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Permanent magnet (PM) machines have been extensively used for various applications. Nevertheless, thermal effect, particularly hotspot temperature, not only severely restricts power/torque density but also leads to deteriorations in electromagnetic performance, service life, and reliability. Starting with foundations of PM machines and heat transfer mechanisms, this paper reviews the development of thermal analysis methods over the last thirty years and the state-of-the-art research achievements, and the hotspot temperatures of winding and PM are particularly evaluated. In the overview, various machine losses and cooling techniques are first introduced, which are the essential reasons for temperature rise and the most straightforward way to remove the generated heat. Afterwards, the mainstream thermal analysis techniques, i.e., numerical techniques, lumped-parameter thermal model, and hybrid thermal models, as well as the online electrical parameter-based and thermal model-based temperature monitoring techniques, are reviewed and assessed in depth. In addition, this paper also reviews the analytical thermal modelling methods for winding and PM. Finally, future research trends are highlighted.

The effect of hydrogen atoms and temperature on the mechanical properties of 〈100〉 α-Fe nanowires with different cross section sizes is investigated by molecular dynamics simulation method. The results show that the difference of peak stress of samples with and without hydrogen increases with the increase of cross section size at 300 K, while there is no distinct regularity at 10 K. The deformation behavior in 〈100〉 α-Fe nanowires is governed by the nucleation and growth of twins. The studies also indicate that hydrogen atoms decrease peak stress and don't affect the deformation mechanism of nanowires.

Electromagnetic performance of Vernier machines largely depends on choosing the correct slot/pole number combinations. For a given gear ratio, designs with different slot/pole number combinations are possible. This paper investigates the impact of these slot/pole number combinations on electromagnetic performance such as torque, power factor and demagnetization. The study is carried out through detailed finite element analysis on a 3MW outer rotor direct drive generator targeted at wind power application. The torque/cost, torque/mass and efficiency, which are critical parameters for this application, are compared with a conventional direct drive PM generator. The study shows that Vernier designs with lower values of slot/pole number combinations exhibit much better performance in terms of torque and power factor. However, the potential magnet demagnetization and also core saturation limit these designs and hence play a critical role in selecting the optimal slot/pole number combination.

The first-passage time of an inverted pendulum subject to a combination of high frequency harmonic excitation and Gaussian white noise excitation is investigated. The high frequency harmonic excitation term is simplified to an equivalent autonomous nonlinear stiffness term by using the method of direct partition of motions. Then, the equations of motion of the equivalent system are reduced to an averaged I t o ˆ stochastic differential equation by using the stochastic averaging method of energy envelope. After that, a backward Kolmogorov equation governing the conditional reliability function of first-passage time is established by using the averaged I t o ˆ equation. The conditional reliability function and the conditional probability density of first-passage time from numerical solution of the backward Kolmogorov equation agree well with those from digital simulation of the equivalent system. The effects of system parameters on the conditional reliability function and the conditional probability density of the system are discussed.

Transverse magnetic (TM) and transverse electric (TE) defective bands will split with different incident angles (wave-vectors) in the one-dimensional coupled cavity waveguide. Different defective band properties are shown, including the shift of pass-band frequency and the variation of defective band width resulting from different localization properties of the electric field in the defective layer. The critical splitting angle, at which splitting of the TE and TM defective bands emerges, will decrease with increasing dielectric index of the defective layer.

KEYWORD:HTS; Cryogenic; Forced circulation; Heat loss; HTS substation; HTS apparatus; Cool- ing system ABSTRACT:A 10 kV High Temperature Superconducting power substation with a cooling system was developed and has been put into operation in power distribution system for more than three years. The working conditions, heat resource and the distribution character of the four apparatuses working at the 10 kV/630 kVA HTS substation were analyzed. The heat load is distributed along the length for the cable for which thus a forced enclosed circulation system is necessary; while it is con- centrated within only several cryostats for the other three HTS apparatus for which it is enough to cool only with an opened loop cooling system by consuming of liquid nitrogen. And an independent cooling system with refrigerator for the 1 MJ SMES is a good selection due to the different working temperature range. Based on the analysis and discussion, a concentrated evaporative cooling station which includes an opened loop cooling system without circulation and a forced circulation system with a closed circle was designed and constructed.

The steady-state dynamic performance of a direct torque controlled brushless DC drive when operated in single- and double-switch chopping modes is compared. It is shown that the vibration of the machine is reduced significantly when the influence of the cogging torque is accounted for in the torque controller.

It is a challenge to realise an EKF-based sensorless controller for an interior permanent magnet (IPM) brushless ac motor drive due to the influence of non-linearity and rotor saliency. An improved reduced-order EKF method is presented which reduces the rotor position estimation error of an IPM motor, which was evident in [1] due to the neglect of saliency. The effectiveness of the proposed method is verified experimentally.

Calcaneus quantitative ultrasound (QUS) assessment is a safe and reliable method for evaluating skeletal status. Until now, considerable data have been accumulated on the distribution of QUS in Caucasian populations, whereas such data are still insufficient in Asian populations, especially in Chinese mainland. The present study aimed to obtain the distribution characteristic of calcaneus QUS in healthy Chinese women, and to further investigate the distribution of low bone mass by QUS stiffness index (SI). This study included 2,498 healthy Chinese females aged 10–87 yr. The QUS exhibited a characteristic mild rise and then fall pattern with increasing age. Age, body height, and weight were significant influencing factors on SI, especially age and weight. The prevalence of osteoporosis detected using instrument-derived T-score or internal T-score was different from that calculated according to calcaneus bone mass density (BMD) previously reported. Furthermore, between instrument-derived T-scores and internal T-scores, there were also significant differences. We concluded that the World Health Organization criteria from BMD may not be appropriate for QUS, and the instrument-derived T-score may also not be appropriate for the studied population. The results will be useful for predicting fracture risk of Chinese women and determining diagnostic criteria of osteoporosis by QUS.