France



&lt;br/&gt;This paper overviews recent developments and novel topologies of a new class of asymmetric rotor pole interior permanent magnet (AIPM) machines for torque enhancement. The principle for torque enhancement by utilizing magnetic-field-shifting is introduced firstly. AIPM machine topologies are then categorized in terms of asymmetries of PM configurations and rotor core geometries. Subsequently, various AIPMs in each category are described and analyzed with respect to merits and demerits. Finally, electromagnetic performances of selected AIPM machines are compared.&lt;br/&gt;INDEX TERMS: Asymmetric interior permanent magnet (AIPM), Magnetic-field-shifting (MFS), PM torque, Reluctance torque&lt;br/&gt;I. Introduction&lt;br/&gt;Interior permanent magnet (IPM) machines having PMs buried inside the rotor cores are of growing interests due to superior torque density, high efficiency, wide constant power operating speed range, and high rotor robustness [1]. In IPMs, the reluctance torque resulted from the rotor saliency can be utilized to enhance the torque density without increasing the PM usage. However, in conventional IPM machines with symmetrical rotor structures, the maximum PM and reluctance torque components are achieved at different current angles whose difference is theoretically 45 electrical degrees. Consequently, only a portion of both torque components can be utilized at the current angle of maximum synthetic torque. To deal with this issue, a novel design concept for torque enhancement of IPMs by making the maximum PM and reluctance torque components to be reached with a smaller difference of current angles has been firstly proposed by setting the optimal displacement angle between the surface-mounted PM rotor and the reluctance rotor in a two-part rotor PM machine [2] and by employing asymmetric rotor flux barriers in a V-shape IPM [3], respectively. To utilize the concept designated as magnetic-field-shifting (MFS) effect in this paper, the PM field and reluctance axes of IPM machines need to be shifted, resulting in a new class of novel asymmetric rotor IPM machines. The torque enhancement principle of AIPM is illustrated in Fig. 1. This paper overviews various novel AIPM topologies which are categorized in terms of asymmetries of PM configurations and rotor core geometries, analyses various AIPMs in each category with respect to merits and demerits, and compares electromagnetic performances of selected AIPM machines.&lt;br/&gt;II. AIPM Machine Topologies&lt;br/&gt;In this section, novel AIPM machine topologies in literature are categorized according to whether their PM configurations and rotor core geometries are symmetrical or asymmetric, respectively. The proposed categorization method and some examples reported in references for each category are shown in Fig. 2 (a).&lt;br/&gt;An AIPM topology with the asymmetric hybrid-layer PM configuration and asymmetric rotor cavity has been proposed in [4], which achieves torque enhancement with simple structure due to utilizing MFS effect and also shows reduced torque ripples. A hybrid-pole AIPM machine is proposed in [5] that employs V-shape and inset PMs in adjacent poles alternatively, which has asymmetric PMs due to shifted positions of inset PMs but symmetrical rotor core geometry. This hybrid-pole AIPM has higher torque density compared with a V-shape IPM with the same PM usage. An AIPM machine with asymmetric PMs and symmetrical rotor structure is also reported in [6] that can achieve fully aligned maximum PM and reluctance torque components, although the increase of synthetic torque is not notable compared with a PM-assisted reluctance machine because of significant reduction of maximum reluctance torque. The asymmetric flux barrier in one side of symmetrical V-shape PMs in each pole is used in [3] to utilize the MFS effect by shifting the angle of reluctance axis and to clearly increase the synthetic torque. Similar to [2], a two-part rotor design with a SPM rotor and a multi-layer reluctance rotor is proposed in [7] that exhibit symmetrical PM configuration and rotor cavity design, respectively. The MFS effect is utilized by adjusting the displacement angle between both rotor parts, which can also achieve fully aligned maximum PM and reluctance torque components and shows a clear torque enhancement. Four selected AIPM machines with rotor topologies proposed in references [3]-[5] and [7] are redesigned by using the same stator, rotor diameter and PM usage to the conventional Toyota Prius 2010, and their torque performances at 750 r/min and 236A are compared in Fig. 2 (b). Comprehensive overview of more AIPM topologies will be given in the full paper.

**References:**

[1] Z. Zhu and D. Howe, &lt;i&gt;Proc. IEEE&lt;/i&gt;, vol. 95, p.746-765 (2007).&lt;br/&gt;[2] P. Winzer and M. Doppelbauer, &lt;i&gt;2014 Int. Conf. Electr. Mach&lt;/i&gt;. &lt;i&gt;(ICEM)&lt;/i&gt;, Berlin, 2014, p. 641-647.&lt;br/&gt;[3] W. Zhao, F. Zhao, T. A. Lipo, and B.-I. Kwon, &lt;i&gt;IEEE Trans. on Magn.&lt;/i&gt;, vol. 50, no. 11, p. 1-4 (2014).&lt;br/&gt;[4] Y. Xiao, Z. Q. Zhu, J. T. Chen, D. Wu, and L. M. Gong, &lt;i&gt;2020 Int. Conf. Electr. Mach&lt;/i&gt;. &lt;i&gt;(ICEM)&lt;/i&gt;, Gothenburg, 2020, p. 26-32.&lt;br/&gt;[5] G. Xu, G. Liu, W. Zhao, Q. Chen, and X. Du, &lt;i&gt;IEEE Trans. Ind.&lt;/i&gt; &lt;i&gt;Electron.&lt;/i&gt;, vol. 66, no. 4, p. 2580-2591 (2018).&lt;br/&gt;[6] F. Xing, W. Zhao, and B.-I. Kwon, &lt;i&gt;IET Electr. Power Appl.&lt;/i&gt;, vol. 13, no. 5, p. 573-580 (2018）.&lt;br/&gt;[7] H. Yang, Y. Li, H. Y. Lin, Z. Q. Zhu, et al., &lt;i&gt;2017 IEEE Energy Convers. Congr.&lt;/i&gt; &lt;i&gt;Exposition (ECCE)&lt;/i&gt;, Cincinnati, 2017, pp. 2362-2367.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/339b97d20cc7f72fd8fd7d97e5455425.jpg)
Fig.1.Principle of torque enhancement of AIPM. (a) Conventional IPM. (b) AIPM with reduced △&lt;i&gt;β&lt;/i&gt;. &lt;i&gt;T&lt;sub&gt;syn&lt;/sub&gt;&lt;/i&gt;, &lt;i&gt;T&lt;sub&gt;pm&lt;/sub&gt;&lt;/i&gt; and &lt;i&gt;T&lt;sub&gt;rel&lt;/sub&gt;&lt;/i&gt; denote maximum synthetic, PM, and reluctance torques, respectively, and △&lt;i&gt;β&lt;/i&gt; denote the current angle difference between maximum PM and reluctance torque components.

![](https://assets.underline.io/uploads/markdown_image/1/image/4d44aa957f2775e6ab24c779072c37ef.jpg)
Fig.2. Categorization of some typical AIPM machine topologies. In (a), PMs in red and blue denote N- and S-poles.

INTERMAG 2021

 Novel Asymmetric Rotor Pole Interior Permanent Magnet Machines with Enhanced Torque Density: An Overview

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This paper overviews recent developments and novel topologies of a new class of asymmetric rotor pole interior permanent magnet (AIPM) machines for torque enhancement. The principle for torque enhancement by utilizing magnetic-field-shifting is introduced firstly. AIPM machine topologies are then categorized in terms of asymmetries of PM configurations and rotor core geometries. Subsequently, various AIPMs in each category are described and analyzed with respect to merits and demerits. Finally, electromagnetic performances of selected AIPM machines are compared. INDEX TERMS: Asymmetric interior permanent magnet (AIPM), Magnetic-field-shifting (MFS), PM torque, Reluctance torque I. Introduction Interior permanent magnet (IPM) machines having PMs buried inside the rotor cores are of growing interests due to superior torque density, high efficiency, wide constant power operating speed range, and high rotor robustness [1]. In IPMs, the reluctance torque resulted from the rotor saliency can be utilized to enhance the torque density without increasing the PM usage. However, in conventional IPM machines with symmetrical rotor structures, the maximum PM and reluctance torque components are achieved at different current angles whose difference is theoretically 45 electrical degrees. Consequently, only a portion of both torque components can be utilized at the current angle of maximum synthetic torque. To deal with this issue, a novel design concept for torque enhancement of IPMs by making the maximum PM and reluctance torque components to be reached with a smaller difference of current angles has been firstly proposed by setting the optimal displacement angle between the surface-mounted PM rotor and the reluctance rotor in a two-part rotor PM machine [2] and by employing asymmetric rotor flux barriers in a V-shape IPM [3], respectively. To utilize the concept designated as magnetic-field-shifting (MFS) effect in this paper, the PM field and reluctance axes of IPM machines need to be shifted, resulting in a new class of novel asymmetric rotor IPM machines. The torque enhancement principle of AIPM is illustrated in Fig. 1. This paper overviews various novel AIPM topologies which are categorized in terms of asymmetries of PM configurations and rotor core geometries, analyses various AIPMs in each category with respect to merits and demerits, and compares electromagnetic performances of selected AIPM machines. II. AIPM Machine Topologies In this section, novel AIPM machine topologies in literature are categorized according to whether their PM configurations and rotor core geometries are symmetrical or asymmetric, respectively. The proposed categorization method and some examples reported in references for each category are shown in Fig. 2 (a). An AIPM topology with the asymmetric hybrid-layer PM configuration and asymmetric rotor cavity has been proposed in [4], which achieves torque enhancement with simple structure due to utilizing MFS effect and also shows reduced torque ripples. A hybrid-pole AIPM machine is proposed in [5] that employs V-shape and inset PMs in adjacent poles alternatively, which has asymmetric PMs due to shifted positions of inset PMs but symmetrical rotor core geometry. This hybrid-pole AIPM has higher torque density compared with a V-shape IPM with the same PM usage. An AIPM machine with asymmetric PMs and symmetrical rotor structure is also reported in [6] that can achieve fully aligned maximum PM and reluctance torque components, although the increase of synthetic torque is not notable compared with a PM-assisted reluctance machine because of significant reduction of maximum reluctance torque. The asymmetric flux barrier in one side of symmetrical V-shape PMs in each pole is used in [3] to utilize the MFS effect by shifting the angle of reluctance axis and to clearly increase the synthetic torque. Similar to [2], a two-part rotor design with a SPM rotor and a multi-layer reluctance rotor is proposed in [7] that exhibit symmetrical PM configuration and rotor cavity design, respectively. The MFS effect is utilized by adjusting the displacement angle between both rotor parts, which can also achieve fully aligned maximum PM and reluctance torque components and shows a clear torque enhancement. Four selected AIPM machines with rotor topologies proposed in references [3]-[5] and [7] are redesigned by using the same stator, rotor diameter and PM usage to the conventional Toyota Prius 2010, and their torque performances at 750 r/min and 236A are compared in Fig. 2 (b). Comprehensive overview of more AIPM topologies will be given in the full paper.

**References:**

[1] Z. Zhu and D. Howe, Proc. IEEE, vol. 95, p.746-765 (2007). [2] P. Winzer and M. Doppelbauer, 2014 Int. Conf. Electr. Mach. (ICEM), Berlin, 2014, p. 641-647. [3] W. Zhao, F. Zhao, T. A. Lipo, and B.-I. Kwon, IEEE Trans. on Magn., vol. 50, no. 11, p. 1-4 (2014). [4] Y. Xiao, Z. Q. Zhu, J. T. Chen, D. Wu, and L. M. Gong, 2020 Int. Conf. Electr. Mach. (ICEM), Gothenburg, 2020, p. 26-32. [5] G. Xu, G. Liu, W. Zhao, Q. Chen, and X. Du, IEEE Trans. Ind. Electron., vol. 66, no. 4, p. 2580-2591 (2018). [6] F. Xing, W. Zhao, and B.-I. Kwon, IET Electr. Power Appl., vol. 13, no. 5, p. 573-580 (2018）. [7] H. Yang, Y. Li, H. Y. Lin, Z. Q. Zhu, et al., 2017 IEEE Energy Convers. Congr. Exposition (ECCE), Cincinnati, 2017, pp. 2362-2367.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/339b97d20cc7f72fd8fd7d97e5455425.jpg)
Fig.1.Principle of torque enhancement of AIPM. (a) Conventional IPM. (b) AIPM with reduced △β. Tsyn, Tpm and Trel denote maximum synthetic, PM, and reluctance torques, respectively, and △β denote the current angle difference between maximum PM and reluctance torque components.

![](https://assets.underline.io/uploads/markdown_image/1/image/4d44aa957f2775e6ab24c779072c37ef.jpg)
Fig.2. Categorization of some typical AIPM machine topologies. In (a), PMs in red and blue denote N- and S-poles.

technical paper

Ι. Introduction The anode saturable reactor is a critical element in the thyristor converter vavle of HVDC (high voltage direct current) transmission system, which is designed for limiting the current rise of the thyristor so as to protect it. However, the non-uniform distribution of core loss of anode saturable reactor can cause overheating and thermal aging of the insulating material, eventually lead to the failure of the reactor [1-2]. It is difficult to measure the local core loss of reactor directly so we have to monitor real-time temperatures with the infrared thermocamera [3]. Because of the complex working current waveform of saturable reactor, Bertotti core loss separation model suitable to sinusoidal excitation is no longer available [4]. Therefore, the dynamic core loss calculation method is used to calculate core loss of the reactor [5-6]. In this paper, the model of saturable reactor is established, and the core loss is analyzed by electro-magnetic finite element method (FEM). To couple the data from magnetic field to temperature field accurately, core loss is mapped between heterogeneous meshing. Meanwhile, the thermal network model of the saturable reactor is built up. Based on the calculation results of computing fluid dynamics (CFD) software, the convective heat transfer coefficients on the reactor surfaces are extracted for thermal resistances calculation. Finally, the steady-state temperature distribution is obtained. The validity of the FEM and thermal network is verified by the temperature rise experiment. ΙΙ. Anode saturable reactor model The model of the saturable reactor is shown in Fig.1(a). Located inside the reactor, the hollow aluminum winding consists of 5 turns, which is wrapped by epoxy resin and cooled by circulated water in the aluminum tubes. The 9 pairs of cores, epoxy resin and winding are encapsulated into the reactor fiberglass enclosure with polyurethane elastomer. The outside surfaces of the reactor dissipate heat by natural convection, while the inside surfaces of the reactor can transfer the heat through the circulation aluminum tubes due to highly efficient forced water cooling. In addition, because of the geometric symmetry of the reactor, a one-ninth model of saturable reactor is established for temperature simulation, as shown in Fig.1(b). Other boundary conditions of the model are shown in Fig.1(c). ΙΙΙ. Magnetic-thermal- fluid coupling analysis A. Magnetic field calculation In order to reduce eddy loss, the core is made of ultra-thin silicon steel sheets with 0.1mm thickness. The leakage magnetic flux penetrates into the silicon steel normally, so the outermost layers silicon steel sheets have significant eddy current. The exact laminated model of sheet-by-sheet reactor is difficult to computed. In order to simulate the surface local eddy current, the homogenous numerical technique is adopted for FEM modelling. The distribution of magnetic flux density is shown as Fig.2(a). Under the impact of air gap, winding structure and leakage magnetic field, the eddy loss is concentrated in the core surfaces and the air gap as shown in Fig.2(b). B. Calculation of temperature field and fluid field In traditional magneto-thermal coupling method, the loss from magnetic field is obtained by integrating over the whole region and then distributed evenly to each element. This coupling mode with equally distributed loss density underestimates the highest hot-spot so as not to be accurate enough for the reactor model. Consequently, the node-to-node mapping method can predict the loss distribution inside the saturable reactor more precisely. The triangulation element in magnetic field calculation is tetrahedron, while the element in the solid region of CFD is hexahedron. Namely, the meshes of the two physical fields are heterogeneous, so the data cannot be delivered directly. The method of interpolation between the adjacent nodes is proposed in the paper to map the core loss to CFD. The heat sources of saturable reactor are consisted of core loss and hollow aluminum winding loss. Since the temperature in aluminum winding is lower than that in epoxy resin and core, and the cooling water inside winding is a fluid with stable flow rate, the convection heat transfer coefficient is constant. So the winding can be regarded as an internal convective heat transfer boundary condition, which convection heat transfer coefficient on the interface of the winding is 6 W/(m2●K) by experiment [7]. Contacting with air, the exterior surfaces of reactor dissipate heat by natural convection. By solving energy conservation, momentum conservation and mass conservation equations, the distributions of reactor temperature and air velocity are shown in Fig.2(c) and Fig.2(d). ΙV. Experimental results and discussion The current of the reactor under actual operating conditions is excited into the winding. When the overall temperature is stable, the infrared thermograph is used to record the temperature distribution on the reactor housing. The experimental results show that the highest temperature on the shell is located in the inner toroidal surface, which is 317.15K and in good agreement with CFD simulation results. V. Conclusion The average surface temperature of the saturable reactor is 315.15K, and the highest temperature is 317.15K at the top of the inner ring surface. Affected by the buoyancy and the uneven distribution of loss, the hottest spot of core is located at the inner and upper position with 354.15K.

**References:**

[1] C. Peng, S. Baokui, and J. Feng, High Voltage Engineering., Vol.42, p.2612-2617 (2016) [2] Z. Yang, 2019 IEEE 10th International Symposium on Power Electronics for Distributed Generation Systems., p.294-298, (2019) [3] J. Cao, F. Ji, and J. Liu, IET Science, Measurement & Technology., Vol.10, p.77-83 (2016) [4] G. Wenjun, H. Shaogang, and Y. Yuwen, Motor and Control Application., Vol.43, p.82-85 (2016) [5] S. Barg, K. Ammous and H. Mejbri, IEEE Transactions on Power Electronics., Vol.32, p.2146-2154 (2017) [6] D. Lin, P. Zhou, and W. N. Fu, IEEE Transactions on Magnetics., Vol.40, p.1318-1321 (2004) [7] M. Yan, D. Shengchu, and G. Lu, High Voltage Engineering., Vol.44, p.3359-3367 (2018)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/9cf6e1206600c2719dceffe99c377d82.jpg)
Fig.1 Establishment of anodic saturation reactor model

![](https://assets.underline.io/uploads/markdown_image/1/image/9753a737299e46d235b4eec5a0573616.jpg)
Fig.2 Simulation results of one-ninth model

 Magnetic-Thermal Coupling Analysis of Anode Saturable Reactor

1. This research aims to study the edge computing devices with a faster processing and signal connecting function based on development of the physical layer and magnetic sensing devices. It is important matter for smart robot in multi-axis motor control. Based on the variable robot properties, it includes humanoid robots, wheeled machines, and fixed robots, respectively, are contented. This research is constructed as follows: to establishing an edge computing device system, the image vision system with neural-network learning theory to control robot arm path, multiple magnetic sensors in physical layer to analyze the signals of the motor, voltage, current, temperature, etc., are transmitted signal to the edge computing device and IoTs computing server system. 2. Introduction The Industry 4.0 concept represents the trend of data exchange and automation in the manufacturing industry. It is defined by cloud computing, cyber-physical systems and the IoTs. In Industry 4.0, computers and automation technologies are integrated with robots and their components [1,2]. These robots and other components are remotely connected to a computer system, and the computer system is equipped with algorithms that can control and learning robots with minimal human intervention. For the motor device, the robot composes the control of the DC motor and relate to the accessories vital role. However, there are many factors that can misguide the controller's work, to make an unable to accurately control and/or have the desired dynamic behavior. For example, the resistance (Ohmic) of the coil winding of the motor is changed due to the temperature is different. If the vibration level is high and the wear of the rotor ball bearing becomes larger, the friction coefficient will also be affected. Therefore, the cloud computing environment of industrial factories, a continuous processing is required to re-evaluate the precise values of motor parameters and update the corresponding controller settings. In addition, it should be noted that the torque and speed sensors of the motor must have the correct selection to assist for achieving the correctness of the program. 3. Theory and methods: multi-axis motor sensing and visual images of robotic arms Collaborative robots focus on intelligent motor control. Based on this construction, multiple sensor component signals are added. The physical information such as voltage, current, vibration, electric heating, magnetic flux sensing, and motor position is diagnosed through integrated control. This study, the artificial intelligent motor with the sensing signals, is used to control motor speed, positioning, constant horsepower, constant torque, force feedback, vibration resistance, overheating, overload, and instantaneous short circuit, as shown in Figure 1. The electromagnetic control of this paper is as follows: A. Single robotic arm function automation: Directly control the robot motor, at the same time, it has higher precision and speed to perform specific tasks repeatedly, but most of them cannot clearly actuate without an electromagnetic sensor. B. Part of the arm automation: It assists decision-making through environmental sensing input signals. In this study, robots use vision and sensors to determine the decision-making process, which is not easy to deal with accidental arm interference. C. Conditional autonomous robot: Control the arm according to the environmental monitoring behavior, but the external server can operate in real time. D. Highly autonomous robot: an environment that needs to be defined in an area or any situation without human operation. 4. Experimental results and discussion Based on the motor control of intelligent robots, this research proposes a better and faster algorithm structure, which is a neural network-like combined with particle swarm method, which is used to calculate the convergence result of a lower loss function, which can accurately control the motor parameters and combine the IoTs, as shown in Figure 2. First, the robotic arm establishes multi-input sensing values, using the above algorithm to evaluate the robotic arm motor parameters, the prevention of interference from peripheral physical sensing, and the signal processing of external visual images. The issues raised based on past research experience include:(1) Establish edge and fog calculations to control the voltage and current of the motor, (2) establish neural network algorithm to calculate motor parameter, (3) construct the image vision system, (4) establish a smart robot platform, including wheel-shaped and human-shaped robots as experiments, which uses the above-mentioned deep learning theory to construct the test of the robot's motor motion and signal transmission response, (5) to use the multiple sensors, motor electromagnetic signals, piezoelectric sensors, and load signals, as the force feedback of the robot to calculate and judge. Finally, (6) to integrate the edge computing of the sensing layer, the fog computing of the signal processing layer, and faster computing layer through the IoTs cloud server. The IoTs chip is to use the dual-core Linkit-7697 (Taiwan’s MediaTek Inc). The chip can perform as a cloud computing and remote device, which indeed meet the requires of providing multi-sensing force feedback for cooperative robot handling objects.

**References:**

[1]. Chang-Hung Hsu*, et. al., “Effect of Magnetostriction on the Core Loss, Noise, and Vibration of Fluxgate Sensor Composed of Amorphous Materials,” IEEE Trans. on Magnetics, vol. 49, no. 9, pp: 3862-3865, 2013. [2]. Chang-Hung Hsu*, “Fractional Order PID Control for Reduction of Vibration and Noise on Induction Motor, IEEE Transactions on Magnetics, vol. 55, no. 11, pp. 6700507-1-7, Nov. 2019.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/25aedc186791a6c6ab6b9b1e787bf147.jpg)
Figure 1 The artificial intelligent motor with the sensing signals including as motor speed, positioning, horsepower, torque, force feedback signals.

![](https://assets.underline.io/uploads/markdown_image/1/image/4f2f81175e1c787ad9280be42610481b.jpg)
Figure 2 The smart motor of the robot performance testing results and AI vision detection.

 Research on Electromagnetic Control of Robot Arm using Smart Motor Combined with Internet of Things

The renewable energy is introduced because of global environmental problems. The vibration energy generated by the electric vehicle and the buildings is considered. Using the linear synchronous generator, this energy is converted to electric energy. The charging circuit with the EDLC (Electric Double-Layer Capacitor) for the linear synchronous generator is introduced. The linear synchronous generator extends the cruising distance of the electric vehicle and lighting of the buildings. In addition, it also suppresses vibration. Thus it is used as the damping device such as the mechanical damper [1]. Fig.1 shows the linear synchronous generator. The electric energy is generated by using the linear synchronous generator. The linear synchronous generator consists of the stator part and the vibration part. The permanent magnet and the iron yoke are set on the stator part. The coil for the generation is set on the vibration part. The vibration is generated by giving the initial energy (the elastic energy by the mechanical spring) to the vibration part. When the coil moves in the x-axis direction on the permanent magnet, the linkage flux from the permanent magnet is changed. The electromotive force in the coil is generated by the linkage flux is changed [2]. In this paper, the charging characteristics and the damping characteristics of the linear synchronous generator are studied. The charging characteristics are determined by the charging energy of the EDLC. The vibration waveform is damped by the charging energy of the EDLC, the power consumption in the wire-wound resistance of the coil and the internal resistance of the EDLC, the mechanical loss. The mechanical loss is calculated as the loss proportional to the velocity using the viscosity coefficient c = 2.0 derived from the vibration waveform of the linear synchronous generator. Their characteristics are examined by changing the initial energy given to the vibration part and the frequency of the vibration waveform. The initial energy is changed by the initial displacement of the vibration part. The frequency is changed by the spring constant [3]. In this study, MATLAB/Simulink and PSIM (the electronic circuit simulation software) are used for analysis. The generated voltage Vin is converted to DC voltage by the rectifier. The analysis conditions are as follows; the coil inductance L = 1.4 mH and the wire-wound resistance of the coil RL = 3.0 Ω, the EDLC capacitance C = 0.141 F and the internal resistance of the EDLC RC = 6.67 Ω. The charging characteristics and the damping characteristics are studied by changing the initial energy (0.073 ~ 7.3 J). The initial displacement of the vibration part is changed (10 ~ 100 mm) and the spring constant is 1465 N/m. The frequency is 5 Hz. From the result, the charging energy of the EDLC is increased proportionally as the initial energy increases. This is because the electromotive force in the coil is increased as the initial energy increases. And charging efficiency of the EDLC is increased as the initial energy increases. The linear synchronous generator can be charged with high efficiency as the initial energy increases. The stop time of the vibration part compared to the case that the charging circuit is not connected is the fastest and the vibration part is stopped 38.6% faster when the initial energy is 7.3 J. But the power consumption in the wire-wound resistance and in the internal resistance of the EDLC, and the mechanical loss are increased. The charging characteristics and the damping characteristics are studied by changing the frequency (1 ~ 10 Hz). The initial energy is fixed at 0.36 J. Figs.2(a) shows the vibration waveform (1, 5, and 10Hz), and Figs.2(b) shows the charging energy of the EDLC by changing the frequency (1 ~ 10 Hz). From the result, the charging energy of the EDLC is decreased as the frequency increases. This is because the current in the circuit and the velocity of the vibration part is increased as the frequency increases, and the power consumption in the wire-wound resistance and in the internal resistance of the EDLC, and the mechanical loss is increased. The stop time of the vibration part is shortened as the frequency increases. To improve the charging characteristics, the circuit switching the EDLC is created. Switching uses two EDLCs. The charging characteristics are improved. This is because a low voltage that isn't charged can be charged. And the damping characteristics are improved because the kinetic energy of the vibrating part is consumed faster. In conclusion, the charging characteristics are improved when the initial energy is large and the frequency is low. The damping characteristics are improved when the initial energy is large and the frequency is high. When using as the power generator, the vibration with the large energy amount and low frequency is effective. And when using as the vibration damping device, the vibration with the large energy amount and high frequency is effective. The circuit that switching the EDLC is effective for both the charging characteristics and the damping characteristics.

**References:**

[1] M. Mueller, P. Brooking and J. Xiang, “Low Speed Linear Electrical Generators for Renewable Energy Applications,” Proc. of Int. Symposium on Linear Drives for Industry Applications, pp.29 -32 (2003) [2] K. Ishida, J. Muranishi, T. Aoki, S. Ohashi, “The Generation Characteristics of the Improved Configuration of the Stator and the Mover in the Linear Generator Using Vibration Energy,” IEEE Region 10 Conference (TENCON), pp.2634-2637 (2016) [3] S. Ohashi, T. Matsuzuka, “Basic Characteristics of the Linear Synchronous Generator Using Mechanical Vibration,” IEEE Trans. Magnetics, vol.41, No.10, pp.3829-3831 (2005)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/a9f91f4198fd736a3b8444300cac1f0c.jpg)
Fig.1 The linear synchronous generator

![](https://assets.underline.io/uploads/markdown_image/1/image/a2e1256195b4fcdf29ac95773ca348b4.jpg)
Fig.2 The charging characteristics and the damping characteristics by changing the frequency

 Dependence of the Vibration Energy and Frequency on the Charging Characteristics and the Damping Characteristics of the Linear Synchronous Generator

1. In this paper, an improved modal frequency calculation theory of the stator assembly of the electrical machine is proposed based on the first-order shear deformation laminated theory. The frame, stator core and windings of the assembly are modeled as multilayer cylindrical shell, which are laminated along the radial direction. In order to increase the accuracy, the interference fit is considered in the proposed model, which is widely used in manufacture of the assembly. Due to the lamination characteristics of stator core and the arrangement of copper and insulation of windings, the orthogonal properties of these materials are considered in the modeling. The motion and boundary equations are deduced via variational method, and the modal frequency can be obtained by calculating the eigenvalues of the equations. Then, the experiments is conducted by hammer impact test. The experimental results of the free and simply supported boundary conditions are compared with the calculated results, and the comparison shows good arrangement for the proposed model. 2. Introduction: Electrical machines are widely used in electric vehicles, washing machines, compressors and other people involved areas, and the concomitant electromagnetic vibration and noise have aroused attention to comfort. Based on the modal superposition method, the vibration response can be obtained depending on pressure distribution, excitation frequencies, modal frequencies and shapes. In order to avoid coincidence between excitation frequencies and natural frequencies, the modal frequency of the machine stator should be accurately calculated [1]. Because machine stator assembly contains many parts, such as frame, windings, end covers and stator core, some simplifying assumptions have been made in existing studies [2]-[3]. The ring type model takes all the parts as a single ring and neglects the axial direction, but it can only calculate the pure radial modes and cannot consider the boundary conditions. Other researchers propose different simplification method of teeth, windings and frame, but the calculated modes are only in partial agreement with experimental. As for the materials, most studies consider them as isotropic and continuous. However, this can lead to a noticeable discrepancy between the mode of the analytical result and that of the test result. The interference fit will increase the equivalent stiffness of the stator assembly, but the effect of the fit on the modal frequency are not deeply investigated. In this paper, a modal frequency calculation method is proposed, and the orthogonal properties of materials and the interference fit are considered. 3. Calculation model: A nature frequency calculation theory is proposed based on the first-order shear deformation laminated theory. In the proposed method, the stator assembly is modeled as multilayer cylindrical shell laminated along radial direction. Due to the lamination characteristics of silicon steel sheet and the arrangement of copper and insulation of winding, these two materials can be model as orthotropic materials. In order to approach the realistic situation, the interference fit is modeled in the proposed method, which is a single layer between the frame and stator core. Then, the motion and boundary equations are deduced via the variational method, as shown in Fig. 1. The modal frequencies of three translational and two rational directions can be obtained by calculating the eigenvalues of the equations. The modal frequencies of the stator assembly under free and simply support boundary condition are calculated, and compared with simulation results of the finite element method. In addition to calculating the modal frequency of the radial-flux electrical machines, the proposed model can also be applied to calculated modal frequency of the axial-flux machines. 4. Experimental verification: To verify the accuracy of the proposed model, a 27-slot stator assembly of a radial-flux machine is utilized. The hammer-impact test of the free boundary condition is realized by suspending the assembly using an elastic cord, as shown in Fig. 2 (a) and (b). Then, the force and vibration signals of the impact test are input into the signal-processing model to obtain the modal frequency, and the experimental result is shown in Fig. 2 (c). The modal frequencies calculated from isotropic model, the proposed method excluding and including interference fit are compared with the experimental results. The errors between isotropic model and experimental results are up to 30%, especially the interested low-order modal frequencies. Due to considering the interference fit, the calculation results of the proposed model are closer to the experimental results. Then, the experiment of simple support boundary conditions is conducted by fixing the stator assembly on the bench, and the results are compared with the proposed model. The maximum errors between the proposed method and the results are within 5%, which verifies the accuracy of the proposed method.

**References:**

[1] Lin F. , S. Zuo and W. Deng, IEEE Trans. on Ind. Electron., Vol. 63 (12), p.7455-7466, (2016) [2] J. Le Besnerais, V. Lanfranchi and M. Hecquet, IEEE Trans. Ind. Appl., vol. 46(4), pp. 1367–1373, (2010) [3] D. Torregrossa, B. Fahimi and F. Peyraut, IEEE Trans. Ind. Electron., vol. 59(2), pp. 839–847, (2012)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/09d93fcb2ec6baf3c27351c6ed39c6df.jpg)
Fig. 1 Motion equations of the proposed modal frequency calculation theory

![](https://assets.underline.io/uploads/markdown_image/1/image/a1e101a1733ca4f2c6009405f245f957.jpg)
Fig. 2 Modal test and experimental result

 Modal Frequency Calculation of Stator Assembly of the Electrical Machine Considering Interference Fit and Orthogonal Properties of Materials

I. Introduction The electric motors have been widely used in various applications such as automobiles, and home appliances. Among the various types of electric motors, the interior permanent magnet synchronous motors (IPMSM) in which permanent magnets (PM) are inserted in the rotor receive a lot of attention due to the advantage of high efficiency and high power density. Since these applications are closely related with daily life, the vibration and noise reduction of IPMSM used in these applications are important. Further, most of these applications require continuous driving under certain load condition. Thus, it is important to reduce the vibration and noise of IPMSM used for continuous driving under certain load condition [1]. To reduce the vibration of IPMSM under certain load condition, the asymmetric rotor design which changes mechanical air-gap length has been proposed in [2]. However, the average torque is decreased as mechanical air-gap length is changed. Therefore, in this paper, arrangement of the PM and flux barrier is modified to make the asymmetric rotor shape which changes magnetic air-gap length instead of mechanical air-gap length. Through this method, the vibration can be reduced maintaining average torque under certain load condition. To confirm the vibration reduction of IPMSM with asymmetric rotor shape under certain load condition, the vibration analysis of the 4-pole 24-slot IPMSM with the symmetric and asymmetric rotor shape is conducted using 2-dimensional finite element analysis (2D FEA). II. Relationship between radial force density and air-gap magnetic flux density The radial force density can be expressed by the Maxwell stress tensor method. The radial force density generates the stator displacement which causes the vibration of motors. The spatial harmonic order of the radial force density is called as the vibration order. The stator displacement is inversely proportional to the fourth power of the vibration order [3]. Thus, the radial force density with low vibration order should be decreased to reduce the vibration. As a result, it is necessary to make the radial air-gap magnetic flux density sinusoidal. The radial air-gap magnetic flux density can be calculated by multiplying the sum of the air-gap magnetic flux density neglecting slotting effect by the PM and armature with the relative specific permeance of the stator and rotor. Therefore, to make the radial air-gap magnetic flux density sinusoidal, the rotor permeance should be uniform. In this paper, the arrangement of the PM and flux barrier is modified to make the rotor permeance uniform. III. Vibration analysis using FEA The configuration of the 4-pole 24-slot IPMSM with the symmetric and the asymmetric rotor shape is shown in Fig. 1. The symmetric and asymmetric model have same geometric shapes only except for the rotor. Under the load condition of 1.92 Nm at 5000 rpm, the radial force density is calculated from (1) using 2D FEA. The spectrum analysis result of the radial force density using 2D fast Fourier transform is shown in Fig. 2(a). As shown in Fig. 2(a), at most time harmonic orders, the radial force density of the asymmetric model is less than that of the symmetric model. Specifically, at the 2nd time harmonic order, the radial force density with the lowest vibration order of 4 is decreased by 12.4% from 125.62 kN/m2 to 110.04 kN/m2. Also, at the 10th time harmonic order, the radial force density with the lowest vibration order of -4 is decreased by 44.5% from 12.79 kN/m2 to 7.10 kN/m2. Next, the vibration analysis is conducted to calculate the stator displacement using 2D FEA by applying the radial force density on the stator. The time harmonic analysis result of the stator displacement of the symmetric and asymmetric model is shown in Fig. 2(b). As shown in Fig. 2(b), at most time harmonic orders, the stator displacement of the asymmetric model is reduced. Particularly, at the 2nd, 10th, and 22nd time harmonic orders, the stator displacement of the asymmetric model is decreased by 16.1%, 45.0%, and 68.4%, respectively. According to these results, the vibration reduction of the asymmetric model compared with that of the symmetric model is confirmed under the load condition of 1.92 Nm at 5000 rpm. This is because under the load condition, rotor permeance of the asymmetric model is more uniform than that of the symmetric model due to the current phase angle. IV. Experimental verification and conclusion In this paper, the vibration analysis of the symmetric and asymmetric model is conducted using 2D FEA under the load condition of 1.92 Nm at 5000 rpm. As a result, the vibration reduction of the asymmetric model is confirmed. This is because the radial force density with a low vibration order is decreased as the rotor permeance becomes uniform. Therefore, it is expected that the 4-pole 24-slot IPMSM with asymmetric rotor shape is effective to reduce the vibration. To verify the vibration reduction of the asymmetric model, the vibration experiments will be conducted under the same load condition of 1.92 Nm at 5000 rpm.

**References:**

 [1] C.-H. Lin and C.-C. Hwang, “Multiobjective optimization design for a six-phase copper rotor induction motor mounted with a scroll compressor”, IEEE Trans. Magn., vol. 52, no. 7, July 2016. [2] Y.-H. Jung, M.-R. Park, and M.-S. Lim, “Asymmetric rotor design of IPMSM for vibration reduction under certain load condition”, IEEE Trans. Energy Convers., vol. 35, no. 2, pp. 928-937, June 2020. [3] J.-F. Gieras, C. Wang, and J.-C. Lai, “Magnetic fields and radial forces in polyphase motors fed with sinusoidal currents”, in Noise of Polyphase Electric Motors, 1st ed., Boca Raton: CRC Press, 2006, ch. 2, pp. 21-64.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/8bc9e324f08558d09564cb3afc523305.jpg)
Fig. 1. Configuration of the 4-pole 24-slot IPMSM with (a) the symmetric rotor shape (b) the asymmetric rotor shape

![](https://assets.underline.io/uploads/markdown_image/1/image/20b87d2c49e47fc9c0bcd788f10c19c7.jpg)
Fig. 2. Under the load condition of 1.92 Nm at 5000 rpm (a) spectrum analysis result of the radial force density (b) time harmonic analysis result of the stator displacement

 Vibration Reduction of IPMSM with Asymmetric Rotor Shape under Certain Load Condition

Critical raw materials are key issues in many applications in the field of energy and transportations since their stock market price is highly unstable due to geopolitical reasons and increase of the demand. The problem is that all efficient hard magnets needs critical materials, either cobalt, platinum, rare-earth (RE) in a small or large extend (see Fig. 1). Everybody knows that the problem with Pt is its low abundance in earth-crust and relatively high demand in jewelry, for catalysis and magnetic recording, but its price is quite stable around 35 000 $/kg. In contrast, cobalt market is volatile. It oscillates between 20 and 100 $/kg depending mainly on the political situation in Democratic Republic of Congo, (because RDC produces 60%, i.e. 90 kt in 2018) and, more recently, because of the speculation crisis mainly linked with Chinese demand. The situation with RE is more complicated, one can classify RE into 2 categories: heavy RE (64Gd to 71Lu), light RE (57La to 63Eu) from which 57La, 58Ce and 39Y are almost free, though Y is not exactly a RE but chemically behaves as such. Dy oxide price was around 125$/kg in 2009, grows to 2300$ during summer 2011 and then stabilized between 150 and 300$. RE market is controlled by China where 70% of RE ore is produced though having 30% only of reserves. So the question is why this critical materials are necessary and in which extend we can get rid of them? The answer to this question is not straightforward because many factors have to be taken into account : price of raw elements, volatility of their market, processing cost, added value, application class and life cycle. More than the price itself, volatility can affect the profit if the cost of raw material changes appreciably between design and production stages of a product. The processing cost may be involved if substituting a expensive element or material by a cheaper one is counterbalanced by an increase in processing cost. In contrast, added value can compensate the price of raw elements if it stands only for a tiny part of the total cost. For example, a luxury watch can use a 0.1g PtCo magnet because its cost would be negligible compared to advertising, total cost of precious metals or stones, trade mark rights… The class of application is a key parameter : the 3 main classes are aeronautics, energy production and automobile. In aeronautics price doesn’t matter compared to weight (or safety), so any element can be used if for a given energy the magnet is lighter. For energy production, e.g. in a wind turbine, the price of magnet is easily balanced by the cost of Joules losses summed over 30 years if a DC excitation is used instead of a hard magnet. By opposition, a car runs typically 1000h in 3 years, so the situation is reversed compared to the wind turbine. At last, life cycle is an important issue, magnets can be either milled and reprocessed – to the price of downgrading – or or reused from the fist step of synthesis. In the latter case, separation of RE elements would be necessary and this process is costly. Among magnets, it is well known that the RE-based are the harder, this is typically due to the strong spin-orbital coupling of RE elements which arises from the unfilled inner electronic shell and to the two fold symmetry of the crystal. FeNdB is the most powerful magnet known, but its coercive field has a quite large dependence on temperature. Dysprosium substitution is therefor necessary for power applications. A strategy to reduce the Dy content will be described [2]. Another way could be getting rid of heavy RE by cooling more efficiently the magnets. In this case, even reducing the Nd content can be envisaged, using cerium [3] or mischmetal, which is a mix of RE containing Ce, La, Nd and Pr obtained at an intermediate step of separation and therefor cheaper . SmCo can be synthesized into two structures having are RE-TM ratio 1-5 or 2-17. Both are very good at high temperature though having lower energy product than NdFeB. Sm is not expensive and can be substituted by Y, but the problem is that they contains mainly cobalt [4]. Also magnet with a 1-12 ratio , thus containing less RE, can be synthesized but at the present date the phase is difficult to stabilize. Hexagonal ferrites remains still an interesting option because they are near perfect magnets and have a positive thermal dependence of coercivity. They where discovered 60 years ago, but they have been improved continuously and remained cheap. There are many possibilities to make RE free magnets base don cobalt: alnico, carbides, Co-Zr, nanowires. Some have quite good properties, but actually not better than SmCo and not cheaper. Lastly, research on RE free hard magnets based on manganese will be reviewed. Focus will be done on Mn-Al which exhibits a good potential and uses only almost free elements. At last, a comparison will be tried on the basis of cost per Joule.

**References:**

[1] JMD Coey, Scripta Materialia 67 (2012) 524–529 [2] H. Nakamura, K. Hirota, M. Shimao, T. Minowa, M. Honshima, IEEE Trans. Magn. 41 (2005) 3844 [3] Z.B. Li et al., Journal of Alloys and Compounds 628 (2015) 325–328 [4] K.P. Skokov, O. Gutfleisch, Scripta Materialia 154 (2018) 289–294 [5] A.M. Gabay, G.C. Hadjipanayis, Scripta Materialia 154 (2018) 284–288 [6] Muriel Tyrman, AIP Advances 8 (2018) 056217

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/92f08a97a9b11b04e1f0c7a4a738919e.jpg)
Cost periodic table (reviewed 2020) in $ per kg of pure element.

 Getting rid of critical raw materials in hard magnets: is it feasible?

Amidst burgeoning attention for local manufacturing, manufacturing must adopt innovations that lie at the heart of the Industry 4.0 transformation. All need to offer (or at least start to think about offering) a unique combination of high-quality electric drives that incorporate electrical machines, software, mathware, mechatronics, electronics, assembly ánd predictive maintenance. In integrated drives data driven rapid development will be paramount to the electric drive systems (motor with power electronics drive and embedded intelligence). This will allow for predictive maintenance to illustrate the state of both the electrical machine as the power electronics. Integrating or bringing the power electronics in very close proximity to the electrical machines is not new. Engineers have been pursuing this for a few decades due to the obvious potential benefits including: higher system power density/smaller system footprint, reduced system cost, reduced cabling, reduced EMI issues, and more potential for modular systems [1]. However, integrating power electronics components as close as possible to an electrical machine is not an easy task, because inside an electrical machine is a very disturbed environment: strong electric and magnetic fields can occur, temperature conditions are way beyond power electronics standards and the drives may be subjected to unusual mechanical vibrations and stress [2]. Although all the aforementioned arguments are in effect true, and integrated drive with predictive maintenance using motor current signature analysis (MCSA) and condition monitoring will introduce a paradigm shift for future electric drive applications by utilizing the full potential of electrical motor drives. For example, by implementation of GaN-based inverters with the addition of condition monitoring. This shift is essential to embrace the advantages of smaller footprint/higher power density, minimization of cost and implementation, increased system efficiency, reduced Electromagnetic Emission (EME) issues. For many years the condition monitoring industry relied on vibration analysis and other traditional techniques to identify developing faults in electric motors. In recent years, however, condition monitoring based on motor current signature analysis has begun to provide a more effective and efficient alternative to traditional techniques [3]. As such we have identified research challenges and will highlight there current status, these include: - Thermal/cooling management - Hard- and soft magnetic materials - Power electronics that can tolerate higher temperatures - Distribution of the power electronics using modular/segmented machine topologies - Synchronization of the commutation control algorithms - Integrated condition and predictive maintenance algorithms - Coil/teeth/Magnet configurations - Cabling, manufacturing and integration challenges Within this invited symposium, Electrical Machines and Drives 2020 and Beyond these various aspect will be highlighted. We look forward to your presence to discuss this truly multi-disciplinary challenges!

**References:**

[1] Ayman M. EL-Refaie, 2015, “Integrated Electrical Machines and Drives: An Overview”, 2015 IEEE International Electric Machines & Drives Conference (IEMDC), 10.1109/IEMDC.2015.7409083 [2] Hossam Al Ghossini, Thu Thuy Dang, and Stéphane Duchesne, 2019, “A New Concept for Deeper Integration of Converters and Drives in Electrical Machines: Simulation and Experimental Investigations”, Open Physics Volume 17: Issue 1, 10.1515/phys-2019-0084 [3] https://www.semioticlabs.com/resources/motor-current-signature-analysis

**Images:**

 Integration of electrical machine and drive

In 1911, Heike Kamerlingh Onnes discovered the superconducting state of the mater. After more than a century of intensive researches worldwide, significant improvement of the performance of high temperature superconducting wires and the cryogenic cooling systems has been done. This led to a rising motivation and interest of users and manufacturers to develop HTS electrical machines for their energy savings potential. Furthermore, the HTS motor will also be smaller in size than its conventional motor counterpart, particularly for high torque/low speed applications like marine propulsion and wind energy generation. Among the problems encountered in HTS motor drive systems, the torque transmission from the cryogenic environment to the load at room temperature is a key factor. Contactless torque transmission devices like magnetic couplings and gears constitute interesting solutions. The following items will be discussed in the presentation: 1- Operating current of an HTS coil HTS materials exhibit a non-linear relation between the electric field E and the current density J. This non-linearity is usually described by the power law which depends on an important parameter called the critical current Ic [1]. The operating current is defined as the maximal allowable current avoiding thermal limits. It depends on magnetic flux density components, cooling temperature and mechanical constraints [2]. A simple method to determine the operating current of a coil made from HTS tapes and supplied with a current Is is to determine the intersection between the Ic(B) curve of the tape and the Is(B) curve of the coil. An illustrative example for a stack composed of 4 tapes is given in Fig. 1. 2- HTS electrical machines and HTS magnetic couplers design The design of HTS machines is different from that of conventional machines because it is necessary to include operating current calculation during the sizing procedure. Furthermore, the inclusion of a magnetic coupling to transmit the torque from the cryogenic environment to the load increases the design difficulties. An example of an HTS machine with integrated coupling is shown in Fig. 2. It is an axial flux topology intended for high torque/low speed applications. The modelling and optimization of such a machine topology will be detailed [3], [4]. Finally, the potential of HTS motors/generators with integrated HTS torque transmission in making a real jump in performance will be discussed.

**References:**

[1] Y. Kim, C. Hempstead, and A. Strnad, Physical Review Letters, Vol. 9, p. 306–309 (1962). [2] J. Pitel, Supercond. Sci. Technol., Vol. 26, p.1 -13 (2013). [3] L. Belguerras, S. Mezani, T. Lubin and al., Superconductor Science and Technology, Vol. 28, p. 095003 (2015). [4] B. Dolisy, S. Mezani, T. Lubin, and al., Superconductor Science and Technology, Vol. 30, p. 35015 (2017).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/db35b587c0410681c56b1da69ef95894.jpg)
Fig.1 Definition of the operating current

![](https://assets.underline.io/uploads/markdown_image/1/image/888fa9c840d298e18c6a656d106405a0.jpg)
Fig.2 Axial HTS motor with integrated HTS magnetic coupling

 HTS machines

In order to develop the next generation of fixed wing and vertical lift aircraft, the aircraft efficiency, emissions, reliability, and noise needs to be improved [1]. An electric aircrafts drivetrain needs to operate at a very high mass torque density whilst also being exceptionally reliable, efficient, robust and environmentally benign. Mechanically geared drivetrains are often utilized as they enable the aircraft drivetrain to be more compact. However, the use of mechanical gears within an aircraft introduces a number of system level consequences such as the need for a lubrication system to reduce tooth friction and remove heat [2]. A back up lubrication system is then also required to meet certification requirements in the advent of loss of lubrication performance. The mechanical gearing system also introduces significant cabin noise due to the gear-tooth vibrations [2]. To mitigate tooth wear and failure, the aircrafts need to be grounded periodically for inspection and maintenance. One of the main alternatives to using mechanical gearing is the use of a direct-drive permanent magnet (PM) motors [3]. The use of a direct-drive PM motor removes the reliability concerns with respect to the mechanical gearbox. However, the torque density of a direct-drive PM motor is thermally limited (by current) and therefore a PM motor does not normally achieve torque densities much greater than 50Nm/L [4-10]. For this reason, direct-drive PM generators become very large when scaled-up in size. Superconducting motors are being considered for use in electric aircraft as the torque density can be much higher [11], however the required cooling system is highly complex. Recently the use of magnetic gearing (MG) within an aircraft drivetrain has been proposed as a means of achieving a higher mass torque density and power density that is competitive to mechanically geared systems [1, 2]. Magnetic gears (MGs) utilize magnetic field space modulation to create speed amplification without any physical contact [12]. As a MG does not rely on current excitation, the MG can sustain a very high magnetic air-gap sheer stress value. MGs can operate with low noise and vibration and its noncontact operation means that no gear lubrication is required. In addition, MGs have the unique ability to pole slip when overloaded rather than catastrophically failing, thereby providing built-in overload protection [2]. Recently, MGs have been shown to be able to operate at 99% efficiency [13]. The MG can be nested internally with a much smaller motor or connected in series with a motor thereby enabling a compact electric drivetrain typology. This presentation will review the performance potential of MGs relative to alternative direct-drive aircraft drivetrains. The paper will provide an up-to-date review of electric aircraft drivetrain motor research conducted at government agencies, such as NASA [1, 2], as well as at universities and companies (such as Magnix and Siemens [14]) The performance potential of utilizing a magnetically geared aircraft drivetrain relative to the alternative direct drivetrain technology will be discussed.

**References:**

[1] J. J. Scheidler, V. M. Asnani, and T. F. Tallerico, "NASA’s magnetic gearing research for electrified aircraft propulsion," presented at the AIAA Propulsion and Energy Forum, Cincinnati, Ohio, July 9-11, 2018. [2] V. Asnani, J. Scheidler, and T. Tallerico, "Magnetic gearing research at NASA," presented at the AHS International 74th Annual Forum & Technology Display, Phoenix, Arizona, USA, May 14-17, 2018. [3] I. Pazdera, P. Prochazka, D. Cervinka, and B. Klima, "Electrical drivetrain of the small airplane and mutual interaction of this drivetrain," presented at the 39th Annual Conference of the IEEE Ind. Elect. Society, Vienna, 2013. [4] M. R. J. Dubois, "Optimized Permanent Magnet Generator Topologies for Direct-Drive Wind Turbines," Ph.D. Thesis, Delft University of Technology, Delft, Netherlands, 2004. [5] W. M. Arshad, T. Backstrom, and C. Sadarangani, "Analytical design and analysis procedure for a transverse flux machine," in IEEE Inter. Elect. Mach. Drives Conf., Cambridge, MA, pp. 115-121,June,2001. [6] M. R. Harris, G. H. Pajooman, and S. M. A. Sharkh, "Comparison of alternative topologies for VRPM (transverse-flux) electrical machines," in IEE Coll.on New Topologies for Perm. Magnet Mach., London, pp. 2/1- 2/7,1997. [7] M. R. Harris, G. H. Pajooman, and S. M. A. Sharkh, "The problem of power factor in VRPM (transverse-flux) machines " presented at the 8th Inter. Elect. Mach. Driv. Conf., Sep. , 1997. [8] S. Jinhao, L. Yongbin, and Z. Wenpeng, "Survey on the development of transverse flux machines," in Inter. Conf. Elect. Mach., Beijing, China, pp. 127-141,2003. [9] P. Kasinathan, A. Grauers, and E. S. Hamdi, "Force density limits in low-speed permanent-magnet machines due to saturation," IEEE Trans. Energy Conv., vol. 20, no. 1, pp. 37-44, Mar. 2005. [10] D. G. Dorrell, S. S. Ngu, and C. Cossar, "Comparison of high pole number ultra-low speed generator designs using slotted and air-gap windings," IEEE Trans. Mag., vol. 48, no. 11, pp. 3120-3123, Nov. 2012. [11] K. S. e. al., "Development of a High Speed HTS Generator for Airborne Applications," IEEE Trans. Applied Super., vol. 19, no. 3, pp. 1656-1661, June 2009. [12] K. Atallah, J. Wang, S. Mezani, and D. Howe, "A novel high-performance linear magnetic gear," IEEJ Trans.Ind. Appl., vol. 126, no. 10, pp. 1352-1356, 2006. [13] M. C. Gardner, M. Johnson, and H. A. Toliyat, "Performance Impacts of Practical Fabrication Tradeoffs for a Radial Flux Coaxial Magnetic Gear with Halbach Arrays and Air Cores," presented at the IEEE Energy Conversion Congress and Exposition (ECCE), Baltimore, MD, USA, , 2019. [14] M. Duffy, A. Sevier, R. Hupp, E. Perdomo, and S. Wakayama, "Propulsion Scaling Methods in the Era of Electric Flight," presented at the AIAA/IEEE Electric Aircraft Technologies Symposium Cincinnati, Ohio, July, 9-11, 2018.

**Images:**

 A Review of Electric Aircraft Drivetrain Motor Technology

I. Introduction Hybrid excited synchronous machines (HESM) combine permanent-magnet (PM) excitation with wound field excitation. The goal behind the principle of hybrid excitation is to combine the advantages of PM excited machines and wound field synchronous machines. The principle of hybrid excitation allows responding to many problematic related to electric machines: flux weakening [1], energy efficiency [1], and fluctuations of permanent magnets price [2]. Due to their advantageous characteristics, this type of machines is gaining more and more attention [1]–[8]. They have been identified as one of the emerging technologies of modern energy conversion systems [3]–[5]. They have been the subject of many review papers [6]. Figure 1 shows the evolution of the number of contributions dedicated to HESM in the IEEE Xplore Digital Library, between 1989 and 2019. As can be seen this number is in constant evolution, going from one contribution in 1989 [6], to more than 350 contributions in 2019. In this contribution, after a description of the operating principal of HESM, a brief literature review of scientific and technical literature dedicated to HESM will be established. Then, the use of this type of electric machines for different applications (constant and variable speeds applications) will be discussed. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications [7] [8], and the third one has been designed as generator for renewable energies conversion [2]. All of them are flux switching structures. II. Hybrid Excitation Synchronous Machines The hybrid excitation principle allows a wide variety of structures to be realized. Figure 2 shows three different structures of rotating HESM. All of them are flux switching hybrid excited synchronous machine (FSHESM). Due to their advantageous characteristics FSHESM are the subject of increasing attention. This figure illustrates the variety of HESM structures. More structures will be presented in the full version of the contribution. In most references dedicated to HESM, it is mainly rotating machines which are studied. Nevertheless, many linear HESM are also studied. Examples will be provided in the full version. III. Study of Three HESM Prototypes HESM characteristics make them well suited for transportation applications [1] [5] [7] [8]. Nevertheless, HESM could also be used as renewable energy conversion generators [2], even if, in these applications, it is not all of their advantageous characteristics which are exploited. In fact, it is mainly economic considerations which are driving the use of an electric machine technology [2]. The use of HESM in renewable energies applications is mainly driven by fluctuations of rare earth PM price and their availability [2]. Another important reason is the fault tolerance characteristic which could be brought by HESM. Considering the evolution of wind energy market toward the use of large power rated offshore wind turbines, the fault tolerance characteristic is very important. In fact, the HESM allow controlling the air-gap magnetic field, even with the presence of permanent magnets, and they therefore offer a protection against faults as stator short circuits, for example. The fault tolerance allows the reduction of maintenance requirements, and consequently exploitation costs. The fault tolerance they bring increases their attractiveness in many applications. The design studies of three HESM prototypes (Fig. 2) will be presented. The first one [Fig. 2(a)] has been studied for an aircraft DC electric power generation [7]. This prototype weight 3.5 kg, and was designed to deliver 6 kW at 6000 rpm. It is a 2D flux switching structure. The second prototype can be used as a car alternator [Fig. 2(b)] [8]. Instead of having a distributed excitation windings, the excitation coil is annular without end windings. The excitation flux has a 3D nature, which requires the use of massive ferromagnetic material to channel it. This prototype was able to deliver 2.5 kW at a speed of 11 krpm. The third prototype [Fig. 2(c)] was designed to be used as a generator for renewable energy conversion (10 kW at 300 rpm). As compared to transportation applications, where the speed is relatively high, renewable energy conversion systems operate at relatively low speed, which requires the development of high torque machines. This prototype includes the Vernier effect in order to be able to cope with the torque production requirement. It is a water cooled machine. It has a 2D structure. The full version will include more details about the three prototypes. HESM machines may seem more complicated as compared to classical machines, as PM machines for example, but regarding the worldwide shift toward a greener economy, economic considerations will be in the favor of the development of even more complex electric machines technologies [5]. Indeed, considering the number of pieces required for the construction of even the simplest IC engine, the construction of even the much complex electric machines requires much more less operations, and simpler production lines.

**References:**

[1] Y. Amara, S. Hlioui, A. H. Ben Ahmed and M. Gabsi, "Power capability of hybrid excited synchronous motors in variable speed drives applications," IEEE Trans. Magn., vol. 55, no. 8, paper 8204312, August 2019. [2] A. S. McDonald, "Hybrid Excitation of Synchronous Generators for Wind Turbines," Proceedings of the 2nd IET Renewable Power Generation Conference (RPG2013), 9-11 September 2013, Beihang University (BUAA), Beijing, China. [3] G.-A. Capolino and A. Cavagnino, “New trends in electrical machines technology—Part II,” IEEE Trans. Ind. Electron., vol. 61, no. 9, pp. 4931–4936, Sep. 2014. [4] C. Liu et al., "Guest Editorial Emerging Electric Machines and Drives for Smart Energy Conversion," in IEEE Transactions on Energy Conversion, vol. 33, no. 4, pp. 1931–1933, Dec. 2018. [5] K. Akatsu et al., "Message from Editors", CES Transactions on Electrical Machines and Systems, vol. 3, no. 3, pp. 231–232, Sept. 2019. [6] E. Spooner, S. A. W. Khatab and N. G. Nicolaou, "Hybrid excitation of AC and DC machines," in Proc. 1989 Fourth International Conference on Electrical Machines and Drives Conf., London, UK, 1989, pp. 48–52. [7] A. Nasr, S. Hlioui, M. Gabsi, M. Mairie, and D. Lalevee, “Design optimization of a hybrid-excited flux-switching machine for aircraft-safe DC power generation using a diode bridge rectifier,” IEEE Trans. Ind. Electron., vol. 64, no. 12, pp. 9896–9904, Dec. 2017. [8] A. Dupas, S. Hlioui, E. Hoang, M. Gabsi and M. Lécrivain, "Investigation of a new topology of hybrid-excited flux-switching machine with static global winding: experiments and modeling," IEEE Trans. Ind. Appl., vol. 52, no. 2, pp. 1413–1421, March/April 2016.

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