• International Journal of Technology (IJTech)
  • Vol 11, No 7 (2020)

Two-Steps Slotting Method in Magnet Edge of PMG for Wind Energy Harvesting

Two-Steps Slotting Method in Magnet Edge of PMG for Wind Energy Harvesting

Title: Two-Steps Slotting Method in Magnet Edge of PMG for Wind Energy Harvesting
Tajuddin Nur, Marsul Siregar

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Cite this article as:
Nur, T., Siregar, M, 2020. Two-Steps Slotting Method in Magnet Edge of PMG for Wind Energy Harvesting. International Journal of Technology. Volume 11(7), pp. 1442-1450

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Tajuddin Nur Department of Electrical Engineering Faculty of Engineering Atma Jaya Catholic University of Indonesia, Jl Sudirman No 51 Jakarta 12930, Indonesia
Marsul Siregar Department of Electrical Engineering Faculty of Engineering Atma Jaya Catholic University of Indonesia, Jl Sudirman No 51 Jakarta 12930, Indonesia
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Abstract
Two-Steps Slotting Method in Magnet Edge of PMG for Wind Energy Harvesting

This paper focuses on the study of how to decrease the value of the cogging torque in an Inset Permanen Magnet Generator. The permanent-magnet generator of an integral slot number with 24 slots and 8 poles was selected and investigated for the purposes of this study. The cogging torque of the permanent-magnet generator can be minimized by combining two slottings in the magnet edge with a gradually inclined surface end. The electromagnetic simulations and analysis of the permanent-magnet generator studied were performed using numerical analysis by means of FEMM 4.2. To obtain a faster computation, FEMM 4.2 was combined with LUA 4.0 programming. Using FEMM 4.2, it was found that by applying two-step slotting in the magnet edge combined with a gradually inclined surface end, the cogging torque of the permanent-magnet generator selected can effectively reduce the cogging torque of the machine by approximately 98.14% compared against the initial magnet model. It can be concluded that the integration of the two-step slotting in the magnet edge and the gradually inclined surface end can effectively reduce the cogging torque of the permanent-magnet generator machine. Furthermore, decreases in the density of the magnetic flux in the core of the permanent-magnet generator can also be found.

Cogging torque; Finite element; Integral slot number; Permanent-magnet generator

Introduction

The application of permanent-magnet generators (PMGs) in our daily lives is now becoming more attractive and can be used with robotics, electric vehicles, wind turbines, and many other applications. Any PMG has some merit over other types of electrical machines. Wind power generation has recently been increasing in popularity because it is clean, has a low production cost, is abundant, and because market volume has tended to significantly increase compared with other energy sources. Using PMGs in renewable energy systems has benefits including high performance and efficiency, simplicity, and reliability of construction. However, the most important issue for PMG applications is the presence of cogging torque (CT). The CT in any PMG is impacted by the interaction among the magnetic flux force from the rotor core and stator teeth or stator slot in the stator core of the machine. The CT in electrical machines and in PMGs can produce noise, vibration, and many other complicated conditions that might appear in the machine application system.

Over the last few years, much research has addressed these issues and sought to reduce and overcome the CT of Permanent Magnet Synchrounous Machine. Furthermore, many techniques for CT reduction have been proposed and developed worldwide; these reports are well documented (Chen et al., 2010; F.Scuiller, 2014; Zhou et al., 2015). Other CT-decreasing techniques have been reported in research, such as using a fractional slot number and phase, optimizing the magnet pole arc (Chen et al., 2010; F.Scuiller, 2014; Zhou et al., 2015), skewing stator slots or magnets (Chabchub et al., 2012; Ling and Nur, 2016), optimizing the stator slot opening width (Bianchi and Bolognani, 2002), applying a dummy slot in the stator core (Chabchub et al., 2012), and shifting magnet slotting (Chen et al., 2010) at the magnet edges of the Permanent Magnet Synchronous Machine (Dosiek and Pillay, 2007). However, the most effective technique for lessening the CT in PMG is combining two-step slotting with shaping the magnet edge in terms of a gradually inclined surface end (GISE). Two-step slotting at the magnet edge and shaping the magnet on the magnet surface provides more frequent interactions between the magnet fluxes in the rotor core and the stator slot opening of the machine.

The purpose of this paper is to propose a new technique for CT reduction in any PMG and to prove that employing the combination of TSS in the magnet edge with GISE in the magnet edge could effectively lessen the peak CT value in any PMG. The new technique of CT reduction can be applied to both integral slot numbers and fractional slot numbers; however, in this work, the analysis of PMGs focuses on the integral slot number. The authors have selected a PMG structure with 24 slots and 8 poles. Figure 1 illustrates the magnet structure of the PMGs, which is the initial structure. Figure 3a shows one-step slotting (OSS), and the Figure 3b presenst TSS.  From Figure 1 it can be observed that the initial magnet structure is a conventional magnet structure, which means no slotting was applied in the magnet structure of the machine. Figure 3a demonstrates the use of OSS on the magnet edge, while Figure 3b shows the application of TSS on the magnet edges of the PMG.  All PMG structures have been studied and contrasted in this paper. The three structures for a 24 slot/8 pole of PMG are analyzed and compared in this paper.

In general, the magnet rotor in any PMG is similar to that used in surfaced-mounted permanent-magnet rotors. The difference between the PMGs studied in this paper and a surface-mounted machine is the iron tooth or rotor teeth within the rotor core.  As a surface-mounted machine, the permanent magnets in the rotor core of the machine are the main causes of the magnetix flux in a PMG. In the PMG structures studied, the magnets of the machine are buried in the rotor core, leading to a compact and strong rotor construction compared against surface PMGs. The structures of PMGs proposed in this study are shown in Figure 3b.

 

Figure 1 Construction of the Initial Structure (IS) of PMG



Figure 2 Classification of cogging torque (CT) reduction techniques for PMGs.

Conclusion

This paper recommends combining TSS with GISE to reduce CT for the proposed PMSM. In comparison with the performance of the initial structure, the ability of the PMG to harvest electrical energy from wind can be improved by around 98.14%. Using the FEMM, it was found that the CT of the PMG proposed as much as 98.14% in contrast with the PMG of the initial structure. It can be concluded that combining TSS and GISE effectively reduces the CT of a PMG. The combination of TSS and GISE on the magnet edge significantly decreased tangential flux. It can be concluded that combining TSS and GISE in PMGs enhances the energy harnessed from wind power.

Acknowledgement

Thank you to the Atma Jaya Catholic University especially the Engineering Faculty for supporting this research.

References

Bianchi, N., Bolognani, S., 2002. Design Techniques for Reducing the Cogging Torque in Surface Mounted Permanent Magnet Motors. In: IEEE Transaction on Industry Application, Volume 38(5), pp. 12591265

Chabchub, M., Ben Salah, I., Krebs, G., Neji, R., Marchand, C., 2012. PMSM Cogging Torque Reduction: Comparison between Shape of Magnet. In: First International Conference on Renewable Energy Vehicle Technology, pp 206211

Chen, N., Ho, S.L., Fu, W.N., 2010. Optimization of Permanent Magnet Surface Shape of Electric Motor for Minimization of Cogging Torque using FEM. In: IEEE Transaction on Magnetics, Volume 46(6), pp. 24782481

Dosiek, L., Pillay, P., 2007. Cogging Torque Reduction Permanent Magnet Machine. In: IEEE Transaction on Industry Applications, Volume 43(6), pp. 16561571

Ling, J.M., Nur T., 2016. Influence of Edge Slotting of Magnet Pole with Fixed Slot Opening Width on the Cogging Torque in Inset-Permanent Magnet Synchronous Machine. Advanced Mechanical Engineering, Volume 8(8), pp. 19

Nur, T., Joe, L.E., Siregar, M., 2020. Novel of Cogging Torque Reduction Technique for Permanent Magnet Generator by Compounding of Magnet Edge Shaping and Dummy Slotting in Stator Core. International Journal on Advanced in Science Engineering and Technology, Volume 10(3), pp. 11911199

Scuiller, F., 2014. Magnet Shape Optimization to Reduce Pulsating Torque for a Five-Phase Permanent Magnet Low Speed Machine. In: IEEE Transsaction on n Magnetics, Volume 50(4), pp. 19

Siregar, M., Wohon, D.R., Nur, T., 2020. A New Technique to Reduce the Cogging Torque of Integral Slot Number in Permanent Magnet Synchronous Machine. International Journal on Advanced in Science Engineering and Technology, Volume 10(4), pp. 14361443

Zhou, Y.Y., Li, H., Meng, G., Shou, S., Cao, Q., 2015. Analytical Calculation of Magnetic Field and Cogging Torque in Surface-Mounted Permanent–Magnet Machines Accounting for any Eccentric Rotor Shape. In: IEEE Trans. on Industrial Electronics, Volume 62(6), pp. 34383447