The impact of the rotor slot number selection on the induction motors is investigated. Firstly, analytical equations will reveal the spatial harmonic index of the air gap magnetic flux density, connected to the geometrical features and the saturation of the induction motor. Then, six motors with different rotor slot numbers are simulated and studied with FEM. The stator is identical in all motors. The motors are examined under time-harmonic analysis at starting and at 1440？rpm. Their electromagnetic characteristics, such as electromagnetic torque, stator current, and magnetic flux density, are extracted and compared to each other. The analysis will reveal that the proper rotor slot number selection has a strong impact on the induction motor performance. 1. Introduction During the last years, ships have become increasingly dependent on electricity. The new trend to the electric ship design, the integrated electric ship, combines the propulsion system and the ship service electrical system, into a single power system. In this system, the induction motor is used in several applications. Such applications are the propulsion motor, the thrusters, and other various drives, such as pumps and hoists [1]. It is known that the application of electric machines in an electric ship should meet special requirements [2]. Reliability and improved efficiency come first, where there is also a great need for low-noise operation. In the past, the design and analysis of electric machines were carried out with the use of equivalent circuits and analytical equations. Those methods did offer sufficiently accurate results for a reasonable amount of time. Despite that, those methods did not take into consideration the geometric features of the machine, as well as the complex nonlinear behavior of the magnetic materials. The rapid advance in computer science, in the last years, gave the opportunity for computational methods to evolve. One of those methods is the finite-element method (FEM). With the aid of a FEM software, an engineer can design accurately the machine, by also providing the conducting and magnetic properties of the materials used. Then, the simulation carried out solves the Maxwell equations, in space and time, offering a much more accurate solution than the classical methods. The induction motor design is strongly connected to the power electronics design, since different motor configurations strongly affect its electromagnetic characteristics. This is the reason for extensive research worldwide [3, 4]. This paper constitutes a study of the impact of the rotor
References
[1]
T. J. McCoy and J. V. Amy Jr., “The state-of-the-art of integrated electric power and propulsion systems and technologies on ships,” in Proceedings of the IEEE Electric Ship Technologies Symposium (ESTS '09), pp. 340–344, April 2009.
[2]
J. M. Prousalidis and P. S. Mouzakis, “Analysis of electric power demands of podded propulsors,” Journal of Marine Engineering and Technology, vol. 2010, no. 16, pp. 3–13, 2010.
[3]
G. D. Marques and D. M. Sousa, “A new sensorless MRAS based on active power calculations for rotor position estimation of a DFIG,” Advances in Power Electronics, vol. 2011, Article ID 970364, 8 pages, 2011.
[4]
L. Charaabi, “FPGA-based fixed point implementation of a real-time induction motor emulator,” Advances in Power Electronics, vol. 2012, Article ID 409671, 10 pages, 2012.
[5]
J. Pyrhonen, T. Jokinen, and V. Hrabovcova, Design of Rotating Electrical Machines, John Wiley & Sons, 1st edition, 2008.
[6]
S. Nandi, “Modeling of induction machines including stator and rotor slot effects,” IEEE Transactions on Industry Applications, vol. 40, no. 4, pp. 1058–1065, 2004.
[7]
J.-W. Kim, B.-T. Kim, and B. I. Kwon, “Optimal stator slot design of inverter-fed induction motor in consideration of harmonic losses,” IEEE Transactions on Magnetics, vol. 41, no. 5, pp. 2012–2015, 2005.
[8]
J. Kappatou, K. Gyftakis, and A. Safacas, “FEM study of the rotor slot design influences on the induction machine characteristics,” in Studies in Applied Electromagnetics and Mechanics, vol. 30 of Advanced Computer Techniques in Applied Electromagnetics, IOS Press, 2008.
[9]
I. Boldea and S. A. Nasar, The Induction Machines Design Handbook, Taylor & Francis Group, 2010.
[10]
J. F. Gierras, C. Wang, and J. C. Lai, Noise of Polyphase Electric Motors, CRC Press, 2006.
[11]
M. Dabrowski, Magnetic Circuits and Fields of Electrical Machines, WNT, Warsaw, Poland, 1971.
[12]
A. Voldek, Electrical Machines (in Russian), Energia, Leningrad, Russia, 2nd edition, 1974.
[13]
B. Heller and V. Hamata, Harmonic Field Effects in Induction Machines, Academia Publishing House, Prague, Czech Republic, 1977.
[14]
W. Weber, Der Nutungsfaktor in Elektrischen Maschinen, ETZ, 1928.
[15]
H. Frohne, über die Prim？ren Bestimmungsgr？？en der Lautst？rke bei Asynchronmaschinen [Ph.D. thesis], Hannover, Germany, 1959.
[16]
M. Purkemani, Beitrag zur Erfassung der Sattigungsoberfelder in Drehstromasynchromaschinen [Ph.D. thesis], Technischen Hochschule Hannover, Fakult at fur Maschinenwesen, Hannover, Germany, 1971.
[17]
J. Le Besnerais, V. Lanfranchi, M. Hecquet, and P. Brochet, “Optimal slot numbers for magnetic noise reduction in variable-speed induction motors,” IEEE Transactions on Magnetics, vol. 45, no. 8, pp. 3131–3136, 2009.
[18]
I. Boldea and S. A. Nasar, The Induction Machines Design Handbook, CRC Press, 2nd edition, 2010.
