2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media,

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1 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in an current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of an coprighted component of this work in other works.

2 1 Measurement of Soft Magnetic Composite Material Using an Improved 3D Tester with Fleible Ecitation Coils and Novel Sensing Coils Yongjian Li 1,2, Jianguo Zhu 2, Senior Member, IEEE, Qingin Yang 1, Zhi Wei Lin 2, Youguang Guo 2, Senior Member, IEEE, and Yi Wang 2 1 Province-Ministr Joint e Laborator of Electromagnetic Field and Electrical Apparatus Reliabilit, Hebei Universit of Technolog, Tianjin, , China 2 School of Electrical, Mechanical and Mechatronic Sstems, Universit of Technolog, Sd ne, NSW 2007, Australia In this paper, accurate measurement of three dimensional (3D) magnetic properties of soft magnetic composite (SMC) material is carried out b using an improved 3D tester with adjustable ecitation coils and novel sensing coils attached upon the surface of the SMC specimen. Comparing with the conventional 3D tester operating at 50 Hz, the improved 3D tester enables measurements over wide frequenc range from 2 Hz to 1000 Hz. The relationship between the B vector an vector are measured under both alternating and rotating flu conditions, and the core loss features are analzed. These eperimental results are crucial for designing new SMC electrical machines, which are epected to operate at 200 Hz or above. Inde Terms Fleible ecitation coil, improved 3D magnetic tester, sensing coil, soft magnetic composite (SMC). T I. INTRODUCTION HREE DIMENSIONAL (3D) magnetic properties of the soft magnetic composite (SMC) material are important for analzing the operational performance of electrical machines [1], in which the magnetic flu densit in SMC is rotational. The SMC materials displa complicated relationship between magnetic field strength vector H and magnetic flu densit vector B under 3D ecitation due to the magnetic domain wall dnamics and non-uniform distribution of local magnetization [2]. Magnetic properties of SMC materials over wide frequenc range are crucial factors for accurate analsis of magnetic field in 3D flu machines [3]. B using a 3D magnetic propert tester developed at Universit of Technolog, Sdne (UTS), a kind of SMC material, SOMALOY 500 developed b Höganäs AB, Sweden, has been measured and analzed under 50 Hz ecitation [4]-[8]. However, there are no studies on 3D magnetic measurement over wide range of ecitation frequenc, which is strongl demanded b electrical machine designers. In this paper, an improved 3D tester with adjustable multi-laer ecitation coils is discussed, in the centre of which novel precision B-H sensing coils are attached on a cubic SMC specimen. Various hsteresis loops and core losses at different frequencies under alternating ecitation are presented and analzed. Additionall, 3D B-H loci and corresponding core losses are also analzed in detail when the B vector is controlled to be ellipses evolving from a straight line into a circle in three orthogonal planes. II. IMPROVED 3D MAGNETIC TESTING SYSTEM A. Structure of Improved Ecitation Coil The first 3D magnetic propert tester was set up to measure 3D hsteresis loci and losses at 50 Hz [5]. In order to measure properties over wide range of frequenc the original ecitation coil was reformed to cover three ranges of frequenc, 2 Hz-20 Hz, 20 Hz-200 Hz, and 200 Hz-1000 Hz. Each new coil is consisted of three coils. Fig. 1 shows the structure of improved multi-laer ecitation coil. The first two laers, 70 turns, are designed for high frequenc range. The middle si laers combining with the first two laers are for medium frequenc range. The outer eight laers together with inner eight laers are for low frequenc range. 120mm 57mm 51mm 40mm 6mm Fig. 1. Scheme of the improved ecitation coil. 2-20Hz 80mm Hz 200-1kHz Fig. 2. Numerical analsis of 3D tester: structure of the 3D tester, magnetic field distribution corresponding to 3D field ecitation.

3 2 TABLE I COEFFICIENTS OF THE H AND B SENSING COILS (UNIT: m 2 ) H H Hz B B Bz H Hz H Hz Hz Hz In order to validate the ecitation coil structure, 3D finite element magnetic field analsis has been performed to ehibit the flu distribution in the Hi-B lamination oke and SMC specimen. Fig. 2 shows the tester structure and magnetic field distribution under 3D ecitation when three pairs of ecitation coils in three orthogonal aes are connected in series. The simulation result shows that generated fields are uniform and the field can be up to 1.9 T in the center of 3D tester. B. Improved Structure of the Sensing Coils The original sensing bo was composed of si cross-tpe H coils attached on si surfaces of a cubic specimen. Three B coils was wound around three aes of the cubic specimen [5]. The size of the H coil is approimate equal to that of the specimen side surface. Therefore, the magnetic field at the measured area is not uniform since the demagnetization factor. The improved sensing bo combines si H coils and si B coils, as shown in Fig. 3. The small circle B coil is embedded in the center of the epo resin frame, around which H coil is wound and covers the B coil. A double-laer winding structure is adopted to eliminate electromotive force (emf) induced b unwanted stra field, as shown in Fig. 3. Be noted that the two terminals of each coil are twisted to eliminate interference from stra field. The si B-H sensing coils are integrated to a sensing bo and all coils are located at the center of each surface. As a result, a cubic specimen can be easil mounted into the sensing bo and the surface of specimen is as close as possible to the B-H sensing coils, as shown in Fig. 3. Also the measured field is uniform and close to the fields in specimen. ecitation frequenc. The coefficients are used to calculate B an vectors in the specimen as shown in (2), (3). The average values are shown in Table I. The off-diagonal coefficients for B coils are ignored since the are ver small comparing with diagonal values. Hence, the B vector can be simpl calculated from (2). However, for H coils, the off-diagonal elements cannot be ignored because the field perpendicular to the laminar H coil also induced large emf due to irregularit of the H coil. According to Farada Induction Law, the inducted voltages crossing H an coils can be epressed as U U U H H Hz H H Hz U U U B B Bz Bz B B H H Hz 0 t d d B t d d B z Hz 0 Hz Hzz z z z The magnetic field strength and flu densit components can then be worked out. (2) (3) Fig. 3. Structure of the improved sensing coils: schematic B-H coil, cubic specimen with sensing coils. C. Calibration of the Sensing Coils For accurate measurement of 3D magnetic properties, the sensing bo was calibrated in a long solenoid to obtain bo coefficients [9],. E (1) 2f 0 H m where E is the rms value of the induced emf, μ 0 H m is the peak value of the flu densit in the center of the solenoid, f is the III. EXPERIMENTAL MEASUREMENT B using the improved 3D tester, eperiments in wide ranges of ecitation frequenc have been carried out under both alternating and rotating magnetization conditions. A. Alternating Magnetic Properties Fig. 4 shows a group of B-H hsteresis loops at different flu densities at 5 Hz, 20 Hz, 500 Hz, and 1000 Hz. It can be found out that the maimum flu densit at 1000 Hz is improved to 0.54 T, compared with 0.1 T of original tester. Fig. 5 shows the loops at 50 Hz along -, -, and z-aes. As shown, the loops for the - and z-ais are similar, while the - ais seems to be the eas ais, though the specimen is epected to be magneticall isotropic. This phenomenon is also observed at other frequencies. It ma impl that the particles of the SMC specimen are much closer along the - direction than along the - and z-directions, that is, higher mass densit and weaker demagnetization field along the - direction [10]. Fig. 6 plots core losses along -ais at different frequencies. It is noted that the core loss increases quickl at high frequenc range. Therefore, for SMC electrical machine the flu densit in the SMC core should be chosen lower than

4 3 0.5 T to reduce the total core loss [6]. The rotational B-H properties are also investigated. The controlled circular B loci and the corresponding H loci are measured at 50 Hz with increasing B amplitude (up to 1.3 T) in the o-, oz- and zo-planes, as shown in Fig. 7. It is observed that the B an loci lie in the same magnetization plane. The H loci in the o- and oz-planes evolve from ellipses into rectangular loops while the H loci in the zoplane changes from circles into square loops. This result is consistent with alternating hsteresis loops as shown in Fig. 5, due to eas magnetization along the -ais. Fig. 5. Hsteresis loops at 50 Hz on -, - and z-aes. Fig. 6. Core losses at different frequencies on -ais. (d) Fig. 4. Hsteresis loops in alternating magnetic field ecitations: B-H loops at 5 Hz on the -ais, B-H loops at 20 Hz on the -ais, B-H loops at 500 Hz on the -ais, (d) B-H loops at 1000 Hz on the -ais. B. 3-D Magnetic Properties Fig. 7. Roun loci and corresponding H loci in o-, oz-, zo-planes and projections in three planes, B = B = B z = 1.3 T: B loci and corresponding projections, H loci and corresponding projections.

5 4 The rotational loci at low frequenc are similar with that at 200 Hz, but at high frequenc range loci are distorted due to higher-order harmonics. The H loci change to irregular shapes with increasing ecitation frequenc. Fig. 8 illustrates the B an loci at 200 Hz when the B loci are controlled to be a series of ellipses, where the ais ratio, ε, of the minor ais to the major ais changes from 0 to 1. Compared with the H locus at 50 Hz, as shown in Fig. 7, the H locus obtained at 200 Hz is slightl different when B locus are also controlled to be a circle (ε = 1) though the are epected to be the same. IV. CONCLUSION The 3D magnetic propert tester is reformed to epand measurement frequenc up to 1000 Hz b using fleible multilaer ecitation coils. In addition, new designed sensing bo can measure B an vector in a cubic specimen more accuratel and has a fleible structure to change the specimen. The results show that H loci in a cubic SMC specimen are different at 50 Hz and 200 Hz when B loci are controlled to be the same probabl due to higher-order harmonics. The eperimental data provide valuable reference to design and optimize the 3D flu electrical machines. ACNOWLEDGMENT This work is supported in part b the China Hebei Provincial Natural Science Foundation under Grant No. E (d) Fig. 8. 3D magnetic properties of the SMC specimen with elliptical rotating flu densit vector at 200 Hz: elliptical B loci (the ais ratio ε is controled from 0 to 1) and projections in o-, oz-, zo-plane, and the major ais is,, and z respectivel, H loci and projections corresponding to in three planes, elliptical B loci and projections in o-, oz-, zo-plane, and the major ais is, z, and respectivel, (d) H loci and projections corresponding to in three planes. REFERENCES [1] P. Ole, Apparatus for Magnetization and Efficient Demagnetization of Soft Magnetic Materials, IEEE Trans. Magn., vol. 45, no. 9, pp , [2] V. Basso and G. Bertotti, Hsteresis in soft magnetic materials, J. Magn. Magn. Mater., vol. 215, pp. 1-5, [3] Y. G. Guo, J. G. Zhu, and D. G. Dorrell, Design and Analsis of a Claw Pole Permanent Magnet Motor With Molded Soft Magnetic Composite Core, IEEE Trans. Magn., vol. 45, no. 10, pp , [4] Soft magnetic composites from Höganäs Metal Powders-SOMALOY TM 500, Höganäs Product Manual, [5] J. G. Zhu, J. J. Zhong, Z. W. Lin, and J. D. Sievert, Measurement of magnetic properties under 3-D magnetic ecitations, IEEE Trans. Magn., vol. 39, no. 5, pp , [6] Y. G. Guo, J. G. Zhu, P. A. Watterson, and W. Wu, Comparative stud of 3D flu electrical machines with soft magnetic composite core, IEEE Trans. Ind. Appl., vol. 39, no. 6, pp , [7] J. J. Zhong, Y. G. Guo, J. G. Zhu, and Z. W. Lin, Characteristics of soft magnetic composite material under rotating magnetic flues, J. Magn. Magn. Mater., vol. 299, pp , [8] Z. W. Lin and J. G. Zhu, Three-dimensional magnetic properties of soft magnetic composite materials, J. Magn. Magn. Mater., vol. 312, pp , [9] Y. G. Guo, J. G. Zhu, Z. W. Lin, J. J. Zhong, H. Y. Lu, and S. H. Wang, Calibration of Sensing Coils of a Three-Dimensional Magnetic Propert Tester, IEEE Trans. Magn., vol. 42, pp , [10] Z. W. Lin, J. G. Zhu, and Y.G. Guo, Three-dimensional hsteresis of soft magnetic composite, J. Appl. Phs., vol. 99, 08D909, 2006.