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This work investigates the effect of design parameters of permanent magnet (PM) and flux barriers (FBs) in the rotor on the anti-demagnetization ability (ADA) of fractional slot concentrated windings interior permanent magnet (IPM) motors for electric scooters. A 2.5 kW IPM motor (12 slots and 8 poles) is designed for a wide speed range, and its ADA associated with different PM and FB arrangements is studied under high temperature and high current density operations. The analysis shows the relationship between the ADA and characteristic current (Ich, defined as the ratio of PM flux linkage to d-axis inductance). It is also found that proper designs of flux barriers can significantly improve the ADA of the IPM motor without much affecting Ich. Thus, the motor ADA and performance can be simultaneously improved. Finite element analysis is used for evaluation, and experiments are conducted to validate the analysis.

This article presents an analysis on the field weakening capability of a flux intensifying synchronous motor (FI-SM) with a small quantity of inset permanent magnets (PMs) on the rotor surface. Differing from other FI-SMs whose rotors are constructed by interweaving PMs and flux barriers (FBs), for the presented FI-SM, the PM dimensions can be easily adjusted without significantly altering the rotor configuration, thus offering more flexibility in rotor design and making it more feasible to analyze the influence of the added PM on flux density distribution, inductances, PM flux linkage, and field weakening capacities in conjunction with armature current. This article, through investigating this design potential, aims to provide an approach for design and analysis of this type of motor to enhance the performance and improve the field weakening capability. Experiments are conducted to validate the simulation.

This paper investigates the demagnetization problem of permanent magnets for permanent magnet-assisted synchronous reluctance motors (PMa-SynRM) and applies “demagnetization ratio” as an index to evaluate demagnetization of permanent magnet (PM). The PMa-SynRM is often designed with multilayer flux barriers to improve saliency and reluctance torque in the rotor. Weaker or less PM (than that for interior PM motors) is embedded into the rotor which could be demagnetized in high-performance operation. PM demagnetization involves temperature, current magnitude, current phase angle, designed PM operating point, or combined effect of the above factors. This work investigates the demagnetization risk for PMs in all the layers of PMa-SynRM rotor considering these factors. In particular, the current phase angle for flux weakening operation is often omitted in demagnetization analysis. First, the motor performance to satisfy the operation condition over a wide speed range is analyzed and the proportion of motor torque components, i.e., reluctance torque and electromagnetic torque, considering temperature is investigated. Then, the flux density distributions on PMs at each position/layer are studied and the PM operating points are obtained based on the variation of excitation current, current phase angle, and temperature in order to evaluate the demagnetization risk. The analysis suggests that the high current phase angle combining the effect of high temperature is the major cause of irreversible demagnetization. Finally, a method incorporating the index “demagnetization ratio” is proposed to redesign the PMa-SynRM to avoid demagnetization. Experiments are conducted to validate the simulation.

This paper proposes a flux-intensifying permanent magnet-assisted synchronous reluctance motor (FI-PMa-SynRM) using surface-inset permanent magnet (PM) instead of embedded PM in the rotor. The proposed FI-PMa-SynRM employs a small amount of PM that is inset on the rotor surface facing $d$ -axis instead of facing $q$ -axis as in common PMa-SynRMs. It also differs from conventional flux-intensifying interior PM motor, where the PM is embedded inside the rotor. The proposed motor enables making use of the arrangements of two types of flux barriers (FBs): the cutoff FB and the magnet FB, collectively referred to the outer FBs, to enhance the torque output and reduce the torque ripple. The first objective in this paper is to explain the principles of the proposed FI-PMa-SynRM, and the second is to analyze the proposed technique for enhancement of the torque output with small PM volume while keeping the lowest possible torque ripple. The finite-element analysis is employed to validate the proposed motor and analyses, and the results demonstrate their advantages and effectiveness.

This work analyzes and compares the performances of permanent-magnet-assisted synchronous reluctance machines (PMa-SynRM) and interior permanent magnet synchronous machine (IPMSM) on their constant power speed range (CPSR) capability for electric vehicle (EV) applications. The CPSR is a key performance index for traction motors to achieve wide speed range where the IPMSM is known to be an excellent candidate. However, a recent trend for traction motor development is to reduce the amount of rare earth magnet used due to its high cost and possible supply uncertainty. As an alternative, the PMa-SynRM possesses a higher saliency (thus higher reluctance torque) and lower PM quantity (thus lower PM torque) compared to IPMSMs. With the same power or torque output, the major distinction between these two types of machines would be the proportions of different torque components (PM and reluctance torques) due to rotor designs. The distinctive rotor designs would significantly affect the CPSR and this needs to be investigated for traction motor designs and various EV applications. Five 10 kW-30 Nm/L designs, with three IPMSMs and two PMa-SynRMs are studied. The analysis results show that the PMa-SynRMs can achieve higher peak speed despite the torque and power are lower at high speed. In contrast, the IPMSM can maintain the power beyond the base speed to achieve superior CPSR but the power drops quickly to zero at high speed. The high efficiency region appears at the mid speed range for the IPMSM but at high speed region for the PMa-SynRM due to their different PM and reluctance torque profiles. Two prototypes were tested, one being IPMSM and the other PMa-SynRM to validate the analysis results.

In this paper, a study was conducted using a unit equivalent magnetic circuit (EMC) in correlating the relationship between the magnet thickness, the modulating ring pole-piece thickness, and their circumferential pitch. A numerical optimization method is employed in selecting the optimum ratio of the magnet to pole-piece thickness. The study reveals the need to simultaneously consider these parameters during the design of a magnetic gear electric machine because of their strong mutual dependency. A finite element analysis (FEA) was conducted using the optimum ratios. The results correspond to those of the EMC. Also, the performance of the machine is analyzed and found to have a power factor of 0.78. To further verify the results of FEA, a prototype was built using the same configurations of the FEA model. Measurements taken from the prototype are on par with the simulated results.

This paper presents the analysis of a brushless doubly fed reluctance machine (BDFRM) for renewable energy applications with an emphasis on the rotor design. The BDFRM stator includes two sets of windings, i.e., the control winding (CW) and power winding (PW). The PW is connected to the grid, while the CW links the grid by a power converter of fractional rating to regulate the operating speed. This reduces the converter cost, and the brushless configuration enhances the reliability. In this paper, the reluctance rotor of the BDFRM, which is similar to that of a synchronous reluctance machine, is designed and analyzed in order to improve the performance. The influence of the total MMF and its allocation to the two stator windings are also discussed in relation to the machine performance. Finite-element analysis is used for performance simulation. The experimental study validates the proposed design for a small BDFRM.

This paper develops an approach that is capable of accurately predicting the performance of synchronous reluctance motors (SynRMs). The SynRMs receive increasing attention and have been used in many industrial applications. The 2-D finite element analysis (FEA) is usually considered to be competent for design and analysis of SynRMs. However, the power factor of SynRMs is likely to be considerably overestimated. This would then lead to an underestimation of current required and cause problems for the design of electronic drivers. Compensation should be made to improve the accuracy of the analysis for SynRMs although there does not seem to be a solution put forward so far. The research in this paper shows that the exclusion of end turn leakage inductances in 2-D analysis is a key factor to cause such a significant difference. To resolve this problem, this paper analytically calculates the end turn leakage inductance, which is then incorporated into the 2-D FEA. The developed method is found to agree well with the experimental results, and it significantly improves the design accuracy and efficiency using only the 2-D FEA.

This paper provides the design of 1 MVA three-phase oil-immersed distribution transformers considering short-circuit testing (SCT) and its impact on the windings. To maintain the transformer function after the SCT, only an impedance variation within 5% is allowed. Therefore, in conjunction with the particle swarm optimization (PSO), a simulation-based optimal approach is developed for the design of the distribution transformers. Finite-element analysis is used to work with the PSO for the calculation of flux densities, costs, core losses, and magnetostriction variations for the transformers under a prescribed noise level. Three transformer prototypes are then built using two types of amorphous cores and a conventional silicon steel core, respectively. The performance after the SCT is evaluated for the prototypes constructed. From the test results, it is found that the amorphous core is suitable for transformers in terms of lower noise level, core loss, and magnetostriction variation.

Electric motors consume around half the global electric power generation and increased concern with reducing electric energy consumption has made the development of high efficiency motors more important. As the core material in electric motors, electrical steels may suffer from degradation of magnetic properties caused by manufacturing processes. For example, the punching may cause dislocations, residual stress, cracking or deformation to the grains at the lamination cut edges [1]. This would then result in lower motor efficiency than expected. Previous research [2,3] has investigated the effects of fabrication on electric motors but focused on iron losses. More effort is much needed to fully understand this impact. It would be beneficial if the motor performance considering manufacturing impact can be accurately predicted in design stage. However, this remains a challenge since there are still many uncertain factors. For instance, it is difficult to estimate the depth of the damaged zone due to punching [4], and one of the factors that greatly affect this depth is molding quality. The magnetic property, such as iron loss of the material in the damaged zone is also hard to predict.

This paper presents the reduction of noise and vibration concerning the magnetostriction effects for a single-phase power transformer with a large capacity of 200 MVA. Two magnetic core shapes are investigated: 1) D-yoked core and 2) square-yoked core. The D-yoked core is used for the construction of the transformer prototype in this paper. The magnetostriction and the hysteresis loop of the core material are measured for the simulation and analysis of noise and vibration. The transformer prototype is assembled with an external clamping force applied on the core, and the core vibration and sound-level are observed. The transformer operates with a periodic excitation that may induce resonance in the core. To avoid this, a finite-element analysis is used for modal analysis to identify the natural frequencies of the core. A tank is also designed with a sufficiently rigid structure to avoid resonances. The sound-level of the fully assembled transformer prototype is measured, and it is found to have a low-noise level below 65 dB.

This paper compares the microstructure and magnetic properties of punched electrical steel before and after annealing. The effects of this manufacturing process on performance of a switched reluctance motor (SRM) are also investigated. The punching of laminations distorts the grains near the cut edges, and therefore an anneal process is used to recover the damage caused by punching. In this paper, samples are annealed at 750°C for an hour under a N 2 atmosphere. The damaged regions and corresponding recovery after annealing are observed under microscope as the measured core losses are improved up to 37%. The SRM performance is measured and it is found that the torque density can be enhanced when using the annealed electrical steel.

This paper presents an analytical method that integrates the equivalent circuit (EC) and magnetic circuit (MC) in order to analyze and design a brushless doubly fed reluctance generator (BDFRG). The proposed method is capable of evaluating the BDFRG performance at the design stage because the terminal voltage can be predicted through the MC and the torque can be calculated from the EC. The MC is used to calculate the air gap flux density so that the flux linkage can be further obtained for the calculation of the machine performance using the EC and a set of particular operating conditions. The integration of the EC and MC provides a rapid analysis for a direct connection between the physical dimensions and the machine performances, including torque, mechanical power, electric power, and efficiency. The proposed analytical method is applied to two BDFRG designs. One is a manufactured prototype. Finite element analysis and experiments are used to verify the analytical results.

In this paper, a rigorous design of a brushless permanent-magnet (PM) motor with both lower cogging torque and higher efficiency, using response surface methodology (RSM) with a quantum-behaved PSO (QPSO) operator for a portable electric power drill application, has been presented. To decrease noise and vibration of a slotted PM motor, cogging torque must be reduced. Some skew techniques have obvious advantages of reducing cogging torque. In particular, the stepped equivalent model with its cost-effectiveness can be employed to design a high-performance PM motor for portable electric power drills in this paper. To find the most suitable combination of the geometric parameters of a brushless PM motor with skewed magnets to achieve the design goal, the RSM with a QPSO operator is employed. The 3-D finite element method (FEM) is employed as the tool for analyzing the cogging torque and performance of the proposed PM motor. The experimental results show that the proposed method can obtain the best combination of the geometric parameters for reducing the cogging torque and enhancing the operating efficiency.

This paper investigates the effect of a postassembly magnetization (PAM) process on the performance of a permanent-magnet (PM) generator with anisotropic rare-earth magnets. This process utilizes the stator windings of the generator to magnetize the magnets after complete assembly. For manufacture using this method, two orthogonal directions of a magnet may be subjected to magnetizing flux including the nonpreferred direction and this may result in weaker magnetization for anisotropic magnets. The performance can thus be affected and needs to be evaluated. The magnet characteristics are initially studied using a commercial magnetizing fixture for understanding of the magnet behavior under incomplete magnetization and magnetization in nonpreferred directions. A prototype PM generator manufactured using PAM is first simulated using finite element analysis and then tested to validate the performance.

This paper evaluates the performance of surface-mounted permanent-magnet (PM) machines with anisotropic rare-earth magnets magnetized using its own stator windings. The magnets in this process (often called in-situ magnetization) are magnetized after complete assembly. For manufacture of PM machines using this process, part of the magnet may suffer from weaker magnetization due to the magnetizing flux pattern, in particular on the two sides of the anisotropic magnets. The machine performance can thus be affected and needs to be evaluated. The current required to sufficiently magnetize the machine should be carefully studied. In this paper, both finite element analysis and experiments on prototype PM machines manufactured with in-situ magnetization are used. The concentrated and distributed winding machines are both considered. The results show that distributed winding machines can magnetize the rotors more easily than concentrated winding ones. Also, it is found that a magnetizing field of 2.5 times coercivity allows the machine back EMF magnitude to achieve the levels of pre-magnetized cases.

This paper discusses the effect of rotor eccentricity on cogging torque of a permanent-magnet (PM) generator applied to small wind turbines. The 1.4 kW radial-flux PM generator was designed to improve the start-up wind speed ( $ 3 m/s) by reducing the cogging torque. Finite element analysis (FEA) is first used to simulate the generator for a range of eccentricities and their corresponding cogging torques. In experiment, the cogging torque of a prototype generator with a particular eccentricity of 0.25 mm (33% of the air-gap length) is measured and the result matched that of the FEA. This gives confidence in terms of using FEA for further studies. The relationship between the starting torque provided by turbine blades and the cogging torque is also discussed. From the simulation, it is found that the dynamic eccentricity can be detected by measuring the cogging torque waveform.

This paper presents a magnetic circuit modeling (MCM) technique for analysis of the brushless doubly-fed machine (BDFM). Two rotor types are considered: the induction type and the reluctance type. The flux density in both the stator and rotor can be calculated by the developed MCM. This is particularly beneficial to the BDFM with the induction rotor since the generated rotor currents may saturate the rotor or stator and this is difficult to foresee at the design stage due to the complex flux patterns in the machine. A coupling factor is proposed to determine the flux coupling between the stator and rotor teeth of the induction type of BDFM. Saturation is also considered in the MCM. Finite element analysis is used to verify the analytical results.

This paper reports on the development of a permanent-magnet (PM) generator for a wind turbine which has variable winding connections for load matching. This means that the generator characteristics can be regulated via winding changeover so that the wind turbine can be controlled and maximum power point tacking (MPPT) followed; constant power output is possible without pitch control, complex algorithms or expensive power converters. The operating range (up to the cut-out point) can be extended into the high wind speed zone without drawing high power from the wind. This is achieved by maintaining the generator at the rated power when the wind speed increases beyond the rated point. Therefore, the specifications and costs of the generator and power electronics can be reduced. Experiments are conducted to demonstrate the effectiveness of the presented method.

This paper proposes a magnetic circuit model (MCM) for the design of a brushless doubly-fed machine (BDFM). The BDFM possesses advantages in terms of high reliability and reduced gearbox stages, and it requires a fractionally-rated power converter. This makes it suitable for utilization in offshore wind turbines. It is difficult for conventional design methods to calculate the flux in the stator because the two sets of stator windings, which have different pole number, form a complex flux pattern which is not easily determined using common analytical approaches. However, it is advantageous to predict the flux density in the teeth and air-gap at the initial design stage for sizing purposes without recourse finite element analysis. Therefore a magnetic circuit model is developed in this paper to calculate the flux density. A BDFM is used as a case study with FEA validation.

This paper investigates different rotor topologies based on the spoke design as an alternative to the internal permanent magnet design currently used in the Toyota Prius 2004 design. Reference is made to the 2010 model where the magnet material and maximum torque are reduced, but the speed is doubled. A rare-earth spoke design is shown to be a viable alternative. The paper then goes further and investigates a ferrite alternative. While the torque density is reduced, it illustrates that the spoke magnet arrangement may a viable solution and may open up ferrite magnet use. To offset the reduction in torque density then the speed may be increased; this is the solution Toyota used in the 2010 machine for rare-earth magnet material reduction. © 2012 IEEE.

The paper addresses unbalanced magnet pull (UMP) due to rotor eccentricity in cage induction generators used in wind turbines. The rationale for the work is to investigate ways to reduce bearing wear. The paper studies both static and dynamic rotor eccentricity with axial uniformity and also non-uniformity (e.g., due to a misplaced bearing). The damping action of the cage is discussed and a suitable analytical model used to calculate the UMP. Both sub- and super-synchronous UMP is investigated. It is found that the characteristic for the UMP varies depending on whether there is static or dynamic eccentricity. A use of additional damper windings is also investigated and it is found that these can help substantially reduce the UMP when the machine is lightly loaded with dynamic eccentricity. A previously investigated 10-pole machine is used in the simulations. The analytical model has previously been validated for this. The range of simulation covers both motoring and generating modes (±10% slip). This, together with the simulation of the UMP damping windings, represents a good contribution to the literature since they have not been previously addressed. © 2011 IEEE.

The rare-earth permanent magnets adopted in transverse flux motors (TFMs) may cause manufacturing problems due to their strong magnetism as the motor size and output power increase. For example, large magnetic forces may attract ferrous debris during the process of handling and assembling, and, hence, increase manufacturing cost. To solve the aforementioned problems, this paper applies the subassembly magnetization (SAM) strategy for a TFM. Finite element analysis was employed to design the SAM fixture such that the desired magnetization can be achieved. The SAM approach is advantageous for manufacturing the presented TFM using a ring magnet as the rotor. Simulation results confirm that the permanent magnet of the TFM can be successfully magnetized.

In this paper, the radial forces in an induction motor are calculated using finite element analysis. These radial forces (or unbalanced magnetic pull-UMP) are generated when the rotor is eccentric. The work illustrates the importance of higher winding harmonics and rotor differential leakage in the starting UMP. Examples of a 6 pole machine with 26 and 40 bar rotors show that increasing the bar number and air-gap length will reduce the UMP. Further studies are carried out using parameter variation and a 10-pole machine is also addressed, where experimental results exist, in order to validate the calculation.

Permanent magnet motors are now the focus of application in larger drive and generator systems. They often utilize rare-earth magnets where attractive forces are large and unbalanced magnetic pull (UMP) will be generated even when unexcited. In this paper, a 4-pole machine design is utilized which has either surface magnets or consequent poles. Dynamic eccentricity up to 80% is put into the machine model and a variety of simulations carried out to investigate the UMP. It is found that with strong and thick magnets the machine is robust and the UMP is almost load independent. The consequent pole rotor arrangement produces much higher UMP when the dynamic eccentricity aligns with the steel poles. In the simulations, the different stress components are investigated to assess the validity of a commonly held approximation where the radial force is taken to be a function of the square of the radial air-gap flux.

This paper presents a design for a new DC brushless motor with an interior rotor for the cooling fan. The design differs fundamentally from conventional configurations using motors with exterior rotors, the difference being in the motor structure, where the arrangement for the rotor, the stator, and the blades in the fan gives the fan motor a higher stall torque, better efficiency, and reduced noise. The paper first models the fan motor analytically with an equivalent magnetic circuit, then develops a design to meet the desired performance, and follows with a finite-element analysis (FEA) for refinement and verification of this preliminary design. The FEA result confirms the accuracy of the analytical model. With other considerations such as the reduction of waste material taken into account, two other finite-element models are created, based on the foregoing design example, but with different parameters. The paper compares output characteristics of these three models to provide a brief reference for factors to be considered in motor design.

This paper presents an analytical approach for the calculation of end winding inductance in motor windings. The method aims to provide a rapid and accurate solution for inclusion in motor and drive design, analysis and simulation programs. In this paper, Laplace's equation is first applied to derive the magnetic vector potential within the end winding region. The flux density is then obtained from the magnetic vector potential. Hence, the inductance can be determined by consideration of the flux linkage. This analytical method is experimentally verified using a specially constructed experimental rig. Comparison with other available methods is also made. It is found that the presented method has a better accuracy than the others based on the experimental results. The experiments also show that the end winding inductance can be increasingly significant as the stack length decreases

This paper illustrates a method for verifying the full magnetization of a rare-earth permanent-magnet motor when it is magnetized using a post-assembly method. The usual method of manufacturing a rare-earth magnet machine is to premagnetize before assembly, however, the assembly can be cumbersome. It is possible to magnetize after assembly. This is a critical procedure. If the magnetizing current is too low, then incomplete magnetization occurs. If it is too high, then the winding will overheat and be damaged. A simple method can be used to ascertain the correct magnetization current and this is put forward here. The method is verified experimentally

This paper proposes a technique for manufacturing permanent-magnet (PM) motors by means of post-assembly magnetization (PAM) rather than assembling with the rotor premagnetized. This can be used to vary the operating characteristics of the motor. PAM utilizes the stator windings of the PM motor to magnetize the magnets after complete assembly, where large current pulses are applied to magnetize the machine. However, in this paper, it is shown that PAM can be used in a manner where a degree of unsaturated magnetization is allowed, so that the motor back EMF constant can be regulated without modifying windings or geometry. Various magnetizing current pulses are applied which result in a range of back EMFs. These are measured for verification. From the experimental results, the feasibility of this magnetizing technique is demonstrated for a rare-earth magnet motor. It is also suggested that the magnetizing efficiency can be improved and the copper ratings reduced since it is found that large magnetizing currents may not contribute to magnetization beyond a certain current level