France



1. Introduction. Due to the merits of simple structure, mechanical robustness and high power density, flux reversal permanent-magnet machine (FRPMM) has been an appealing choice in many industrial applications [1]. However, similar to other solely PM-excited machines, the constant-power operation range of FRPMM is restricted by the uncontrollable PM flux [2]. To improve the flux regulation ability, the hybrid-excited design concept is introduced into flux reversal machine [3]. With the participation of direct current (dc) excitation, the air-gap flux density can be regulated flexibly. However, the dc-field winding and armature wingding placed in the same stator results in a serious space confliction, which deteriorates the torque production and flux regulation ability. To cope with the space problem, the partitioned stator hybrid excited flux reversal machine (PSHEFRM) is developed [4], in which the armature windings and field windings are placed separately in the inner and outer stators. Nevertheless, the solely stator-PM excitation limits the torque capability of PSHEFRPM. To further enhance the torque production and obtain the flexible flux regulation ability, this paper proposes a new partitioned stator hybrid-excited flux reversal machine with dual-PM (DP-PSHEFRM), in which the field windings are placed in the inner stator and the PMs are employed on both the rotor and outer stator. The topology and operation principle of the proposed DP-PSHEFRM are described. The electromagnetic performances of the machine are investigated by finite element analysis (FEA). 2. Machine topology and operation principle. Fig. 1 shows the topology of the proposed DP-PSHEFRM, which consists of two stators and one sandwiched rotor. It can be seen that the machine employs the outer stator to accommodate three-phase armature windings and PMs, and inner stator to place field winding. The PMs mounted on the top of outer stator teeth are separated by iron poles, which composes a consequent-pole PM arrangement. The non-overlapping armature windings and field windings are wound on the teeth of outer and inner stators, respectively, which offers the merits of short ending-length and low copper loss. In addition, the outer stator teeth are aligned with inner stator slots, which means the two stators have half teeth pitch displacement. Moreover, the alternate PMs and iron poles composes a consequent-pole PM rotor structure. The PMs on the rotor and outer stator are magnetized with the identical radially direction to enhance the flux densities in the air-gap and stator core. The operation principle of the proposed DP-PSHEFRM is based on the flux modulation effect, and the torque of machine is generated by taking advantage of the modulated air-gap field harmonics. In addition, the dc flux is mainly used to regulate the air-gap flux density to improve the flux weakening capability. 3. Electromagnetic performance evaluation. Fig. 2(a) shows the no-load back-electromotive forces (back-EMFs) of the proposed DP-PSHEFRM excited by stator-PM only, rotor-PM only and dual-PM at the field current density of 0 A/mm&lt;sup&gt;2&lt;/sup&gt;. It can be seen that the back-EMFs excited by different PM excitations all have a symmetrical and sinusoidal waveform. In addition, compared with stator-PM, rotor-PM makes more contribution for the back-EMF production. Fig. 2(b) compares the torques of proposed machine under different PM excitation at the armature current of 6A. It can be seen that the torque with dual-PM excitation is 82% higher than that with stator-PM excitation only and 47% higher than that with rotor-PM excitation only, which illustrates a great enhancement of torque production by using dual-PM excitation. Then, in order to verify the flux regulation ability of DP-PSHEFRM, the dual-PM excited outer air-gap flux density and its harmonic spectra at different field current density are evaluated, as shown in Fig. 2(c) and (d). It can be observed that the amplitudes of working harmonics can be continuously regulated with the change of the field current density. Thus, the flux linkage at armature terminal can be effectively adjusted, as shown in Fig. 2(e). When the armature current is fixed as 6 A, the variation of average torque with field current density is investigated. As shown in Fig. 2(f), the average torque decreases by 9.2Nm from J=0A/mm&lt;sup&gt;2&lt;/sup&gt; to J=-15A/mm&lt;sup&gt;2&lt;/sup&gt;, which illustrates the excellent flux weakening capability of the proposed DP-PSHEFRM. More detailed design considerations and electromagnetic performance analysis will be presented in the full paper.

**References:**

&lt;br/&gt;[1] Y. Gao, R. Qu, D. Li, “Torque performance analysis of three-phase flux reversal machines,” &lt;i&gt;IEEE Trans. Ind. Appl.&lt;/i&gt;, vol. 53, no. 3, pp. 2110–2119 (2017).&lt;br/&gt;[2] X. Zhao, S. Niu, and W. Fu, “Design of a novel parallel-hybrid-excited dual-PM machine based on armature harmonics diversity for electric vehicle propulsion,” &lt;i&gt;IEEE Trans. Ind. Electron.&lt;/i&gt;, vol. 66, no. 6, pp. 4209–4219 (2019).&lt;br/&gt;[3] L. Xu &lt;i&gt;et al&lt;/i&gt;., “Design and analysis of a new linear hybrid excited flux reversal motor with inset permanent magnets,” &lt;i&gt;IEEE Trans. Magn.&lt;/i&gt;, vol. 50, no. 11, Art. ID 8202204 (2014).&lt;br/&gt;[4] Z. Zeng, Q. Lu and X. Huang, &quot;Analysis of a new partitioned-primary flux-reversal hybrid-excited linear motor,&quot; in &lt;i&gt;Proc&lt;/i&gt;. &lt;i&gt;IEEE Int&lt;/i&gt;. &lt;i&gt;Elect&lt;/i&gt;. &lt;i&gt;Mach&lt;/i&gt;. &lt;i&gt;Drives&lt;/i&gt; &lt;i&gt;Conf&lt;/i&gt;. &lt;i&gt;(IEMDC)&lt;/i&gt;, pp. 74-79 (2019).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/bbde9754c49229479494cfe02b661303.jpg)
Fig. 1 Topology of the proposed DP-PSHEFRM

![](https://assets.underline.io/uploads/markdown_image/1/image/46d6a83d3bdaec0953d3139401617155.jpg)
Fig. 2 Electromagnetic performances analysis

INTERMAG 2021

 Design and Analysis of a New Partitioned Stator Hybrid-Excited Flux Reversal Machine With Dual-PM

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1. Introduction. Due to the merits of simple structure, mechanical robustness and high power density, flux reversal permanent-magnet machine (FRPMM) has been an appealing choice in many industrial applications [1]. However, similar to other solely PM-excited machines, the constant-power operation range of FRPMM is restricted by the uncontrollable PM flux [2]. To improve the flux regulation ability, the hybrid-excited design concept is introduced into flux reversal machine [3]. With the participation of direct current (dc) excitation, the air-gap flux density can be regulated flexibly. However, the dc-field winding and armature wingding placed in the same stator results in a serious space confliction, which deteriorates the torque production and flux regulation ability. To cope with the space problem, the partitioned stator hybrid excited flux reversal machine (PSHEFRM) is developed [4], in which the armature windings and field windings are placed separately in the inner and outer stators. Nevertheless, the solely stator-PM excitation limits the torque capability of PSHEFRPM. To further enhance the torque production and obtain the flexible flux regulation ability, this paper proposes a new partitioned stator hybrid-excited flux reversal machine with dual-PM (DP-PSHEFRM), in which the field windings are placed in the inner stator and the PMs are employed on both the rotor and outer stator. The topology and operation principle of the proposed DP-PSHEFRM are described. The electromagnetic performances of the machine are investigated by finite element analysis (FEA). 2. Machine topology and operation principle. Fig. 1 shows the topology of the proposed DP-PSHEFRM, which consists of two stators and one sandwiched rotor. It can be seen that the machine employs the outer stator to accommodate three-phase armature windings and PMs, and inner stator to place field winding. The PMs mounted on the top of outer stator teeth are separated by iron poles, which composes a consequent-pole PM arrangement. The non-overlapping armature windings and field windings are wound on the teeth of outer and inner stators, respectively, which offers the merits of short ending-length and low copper loss. In addition, the outer stator teeth are aligned with inner stator slots, which means the two stators have half teeth pitch displacement. Moreover, the alternate PMs and iron poles composes a consequent-pole PM rotor structure. The PMs on the rotor and outer stator are magnetized with the identical radially direction to enhance the flux densities in the air-gap and stator core. The operation principle of the proposed DP-PSHEFRM is based on the flux modulation effect, and the torque of machine is generated by taking advantage of the modulated air-gap field harmonics. In addition, the dc flux is mainly used to regulate the air-gap flux density to improve the flux weakening capability. 3. Electromagnetic performance evaluation. Fig. 2(a) shows the no-load back-electromotive forces (back-EMFs) of the proposed DP-PSHEFRM excited by stator-PM only, rotor-PM only and dual-PM at the field current density of 0 A/mm2. It can be seen that the back-EMFs excited by different PM excitations all have a symmetrical and sinusoidal waveform. In addition, compared with stator-PM, rotor-PM makes more contribution for the back-EMF production. Fig. 2(b) compares the torques of proposed machine under different PM excitation at the armature current of 6A. It can be seen that the torque with dual-PM excitation is 82% higher than that with stator-PM excitation only and 47% higher than that with rotor-PM excitation only, which illustrates a great enhancement of torque production by using dual-PM excitation. Then, in order to verify the flux regulation ability of DP-PSHEFRM, the dual-PM excited outer air-gap flux density and its harmonic spectra at different field current density are evaluated, as shown in Fig. 2(c) and (d). It can be observed that the amplitudes of working harmonics can be continuously regulated with the change of the field current density. Thus, the flux linkage at armature terminal can be effectively adjusted, as shown in Fig. 2(e). When the armature current is fixed as 6 A, the variation of average torque with field current density is investigated. As shown in Fig. 2(f), the average torque decreases by 9.2Nm from J=0A/mm2 to J=-15A/mm2, which illustrates the excellent flux weakening capability of the proposed DP-PSHEFRM. More detailed design considerations and electromagnetic performance analysis will be presented in the full paper.

**References:**

 [1] Y. Gao, R. Qu, D. Li, “Torque performance analysis of three-phase flux reversal machines,” IEEE Trans. Ind. Appl., vol. 53, no. 3, pp. 2110–2119 (2017). [2] X. Zhao, S. Niu, and W. Fu, “Design of a novel parallel-hybrid-excited dual-PM machine based on armature harmonics diversity for electric vehicle propulsion,” IEEE Trans. Ind. Electron., vol. 66, no. 6, pp. 4209–4219 (2019). [3] L. Xu et al., “Design and analysis of a new linear hybrid excited flux reversal motor with inset permanent magnets,” IEEE Trans. Magn., vol. 50, no. 11, Art. ID 8202204 (2014). [4] Z. Zeng, Q. Lu and X. Huang, "Analysis of a new partitioned-primary flux-reversal hybrid-excited linear motor," in Proc. IEEE Int. Elect. Mach. Drives Conf. (IEMDC), pp. 74-79 (2019).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/bbde9754c49229479494cfe02b661303.jpg)
Fig. 1 Topology of the proposed DP-PSHEFRM

![](https://assets.underline.io/uploads/markdown_image/1/image/46d6a83d3bdaec0953d3139401617155.jpg)
Fig. 2 Electromagnetic performances analysis

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I. Introduction The electrical energy can be directly converted to the linear mechanical energy through linear motors. Containing no transmission mechanisms, linear motors have many remarkable advantages, such as high speed and high positioning accuracy. Therefore, linear motor servo systems have received more and more attentions in academic and industrial fields in recent decades [1-6]. However, the testing methods for the linear motor servo systems is not well elaborated and researched compared with conventional rotary motors. Among all the indexes of the linear motor servo systems, the position loop stiffness defined as the ratio between the dynamic disturbing force and the consequent maximal position deviation is an important one to evaluate the closed-loop performances of linear motor servo systems. In the conventional position loop stiffness testing systems, the weight lifting, hydraulic, and the rotating motor plus ball screw are three common loading methods. Nevertheless, some inherent defects exist in these loading methods, such as low repeatability, complex system structure, and low dynamic response. In [7], a novel position loop stiffness testing method for the linear motor servo systems is proposed, in which a high thrust linear voice coil motor is served as the loading motor. This paper will focus on the electromagnetic analysis and cooling design of the proposed high thrust linear voice coil motor. II. Configuration and Model The configuration of the position loop stiffness testing platform for linear motor servo system is shown in Fig. 1. The linear voice coil motor is connected to the tested linear motor by a load sensor, and the tested linear motor operates in position loop state. The thrust generated by the linear voice coil motor can be seen as a step disturbance for the linear motor servo system. Therefore, low thrust ripple performance of the loading motor is required to improve the testing accuracy of position loop stiffness. The cooling structure is also needed to increase the force density and decrease the motor mass. Basically, the magnetic charge method can be used to calculate the magnetic flux density of permanent magnet, and the image method is applied to consider the influence of ferromagnetic boundary [8-9]. The thrust expression with different parameters is obtained using Lorentz force equation. III. Thrust Analysis and Cooling Design In this section, the influence of the parameters on the thrust and thrust ripple are analyzed based on the established model. To enhance the structural strength of primary, two layers arrangement are selected and two layers coils are inserted into a common coil frame. Additionally, the cooling structure for the high thrust linear voice coil motor is designed. The water channels are evenly distributed in the coil frame. To further improve the cooling effect and realize thermal shielding of primary, two aluminum sheets are fixed onto both sides of the primary with heat-conducting glue. The cooling effect is analyzed using temperature field simulation. IV. Experiment To verify the related analysis, a prototype of the high thrust linear voice coil motor is manufactured. The thrust linearity test shows that the thrust varies linearly with the current. The rated thrust is 800N when the current is 9.6A. the experiment values of thrust match well with the ones from analysis and FEM. The thrust ripple within 4mm displacement is less than 1%, which could provide a nearly constant thrust during stiffness testing. In addition, the temperature test is achieved. The temperature rises of the primary with and without the cooling water are compared. The aluminum sheets could quickly transfer the coils heat to the coil frame, and the surface temperature of primary with cooling is 37 degrees under 12A coil current. V. Conclusion In this paper, a linear voice coil motor is analyzed and designed. Considering the practical requirements in the stiffness testing of linear motor servo system, high thrust and low thrust ripple are two critical indexes. Additionally, the effective cooling structure is important. The related experimental results show a good agreement with the analytical model and finite element simulation results.

**References:**

[1] W. Zhao, J. Zheng, J. Wang, IEEE Trans. Ind. Electron., vol. 63, no. 4, pp. 2072–2082, Apr. 2016. [2] Q. Lu, Y. Li, X. Huang, IEEE Trans. Magn., vol. 51, no. 11, pp. 8108804, Nov. 2015. [3] Y. Fujimoto, T. Kominami, and H. Hamada, IEEE Trans. Ind. Electron., vol. 56, no. 5, pp. 1383–1392, Mar. 2009. [4] Y. Gao, R. Qu, J. Li, D. Li, and F. Chen, IEEE Trans. Magn., vol. 53, no. 6, 7001905, Jun. 2017. [5] Z. Liu, W. Zhao, J. Ji, IEEE Trans. Magn., vol. 51, no. 7, 8105807, Jul. 2015. [6] H. Zhang, B. Kou, Z. Q. Zhu, IEEE Trans. Ind. Electron., vol. 65, no. 12, pp. 9853–9862, Dec. 2018. [7] H. Zhang, B. Kou, Y. Zhou, ICEMS Conference, Harbin, 2015. [8] S. A. Nasar and G. Y. Xiong, IEEE Trans. Magn., vol. 24, no. 3, pp. 2038–2044, May 1988. [9] S. H. Lee, S. B. Park, S. O. Kwon, IEEE Trans. Magn., vol. 42, no. 4, pp.1327-1330, Apr. 2006.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/d4e8d9f3608916dcdb7f56ffad01ea1f.jpg)
Fig. 1. Configuration of the position loop stiffness testing platform for linear motor servo system.

![](https://assets.underline.io/uploads/markdown_image/1/image/a359460ad8f8de83524842499e11821e.jpg)
Fig. 2. Prototype of the high thrust linear voice coil motor.

 Design and Analysis of a High Thrust Linear Voice Coil Motor using for the Stiffness Test of Linear Motor Servo System

1. Introduction Aiming at the nonlinear permanent magnet(NPM) degradation modeling problem in a type of differential magnetic system, firstly, for the NPM magnetization and demagnetization process, the first-order reversal curves of the permanent magnet of different segments is solved based on the Preisach model[1]. Based on this model, a finite element simulation model of the electromagnetic system of a Small Rotation Actuator(SRA) is built, and the model is verified by actual measurement. Combining the simulation data with the physical model, a NPM degradation model is proposed. Based on this model, the single factor analysis of the electromagnetic system is carried out to determine the key parameters of SRA, and a fast calculation model of the degradation process is built. Kriging method[2] is used to perform error fitting, and the SRA magnetic system is optimized with the degradation degree of PEM as the target. The actual measurement results of the prototype are made to verify the effectiveness of the model. 2. Permanent magnet degradation model based on Preisach theory Usually in the finite element simulation, the permanent magnet B-H curve is set according to the return line model[3], but there are still large errors for the magnetic system after the magnetization and demagnetization process. An operating point model of PEM is built based on the Preisach theory and applied to the finite element simulation model considering the process of magnetization and demagnetization. The simulation results of the model's suction characteristics have a smaller error with the actual measurement, and the simulation accuracy is significantly better than the traditional model. At the suction position, the error is the largest, which is only 6.7%. As shown in Figure 1. After the calculating of the initial state of the actuator, through accelerated tests, the permanent magnet magnetic performance degradation data with time and temperature is obtained, and the function relationship between the degradation degree of magnetic properties of the NPM and temperature and time based on data is deduced. Firstly, analyze the degradation mechanism of the NPM, and the demagnetization rate based on the surface magnetic intensity is determined as the characteristic parameter of magnetic properties of the NPM. The permanent magnets are subjected to degradation tests at different temperatures. Based on the measured data, select the logarithmic function model, combined with Preisach model to build degradation model based on Arrhenius equation. The calculation shows that the model is in good agreement with the measured data. 3. Fast calculation model of electromagnetic system of SRA considering degradation In order to optimize the structure of the electromagnetic system, it is necessary to determine the key size parameters that have a greater impact on the performance of the electromagnetic system, and build a fast calculation model based on them. First, through the single factor simulation, the key size parameters are determined, and then based on the self-defined model, establish a fast calculation model that takes voltage, armature rotation angle, permanent magnet remanence, and the size parameters as input, and static suction torque as output. Kriging method is used for error correction. The calculation error using this model is not more than 3%, The average calculation time of a single group of electromagnetic torque is 1.07s, which meets the requirements of optimal calculation accuracy and speed. 4. Optimized design and test verification of principle prototype Based on the completed permanent magnet degradation model and the fast calculation model of the static magnetic torque of the magnetic system which takes voltage, armature rotation angle, permanent magnet remanence, and size parameters as inputs, the optimization objective is the absolute value of the static magnetic torque of the armature at the release position when there are no excitation and pull-in voltage, and at the same time, the tolerance during production and processing is considered, the optimization problem is solved using the NSGAII algorithm. After optimization, the static magnetic torque of the armature at the release position is increased by 29.6% when no excitation is applied. The static magnetic torque under the pull-in voltage is increased by 41.5%, as shown in Figure 2.

**References:**

[1] S. R. Naidu, "Simulation of the hysteresis phenomenon using Preisach's theory," in IEE Proceedings A - Physical Science, Measurement and Instrumentation, Management and Education, vol. 137, no. 2, pp. 73-79, March 1990.doi: 10.1049/ip-a-2.1990.0010. [2] Krige, D.G. A statistical approach to some basic mine valuation problems on the Witwatersrand[J]. Journal of the Southern African Institute of Mining and Metallurgy, 1952, 52(9): 201-203. [3] Huimin Liang, Jiaxin You, Wenying Yang, and Guofu Zhai. A Type of Subsection Model for a Permanent Magnet Bar and its Leakage Permeance Calculation Method in an Open Magnetic Circuit[J]. Journal of Magnetics, 2014, 19(1), 37-42.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/b98f1ca2f62e7ea84fec576cbdf6047a.jpg)
Figure.1 Comparison of simulation calculation results based on Preisach theory and actual measurement results

![](https://assets.underline.io/uploads/markdown_image/1/image/cd381fccd3737f437a706bf0e3dd94c8.jpg)
Figure.2 The performance degradation calculation result of the SRA and the degeneration formula

 Nonlinear Permanent Magnet Degradation Model and its Application in Magnetic System Optimization

1.Background Nowadays, more and more vehicles are starting to use an automotive display to enhance vehicle infotainment function with high resolution, large screen, and highly accurate in-touch technology, especially haptic feedback. The linear vibration motor is attached to the automotive display to provide efficient haptic performance. A permanent magnet with high remanence can generate massive flux inside a linear vibration motor and cause high acceleration. However, it also causes lots of static magnetic flux leakage in front of the display, potentially having indirect adverse effects on passenger’s implanted medical devices. International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines [1] are applied to occupational exposures and exposure of the general public. Many individuals are wearing implanted ferromagnetic or electronic medical devices sensitive to magnetic fields. ICNIRP guidelines mention that the statice magnetic field at or below the 0.5 mT will not create a health hazard on implanted medical devices from studies to date. The prototype linear vibration motors are designed for use in an organic light-emitting diode (OLED) display panel, a thin display that each pixel emits light itself individually. Owing to the display's thinness, the prototype linear vibration motor ware placed around the center of the display. In contrast, liquid crystal display (LCD) pixels require backlight units (BLUs) to emit lights. The BLUs cover the entire display that makes the LCD panel thicker than the OLED panel; thus, the prototype can no longer be used. The available space for placing linear vibration motors are in the bezels around the LCD panel, requiring a slim-width linear vibration motor with acceptable haptic performance and less static magnetic flux leakage (&lt; 0.5 mT). 2. Analysis methods Maxwell's equations [2] are employed to do the magnetostatic analysis by considering the nonlinearity and hysteresis of magnetic material. The electromagnetic-mechanical coupled method is used to verify the linear vibration motor's haptic performance with the finite element method. 3. Prototype The linear vibration motor consists of an electromagnetic system and a mechanical system. The electromagnetic system includes a voice coil, a top plate, a permanent magnet, and a yoke. The mechanical system consists of an inserted frame, an upper frame, a lower frame, and a plate. The full model, half model, an exploded view of the prototype are shown in Figure 1(a). The final slim linear vibration motor has a smaller size than the prototype, and it has an added magnet to provide an opposite magnetic flux to lower magnetic flux leakage at the measured position, shown in Figure 1(b). The magnetic flux leakage is defined as the magnetic flux that does not pass through the air gaps of the voice coil or other parts of the electromagnetic system. The measured positions are in front and behind of linear vibration motor with an 11.30mm distance. The measurement results in front and behind the prototype are 1.60 mT and 11.70mT, while the analysis results are 1.59 mT and 11.69 mT. The experiment setup to measure magnetic flux leakage is Kanetec Tesla Gauss meter, and the measurement results are shown in Fig. 2(a). Based on the E-M coupled method, the analysis results of displacement and acceleration on dummy jig of the prototype are obtained and verified by the experiment results. The measurement setups for measuring displacement and acceleration are Klippel and vibration tester (Type BK 2120C2). 4. Novel design The slim model is designed to satisfy the requirement of the automotive LCD display panel. With a new upper frame shape, the slim model can be inserted into an automotive display in two directions, while the prototype only can be inserted in one direction. Based on a previous study [3] (application of magnetic shielding), the upper frame of the slim model is made by magnetic material (sus 430), which can create another magnetic circuit to make magnetic flux coming back to yoke. Magnetic circuit design includes voice coil design, added yoke design, added magnet design, and magnetic circuit optimization. Secondly, the movable parts of the linear vibration motor include yoke, magnet, and top plate. The inserted frame is treated as spring, and the thickness of the inserted frame's bridge has a dominant influence on resonance frequency. To maintain the same resonance frequency as the prototype (around 130Hz), the thickness of the inserted frame's bridge is changed from 2.30mm to 1.90mm. With a combination of the above designs, the final slim model's analysis results show that magnetic flux leakages in front and behind the slim model are 0.10 mT and 0.43 mT. Both sides are lower than 0.5 mT. There are 93.71%, 96.32% decreased from the prototype. Samples are manufactured and used to do the experimental measurement. 5. Conclusion The current study proposes a width slim linear vibration motor with a novel magnetic circuit design to achieve low static magnetic flux leakage. Haptic performance of linear vibration motor includes the displacement of movable mass and acceleration on dummy jig, shown in Fig. 2(b). The final slim model has the same resonance frequency as a prototype, around 130 Hz, and it has higher displacement than the prototype due to the smaller movable mass. Eventually, the experiment results are in good agreement with the analysis results.

**References:**

1.International Commission on Non-Ionizing Radiation Protection. Guidelines on limits of exposure to static magnetic fields. Health Physics., Vol. 96(4), pp. 504-14 (2009 Apr 1) 2.Monk P. Finite element methods for Maxwell's equations. Oxford University Press., (2003 Apr 17) 3.Jiang ZX, Park KH, Kim JH. Analysis and Design of a New Linear Vibration Motor Used to Reduce Magnetic Flux Leakage in In-Vehicle Infotainment. Applied Sciences., Vol.10(10), pp. 3370 (2020 Jan)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/6e6ddbd98125d7b2e61ba693da429676.jpg)
Fig.1 Model comparison between prototype and slim model_Final

![](https://assets.underline.io/uploads/markdown_image/1/image/2889d6a55e76aef872060e0d7c230ac7.jpg)
Fig.2 Resutls comparion between experiment and analysis

 Design of a Slim-Width Linear Vibration Motor Used for Automotive LCD Display Panel

-Introduction Smartphones are widely used in daily routines, and microspeakers are widely used in these devices for sound generation. The sound is important since they provide immersive experience when consuming multimedia contents. Therefore, acoustic performance of the microspeaker is an important feature for consumers when selecting smartphones. A round shape microspeaker was widely used in earlier version of cellular phones. The circular or elliptical microspeaker was designed and analyzed [1]. A rectangular microspeaker was developed to utilize the internal space in cellular phone more efficiently [2]. Lee et al. developed a rectangular microspeaker for acoustic performance improvement. Using a piezoelectric effect, engineers developed a piezoelectric speaker [4]. For smartphone featuring bezel-less display, indirect- and direct-vibration actuators were developed [5,6]. In the past, a few components inside the smartphone provided sufficient space for the microspeakers. However, recent design trend to bezel-less display and the slimmer design started to limit the allowable space for the microspeaker. In addition, many components such as sensors, stylus pen, etc., are mounted around the microspeaker that limit the allowable space. These trends reduce back volume of microspeaker that affect the acoustic performance which is SPL (Sound Pressure Level). The back volume is a sealed air volume under the diaphragm that affects acoustic performance. Reduced back volume adds an additional stiffness to the microspeaker system that increase the resonant frequency and decrease SPL at low frequencies. The smaller the back volume, the lower the SPL at low frequency. The prototype microspeaker termed as 1410_1VC consists of single coil with resistance of 6 Ω (DCR). The 1410_1VC can’t provide sufficient SPL at low frequency when placed in small back volume of 0.25 cc. To address this problem, a new microspeaker must be designed. In this paper, while remaining identical exterior size to the prototype, a novel dual-coil microspeaker termed as 1410_2VC is designed and analyzed for low frequency SPL enhancement. - Analysis methods and verifications by experiment (Prototype) The microspeaker is multiphysics system that consists of three domains which are electromagnetic, mechanical and acoustic domain, and they are coupled with certain parameters. The SPL can be obtained by solving theses multiphysics system with coupled analysis. Coupled analysis are conducted for obtaining SPL and displacement using 3D FEA (Finite Element Analysis). The SPL measurement of the prototype 1410_1VC was conducted in an anechoic chamber shown in Fig. 2 (a). The SPL and displacement are measured by B&K equipment and Klippel equipment, respectively. The analysis methods are verified comparing experimental and simulated data which show good agreement. The acoustic performance of the microspeaker at low frequency can be represented by arithmetic mean (average) of SPL at four frequencies which are 200 Hz, 300 Hz, 500 Hz and 700 Hz. The SPL at low frequency of the 1410_1VC is 80.98 dB. -New Microspeaker Design The moveable mass of the speaker consists of coil, center diaphragm, side diaphragm. Increasing moveable mass will decrease the resonant frequency leading to enhanced low frequency SPL. Among components consisting moveable mass, the coil is the heaviest component, and has the highest mechanical density. Maintaining same resistance, the coil mass can be increased by using large diameter coil. Changes in coil design cause magnetic circuit design modifications and affects electromagnetic force which is Lorentz force. The magnetic circuit includes top plates, coil, yoke and magnets. Thus, coil design is an important factor for the performance improvement. The 1410_1VC has a single coil with resistance, diameter, mass and total length as 6Ω, 0.077mm, 69.93mg, 1675.7mm, and 0.499N, respectively. Maintaining same DCR 6 Ω, dual coil can be connected in series with each coil of 3Ω, or parallel with each coil of 12Ω. The coil diameter is chosen to match height of the prototype 1410_1VC coil. The parallel connection shows the inferior force to the series because thicker coil resulted in lower flux density. Two 3Ω coils connected in series are designed with the diameter of 0.084 mm. Instead of two permanent magnets used in 1410_1VC, total seven magnets are used. The yoke is identical to the prototype. Put together, newly designed 1410_2VC has total mass, total length and Lorentz force as 93.4 mg, 1929.2 mm and 0.542 N, respectively. The structure and manufactured sample are shown in Fig. 1 (a) and (b). The SPL and displacement of 1410_2VC are measured through experiments. - Result The experimental data of the prototype and newly designed microspeaker are compared as shown in Fig. 2 (b). The results show that average SPL of 1410_2VC at low frequencies is 83.25 dB. It is 2.27 dB higher than 1410_1VC which is significant improvement. Remaining same exterior size, using dual coils and novel magnetic circuit, low frequency SPL is improved.

**References:**

 [1]. S.M. Hwang, G.Y. Hwag, J.H. Kwon, et al. “Performance comparison between circular and elliptical type micro-speakers for cellular phones.” IEEE Trans. Magn., Vol. 39, p. 3256–3258 (2003) [2] J.H. Kwon, S.M. Hwang, K.S. Kim, et al. “Development of slim rectangular microspeaker used for minimultimedia phones.” IEEE Trans. Magn., Vol.43, p. 2704–2706 (2016) [3] C.M. Lee, and S.M. Hwang, “Development of advanced rectangular microspeakers used for wide liquid-crystal display mobile phones.” J. Appl. Phys., Vol.109, p. 07E504 (2011) [4] S.H. Tseng, S.C. Lo, Y. J. Wang, et al. “Sound Pressure and Low Frequency Enhancement Using Novel PZT MEMS Microspeaker Design.” In Proceedings of the 2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS), p. 546–549 (2020) [5] J.H. Kim; Y.W. Jiang and S.M. Hwang, “Analysis and Design of New Actuator Used for Full-Wide Screen LCD.” Appl. Sci., Vol.9, p. 4599 (2019) [6] K. H. Park, Z.X. Jiang, Y. W. Jiang, et al. “Development of Direct-Vibration Actuator for Bezel-Less Display Panels on Mobile Phones.” Appl. Sci., Vol. 10, p. 4975 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/bae3b24165b8c6a5be00fdedb2c851ad.jpg)
Fig. 1 Structure and manufacutrd componets of new microspeaker

![](https://assets.underline.io/uploads/markdown_image/1/image/a007f77e153a79dfd22ab5f5d7c235fc.jpg)
Fig.2 Experiment setup and result

 Novel dual coil microspeaker with reduced back volume

A biopsy is a medical test to examine the presence or extent of a disease using tools such as a scalpel, a needle, and forceps to extract sample tissues from a patient’s body. While excisional or needle aspiration biopsies take a tissue sample close to human skin, endoscopic or cardiac biopsies collect sample tissues located deep inside the human body by inserting a long tube or catheter along the tubular structure of the human body. Conventional wired biopsies have low steering ability and controllability, and mostly depend on the experience of physicians. Since a target region is sometimes located in a complicated and twisted tubular environment, conventional methods have limitations on reaching the narrow target region. Also, there is a possibility of causing bacteremia due to the penetration of external bacteria into the patient's body through the wires [1], [2]. This may cause sepsis in patients who have low levels of immunity and could lead to death [3], [4]. To overcome these problems, many researchers have studied wireless biopsy robots. Previous researchers have mainly explored biopsy robots for capsule endoscopes. However, such robots do not have their own propulsive force and are driven by the passive peristaltic motion of the intestine. In this paper, we propose a crawling biopsy robot (CBR) that can wirelessly crawl and perform biopsies in tubular environments. The proposed CBR performs various mechanical actions under the control of an external magnetic field, such as a crawling motion with the needle covered, an uncovering motion to expose the needle, the insertion of the needle into the target area, and a covering motion of the needle after the collection of sample tissues. Fig. 1 shows the structure of the proposed CBR, composed of a crawling part and a biopsy part. The crawling part is composed of three crawling bodies, and each crawling body contains an axially magnetized cylindrical magnet (CM) and two flexible legs. Each crawling body is freely rotatable with respect to the y-axis, and the motion of the crawling body is controlled using an external precessional magnetic field for stable navigation and needle insertion. When the CBR reaches a target area, the CBR is designed to open the cover to expose a needle to a target area by controlling the external magnetic field. Once the cover opens, the forward crawling motion of the CBR inserts the needle into the target area. Then, the backward crawling motion takes the needle out of the target area and automatically closes the cover to carry the needle and sampled tissues independently of the crawling motion; this is accomplished by controlling the external magnetic field. To verify the functions of CBR, we made a prototype of CBR using 3D printing technology except for the legs and magnets. The crawling legs are made of silicon rubber, and all magnets are NdFeB 45. The first experiment using the prototype of CBR was measuring the puncturing force of CBR. The proposed CBR should generate a puncturing force enough to insert a needle into the tissue to collect sample tissue. According to Yang et al. [5], a minimum force of 0.3 N is required to puncture the liver tissue of pigs. To verify the puncturing force of CBR, an experiment was done using load cell (Honeywell, Morris Plains, NJ, USA). The pseudo glass tube containing the CBR was fixed in a water container, and a jig connected to the load cell was placed in front of the pseudo glass tube. The experimental setup was then placed inside of the magnetic navigation system which generated external magnetic field [6]. The puncturing force was 0.46 N when the magnitude and the rotational frequency of the external precessional magnetic field were 14 mT and 25 Hz. The second experiment was to evaluate the crawling motion and biopsy performance of the CBR. We used a pseudo tissue made of agar filled at one end of a Y-shaped watery glass tube with a diameter of 14 mm, as shown in Fig. 2(a). In step 1, the CBR crawled to a target point, propelled by the external precessional magnetic field (B=8 mT, f=15 Hz, δ=30°), and the cover was closed during navigation as shown in Fig. 2(b). In the bifurcated branch, we controlled the joystick to change the unit vector of the rotating axis (N), which can be accomplished by controlling the applied currents of the developed MNS. In step 2, the cover was opened by a uniform magnetic field of 12 mT. In step 3, the uncovered biopsy needle punctured the tissue by the crawling motion generated by the external precessional magnetic field (B=14 mT, f=25 Hz, δ=30°). In step 4, the turning motions of the crawling bodies and flexible legs along the y-axis as well as the covering motion of the biopsy needle were performed by rotating the uniform magnetic field of 12 mT by 180° along the y-axis. Finally, in step 5, the CBR crawled back to the original point, propelled by the external precessional magnetic field (B=12 mT, f=15 Hz, δ =30°). Fig. 2 (c) shows the uncovered needle before the biopsy needle was inserted into the pseudo tissue. Fig. 2(d) shows a sampled tissue of 1-mm thickness extracted through this experiment. We confirmed from this experiment that the proposed CBR could crawl through a tubular structure and extract sample tissue successfully.

**References:**

[1] J. Rizzo, D. Bernstein, and F. Gress, Gastrointest. Endosc., vol. 51, no. 3, pp. 257–261, Mar. 2000. [2] K. A. Marr, Ann. Intern. Med., vol. 127, no. 4, p. 275, Aug. 1997. [3] C. Brun-Buisson, F. Doyon, and J. Carlet, Am. J. Respir. Crit. Care Med., vol. 154, no. 3, pp. 617–624, Sep. 1996. [4] M. H. Samore, M. A. Wessolossky, and A. W. Karchmer, Am. J. Cardiol., vol. 79, no. 7, pp. 873–877, Apr. 1997. [5] H. Yang, P. X. Liu, and J. Zhang, IEEE International Conference Mechatronics and Automation, 2005, 2005, vol. 2, p. 592–595 Vol. 2. [6] S. Jeon, G. Jang, H. Choi, and S. Park, IEEE Trans. Magn., vol. 46, no. 6, pp. 1943–1946, Jun. 2010

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/d741c5f391854d56b44ea0b7884f5985.jpg)
Fig. 1. (a) Proposed CBR composed of a crawling part and a biopsy part. (b) Structure of a crawling body. (c) Structure of a biopsy part.

![](https://assets.underline.io/uploads/markdown_image/1/image/c2f464a6517e18db9ae42e258ef2f869.jpg)
Fig. 2. (a) Experiment testing the crawling and biopsy motions. (b) Covered needle. (c) Uncovered needle. (d) Collected sample tissue.

 Crawling Biopsy Robot Magnetically Actuated in Tubular Environments

Recently, Inertia Force Generators (IFGs) was reported to reduce undesirable vibrations in automobiles and precision devices, which consists linear oscillatory actuators (LOAs), sensors and a controller. In the IFG, inertia force for reducing vibrations that generated by the LOA is controlled by a controller and sensors [1]. Here, the LOA should effectively generate inertia force at wide frequency range because the frequency range of undesirable vibrations is wide. However, the conventional LOA can effectively generate inertia force at narrow frequency range because of one mechanical resonance. In this abstract, a LOA with two movers which can effectively drive using two mechanical resonance is developed and the pole configuration is discussed. The proposed LOA mainly consists a stator, an outer mover (0.485 kg) and an inner mover (0.545 kg), as shown in Fig. 1. The stator and outer mover are connected by two leaf springs (totally 139.4 N/mm), and the stator and inner mover are also connected by two leaf springs (totally 44.4 N/mm). The stator is mainly composed of 16 coils and yokes, and the outer and inner movers are mainly composed of magnets and a yoke. Magnets are magnetized at positive or negative radial-direction, and these are axial-directionally arranged with 4 magnetic poles in outer mover, and these are arranged with 8 magnetic poles in inner mover. Coil 1, 2, 5, 6, 9, 10, 13 and 14 are wound clockwise and others are wound counterclockwise. Then, Coil 1, 4, 5, 8, 9, 12, 13 and 16 are connected in series that are called as coil group 1, and others are connected in series that are called as coil group 2. Same-phase or reverse-phase current is applied to coil groups. Here, the former is sinusoidal current with same-amplitude and same-phase in coil groups, and the latter is sinusoidal current with same-amplitude and reverse-phase in coil groups. The 4 poles outer mover is reacted with magnetic fluxes generated by same-phase current, and the 8 poles inner mover is reacted with magnetic fluxes generated by reverse-phase current. In this way, two movers can be independently driven by controlling current. Also, the two movers simultaneously oscillate by superimposing with same- and reverse-phase current. By driving of movers, inertia force is effectively generated at two frequency range because of two mechanical resonance. Next, it is compared between a LOA with 2 and 3 poles movers [2] and the proposed LOA which has 4 and 8 poles movers. In the former, unintentional attractive force was generated between a 3 magnetic-poles and 2 magnetic-poles movers when no current was applied at initial condition because pole-combination of movers is odd and even numbers. So, it must be canceled out by mechanical springs that may have manufactured error or deterioration. In the latter, unintentional attractive force is made to theoretically be zero because that is different even and even numbers. By electromagnetic analysis using 2-D EFM [3], attractive force in the former LOA was calculated as 28.5 N and -9.5 N at each mover, and that in the latter LOA was calculated as 0 N at all movers. Thus, it was verified that the pole combination of the proposed LOA is effective to reduce the attractive force. The prototype of the proposed LOA is manufactured as shown in Fig. 1. The accelerations of outer and inner movers are measured when same-phase or reverse-phase currents with amplitude 0.5 A is applied at each frequency. Then, inertia force is calculated by multiplying measured accelerations and mover’s mass together. As shown in Fig. 2, an outer mover was mainly oscillated when applying same-phase current, and an inner mover was mainly oscillated when applying reverse-phase current. Then, large inertia force was obtained with two frequency at 37 and 84 Hz because of mechanical resonances of the outer and inner movers. For comparison, each mover positions are calculated using motion equations with current thrust and detent characteristics that derived from electromagnetic analysis, and analyzed inertia force is calculated. As shown in Fig. 2, measured results almost agreed with analyzed results.

**References:**

[1] M. Tagami, T. Yamashita and Y. Tagawa et al., Journal of System design and Dynamics., Vol. 2, No. 2, pp. 507-517 (2008) [2] F. Kitayama, K. Hirata and R. Kondo, Proceedings of XXIIIrd International Conference on Electrical Machines., pp. 1586-1592 (2018) [3] A. Yoshitake, K. Harada and T. Todata et al., IEEE transactions on Magnetics, Vol. 33, No.2, pp. 1662-1665 (1997)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/19613de9e4f5f03d0a2df58b863674f4.jpg)
Fig. 1 Proposed LOA.

![](https://assets.underline.io/uploads/markdown_image/1/image/509c3ff2c0a3b0ffbae213910d6fbae5.jpg)
Fig. 2 Measured and analyzed inertia force.

 Development of Linear Oscillatory Actuator with 4 poles and 8 poles Movers.

In recent years, electromagnetic propulsion technology has made many breakthroughs in the fields of aircraft launch and advanced artillery [1]. With the help of pulse strong current, electromagnetic propulsion technology can achieve a target speed of 2000 m/s or higher in a few milliseconds [2]. During the propulsion, the strong magnetic field generated by input pulse current interacts with the armature current to produce electromagnetic force, which propel the armature and the load. At the same time, the high-velocity of the armature will change the current distribution inside the rail and armature, and affect the magnetic field around the armature. However, the magneto-mechanical coupled simulation of moving armature cannot be solved by commercial software. Many scholars have overcome this problem by using various simplified, but it is not sure whether these methods will affect the accuracy of simulation results [3]. Therefore, the measurement is a relatively intuitive research method. In this work, we propose a multi parameter measurement method of magneto-mechanical coupled effect. The acceleration sensor, linear Hall sensor, Hall switch, signal processing module, memory module and control module are integrated into a 27*30 mm storage testing system. Fig.1a is a simulation model of electromagnetic propulsion system considering velocity skin effect. The influence of velocity skin effect on the current distribution in the rail and armature is simulated by reducing the thickness of the rail and the contact area between the rail and armature. Fig.1b is the storage testing system. Fig.2 is the comparison of dynamic storage test results, in which the velocity signal is obtained by integrating the acceleration signal. According to the test value, we can divide the electromagnetic propulsion process into three phases. In the first phase of 0 - 0.75 ms, the armature is stationary due to the influence of preload and static friction. The magnetic induction intensity is affected by the current in armature and rails, and continuously rises to 0.58 T; The second phase is 0.75 - 7.8 ms, when the armature is moving, the velocity increases continuously and reaches the maximum of 844 m/s in 7.8 ms. After that the armature flew out of the rails. At this phase, the maximum magnetic induction intensity is 2.2 T, and it is reduced to 0.54 T when the armature flew out. The third phase is 7.8 -10.75 ms, as the armature flew out of the rails. The circuit disconnected, and the magnetic induction intensity is reduced to 0. Among them, the change of Hall switch corresponds to the value of magnetic induction. The jumping time of Hall switch signal partly reflects the starting time and muzzle time of armature movement, which can be used as a simple method to judge muzzle time. However, the time error at the starting time and muzzle time is 0.75 ms and 2.45 ms, which needs to be corrected by introducing a correction coefficient.

**References:**

[1]. H. D. Fair. Advances in electromagnetic launch science and technology and its applications[J]. IEEE Transactions on Magnetics, vol. 45, no. 1, pp. 225–230, Jan. 2009. [2]. Li J, Li S, Liu P, et al. Design and Testing of a 10-MJ Electromagnetic Launch Facility[J]. IEEE Transactions on Plasma Science, vol. 39, no. 4, pp.1187-1191, Apr. 2011. [3]. Yin Q , Zhang H , Li H J , et al. Analysis of in-bore magnetic field in C-Shaped armature railguns[J]. Defence Technology, vol. 15, pp. 83–88, Feb. 2019.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/a76f2ed704774749b74c4eeca0cc23e5.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/eb5c03e051f27581a78b6bf85c96ef2b.jpg)

 Analysis of magneto-mechanical coupled effect on electromagnetic propulsion

This paper investigates a design method of a Halbach magnet array which can produce multiple MMFs with desired amplitudes and phase position. The construction process and the operation principle of this new type of Halbach array is introduced in this digest. It reveals that through adjusting the proportion of two main working MMFs, higher back EMF and torque density can be achieved than the Halbach flux reversal machines with only one fundamental MMF. I. Introduction Flux modulation machines are attractive for their high torque density due to the magnetic gear effect. It has been validated that multiple airgap flux harmonics can both contribute to the back EMF and torque in flux modulation machines [1]. In stator PM flux modulation machines such as flux switching and flux reversal machines [2], multiple static MMF harmonics can be modulated by single rotor permeance and generate multiple airgap flux harmonics with same frequency, therefore can both contribute to the total back EMF. Different from regular stator PM machine with only fundamental MMF and its odd harmonics, recently a new kind of stator PM flux modulation machines with unequal magnet thickness has been proposed in [3]-[4]. By adjusting the pole arc of each magnet, several other stator MMFs can be generated, and more airgap working harmonics can be introduced to enhance 10% back EMF and torque capacity of machines. However, the oriented design of each working MMF has not been achieved yet in these papers. In [5], the analytical model of Halbach PM array with unequal pole arcs and arbitrary magnetizing directions has been proposed, which can be optimized with algorithm to get multiple main MMFs, but the processing and manufacturing is difficult. In this paper, a design method of Halbach PM array with only radial and tangential magnets has been proposed to produce multiple MMF harmonics with required amplitudes and phase angles. Then, the method is applied into the optimization of Halbach flux reversal machines. II. Forming Process of Multi-MMF Halbach PM Array The forming process of Halbach PM array with two main MMFs is illustrated in Fig. 1. At first, the amplitudes and phase angle of each required MMF harmonic are given, the ideal sine wave of these two MMFs can be presented, respectively. By the accumulation of these two sinusoidal MMFs, a composite MMF can be presented, which has irregular shape and is hard to process. Then, through setting positive and negative threshold values, the composite MMF can be simplified into 3-step PWM composite MMF form. According to this form, the arc length and the magnetization direction of each radial magnet can be determined. On the other hand, the tangential magnets are placed between the radial magnets with different polarities, and the magnetization directions of tangential magnets are determined by the mechanism of conventional Halbach PM array to achieve strong magnetic field on the airgap side. In addition, the gaps are left between two radial magnets with the same polarity. Based on these procedures, the magnet arrangement of Halbach PM array with two MMFs can then be derived. Similarly, the Halbach PM array with more than 2 MMFs can be built by adding the sine wave ideal MMFs at the first step. The simulation results, which will be given in the full paper, validate the accuracy of this method on the construction of required MMFs. III. Application of Multi-MMF Halbach Array in Flux Reversal Machines As one of its interesting applications, the proposed Halbach PM array can be used to increase the airgap working field harmonics in the stator PM flux modulation machines. As shown in Fig. 2 (a), a 6-slots-4-poles flux reversal machine (FRM) with 16-salient-pole rotor is selected as the research object. The proposed Halbach PM array with12th and 18th MMFs is mounted under the stator teeth of this machine. According to the flux modulation theory, the 12th and 18th MMFs are modulated by 16th rotor permeance and generate 4th and 2nd airgap flux harmonics separately, which both contribute to the back EMF but with different coefficients [3]. Fig. 2 (b) shows the back EMF and cogging torque of proposed machine varied with the proportion of 12th MMF. Since 2nd harmonic has two times pole ratio than the 4th harmonic, the FRM with only 18th MMF has higher back EMF than with only 12th MMF. Also, since the least common multiple between 18 and 16 is 144, which is much larger than the least common multiple between 12 and 16, 18th MMF can bring lower cogging torque than the 12th MMF in proposed FRM. However, it is interesting that when increasing the proportion of 12th MMF from 0 to 0.3, the back EMF of proposed machine can still get 10% increased on the basis of Halbach FRM with 18th MMF under the same magnet usage. The reason analysis and the theoretical upper limit of this growth under Halbach PM array with 2 and 3 MMFs will be studied in the full paper. IV. Conclusions A design method of multi-MMF Halbach PM array has been proposed, and its application in a 6-slots-16-poles flux reversal machine has been researched. Compared to regular flux reversal machines with single MMF, the proposed flux reversal machine with composite MMFs can achieve 10% higher back EMF and torque capacity under the same magnet usage. The influence of pole ratio and the selection of threshold values on the performance of machine will be given in the full paper.

**References:**

[1] Tianjie Zou, Dawei Li, Canruo Chen, etc., “A Multiple Working Harmonic PM Vernier Machine with Enhanced Flux-Modulation Effect,” IEEE Transactions on Magnetics, vol. 54, no. 11, June. 2018. [2] Dawei Li, Ronghai Qu, Jian Li, etc., “Synthesis of Flux Switching Permanent Magnet Machines,” Synthesis of Flux Switching Permanent Magnet Machines,” IEEE Transactions on Energy Conversion, vol. 31, no. 1, Mar. 2016. [3] Yuting Gao, Dawei Li, Ronghai Qu, etc., “A Double-Stator Flux Switching PM Machine with Multi-PM MMF Harmonics,” IEEE Transactions on Magnetics, vol. 55, no. 6, June. 2019. [4] You Zhou, Ronghai Qu, Yuting Gao, etc., “A Novel Flux Modulation Linear Machine with Dual-Sided Modular Primary and Multi Pole Pitches,” IEEE International Electric Machines & Drives Conference (IEMDC), May. 2019. [5] Hailin Huang, Libing Jing, Ronghai Qu, etc., "Analysis and Application of Discrete Halbach Magnet Array with Unequal Arc Lengths and Unequally Changed Magnetization Directions," in IEEE Transactions on Applied Superconductivity, vol. 28, no. 3, pp. 1-5, April 2018.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/9c73d18c76d2ea1125f18574efa58316.jpg)
Fig. 1. The Forming method of Halbach PM array with two main MMFs.

![](https://assets.underline.io/uploads/markdown_image/1/image/9ee687a19ed045776c6bf555c0e0b096.jpg)
Fig. 2. Sketch and performance of Halbach flux reversal machine with 12th and 18th MMF.

 A Design Method of Multi-MMF Halbach PM Array and its Application in Flux Reversal Machines

In this paper, dual-winding dual-flux-concentrated magnetic-field modulated brushless compound-structure machine (DDMFM-BCSM) is proposed, combing the magnetic-field modulated brushless dual-rotor machine (MFM-BDRM) and permanent magnet synchronous machine (PMSM) into one. Proposed machine has two sets of windings in stator slots and spoke type PMs on dual rotors. Besides, there are flux barrier on inner rotor to improve the performance of MFM-BDRM. First, the performance of proposed machine is analyzed, including MFM-BDRM part, PMSM part and the whole DDMFM-BCSM. Second, in order to analyze the influence of flux barrier on performance of DDMFM-BCSM, a DDMFM-BCSM without flux barrier is designed to compared their performance. I. Introduction Combination of planetary gear and permanent magnet synchronous machine (PMSM) is widely used in hybrid electric vehicles (HEVs). Considering its maintenance and reliability problem, scholars are searching for new structure to replace this combination. Due to high reliability and low maintenance cost, the magnetic-field modulated brushless dual-rotor machine (MFM-BDRM) has high potential in HEVs. But in HEVs, MFM-BDRM need work together with a PMSM, which raise the system cost and volume. MFM-BDRM with dual windings, which is combination of MFM-BDRM and PMSM, is an alternative solution. In this paper, dual-winding dual-flux-concentrated magnetic-field modulated brushless compound-structure machine (DDMFM-BCSM), which is combination of MFM-BDRM and PMSM, is proposed. Magnetic field modulation principle, working principle of DDMFM-BCSM, is introduced [1,2]. Electromagnetic performance of DDMFM-BCSM, such as back EMF, torque and efficiency, are analyzed and obtained. In order to verify the function of proposed machine, performance of MFM-BDRM and PMSM are also analyzed separately. II. Structure and Working Principle The structure of the proposed DDMFM-BCSM is shown in Fig.1. The stator iron core is similar to that of common PMSM. But there are two sets of windings in stator slots, regular winding and modulation winding. The outer and inner rotor are formed by the alternant placement of magnetic blocks and spoke type PMs whose flux-concentrating effect could improve the flux density efficiently. The difference of two rotors are the magnetic blocks of inner rotor connect together and flux barrier is added in the end of PMs of inner rotor. The MFM-BDRM part consists of modulation winding, magnetic blocks on outer rotor and PMs on inner rotor, while the PMSM part consists of regular winding and PMs on outer rotor. Working principle of DDMFM-BCSM is magnetic field modulation principle which is also the working principle of magnetic gears, magnet-geared machines and vernier machines. Based on analysis of magnetic field modulation principle, torque and speed characteristic of DDMFM-BCSM can be obtained. III. Performance Analysis By finite element method (FEM), the performance of DDMFM-BCSM is analyzed at the inner and outer rotor speed of 1000rpm. Spectrum analysis result of air gap flux density verifies the magnetic field modulation principle. From low mutual-inductance of two sets of windings, we can see the interaction between two sets of windings could be weakened efficiently with reasonable motor design. The power factor of MFM-BDRM is low (0.58), which is the disadvantage of all machines based on magnetic field modulation principle. Loss and efficiency of DDMFM-BCSM is also analyzed. To verify the function of MFM-BDRM part and PMSM part, torque performance of two parts is analyzed respectively and shown in Fig.2. It’s obvious that both of MFM-BDRM part and PMSM part could put out stable torque. The torque of outer rotor and inner rotor of MFM-BDBR satisfies the torque characteristic mentioned above. Dimension parameters of magnetic blocks and spoke array PMs of two rotors are changed to improve the amplitude of needed flux density harmonics. In DDMFM-BCSM model simulated by FEM, flux density harmonics of 4 and 11 PM pole-pairs could generate fundamental wave of back EMF in modulation winding and regular winding respectively. IV. Influence of flux barrier In order to prove the flux barrier effect on performance, DDMFM-BCSM without flux barrier is also simulated. Torque, efficiency and power factor of two topologies are compared. The result shows that flux barrier could improve the torque of MFM-BDRM while the power factor of MFM-BDRM and torque of PMSM is weakened. V. Conclusion A new DDMFM-BCSM topology is proposed, combining the MFM-BDRM and PMSM together. Magnetic field modulation principle, the working principle of DDMFM-BCSM, is introduced. FEM result shows that proposed machine could realize function of two machines. Flux barrier could improve the torque of MFM-BDRM while the power factor of MFM-BDRM and torque of PMSM is weakened.

**References:**

[1] J.G. Bai, P. Zheng, C.D. Tong, et al, “Characteristic Analysis and Verification of the Magnetic-Field-Modulated Brushless Double-Rotor Machine”, IEEE Trans. Ind. Electron., vol. 62, pp. 4023-4033, Jul. 2015. [2] G.P. Liu, Y. Sui, J.Q. Liu, et al, “Comparison of Vernier Machines with Different Rotor PM Configurations”, 2019 22nd Int. Conf. on Electrical Machines and Systems (ICEMS 2019), Harbin (China), Aug. 2019, pp. 1-4.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/c54151c0a80bf0fd16783d5dca99f4e9.jpg)
Fig.1. Structure of proposed DDMFM-BCSM

![](https://assets.underline.io/uploads/markdown_image/1/image/f077aa7ed892dfe45b1510a0d56f7db4.jpg)
Fig.2. Torque waveform of DDMFM-BCSM, PMSM part and MFM-BDRM part

 Investigation of a Dual-Winding Dual-Flux-Concentrated Magnetic-Field Modulated Brushless Compound-Structure Machine

This paper proposes a novel consequent-pole flux-switching permanent magnet (FSPM) machine with magnets in stator slot opening to improve the torque density, which is a critical concern of FSPM machines. The working principle of the proposed topology is investigated based on the magnetomotive force (MMF)-permeance model and numerical finite element analysis (FEA). The electromagnetic performance such as back EMF and electromagnetic torque is compared with the conventional consequent-pole FSPM machine. It is demonstrated that the proposed machine can achieve 27.8% larger back EMF and 20.2% higher torque density than the conventional counterpart. I. Introduction Recently, permanent magnet (PM) machines have been used in many industry applications, such as servo motors and electric vehicle. Flux-switching permanent magnet (FSPM) machine was first proposed in [1]. Due to simple rotor structure and excellent flux-weakening capability [2] [3], FSPM machines have received much attention in recent decades. To improve torque density of FSPM machines, many topologies have been proposed and investigated. Z. Q. Zhu et al. analyzed a novel multi-tooth FSPM machine [4] and the optimal slot/pole pair combination is determined by a simple analytical method in [5]. H. Yang et al. proposed a consequent-pole FSPM machine to increase the contents of low-order harmonics to enhance the torque capability in [6]. In this paper, a consequent-pole FSPM machine with magnets in the slot opening is proposed to increase the torque density. In Section II, the working principle of the proposed topology is analyzed based on magnetomotive force (MMF)-permeance model and numerical finite element analysis (FEA). The electromagnetic performance, such as back EMF and electromagnetic torque, is compared with the conventional consequent-pole FSPM machine in Section III. It is found that the proposed topology can achieve 27.8% larger back EMF and 20.2% higher torque capability than the conventional counterpart. In Section IV, some conclusions are drawn. II. Machine Topology and Working Principle The conventional consequent-pole and proposed FSPM machines are shown in Fig. 1(a) and Fig. 1(b) respectively. Different from the conventional consequent-pole FSPM machine, there are Halbach-type magnets in stator slot opening in the proposed topology. The magnetization directions of the magnets are represented by the yellow arrows. Owing to the unique structure of consequent-pole FSPM machine, there are relatively lower reluctance paths for low-order flux density harmonics. It can be demonstrated that the non-working 6-pole-pair flux density harmonic can be reduced by the magnets in the stator slot opening. Thus, the working flux density harmonics can be enhanced while comparable saturation degrees can be realized in the conventional and proposed FSPM machines. III. Electromagnetic Performance Fig. 2 shows the FEA-predicted phase back-EMF waveforms, FFT analysis results of back EMF and electromagnetic torque curves. It can be seen from the figure that the proposed machine can achieve 27.8% larger back EMF and 20.2% higher torque density than the conventional counterpart. It should be noted that the phase current of proposed machine is smaller than the conventional consequent-pole FSPM machine due to the smaller slot area when the cooper losses are kept constant. IV. Conclusion In this paper, a novel consequent-pole FSPM machine with magnets in stator slot opening is proposed to enhance the torque capability. It is demonstrated that the proposed topology can realize 27.8% larger back EMF and 20.2% higher torque density than the conventional counterpart.

**References:**

 [1] S. E. Rauth and L. J. Johnson, “Design principles of flux-switching alternators,” AIEE Trans., vol. 74, pt. III, no. 3, pp. 1261-1268, Jan. 1955. [2] D. Li, R. Qu, J. Li, W. Xu, and L. Wu, “Synthesis of flux switching permanent magnet machines,” IEEE Trans. Energy Convers., vol. 31, no. 1, pp. 106–117, Mar. 2016. [3] W. Hua, M. Cheng, and G. Zhang, “A novel hybrid excitation flux-switching motor for hybrid vehicles,” IEEE Trans. Magn., vol. 45, no. 10, pp. 4728-4731, Oct. 2009. [4] Z. Q. Zhu, J. T. Chen, Y. Pang, D. Howe, S. Iwasaki, and R. Deodhar, “Analysis of a novel multi-tooth flux-switching PM brushless AC machine for high torque direct-drive applications,” IEEE Trans. Magn., vol. 44, no. 11, pp. 4313-4316, Nov. 2008. [5] J. T. Chen, Z. Q. Zhu, and D. Howe, “Stator and rotor pole combinations for multi-tooth flux-switching permanent-magnet brushless AC machines,” IEEE Trans. Magn., vol. 44, no. 12, pp. 4659-4667, Dec. 2008. [6] H. Yang, Y. Li, H. Lin, Z. Q. Zhu and S. Lyu, "Principle investigation and performance comparison of consequent-pole switched flux PM machines," IEEE Trans. Transport. Electrifi., doi: 10.1109/TTE.2020.3022991.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/77be9b46bb5ba347cd39ca86a71b3594.jpg)
Fig. 1. Basic topologies. (a) Conventional consequent-pole FSPM. (b) Proposed FSPM.

![](https://assets.underline.io/uploads/markdown_image/1/image/fc2f6faeaa2b47661f704ce62af21ac5.jpg)
Fig. 2. Electromagnetic performance. (a) Back EMF. (b) FFT analysis results of back EMF. (c) Electromagnetic torque.

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