Aleksandra Kolano-Burian

Amorphous Soft Magnetic Materials for the Stator of a Novel High-Speed PMBLDC Motor

This paper presents results of a research work related to the development of the production technology of the amorphous cores designed for application in permanent magnet brushless direct current (PMBLDC) motors. The cores were made from the Metglas 2605 SA1 amorphous ribbon, from which rings of the specific external and internal diameters were cut using a laser technique. Next, the rings were stacked up so as to form a core of a required height, subjected later to the consolidation by pressing, followed by an appropriate heat treatment. Finally, the cores were coated with an epoxy resin to protect them against delamination and used as stators in a prototype high-speed electric motor, 1 kW in rated power and 70 000 rpm in a rotary speed. The motor incorporating these amorphous cores was subjected to the performance tests, which confirmed their proper operation and satisfactory mechanical characteristics and efficiency. It was found that power losses in the stators from the amorphous material were considerably smaller than those in the conventional stators from the silicon steel, and they did not exceed 7 W. Therefore, an application of the amorphous soft magnetic materials in the high-speed PMBLDC motors may contribute to eliminating the need of using additional cooling systems in these motors.

Application of Rapidly Quenched Soft Magnetic Materials in Energy-Saving Electric Equipment

The rapidly quenched soft magnetic materials have found many practical applications in power electronics, electric engineering, telecommunications, and other industrial sectors. The aim of this paper was to present the results of a research on fabrication technology of the amorphous and nanocrystalline cores intended for: 1) soft magnetic cores for the stators of the high-speed permanent magnet brushless direct current (PMBLDC) motors; 2) nanocrystalline soft magnetic cores for application in high-frequency power conversion; and 3) three-limb amorphous cores for the three-phase distribution transformers. The cores intended for the stator of the high-speed PMBLDC motor were made from the Metglas 2605 SA1 ribbon and then subjected to the performance tests in a model of an electric motor. The research on soft magnetic materials for high-frequency high-power conversion was concentrated on the Finemet rectangular cores with a gap and the composite ones with distributed gap, and the comodified Finemet cores with the induced transverse magnetic anisotropy. The three-limb cores for 400 kVA three-phase distribution transformer were made from the Metglas 2605 SA1 ribbon and subjected to the performance tests in electricity distribution network. It was found that all the amorphous and nanocrystalline cores fabricated under this paper enable considerable reduction in power losses.

Application of Extended Jiles–Atherton Model for Modeling the Magnetic Characteristics of Fe

This paper presents the result of modeling the magnetic characteristics of ring-shaped cores made of Fe41.5Co41.5Nb3Cu1B13 alloy in both as-quenched and nanocrystalline state. For the modeling, the extended Jiles-Atherton model was used. Extension of Jiles-Atherton model is focused on taking into account the changes of parameter k caused by changes of the average energy required to break pinning site. Determination of models parameters was made on the base of optimization process. This optimization covered both evolutionary strategies and simulated annealing. Finally, good agreement between experimental characteristics and the results of modeling was achieved. This agreement is confirmed by the high value of R2 determination coefficient, which exceeds 99% for both as-quenched and annealed cores. As a result, it was confirmed that the presented method of modeling the magnetic characteristics of Fe41.5Co41.5Nb3Cu1B13 alloy in both as-quenched and nanocrystalline state is suitable for technical applications.

_{41.5}

Two-phase iron-based nanocrystalline alloys are the newest generation of magnetically soft materials. FINEMET and NANOPERM are the well known nanocrystalline materials obtained by partial crystallization of metallic glasses, with magnetic properties better than those found for the amorphous counterparts. The two-phase amorphous-nanocrystalline alloys exhibit very soft magnetic behavior but only up to temperatures close to the Curie point of the amorphous matrix. Thus, their application is limited only up to about 200 ̊C. In order to increase the Curie point of the amorphous matrix and to elevate the application temperature of these alloys, iron is partially replaced by cobalt. Nanomaterials for high-temperature applications must fulfill two basic requirements: (i) very soft magnetic behavior at elevated temperatures, and (ii) stable performance at elevated temperatures for long time (application time). The second requirement is related to thermal stability of nanocrystalline structure and magnetic properties of these materials. This paper summarizes the current status of research in the field of magnetically soft nanocrystalline materials for high-temperature applications, especially highlighting the influence of alloy composition on structure and magnetic properties as well as their stability at elevated temperatures during very long time annealing. The original studies have been oriented on tailoring appropriate alloys for different application temperatures and studies of their stability during annealing for thousands of hours at temperatures up to 500 ̊C. FINEMET and NANOPERM alloys have been modified by alloying elements like Co, Si, Cu, Hf, Zr, Nb and B. The structure was studied using Differential Scanning Calorimetry, X-ray Diffraction and Transmission Electron Microscopy. Hysteresis loop and VSM measurements were used for magnetic properties characterization at room and elevated temperatures.

Co

Several papers have appeared in recent years on the application of the amorphous soft magnetic materials in the stators of the electric motors. In our previous work, we demonstrated that the replacement of a slotless stator from the FeSi electrical steel with the stator from an amorphous alloy Metglas 2605 SA1 in a high-speed permanent magnet brushless direct current (PMBLDC) motor resulted in a substantial decrease of power losses in this stator, even by three times at the rotary frequency of 70 000 r/min. This paper was concentrated on the development of the cores for stators with half-open slots, which are technologically more difficult to produce than the slotless cores. The cores were made by cutting out suitable amount of 25μm-thick rings from the FeSiB amorphous ribbon by a laser technique, followed by stacking up the rings and their consolidation, and suitable heat treatment of the compressed stacks. Next, the measurements of the magnetic properties of the sample cores with half-open slots were made using the Remacomp C-1200 hysteresisgraph and the Lakeshore 450 Gaussmeter. Based on the results of measurements, the sample cores of different heights (17.5 and 10 mm) were selected for application in a stator of the prototype high-speed PMBLDC motor, 800 W in rated power and with a maximum rotary speed of 60 000 r/min. The preliminary performance tests with this prototype motor showed that after 1 h of uninterrupted operation, the temperature of a motor housing did not exceed 60 °C. It was also found that the operating efficiency of the PMBLDC motor incorporating a stator with half-open slots, made from an amorphous material, was almost 90% over a wide range of torques (from 40 to 140 mN · m).

_{41.5}

An effect of interlaminar insulation on the dynamic magnetic properties of the tape-wound FeNiCuNbSiB-type nanocrystalline cores was investigated. This insulation was prepared by three methods. After thermomagnetic treatment of toroidal cores selected types of suitably chosen varnishes were applied onto the core edges so as to enable their in-depth penetration thus forming the desired insulation. In the final stage of thermomagnetic treatment, conducted initially under protective atmosphere of argon, oxygen was introduced to the process to enable formation of interlaminar oxide layer. Finally, the ribbon was coated with SiO layer prior to its winding into the core. Then, dynamic magnetic properties of the cores were measured within a frequency range from 50 Hz to 100 kHz. It was found that the use of a modified acrylic-type resin resulted in the decrease of the Fe73.8Ni5Cu0.6Nb2.6Si9B9 core losses at higher frequencies. In the cores with an oxide insulation, reduction of power losses was observed at lower frequencies. The use of interlaminar SiO insulation resulted in considerable reduction of core losses above the frequency of 5 kHz. The results of this paper can be practically applied in the production of nanocrystalline cores for power electronic equipment.

Nb

The magnetocaloric effect in La0.6Ca0.4MnO3 manganite has been investigated. The isothermal magnetization versus applied magnetic field at various temperatures in the vicinity of Curie temperature was measured, and the temperature dependence of magnetic entropy change was determined using Maxwell’s relation. This value is comparable to that in Gd. Nevertheless, the relative cooling power of La0.6Ca0.4MnO3 was shown to be considerably lower than that of Gd. The experimental results have been analyzed in frames of a phenomenological statistical model. This model considers explicitly Jahn-Teller interactions and allows prediction of the field dependences of the magnetic entropy change and the relative cooling power.

_{3}

This paper presents the main features of magnetically soft metallic glasses and nanocrystalline materials obtained by controlled crystallization of metallic glasses, a brief description of the principal methods of nanocrystallization as well as the recent developments in nanocrystalline materials for high-temperature applications. Two groups of alloys were investigated: (Fe, Co)-Si-Nb-Cu-B (FINE-MET-type) and (Fe, Co)-(Zr, Nb, Hf)-Cu-B (HITPERM-type). For FINEMET-type alloys it was found that the optimum combination of magnetic properties coercivity, Curie temperature, magnetostriction) is obtained when Fe:Co ratio is about 1:1. For HITPERM-type alloys, the best performance and stability are observed when alloys contain Hf, and the worst in the case of Nb. Optimum Hf content is 7 at.%, and 6 at.% B. The HITPERM-type alloys exhibit good stability of properties at 500°C for at least 700 hours.

Cu

Intermetallic compounds with the overall formula Mn1.1Fe0.9P0.5As0.5−xGex (x varies from 0 to 0.1) were investigated in order to study their magnetocaloric effect by monitoring the adiabatic temperature change, magnetic entropy change and their relation to structural parameters. It was found that the maximum of magnetocaloric effect was achieved for x = 0.02. Adiabatic temperature change for consolidated powder was equal to 2.75 K for the magnetic field change ΔB = 1.7 T for the sample with x = 0.02. For the pure non-doped sample, this parameter is much lower: ΔTad = 1.7 K @ ΔB = 1.7 T. This result was correlated with the change of structural parameters such as lattice constants and the unit cell volume.

_{1}

Ni2MnGa alloy exhibits significant magnetocaloric effect due to structural and magnetic transition, which take place at similar temperature range. In this report we present band structure calculations for Ni2MnGa doped with Cu performed within KKR-CPA scheme. We also calculated the estimated temperature of the magnetic transition as a function of dopant concentration within Mean-Field-Approach (MFA). Our calculations show that the Curie temperature increases with Cu doping in agreement with recent experimental data.