I. Introduction Permanent-magnet (PM) machines, which exhibit the merits of high torque/power density and high efficiency, have been widely employed in many industrial applications in recent decades, such as wind power generation and electric vehicles [1-5]. As these applications are safe-critical, the development of new machine structures with improved reliability is speeding up [6, 7]. To achieve the feature of fault tolerance, various design techniques of PM machines have been put forward, such as the redundant designs with multi-phase windings [8] or dual three-phase windings [9], and the modular designs with modular windings [10] or modular stator [11], etc. Recently, the stator-slot PM (SSPM) machine with inherent fault-tolerant ability is proposed to achieve high failure-safe capability during uncontrolled generator operation or winding short circuits [12]. However, relatively low torque density puts this structure at a disadvantage, particularly at light load condition. To improve the torque performances, the split-tooth (ST) structure is introduced in the machine [13], where the PMs are placed between the split tooth and tangentially magnetized with opposite polarities in the adjacent PMs, as shown in Fig. 1(a). In this paper, three new types of split-tooth stator-slot PM (ST-SSPM) machines are proposed as shown in Fig. 1(b)-(d), which are designated as Type-2, Type-3, and Type-4 machine, respectively. Four types of machines share the same structure with the split-tooth stator and salient-pole rotor but the PMs are arranged with different positions and polarities. The operation principles are introduced while the electromagnetic performances of four types of machines are comprehensively analyzed and compared by using finite-element analysis (FEA). Based on the analyzed results, the merits and demerits of four types of machines with different PM arrangements are concluded. II. Methodology Similar to the other stator-PM machine with salient rotor poles, the operation principle of four types of machines can be explained by the field modulation theory [14]. Then, the slot-pole combinations of Type-1 and Type-3 machines can be derived as Pa = min(|iNs/2±Nr|), (i=1, 3, 5…) while those of Type-2 and Type-4 machines can be derived as Pa = min(|iNs±Nr|), (i=1, 2, 3…), where Pa is the pole-pair number of armature winding, Ns is the stator slot number, Nr is the rotor pole number, and i is a positive integer. By performing FEA in JMAG-Designer, the torques and torque ripples of machines with various slot-pole combinations are optimized in Fig. 2. It can be seen that Type-1 to Type-4 machines can produce the largest torque with Nr=22, 16, 23 and 17 respectively, while the torque of Type-4 machine with Nr=17 is the largest among all the machines. However, Type-3 machine with Nr=23 and Type-4 machine with Nr=17 produce large unbalanced magnetic force due to the odd number of Nr, thus undesired electromagnetic vibration and noise will be incurred. To resolve this concern, it is desirable to achieve good torque performances with an even number of Nr. One can see that the torques of Type-3 and Type-4 machines with Nr=22 are the highest among all the machines with even numbers of Nr, despite slightly lower than those of Type-3 machine with Nr=23 and Type-4 machine with Nr=17, respectively. Therefore, the optimal Nr of Type-1 to Type-4 machines are preliminarily selected as 22, 16, 22, and 22, respectively. Furthermore, the torque ripples of these four machines are all lower than 10 %, and hence are acceptable. Finally, taking into consideration all the above factors, Type-1 to Type-4 machines are globally optimized with optimal Nr=22, 16, 22, and 22, respectively, which are further investigated, including the cogging torque, back-EMF, steady torque, PM utilization ratio, loss, efficiency, power factor and PM demagnetization. III. Conclusion Based on the analyzed results of four types of machines, some findings are listed as follows. a) Type-1 machine has the lowest cogging torque due to the circulation of PM flux in the stator at no load condition, whereas Type-2 machine shows the highest cogging torque due to the largest cogging torque factor. b) Type-1, Type-2 and Type-4 machines have the similar and largest average torque at rated condition. However, Type-4 and Type-2 machines offer the highest and lowest PMs utilization ratio, respectively. c) Type-4 machine exhibits the best torque performance at rated and light load conditions, while Type-1 machine has the best overload capability. Type-2 machine shows good torque performances both in light and overload conditions, despite not the best, d) Type-4 machine offers the highest power factor, despite the power factors of four types of machines tend to be low. However, their power factors can be improved by increasing the value of stator inner radius/airgap. e) Type-1 to Type-3 machines show irreversible PM demagnetization with different degrees at the inner corner of PMs under over load and high temperature condition, whereas this does not happen in Type-4 machine with the best PM demagnetization withstand. More detailed analysis and results will be given in the full paper. Acknowledgment This work was supported by a grant (Project No. 17205518) from the Hong Kong Research Grants Council, Hong Kong Special Administrative Region, China.

**References:**

 [1] K. T. Chau, C. C. Chan, and C. Liu, “Overview of permanent-magnet brushless drives for electric and hybrid electric vehicles,” IEEE Trans. Ind. Electron., vol. 55, no. 6, pp. 2246-2257, May 2008. [2] Z. Q. Zhu, and D. Howe, “Electrical machines and drives for electric, hybrid, and fuel cell vehicles,” Proc. IEEE, vol. 95, no. 4, pp. 746-765, Apr. 2007. [3] J. Li, K. T. Chau, J. Jiang, C. Liu, and W. Li, “A new efficient permanent-magnet vernier machine for wind power generation,” IEEE Trans. Magn., vol. 46, no. 6, pp. 1475-1478, May 2010. [4] C. Liu, K. T. Chau, J. Z. Jiang, and S. Niu, “Comparison of Stator-Permanent-Magnet Brushless Machines,” IEEE Trans. Magn., vol. 44, no. 11, pp. 4405-4408, Nov. 2008. [5] L. Cao, K. T. Chau, and C. H. T. Lee, “A new parallel-hybrid-excited permanent-magnet machine with harmonic-differential effect for electric vehicles,” IEEE Trans. Veh. Technol., vol. 69, no. 11, pp. 12734-12750, Sept. 2020. [6] A. M. E.-. Refaie, M. R. Shah, and K. Huh, “High-power-density fault-tolerant PM generator for safety-critical applications,” IEEE Trans. Ind. Appl., vol. 50, no. 3, pp. 1717-1728, Sept. 2014. [7] W. Zhao, L. Xu, and G. Liu, “Overview of permanent-magnet fault-tolerant machines: Topology and design,” CES Trans. Elect. Mach. and Syst., vol. 2, no. 1, pp. 51-64, Mar. 2018. [8] F. Barrero, and M. J. Duran, “Recent advances in the design, modeling, and control of multiphase machines—Part I,” IEEE Trans. Ind. Electron., vol. 63, no. 1, pp. 449-458, Jun. 2016. [9] X. Jiang, W. Huang, R. Cao, Z. Hao, and W. Jiang, “Electric drive system of dual-winding fault-tolerant permanent-magnet motor for aerospace applications,” IEEE Trans. Ind. Electron., vol. 62, no. 12, pp. 7322-7330, Dec. 2015. [10] P. Zheng, Y. Sui, J. Zhao, C. Tong, T. A. Lipo, and A. Wang, “Investigation of a novel five-phase modular permanent-magnet in-wheel motor,” IEEE Trans. Magn., vol. 47, no. 10, pp. 4084-4087, Oct. 2011. [11] G. J. Li, Z. Q. Zhu, M. Foster, and D. Stone, “Comparative studies of modular and unequal tooth PM machines either with or without tooth tips,” IEEE Trans. Magn., vol. 50, no. 7, pp. 1-10, Jul. 2014. [12] I. A. A. Afinowi, Z. Q. Zhu, Y. Guan, J. Mipo, and P. Farah, “A novel brushless AC doubly salient stator slot permanent magnet machine,” IEEE Trans. Energy Convers., vol. 31, no. 1, pp. 283-292, Mar. 2016. [13] H. Qu, and Z. Q. Zhu, “Analysis of split-tooth stator slot PM machine,” IEEE Trans. Ind. Electron., 2020, doi: 10.1109/TIE.2020.3031535 (Early Access). [14] M. Cheng, P. Han, and W. Hua, “General airgap field modulation theory for electrical machines,” IEEE Trans. Ind. Electron., vol. 64, no. 8, pp. 6063-6074, Mar. 2017.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/3045adcb24c5b43ba666bbd3d248727b.jpg)
Fig. 1. ST-SSPM machines with different PM arrangements. (1) Type-1. (b) Type-2. (c) Type-3. (d) Type-4.

![](https://assets.underline.io/uploads/markdown_image/1/image/a177b936336d0e337ea63e54611f8851.jpg)
Fig. 2. Torques and torque ripples of four types of machines with different numbers of rotor poles. (a) Torques. (b) Torque ripples.

 Analysis of Split-Tooth Stator-Slot Permanent-Magnet Machines with Different PM Arrangements

INTRODUCTION Since Nicholas Tesla proposed the concept of wireless power transfer (WPT) in the 1890s, it has been considered as an innovative technology, which offers definite advantages of reliability and electrical isolation [1]. Due to these outstanding advantages, many researchers have applied this emerging technology in the domestic and industrial electronic areas, such as consumer electronics and medical devices [2]. The idea of wireless motor can be traced back to 2016 when Motoki Sato proposed probably the first wireless motor [3], which aims to avoid power cable friction. Although it is favorable in harsh environments, it is ill-suited for isolated environments, because the motor controller is installed in the secondary side, which highly requires regular maintenance. To overcome this problem, wireless switched reluctance (SR) motor [4] is proposed, which adopts a self-drive circuit to replace the motor controller. However, this system needs three receivers to feed three-phase stator windings, and this causes three drawbacks: 1) this topology is bulky and heavy; 2) mutual inductance between receivers will harm system selectability; 3) after commutation, the energy restored in the receiver coil will be discharged by feeding the corresponding stator winding, which extends the commutation time and causes reverse torque. In other words, this topology highly limits motor speed and decreases system efficiency. The purpose of this paper is to propose a new wireless SR motor with single receiver, which takes distinct advantages of compact structure and better dynamic performance. The key is to employ a suitable three-frequency resonating compensation (TFRC) network [5], and a specially designed self-drive inverter. METHODOLOGY Fig. 1 depicts the system configuration, where LT and LR are the inductance of transmitter and receiver; CT, CT1, LT1, CT2, and LT2 are the resonant inductances and resonant capacitance to constitute the primary TFRC network, while CR, CR1, LR1, CR2, and LR2 constitute the secondary TFRC network; LU, CU, LV, CV, LW, and CW constitute three-phase LC tuning circuits to offer the control signal for secondary inverter; CL is the filter capacitance of the bridge rectifier; SU, SV, and SW comprise the three-phase inverter; VS, VCU, VCV and VCW are adopted to represent the voltage of AC power source, CU, CV, and CW, respectively. It should be noted that the TFRC network can fully compensate transmitter and receiver at three frequencies, namely fU, fV, and fW, and the design procedure is described in [5]. Besides, U-phase, V-phase, and W-phase LC tunning circuits are resonant at fU, fV, and fW, respectively. The whole control process can be handle from the primary side by changing the frequency of VS, and the method of extracting control signal for secondary inverter is basically same as wireless SPIM [6]. Taking U-phase as an example, when the primary side transmits the energy at fU, the receiver current mainly flows the U-phase LC tunning circuit, so VCU is high while VCV and VCW are almost zero, thus only SU is switched on while the other switches are off. Therefore, by switching system frequency alternatively, three stator windings can be fed in turns, and rotating stator magnetic field can be acquired. Besides, rotor position can be detected by Hall position sensor, and transmitted to the primary side through Bluetooth. In addition, power balance between three phases is also considered. As the secondary induced voltage is inversely proportional to the transmitting frequency, the effective value of transmitter current should be carefully regulated according to [6]. Circuit simulations are carried out to show the feasibility of the proposed system. The key parameters will be given in the full paper, and the load motor is replaced by 20 Ω resistor, which is the equivalent resistance of SR motor according to [4]. The result is shown in Fig. 2 (a), where three stator windings are fed with IU, IV, and IW in turns, which proves the feasibility of this system. Meanwhile, it can be observed that the value of three-phase current is the same by changing the transmitter current IT in different phases. Besides, self-drive ability is also analyzed. As shown in Fig. 2(b) and (c), VCU, VCV, and VCW are reliably higher than 7V when the system operates at the corresponding frequencies, and these voltages can be employed to control inverter after isolating and rectifying. CONCLUSION In this paper, a novel wireless SR motor system is presented. Compared with [4], the proposed system employed single transmitter and single receiver system to achieve compact structure, and a self-drive inverter is adopted to avoid the freewheeling and the resulting reverse torque. Besides, this system retains the merit of secondary-controller-less, which is favorable for maintenance-free operation. For verification, simulations are conducted and prove system feasibility. Furtherly, the experiment will be given in the full paper. Acknowledgment This work was supported by a grant (Project No. 17207420) from the Hong Kong Research Grants Council, Hong Kong Special Administrative Region, China.

**References:**

[1] Y. Bu, T. Mizuno, and H. Fujisawa, "Proposal of a wireless power transfer technique for low-power multireceiver applications," IEEE Transactions on Magnetics, vol. 51, no. 11 (2015) [2] H. Moon, S. Kim, and H. H. Park, "Design of a resonant reactive shield with double coils and a phase shifter for wireless charging of electric vehicles," IEEE Transactions on Magnetics, vol. 53, vol. 51, no. 3 (2015) [3] M. Sato, G. Yamamoto, and D. Gunji, "Development of wireless in-wheel motor using magnetic resonance coupling," IEEE Transactions on Power Electronics, vol. 31, no. 7, pp. 5270-5278 (2016) [4] C. Jiang, K. T. Chau, and W. Liu, "An LCC-compensated multiple-frequency wireless motor system," IEEE Transactions on Industrial Informatics, vol. 15, no. 11, pp. 6023-6034 (2019) [5] Z. Zhang, X. Li, and H. Pang, "Multiple-frequency resonating compensation for multichannel transmission of wireless power transfer," IEEE Transactions on Power Electronics, to be published. [6] H. Wang, K. T. Chau, and C. H. T. Lee, "Design, analysis and implementation of wireless shaded-pole induction motors," IEEE Transactions on Industrial Electronics, to be published.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/75300181fca23227eb765522c9deab08.jpg)
System configuration of wireless SR motor

![](https://assets.underline.io/uploads/markdown_image/1/image/8127b0ae42bc060b3e750e77ff4a8ec1.jpg)
Simulation results under rated condition. (a) Current of transmitter and load. (b) Voltages of capacitors in LC tunning circuits. (c) Voltages of capacitors in LC tunning circuits after rectification.

 A Wireless Three-Phase Switched Reluctance Motor Using Single Receiver

INTRODUCTION Wireless power transfer (WPT) is increasingly popular in many interdisciplinary areas, such as energy encryption and electric vehicles [1]. As the WPT has unique advantages of higher flexibility and no sparking hazard [2], the WPT changes the conventional usage of energy in industry and domestic applications. Recently, a number of efforts have been made to incorporate WPT into electric motors to achieve wireless motor, which is favorable for harsh and watery environments. [3] can be regarded as a landmark paper for proposing dual controller wireless motor, which cascades the traditional motor system in the receiver side of WPT, thus wire abrasion can be avoided in harsh environments. However, motor controller is fragile and not suitable for isolated environments, so WPT with primary-control systems for DC motor [4], switched reluctance (SR) motor [2], and shaded pole induction motor (SPIM) [5] have been studied, which used self-drive circuit to replace the motor controller. However, DC motor suffers from the fragile carbon brushes and commutator, wireless SR motor needs three receivers, and wireless SPIM needs five controlled switches. To solve these problems, this paper proposed a new wireless system with secondary half-bridge inverter for SPIM, thus the number of controlled switches can be eliminated from five to two, and the key is to employ a three-winding transformer. METHODOLOGY Fig. 1 depicts the system configuration, where LT and LR are the inductance of transmitter and receiver, while CT, CT1, and LT1 are the resonant inductances and resonant capacitance to constitute the multiple-frequency resonating compensation (MFRC) network [6] at the transmitter side, and CR, CR1, and LR1 constitute the receiver’s MFRC network; LP, CP, LN, and CN constitute the positive and negative LC tuning circuits, which are resonant at fP and fN, respectively; CL is the filter capacitance of the bridge rectifier; SP and SN comprise the half-bridge inverter to control two primary transmitter windings, namely, positive and negative windings, respectively, and ILP and ILN are used to represent the current of these two windings; VS, VCP, VCN, and VM are adopted to represent the voltage of AC source, CP, CN, and load motor, respectively. It should be mentioned that the switched-capacitor array is adopted in [5], but this compensation suffers from high voltage switching stress. Thus, a specially designed MFRC network is employed in this paper (the design method is detailed in [6]), which can seamlessly compensate the receiver and transmitter at two frequencies without any voltage stress. The working principle is almost the same as [5], as the whole control process can be separated into positive and negative half-cycles, and the control signal for SP and SP are extracted from VCP, VCN, respectively. Taking positive half-cycle as an example, when the primary side transmits the energy at fP, the receiver current mainly flows the positive LC tunning circuit, so VCP is high while VCN is almost zero, thus SP is on, and SN is off. Therefore, by transmitting at fP or fN in turns, the positive and negative windings of the transformer are fed in turns. As the two primary windings of the transformer are reversely winded, AC voltage can be induced in the secondary winding of the transformer. Circuit simulations are carried out to show the feasibility of the proposed system. It should be mentioned that the load motor is replaced by a 120 Ω resistor, which is the equivalent resistance of SPIM in [5], and the other parameters will be given in the full paper. The simulation results are presented in Fig. 2, which depicts the waveforms of power source VS and load voltage VM, as well as the inverter output current ILP and ILN at different speeds. It should be noted that the power source should be higher when transmitting at a higher frequency [5], i.e., fN, in this paper. Consistent with theory analysis, when the system frequency alternatively changes between fP and fN, ILP and ILN correspondingly change, and an AC voltage VM is induced in the secondary side of the transformer to feed the SPIM. Besides, when the system works at rated condition, i.e., the effective value of VM is 110 V, VS is 70 V and 97 V at positive and negative half-cycles, respectively; when the system works at 25 Hz, and the effective value of VM is 55 V, VS becomes 35 V and 50 V at positive and negative half-cycles, respectively. Thus, it can be calculated that VS/VM is around 0.64 and 0.91 at positive and negative half-cycles, respectively. In other words, both the frequency and voltage of the load can be proportionally controlled from the primary side, thus the speed regulation can be achieved. CONCLUSION This paper proposed a novel WPT system for SPIM with a self-drive half-bridge inverter. Compared with former research [5], less controlled switches are applied, thus the proposed system has higher stability and is more suitable for isolated environments. Besides, in order to compensate the transmitter and receiver at two frequencies, a proper MFRC network is employed, which successfully avoids the voltage switching stress. Finally, the simulation results are presented to show system's feasibility and the speed regulation ability, and the experiment will be given in the full paper.

**References:**

[1] M. H. Mahmud, W. Elmahmoud, and M. R. Barzegaran, "Efficient wireless power charging of electric vehicle by modifying the magnetic characteristics of the transmitting medium," IEEE Transactions on Magnetics, vol. 53, no. 6, (2017) [2] C. Jiang, K. T. Chau, and Y. Leung, "Design and analysis of wireless ballastless fluorescent lighting," IEEE Transactions on Industrial Electronics, vol. 66, no. 5, pp. 4065-4074 (2019) [3] M. Sato, G. Yamamoto, D. Gunji, T. Imura, and H. Fujimoto, "Development of wireless in-wheel motor using magnetic resonance coupling," IEEE Transactions on Power Electronics, vol. 31, no. 7, pp. 5270-5278 (2016) [4] C. Jiang, K. T. Chau, and T. W. Ching, "Time-division multiplexing wireless power transfer for separately excited DC motor drives," IEEE Transactions on Magnetics, vol. 53, no. 11 (2017) [5] H. Wang, K. T. Chau, and C. H. T. Lee, "Design, analysis and implementation of wireless shaded-pole induction motors," IEEE Transactions on Industrial Electronics, to be published. [6] Z. Zhang, X. Li, and H. Pang, "Multiple-frequency resonating compensation for multichannel transmission of wireless power transfer," IEEE Transactions on Power Electronics, to be published.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/e4ef9c6a059853c50387e6570fb6a2c4.jpg)
System topology of wireless SPIM for traditional SPIM

![](https://assets.underline.io/uploads/markdown_image/1/image/d561058d1a9dedd8513312decd22dd95.jpg)
Fig. 2 Circuit simulation results at different frequencies. (a) Voltage at 50 Hz. (b) Current at 50 Hz. (c) Voltage at 25 Hz. (d) Current at 25 Hz.

 A Primary-Controlled Wireless Single-Phase Induction Motor Using Secondary Self-Drive Half-Bridge Inverter

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Analysis of Split-Tooth Stator-Slot Permanent-Magnet Machines with Different PM Arrangements

A Wireless Three-Phase Switched Reluctance Motor Using Single Receiver

A Primary-Controlled Wireless Single-Phase Induction Motor Using Secondary Self-Drive Half-Bridge Inverter

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