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Hysteresis phenomenon is one of the important characteristics of soft magnetic materials. A three-dimensional (3D) magnetic property measurement system has been developed. This system can effectively control the locus of the time-varying magnetic flux density vector B and measure the corresponding magnetic field strength vector H in a cubic sample of soft magnetic material. The sample involved in this study is a soft magnetic composite sample made of highly pure iron powder. This paper investigates the B and H loci in 3D space and the power loss when the B loci are controlled to become circles and ellipses lying in three orthogonal planes. It is found that the B and H loci lie in the same magnetization plane, but the H loci and losses depend strongly on the orientation, position, and process of magnetization. On the other hand, the H vectors evolve into a unique locus pattern, and the power losses approach a unique value when the B vectors evolve into the same loci through either a series of small circles or ellipses. [ABSTRACT FROM AUTHOR]

The incorporation of inorganic nano particles (TiO2, Al2O3 and SiO2 etc.) with polyimide (PI) greatly improves its dielectric property. The dielectric properties of PI films are largely influenced by the absorbed water and humidity. What is more, the water absorption will be affected greatly by nano particles. In this paper, to study the effects of absorbed water on dielectric properties of moistened PI/Al2O3 composite film, PI film specimens were prepared by incorporating 12 wt% nano Al2O3 particles with PI. The original specimens were also prepared for contrast. Then the specimens were immersed in high purity water for 12, 24, 48, 72, 96, 120, 144 and 168 h. The water absorption and breakdown strength under different immersion time were measured. Meanwhile, given that the existence of surface charge had a critical influence on the breakdown characteristics, the corona charging tests were conducted at room temperature under pulse voltage. The pulse frequency was 300, 600 and 900 Hz, respectively. The pulse amplitude was +4 kV. The charge dissipation was investigated based on the demarcation energy theory. Obtained results show that the moisture condition affects more on the nano Al2O3 composite films than the original ones. Compared to original PI films, the water absorption is larger and the breakdown strength falls faster for the nano ones. The decay process of surface charge and the change of detrapping charges in nanocomposite films are affected greatly by the absorbed water. [ABSTRACT FROM PUBLISHER]

For a practical direct torque-controlled (DTC) permanent magnet synchronous motor (PMSM) drive system, the information of the initial rotor position, which is usually obtained by a mechanical position sensor, is essential for starting under the full load. To avoid the disadvantages of using mechanical position sensors, great efforts have been made on the development of sensorless control schemes. An initial rotor position estimation strategy is presented for a DTC PMSM drive based on a nonlinear model of PMSM incorporating both structural and saturation saliencies. In the new scheme, specially designed high-voltage pulses are applied to amplify the saturation saliencies. The peak currents corresponding to the voltage pulses are used, in combination with the inductance patterns, to determine the d-axis position and the polarity of the rotor. The presented initial rotor position identification strategy has been implemented in a sensorless DTC drive for a surface-mounted PMSM. Experiments are conducted to confirm the effectiveness of the method and the performance of the drive system. [ABSTRACT FROM AUTHOR]

Effective and accurate prediction of key motor parameters, such as winding flux, back electromotive force, inductance and core losses, is crucial for design of high-performance motors. Particularly, for electrical machines with new materials and nonconventional topology, traditional design approaches based on the equivalent magnetic circuit, empirical formulas and previous experiences cannot provide correct computation. The paper presents accurate determination of major parameters of a three-phase three-stack claw-pole permanent-magnet motor with a soft magnetic composite (SMC) stator core by finite-element analysis of the magnetic field. The effects of magnetic saturation and armature reaction are considered. The theoretical results by numerical analysis are validated by the experiments on the claw-pole SMC-motor prototype. [ABSTRACT FROM AUTHOR]

This paper presents an improved method for predicting magnetic power losses in electrical machines with soft magnetic composite (SMC) cores. Different formulations are used for magnetic power loss prediction with purely alternating, purely circular rotating, and elliptically rotating flux density vectors, respectively. A series of three-dimensional (3D) finite element analyses is conducted to determine the flux density locus in each element in a claw pole permanent magnet SMC electrical machine when the rotor rotates. The predicted results are compared with the experimental data of the prototype. [ABSTRACT FROM AUTHOR]