This paper presents some design considerations for synchronous machines characterized by a fractional number of slots per pole per phase. The main advantage of this configuration is a smooth torque, ...which is due to the elimination of periodicity between slots and poles. A second advantage is a higher fault-tolerant capability, making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high content of MMF harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot machines is illustrated in this paper, including double-layer and single-layer windings. The analytical computation is extended to determine the harmonics of MMF distribution. Their effect is highlighted in isotropic as well as anisotropic machines. Finally, some considerations are reported to avoid unsuitable configurations
The fractional-slot permanent-magnet (PM) machines are used in many applications due to their high torque density, low torque ripple, and high efficiency. However, the fractional-slot machines are ...characterized by high contents of space harmonics in the air-gap MMF distribution. Such harmonics cause flux variation in the air gap, and the main consequence is the induced losses in the rotor. Depending on the combination of slots and poles of the machine, there are different harmonic contents and then rotor losses. By means of a simple model of the rotor losses, this paper investigates the link between the rotor losses and the combination of the slots and the poles of the fractional-slot PM machines.
Abstract
This study aimed to measure changes in different properties of skeletal muscles and evaluate their contribution and relationship to changes in functional performance after pulmonary ...rehabilitation (PR) in patients with chronic obstructive pulmonary disease (COPD). COPD outpatients attending 5 weeks of conventional PR were recruited. Functional performance 5-repetitions sit-to-stand (5STS), and 4-m gait speed (4mGS), and muscle function (maximal isometric strength, power, force control, and relative concentric and eccentric activation during 5STS) were assessed after PR and 3 months of follow-up. Twenty patients (71 years; 52% of predicted FEV
1
) completed the study. 4mGS and relative concentric activation during 5STS decreased respectively by 7.7% and 26% between the beginning of PR and follow-up. Quadriceps strength, power, and force control improved by 10.4%, 27.3%, and 15.2%, respectively, from the beginning of PR to follow-up the relative eccentric activation during 5STS explained 31% of the variance in 4mGS changes. In conclusion, functional performance appeared to decline after conventional PR, whereas several properties of skeletal muscles were maintained at follow-up in COPD outpatients. Of note, eccentric contractions might play a role in the improvement of functional performance. Therefore, future studies with interventional design should include eccentric training in PR programs during clinical COPD practice.
In this paper, it is shown how to extract a hypothesis with small risk from the ensemble of hypotheses generated by an arbitrary on-line learning algorithm run on an independent and identically ...distributed (i.i.d.) sample of data. Using a simple large deviation argument, we prove tight data-dependent bounds for the risk of this hypothesis in terms of an easily computable statistic M/sub n/ associated with the on-line performance of the ensemble. Via sharp pointwise bounds on M/sub n/, we then obtain risk tail bounds for kernel perceptron algorithms in terms of the spectrum of the empirical kernel matrix. These bounds reveal that the linear hypotheses found via our approach achieve optimal tradeoffs between hinge loss and margin size over the class of all linear functions, an issue that was left open by previous results. A distinctive feature of our approach is that the key tools for our analysis come from the model of prediction of individual sequences; i.e., a model making no probabilistic assumptions on the source generating the data. In fact, these tools turn out to be so powerful that we only need very elementary statistical facts to obtain our final risk bounds.
The torque produced by a synchronous reluctance machine (including the permanent-magnet-assisted machine) is studied analytically, with the aim of pointing out the effect of the position of the flux ...barriers on the torque ripple. It is verified that the position of the flux-barrier ends highly influences the torque waveform. With the aim of reducing torque harmonic contents, a new strategy is proposed based on the choice of couples of flux barriers of different shapes. The flux-barrier geometry is chosen so as to obtain a compensation between the torque harmonics produced by each couple. Experimental results on two prototypes confirm the analytical prediction.
Several techniques may be adopted in designing surface-mounted permanent-magnet motors in order to reduce the cogging torque. This paper describes various classical and innovative techniques, giving ...a theoretical justification for each of them. To this aim, a simple original model of the cogging torque mechanism and a Fourier analysis are introduced. As a result, it is highlighted that some techniques are not always utilizable, and some of them may even be deprecatory when not used correctly. In addition, effects of cogging torque elimination on back electromotive force are discussed.
Hereditary hemochromatosis (HH) is a genetic disorder of iron overload and subsequent organ damage. Five types of HH are known, classified by age of onset, genetic cause, clinical manifestations and ...mode of inheritance. Except for the rare form of juvenile haemochromatosis, symptoms do not usually appear until after decades of progressive iron loading and may be triggered by environmental and lifestyle factors. Despite the last decades discovery of genetic and phenotype diversity of HH, early studies showed a frequent involvement of the endocrine glands where diabetes and hypogonadism are the most common encountered endocrinopathies. The pathogenesis of diabetes is still relatively unclear, but the main mechanisms include the loss of insulin secretory capacity and insulin resistance secondary to liver damage. The presence of obesity and/or genetic predisposition may represent addictive risk factor for the development of this metabolic disease. Although old cases of primary gonad involvement are described, hypogonadism is mainly secondary to selective deposition of iron on the gonadotropin-producing cells of the pituitary gland, leading to hormonal impaired secretion. Cases of hypopituitarism or selected tropin defects, and abnormalities of adrenal, thyroid and parathyroid glands, even if rare, are reported. The prevalence of individual gland dysfunction varies enormously within studies for several bias due to small numbers of and selected cases analyzed, mixed genotypes and missing data on medical history. Moreover, in the last few years early screening and awareness of the disease among physicians have allowed hemochromatosis to be diagnosed in most cases at early stages when patients have no symptoms. Therefore, the clinical presentation of this disease has changed significantly and the recognized common complications are encountered less frequently. This review summarizes the current knowledge on HH-associated endocrinopathies.
Potentials and limits of high-speed PM motors Bianchi, N.; Bolognani, S.; Luise, F.
IEEE transactions on industry applications,
2004-Nov.-Dec., 2004-11-00, 20041101, Volume:
40, Issue:
6
Journal Article
Peer reviewed
This paper illustrates potentials and limits of high-speed permanent-magnet (PM) motors. The influence of materials chosen for PM, stator core, and retaining sleeve is highlighted. Slotted and ...slotless topologies are considered and compared, computing magnetic, electrical, mechanical, and thermal quantities by means of both analytical and finite-element approach. Thermal and PM demagnetization limits as well as rotor losses are evaluated. A criteria of optimization of the motor structure is described, with the diameter ratio and the iron flux density as main design variables.
This paper deals with the cogging torque calculation in permanent-magnet (PM) surface-mounted machines based on energy approach. Three different analytical co-energy methods are assessed, and ...innovative computation techniques for calculating co-energy are applied to reduce the computations time and burden. Also, an air-gap function due to the slot is presented for the simple method. Then, the results achieved by the analytical methods are validated by the finite-element method (FEM). The cogging torque using such methods has a good agreement with FEM. Three case studies consisting of brushless PM (BLPM) motors with slotted stator structure are considered to show the efficiency of the proposed methods. Finally, different methods are compared in terms of their computational complexity and accuracy.
The sensorless control technique based on the superimposition of a high-frequency stator voltage is commonly used to detect the rotor position of a synchronous interior-permanent-magnet (IPM) motor. ...This technique is effective at zero and low motor speed, where back electromotive force is null or extremely low. Then, the accuracy of the rotor-position detection depends strictly on the rotor saliency, that is, on the geometry of the IPM rotor. This paper aims to determine some IPM rotor-design criteria so as to improve the sensorless rotor-position detection. Since the design has to be effective in different operating conditions, both saturation and cross-coupling effects have to be taken into account. It is found that the effectiveness of the sensorless rotor-position detection can be improved by means of a proper design of the IPM motor geometry even under heavy operating conditions
