Performance Of Permanent Magnet Machines Research Articles

Influence of slot/pole number combinations and pole shaping on electromagnetic performance of permanent magnet machines with unbalanced north and south poles

AbstractThe influences of slot/pole number combinations on electromagnetic performances, including flux linkage, inductance, and torque ripple harmonic components etc., resulting from unbalanced characteristics between north and south poles in concentrated winding permanent magnet (PM) machines with symmetrical and asymmetric rotor pole shaping methods are theoretically analysed and experimentally validated in this paper. It shows that for the PM machines with odd number of coils per phase per submachine, including consequent pole (CP) and surface‐mounted PM (SPM) machines, the influences of unbalanced pole characteristics can lead to additional torque ripple harmonics due to additive effects in windings, but can be cancelled in other machines. Compared with symmetrical pole shaping method, asymmetric pole shaping method can result in lower torque ripple for CPPM machines with odd number of coils per phase per submachine, while symmetrical and asymmetric pole shapes have similar effects on torque ripple reduction for other CPPM machines and all the SPM machines. The findings have been validated by finite element analyses on 12‐slot/8‐pole, 12‐slot/10‐pole, 9‐slot/6‐pole, and 12‐slot/14‐pole machines, and by experiments with 12‐slot/8‐pole and 12‐slot/10‐pole CPPM prototypes.

A mechanical flux weakening method via split rotor in permanent magnet aerospace alternators

Whilst permanent magnet (PM) electrical machines often offer very high power density, they suffer from the issue that the voltage output from the machine is a function of speed due to the fixed nature of the flux delivered by the PM poles within the machine. The best performance of PM machines achieved at lower speeds might not be achieved at higher speeds due to the fact that the voltage of the machine at high speeds is greater than the rating. In order to overcome this issue in PM machines, this paper proposes a mechanical flux weakening method via a split rotor. The key feature of the proposed scheme is that the fixed nature of rotor magnet flux can be altered by means of a simple mechanism that helps reduce the magnet flux by realigning part of the rotor at higher speeds. The rotor is axially split into two sections to achieve two states of field excitations: maximum and the least output depending upon the alignment between the rotor sections. A number of key 3-dimensional (3D) finite element (FE) simulations have been used to demonstrate the effectiveness of the proposed mechanical flux weakening approach. The results indicate that the split rotor method can be an alternative to more complicated mechanical flux weakening approaches in safety critical applications such as aerospace. Thus, a PM machine with split rotor could be used over a wide speed range without applying excessive voltages to the load at higher speeds in fault tolerant aerospace applications.

Generalized Algorithm to Deal With Temperature-Dependent Demagnetization Curves of Permanent Magnets for FEA

This article introduces a temperature-dependent demagnetization model and presents a generalized algorithm to deal with temperature-dependent demagnetization curves for permanent magnet materials. It supports the input of both intrinsic curve type and normal curve type. The algorithm is based on the intrinsic curve type. If the input curves are of normal type, they will be converted into intrinsic type and be extended to the whole second quadrant. The presented algorithm is validated by comparing the derived curves at specified temperatures with the original vendor-provided temperature-dependent demagnetization curves of various permanent magnet (PM) materials. The temperature effects on the performance of permanent magnet machines are illustrated in two application examples.

Influence of Electric Loading and Rotor Speed on the Performance of Permanent Magnet Machines

The impact of electric loading such as current, copper loss and current density as well as the effect of rotor speed on the performance of double stator (DS) permanent magnet (PM) machines are analyzed and presented in this work. MAXWELL-2D software package is used in predicting the results. The investigated machine variables include: phase flux-linkage, induced phase voltage, average torque, torque ripple, total harmonic distortion, losses and efficiency. The analysis shows that most of the machines’ output performances are principally dependent on both the operating speed and loading conditions; though, the average torque and phase flux-linkage is fairly insensitive to change in speed.

Magnetic Equivalent Circuit Model Considering the Overhang Structure of an Interior Permanent-Magnet Machine

Overhang is a useful structure for increasing the torque and power densities of permanent-magnet (PM) machines without expansion of the machine space. A 3-D finite-element method (FEM) is needed to evaluate the performances of PM machines with an overhang structure because the overhang structure results in non-uniform magnetic flux distributions in the axial direction. However, it is computationally expensive, especially in the early design stage. In this paper, we propose a magnetic equivalent circuit (MEC) model considering the overhang effects of interior PM (IPM) machines. With the proposed MEC, the performances of IPM machines with an overhang structure were precisely calculated and the computational time was significantly reduced. The proposed MEC was verified by the 3-D FEM.

Investigation of a less rare-earth permanent-magnet machine with the consequent pole rotor

Due to the rising price of rare-earth materials, permanent-magnet (PM) machines in different applications have a trend of reducing the use of rare-earth materials. Since iron-core poles replace half of PM poles in the consequent pole (CP) rotor, the PM machine with CP rotor can be a promising candidate for less rare-earth PM machine. Additionally, the investigation of CP rotor in special electrical machines, like hybrid excitation permanent-magnet PM machine, bearingless motor, etc., has verified the application feasibility of CP rotor. Therefore, this paper focuses on design and performance of PM machines when traditional PM machine uses the CP rotor. In the CP rotor, all the PMs are of the same polarity and they are inserted into the rotor core. Since the fundamental PM flux density depends on the ratio of PM pole to iron-core pole, the combination rule between them is investigated by analytical and finite-element methods. On this basis, to comprehensively analyze and evaluate PM machine with CP rotor, four typical schemes, i.e., integer-slot machines with CP rotor and surface-mounted PM (SPM) rotor, fractional-slot machines with CP rotor and SPM rotor, are designed to investigate the performance of PM machine with CP rotor, including electromagnetic performance, anti-demagnetization capacity and cost.

Effect of Position Sensor Error on the Performance of Permanent Magnet Machine Drives

Accurate knowledge of motor position is required in the motor drive application where smooth torque performance is needed. The error in position causes ripple in the developed current and thereby produce torque ripple. This paper analyzes the various effects of position sensor error in the current developed and in the torque generated in a current controlled permanent magnet synchronous motor drive. This research is focused on analyzing effect of position error on smooth production of torque in an interior permanent magnet synchronous motor (IPMSM) drive due to various inaccuracies. The analysis is verified through simulation and test results by measuring torque and torque ripple performances of an IPMSM drive. The results can be easily extended to surface mount permanent magnet motor drive also.

Influence of rotor design on performance of PM machines for heavy-duty traction applications

Purpose – The purpose of this paper is to study the performance and efficiency of two different permanent magnet (PM) machine rotor configurations under magnetic core saturation conditions. Design/methodology/approach – Since the accuracy of conventional analytical methods is limited under saturation conditions, a finite element model of the machine is built; which is used to predict the various losses over its operating range such as eddy current, hysteresis, copper and magnet losses. Using this model, the efficiency map of the machine is derived which is used to investigate its efficiency corresponding to a heavy vehicle drive cycle. The performance of two different rotor designs are studied and the efficiency of each design is compared under the considered drive cycle. Findings – It has also been proved that the performance advantage due to reluctance torque in the v-shaped interior PM (IPM) machine is offset by its core steel saturation at higher current/torque levels. The magnitude of iron losses in the IPM is higher than that in the surface PM (SPM) machine, however, the magnet loss in the SPM is higher than in the IPM. Originality/value – An investigation of the performance of the IPM design in comparison with the SPM∼design under magnetic saturation conditions is not known to the authors. Hence, in this paper, it will be determined if the assumed performance advantage of the IPM over the SPM still holds true under these conditions.

Influence of Stator Slotting on the Performance of Permanent-Magnet Machines With Concentrated Windings

The use of slotted stator permanent-magnet machines with concentrated windings is increasing in industry. In this paper, the effect of the slot opening on flux linkage, internal voltage, mean torque, rotor eddy current loss, and stator iron losses is evaluated. This gives new insight into the influence of slotting on the performance of machines with a small slot opening. In addition, the slot opening can be chosen to maximize the internal voltage and the mean torque while minimizing the total iron loss. The limitations of the traditional analytical design model with small slot openings for permanent magnet machines are reported. Carter factor expressions found in literature are evaluated by comparing them with finite-element computations. The finite-element computations in turn are validated using measurements on two machines with semi-open slots and one machine with fully open slots. The measured and simulated values for amplitude and waveform of the flux linkage and internal voltages are in good agreement.

Study on Permanent Magnet Demagnetization Characteristics in Permanent Magnet Synchronous Machines

When Permanent Magnet Synchronous Machines (PMSM) working with rated load or overload, stator iron loss and copper loss, bearings friction loss, permanent magnet (PM) eddy-current all will cause PM temperature rise. In this condition, the PM is affected by the temperature and the stator of the reverse magnetic field generated prone to arouse demagnetization phenomenon, it will directly affect the performance of permanent magnet machines. Previous calculation method which used magnetic circuit method to analyze PM demagnetization characteristics cannot reflect the actual working condition of PM. Firstly, the calculation formula of PM thermal stability is deduced in this paper. Secondly, demagnetization characteristics are analyzed based on FEM, which can reflect the actual working condition of PM more accurately. This paper providing reference basis for optimum electromagnetic design, PM selection and optimum PM design.

Self-Sensing Comparison of Fractional Slot Pitch Winding Versus Distributed Winding for FW- and FI-IPMSMs Based on Carrier Signal Injection at Very Low Speed

This paper analyzes the effects of fractional pitch and distributed winding stators on the self-sensing performance of permanent-magnet machines. Three rotor configurations (i.e., a flux-weakened interior permanent-magnet synchronous machine (IPMSM) and two flux-intensified IPMSMs) and two stator designs (i.e., distributed and concentrated windings) are presented to analyze the cross saturation, secondary saliencies, saturation-induced saliencies, and saliency ratio, depending on the possible rotor and stator configurations. Finite-element modeling has been used to obtain a detailed understanding of the self-sensing performance of these machines.

Performance improvement of permanent magnet machines by modular poles

Modular permanent magnet poles have recently been proposed to enhance the performance of permanent magnet machines and improve the exploitation of used magnet materials. An optimisation method for these poles is proposed for use in linear permanent magnet synchronous machines. The main objective of the optimisation is to select proper dimensions and material properties of modular permanent magnet poles to enhance the machine developed thrust. The optimisation is carried out based on a mathematical model of the machine obtained analytically. In particular, the developed thrust of linear permanent synchronous machines with modular poles is given by the model. Genetic algorithm is then employed to optimise pole parameters where the ratio of thrust ripples to average thrust is chosen as an objective function. Extensive investigations carried out by analytical and finite element methods confirm that substantial lower thrust ripples are produced with almost the same average thrust.

STABILITY OF INTERIOR PERMANENT MAGNET SYNCHRONOUS MOTORS

ABSTRACT This paper presents a model to study the stability of interior-type permanent magnet (PM) synchronous motors. It includes the study of sudden change in operating conditions when the machine is operated in open loop conditon. Simulation results show that the reduced order models of FM machines provide sufficient accuracy to predict the machine behaviour. The eigenvalues of the linearized reduced order models are compared with those of the detailed model for seven PM machines of various designs and ratings. The rating: of the machines varies from 1-hp to 25-hp. Attention is given to the frequency of the rotor oscillation, which in general, depends on machine parameters, particularly on the inertia constant. The study indicates the areas in which improved performance of PM machines may be achieved. Simulation results are validated by experiment.

Parameter Sensitivity Analysis for Line-Start Permanent Magnet Motors

ABSTRACT A comprehensive study of the parameter sensitivity on both the synchronous and asynchronous performances of permanent magnet machines is presented. Based on the 2-axis theory for permanent magnet motor, performance equations are derived In terms of normalized machine parameters. Such an analysis can be used successfully in design optimization of permanent magnet machines. A normalized power equation for evaluating the steady-state stability limits of such type of motor is also given. Simulation results obtained are confirmed with experimental results using a number of different rotor designs. Useful conclusions have been provided, which are considered to be a good aid for designing any permanent magnet motor.