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This paper presents a strategy for direct‐driving a turbine with an external rotor high‐speed permanent magnet motor. It is used to improve the large footprint, low efficiency, high maintenance costs, and high vibration risk of turbines. Combining the characteristics of the working conditions of pipeline gas transmission, this paper takes a 200 kW, 10 000 rpm external rotor high‐speed permanent magnet motor as an example. This paper analyzes the eddy current losses in the rotor due to the armature magnetomotive force generated by the stator fundamental and harmonic currents. To reduce eddy current losses in permanent magnets, a circumferentially segmented pole structure is proposed for theoretical comparison and FEA with common surface‐mounted pole structures under different loads and work angles. The results confirm that the circumferentially segmented pole can effectively reduce the eddy current loss of the permanent magnet rotor. The effect of variations in the pole arc coefficient on eddy current losses in permanent magnets is also analyzed. Finally, the temperature field simulation of the motor is carried out under consideration of wind mill losses. By setting up three comparison groups with different conditions, this paper analyses the influence of the temperature and flow rate of the gas on the temperature rise and heat dissipation of the motor in a high‐temperature gas environment. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Abstract in order to study the torque ripple of permanent magnet synchronous motor for electric vehicle, the method of modular poles instead of single pole is adopted to reduce the torque ripple. The modular poles consist of three kinds of permanent magnets with different remanence and are arranged in a sinusoidal distribution. The pole arc length and position of each magnetic pole are calculated according to the cutting area of sinusoidal air gap flux density wave. By changing the cutting area of sinusoidal air gap flux density wave, the optimal pole arc coefficient of each permanent magnet was determined, and the magnet pole combination with the smallest torque ripple value is obtained. The results show that the sine degree of back electromotive force is improved obviously, the cogging torque is decreased greatly, and the motor with modular poles has obvious effect on torque ripple suppression. The torque of the motor with different kinds of magnetic pole combination is more stable than that of the motor with the same kind of magnetic pole combination. In this paper, the method of using modular poles instead of single pole to reduce torque ripple is of positive significance, which provides a reference for the subsequent performance optimization of electric vehicle motor. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Fractional slot concentrated winding (FSCW) is a kind of winding structure with few‐slots/coils multi‐poles. FSCW has the potential value of high torque density due to its short end‐winding and high slot fill ratio and is widely used in low‐speed direct‐drive application situations. However, compared with integral slot winding (ISW), the back EMF coefficient of FSCW is smaller, which leads to smaller output torque under the same condition. To improve the back EMF coefficient of FSCW, equidirectional toroidal winding (ETW) is proposed and applied to the dual rotor slotless axial flux permanent magnet motor (AFPM), in which the unit structure is three slots/coils two poles, and the ideal back EMF coefficient is the same as that of ISW. In this paper, firstly, the structure of ETW is introduced and its operating principle is analyzed. Then, compared with the AFPM with ISW, the open circuit and load characteristics of the AFPM with ETW under two conditions of the same wire gauge and the same coil width are analyzed respectively. The back EMF coefficient and output torque of ETW‐AFPM are similar to that of ISW‐AFPM under the same coil width. The back EMF coefficient and output torque of ETW‐AFPM are a little lower than that of ISW‐AFPM under the same wire gauge. Finally, the experimental results also validate the feasibility of AFPM with ETW and the correctness of the analysis results. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Compared with multi‐phase single‐module permanent magnet motors, three‐phase multi‐modularized permanent magnet motors have stronger fault tolerance ability, widely used in aerospace, ship propulsion, and other special fields. Especially in ship direct‐drive propulsion, low speed and high torque modular combined stator fault‐tolerant permanent magnet motor (MCS‐FTPMSM) has high torque density, and fault‐tolerant operation conditions may appear in actual operation, so it is essential to analyze the temperature of the fault‐tolerant motor accurately. This paper analyzes the temperature of MCS‐FTPMSM under different operating conditions and determines the longest operating time of the motor under different fault‐tolerant operating conditions based on the 3D electromagnetic‐temperature bi‐directional coupling method. Among them, the loss of the motor is calculated by the 3D electromagnetic field, which is added to the 3D temperature field as an excitation, and then the material properties in the 3D electromagnetic field are updated according to the calculated temperature distribution. The cyclic iteration method is used to make the calculated temperature deviation less than the given error value. When analyzing the electromagnetic loss of the motor, the field‐circuit coupling method is adopted to consider the influence of the current time‐harmonics of the controller on the loss of the motor during actual operation. Finally, the 12kw100r/min 3 × 3 modular prototype was tested. By comparing the results of experiments, one‐way coupling method (OWCM) and bi‐directional coupling method (BDCM), it is found that the electromagnetic‐thermal bi‐directional coupling can more accurately predict the temperature of the fault‐tolerant motor. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This paper proposes a simple and efficient method to weaken the cogging torque of the direct‐drive permanent magnet motor with inner enhance force (IEF‐DDPMM). It is characterized by adjusting the relative position of the inner and outer permanent magnets so that the cogging torque generated by the inner and outer air‐gaps is opposite in phase, thus eliminating or weakening a certain order of cogging torque. For IEF‐DDPMM, the expression of cogging torque and the variation law of cogging torque with the staggered‐pole angle are derived by the analytical method. The relationship between optimal staggered‐pole angle and the pole‐slot combination is analyzed. The influence of staggered‐pole on average torque and torque ripple is analyzed. Finally, the commercial finite element software ANASYS‐Maxwell is used for simulation, and the simulation results are consistent with the analytical results. The results show that the cogging torque of IEF‐DDPMM is the linear superposition of cogging torque from inner and outer parts; choosing a suitable staggered‐pole angle can effectively weaken the cogging torque and reduce the torque ripple. Besides, the average torque reduction caused by the staggered‐pole method can be compensated by adopting the internal power factor angle compensation strategy. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Compared to the model predictive control (MPC) technique, the modulated MPC (M2PC) method applies multiple voltage vectors in order within one switching cycle, enabling a fixed switching frequency and better motor control performance. However, the M2PC technique suffers from a significant computational burden and imprecise allocation method of the vector action time, affecting the control performance. To address these two issues, this paper proposes an improved M2PC method that utilizes the information of projection of the reference vector on the selected voltage vectors for efficiently selecting the optimal active vectors and also accurately calculating their action time. Compared to the conventional M2PC, the proposed technique demonstrates both excellent dynamic performance with reduced execution time by 15.3% and superior steady‐state performance in terms of lower torque/speed ripple as well as fewer current harmonics. Those benefits have been proven by the results of a 2.5k rpm permanent magnet synchronous motor drive. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Halbach array has been more frequently used in the field of electromagnetism in recent days because of some unique advantages such as the self‐shielding and sinusoidal field distribution. In order to reduce the impact of the high order harmonic content of the air‐gap flux density of the interior permanent magnet synchronous motor (IPMSM) on the performance of the machine, a new non‐uniform Halbach array structure is proposed in this paper. Firstly, an equivalent analytical model is established to analyze the influence on the air‐gap flux density. At the same time, the interior permanent magnet synchronous motor model is built by using the finite element analysis. Then, the relationship between the air‐gap flux density and the four design parameters (the thickness of the permanent magnet, the magnetization angle, the angle of the permanent magnet, and the proportion of auxiliary magnetic poles) is analyzed by using the Taguchi method orthogonal experiment. The total harmonic distortion (THD) of air‐gap magnetic fields and its fundamental harmonic amplitude are employed as the evaluation criteria. Finally, the effectiveness of this optimization method is verified by comparing the harmonic content of the air‐gap flux density before and after the optimization. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The fractional slot concentrated winding structure effectively solves the difficulty of low‐speed and high‐torque permanent magnet (PM) machines with a large number of poles and slots, but it also brings a wealth of magnetomotive force (MMF) harmonic. The winding function method is used to compare and analyze the stator MMF distribution and harmonic content of the fractional slot PM machines with different pole and slot combinations, and the cogging torque waveform and torque ripple are calculated by the finite element method. The influence of pole and slot combination on radial force and vibration modes of fractional slot PM machines is studied. The main vibration mode can be determined from the lowest order of radial force harmonics. The results show that in a fractional slot PM motor, the radial force is the main cause of noise and vibration, rather than the cogging torque and torque ripple. The dominant radial force is mainly produced by the interaction of rotor field harmonics and armature reaction field harmonics, and the vibration and noise will significantly increase with the decrease of the dominant vibration mode order, which largely depends on the pole and slot combination. This paper provides a certain reference for the selection of pole and slot combination in the electromagnetic design process of low speed high torque fractional slot PM motors. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Hybrid excited machine (HEM) is a novel type of machine which has attracted much attention as it is able to adjust the flux linkage flexibly and ensure the wide speed range operation. In this paper, a novel brushless HEM with permanent magnet (PM) located in rotor is further researched. By supplying specific armature currents, the sub‐harmonic component magnetomotive force (MMF) in stator MMF would be generated and utilized to realize the brushless hybrid excited operation. Firstly, the generation principle of the sub‐harmonic component is derived analytically. Secondly, during the brushless hybrid excited operation, the influence of the stator current amplitude ratio m$$ m $$ is quantitatively studied. Thirdly, based on 2D finite element analysis (FEA), the electromagnetic performance of the brushless HEM is analyzed under different operation statuses over a wide speed range. At last, the experiment is performed based on a 6 kW brushless HEM prototype machine, and the correctness of the theoretical analysis and FEA results are validated by the test. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

According to the air‐gap flux density (AGFD) and the thickness of the permanent magnet (PM) in the direction of magnetization, this paper proposes a modified analytical model for the sine pole‐shaping surface‐mounted permanent magnet motor (SPMM) under parallel magnetization. The construction of the model also involves the Carter coefficient formula, the principle of magnetic‐circuit equivalence, and the distributed magnetic‐circuit method, which are used to deal with such influential factors as stator slotting, interpolar magnetic leakage, edge effect, and magnetic‐circuit saturation. Then, a finite‐element model is established to verify the analytical model through simulation. The results show that the fundamental amplitude of AGFD of the modified sine pole‐shaping motor is respectively 6.4 and 0.15% higher than that of the simplified sine pole‐shaping motor and the eccentric pole‐shaping motor, and that the total harmonic distortion of AGFD the former is respectively 67.2 and 11.1% lower than that of the latter, thereby causing an increase in average torque of the sine pole‐shaping motor and a decrease in its radial electromagnetic harmonics and torque ripple. Experiments show that both the modified analytical and finite‐element model are accurate. And, the proposed analytical model which does not need ergodic scanning as the eccentric pole‐shaping method can further optimize the electromagnetic performance of the motor. It can not only improve the motor design but also provide reference for the optimal design of high‐quality PM motors. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This is a survey paper focusing on permanent magnet motors with variable field capability. The synchronous motors, which have been applied to somewhat limited fields, have garnered attention as attractive electric drives. Due to a connection with rare‐earth magnet and power electronics‐based flexible control, current permanent magnet synchronous motors have achieved the best position in terms of high power and torque densities, high efficiency and flexible control capability. In order to satisfy the diverse demands of users, a motor is requested to ensure high‐efficiency operation at multiple operating points on the speed–torque plane. It is well recognized that maximum efficiency is attained under the condition that the copper loss is equal to the fixed loss, mainly composed of iron loss, at a given operating point. This is why permanent magnet synchronous motors should have the capability of adjusting the field excitation, similar to the direct current shunt motors. In this paper, recent trends of research and development of variable field permanent magnet motors are overviewed from the standpoint of design and control. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

To enhance the torque of short‐time duty permanent magnet (PM) dual‐redundancy brushless DC motors (DR‐BLDCM) and avoid the motor overheating under a fixed outer diameter and length, a design method based on the optimization of split ratio and stator magnetic density (Bm) considering thermal limitations is presented. The global thermal limitation of DR‐BLDCM is set by limiting loss density. The local thermal limitation of the winding is set by limiting current density. The thermal limitations are taken as the boundary of torque enhancement design optimization. Both the cold backup and hot backup DR‐BLDCM are studied in this paper. By researching the relationship between torque, split ratio, and Bm, the optimal combination of split ratio and Bm are calculated analytically. The influences of thermal limitations on the maximum torque and the optimal combination are analyzed, and the principle to determine the optimal combination is obtained. The analytically calculated results are verified by finite element simulation, and the error is less than 6.82%. A prototype is manufactured based on analytical design results. The error between the calculated and measured copper loss is 6.96%. The verification results show that the proposed optimization method can fully enhance the torque of DR‐BLDCM under the condition of fixed overall dimension and thermal limitations. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Since it can be difficult to directly estimate the temperature of permanent magnets (PM) in high‐density permanent magnet motor rotors, this paper proposes a method based on lumped parameter thermal networks (LPTN) for online estimation of PM temperature. Firstly, a parameter model is established that contains a four‐node thermal network model and a loss model. For the online estimation, an extended Kalman filter algorithm with fading factor is used to dynamically update the thermal network parameter model in order to estimate the PM temperature. The simulation and experimental results show that the parameter model can quickly converge to a value that is close to the true value. Therefore, this online estimation method for PM temperature can accurately monitor the PM temperature online without increasing the required motor hardware; thus not affecting the motor operation. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Compared with the traditional single stator permanent magnet (PM) direct‐drive motor, the direct‐drive PM motor with inner enhance force (IEF‐DDPMM) has the advantages of high‐torque density, strong heavy‐load starting ability and flexible operation mode, so it is especially suitable for the occasions such as mine winches with a wide load range, frequent heavy‐load starting, light‐load operation, and limited use environment space. It is very important to check the temperature rise of IEF‐DDPMM according to its different operating conditions, including transient temperature rise during heavy‐load starting and steady‐state temperature rise during rated operation, so as to optimize the electromagnetic and thermal performance at the same time. Based on the bi‐directional coupling method (BDCM) of the electromagnetic field and temperature field, the thermal analysis of IEF‐DDPMM and the transient temperature field analysis of the inner motor as a torque motor for short‐term operation are carried out, and then the rated power of inner motor in S1 working system and the maximum operation time of output peak power are determined. The fluid–solid coupling analysis method is used to optimize the design of the cooling system, and the influence of the number of water channels and inlet water velocity on the heat dissipation effect of the motor is analyzed. A cooling system with strong heat dissipation ability is obtained, which can achieve higher power or torque output within the temperature range of winding insulation or demagnetization limitation of PM. Finally, a prototype is developed and equipped with a temperature rise experimental platform, and the experimental results provided a good verification of the simulation results. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Reliability is an important performance for permanent magnet synchronous machine (PMSM) exploited to industrial applications and electric‐energy vehicles. Both air‐eccentricity and inter‐turn short circuit (ITSC) could induce the machine running in unbalanced status. Once not restored timely, the fault will lead to the whole drive system and its application damage. To enhance the reliability for PMSM, an effective fault diagnosis and classification method is necessary in advance. For this purpose, an improved exponential discriminant analysis (IEDA) algorithm is proposed and optimized. Further, the distortion characteristics of phase current signals with air‐eccentricity and ITSC are extracted and trained by the IEDA, which are applied for diagnosing whether the motor healthy or faulty and distinguishing fault types. Besides, the IEDA can not only identify fault type accurately but also estimate the fault degree precisely. Finally, compared to other common learning methods, several simulations and practical tests accompanying with diverse operating status are implemented, and their results can prove the proposed method has more accuracy and robustness than other methods. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]