(PMSG) skewed for magnet of rotor, the main advantage to be explored with the use of a split core design is the reduction in manufacturing costs and its simplicity in manufacture, compared to the manufacturing costs of a core skew PM machine. This thesis is aiming mainly analyzing the characteristics of the prototype to verify through Finite Element Method(FEM) and tests.

Analytical Modeling of Surface-Mounted PM Machines Accounting for Magnet Shaping and Varied Magnet Property Distribution

This paper develops an analytical model for predicting the magnetic field, back-electromotive force (EMF), and electromagnetic torque of surface-mounted permanent magnet machines accounting for magnet geometrical shaping and varied magnet property distribution. The magnets on the rotor are represented by the remanence, thickness, and magnetization direction functions. They are finitely segmented into magnet pieces of simple regular shape and uniform magnet property. The magnetic field of the machine is obtained by the superposition of the magnetic field due to each segment. The back-EMF and electromagnetic torque are also calculated. Using the developed model, the technique of mixed magnet material is investigated on a four-pole/six-slot machine. The analytical predictions are verified by both finite element and experimental results.

Cogging Torque Reduction of Axial Field Flux-Switching Permanent Magnet Machine by Adding Magnetic Bridge in Stator Tooth

Axial field flux-switching permanent magnet machine (AFFSPMM) is a novel stator PM machine with high torque density and efficiency. The cogging torque in AFFSPMM is larger than that in the traditional PM machine because of the double salient structure. In order to decrease the cogging torque, the analytical expression of the cogging torque is deduced and a cogging torque reduction method by adding magnetic bridge in adjacent stator tooth is proposed. Based on the 3-D finite-element (FE) method, the influence of the magnetic bridge thickness on the cogging torque and the output torque is analyzed and compared with the rotor skewing and notching methods. The influence of the stator tooth and rotor pole width on the output torque is studied. The 3-D FE analysis is compared with the experimental results. The research results show that the proposed method is effective in the reduction of cogging torque for all kinds of stator structures. Moreover, the cogging torque can decrease greatly and the average output torque decreases slightly when combined with the optimization of the stator tooth width and rotor pole width.

Adaptive Controller for Drive System PMSG in Wind Turbine

This paper proposes adaptive Maximum Power Point Tracking (MPPT) controller for Permanent Magnet Synchronous Generator (PMSG) wind turbine and direct power control for grid side inverter for transformer less integration of wind energy. PMSG wind turbine with two back to back voltage source converters are considered more efficient, used to make real and reactive power control. The optimal control strategy has introduced for integrated control of PMSG Maximum Power Extraction, DC link voltage control and grid voltage support controls. Simulation model using MATLAB Simulink has developed to investigate the performance of proposed control techniques for PMSG wind turbine steady and variable wind conditions. This paper shows that the direct driven grid connected PMSG system has excellent performances and confirms the feasibility of the proposed techniques. While the wind turbine market continues to be dominated by conventional gear-driven wind turbine systems, the direct drive is attracting attention. PM machines are more attractive and superior with higher efficiency and energy yield, higher reliability, and power-to-weight ratio compared with electricity-excited machines.