Performance evaluation of synchronous reluctance motors with and without permanent magnets

Nowadays, a growing interest in the efficiency and the cost of electrical machines has been noticed. Therefore, Synchronous Reluctance Motors (SynRMs) have become more attractive, thanks to their higher efficiency and nevertheless acceptable cost compared to induction machines. The rotor design of SynRMs with or without permanent magnets (PMs) has a huge effect on the motor efficiency, torque density and power factor. This paper introduces an evaluation for the performance of SynRMs with and without PMs in terms of efficiency, torque and power factor maps. Three different rotor designs for the same machine have been compared. For one machine, the experimental measurements have been obtained and the validation of the simulation results have been confirme

Performance comparison of conventional synchronous reluctance machines and PM-assisted types with combined star-delta winding

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star-delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star-delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star-delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star-delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts

The Impact of Spatial Segregation on the Employment Outcomes Amongst Bangladeshis Men and Women in England and Wales

Studies of ethnic residential segregation and its impacts on labour market performance have reported both negative and positive outcomes for different groups in different geographies. We revisit the issue with a particular focus on the Bangladeshi minority in England and Wales using both quantitative and qualitative data to explore the impact of living in segregated areas upon their labour market outcomes. We analyse the 2001 UK Census Controlled Access Microdata Sample (CAMS) and a subset (34 Bangladeshis) of qualitative data collected through in-depth interviews with 73 men and women from Indian, Bangladeshi and Black Caribbean backgrounds in 2005. Our quantitative analysis does show a clear negative impact of living in segregated areas (i.e. Bangladeshi ethnic enclaves) on unemployment, economic inactivity and on the occupational returns on education. Qualitative material suggests that cultural and practical reasons very often lead Bangladeshis, including highly qualified persons, to live in enclaves or nearby. Also, ethnic businesses in enclaves appear to offer jobs to many Bangladeshi men and women, but these jobs are normally low-paid that does not require high qualifications increasing the risk of lower occupational returns further.Ethnicity, Residential Segregation, Bangladeshis in UK, Enclave Economy, Multilevel Analysis, England, Employment Outcomes

Hybrid photovoltaic-thermoelectric generator powered synchronous reluctance motor for pumping applications

The interest in photovoltaic (PV) pumping systems has increased, particularly in rural areas where there is no grid supply available. However, both the performance and the cost of the whole system are still an obstacle for a wide spread of this technology. In this article, a hybrid photovoltaic (PV)-thermoelectric generator (TEG) is investigated for pumping applications. The electric drivetrain comprises a synchronous reluctance motor and an inverter. A control strategy for the drivetrain is employed to execute two main tasks: 1) driving the motor properly to achieve a maximum torque per Ampere condition and 2) maximizing the output power of the PV system at different weather conditions. This means that the conventional DC-DC converter is not used in the proposed system. Moreover, batteries, which are characterized by short life expectancy and high replacement cost, are also not used. It is found that the motor output power and the pump flow rate are increased by about 9.5% and 12% respectively when the hybrid PV-TEG array is used compared to only using PV array. Accordingly, the performance, cost and complexity of the system are improved. Measurements on an experimental laboratory setup are constructed to validate the theoretical results of this work

Solar array fed synchronous reluctance motor driven water pump : an improved performance under partial shading conditions

An improved performance of a photovoltaic (PV) pumping system employing a synchronous reluctance motor (SynRM) under partial shading conditions is proposed. The system does not include the dc-dc converter that is predominantly being utilized for maximizing the output power of the PV array. In addition, storage batteries are also not contained. A conventional inverter connected directly to the PV array is used to drive the SynRM. Further, a control strategy is proposed to drive the inverter so that the maximum output power of the PV array is achieved while the SynRM is working at the maximum torque per Ampere condition. Consequently, this results in an improved system efficiency and cost. Moreover, two maximum power point tracking (MPPT) techniques are compared under uniform and partial shadow irradiation conditions. The first MPPT algorithm is based on the conventional perturbation and observation (P&O) method and the second one uses a differential evolution (DE) optimization technique. It is found that the DE optimization method leads to a higher PV output power than using the P&O method under the partial shadow condition. Hence, the pump flow rate is much higher. However, under a uniform irradiation level, the PV system provides the available maximum power using both MPPT techniques. The experimental measurements are obtained to validate the theoretical work

Gender Differences in the Corporate Social Responsibility Orientation of Credit Union Board Members

Credit unions serve an important purpose in the U.S. economy by providing financial services to low- and moderate-income individuals. Their assets have steadily grown from $217 billion to$655 billion between 1990 and 2004. In spite of these impressive growth rates, a number of writers have expressed great concern regarding credit union governance, particularly over the role and functions of the board\u27s members. More recently, the financial crisis has raised important questions regarding the board\u27s level of involvement and its ethical and social responsibilities in corporate decision making. One area which has remained relatively unexplored concerns the attitudes of credit union board members toward corporate social responsibility. Furthermore, to date very little is known regarding the extent of similarities and differences between these organizations\u27 male and female board members with respect to this issue. The present study was designed to investigate this issue. A survey of 470 directors of 80 credit unions revealed significant differences between the genders with respect to the legal and ethical components of corporate social responsibility. Compared to their male counterparts, the female directors exhibited greater concern about the legal dimension of corporate responsibility and a weaker orientation toward ethics. No significant differences between the two groups were observed with respect to the economic and discretionary components

The Balanced Two-String Technique for Sulcus Intraocular Lens Implantation in the Absence of Capsular Support

Purpose. To describe and explore an alternative approach for sulcus intraocular lens (IOL) implantation in the absence of capsular support. Methods. The commonly available one-piece poly(methyl methacrylate) (PMMA) lens is stabilized in the sulcus by two intraocular horizontal strings of 10/0 polypropylene suture passed through the lens dialing holes in opposite directions to achieve a mechanical balance. The horizontal strings of 10/0 polypropylene work as a rail track for the IOL optics, allowing some side to side lens adjustment even following wound closure. The stability of the IOL was tested in vitro. Six aphakic patients underwent in-sulcus IOL secondary implantation using the balanced two-string technique. Patients were followed up for a minimum of six months. Best spectacle corrected vision was assessed. Lens centration and lens tilt were measured by anterior segment optical coherence tomography (AS-OCT). Results. All patients had successful lens insertion. Best spectacle corrected visual acuity (BSCVA) improved in all patients. Lens decentration ranged between 0.21 mm and 0.9 mm (average 0.53 mm). Lens tilt ranged between 1.2° and 2.8° (average 2.17°). Conclusion. The mechanically balanced two-string technique is an alternative option for sulcus IOL implantation in absence of capsular support, allowing lens centration adjustment with no additional risks

Service-Learning Projects Enhance Student Learning in Strategic Management Courses

Academia has been criticized for Its supposed isolation from society and its lack of emphasis on practical applications and hands-on experience. Institutions of higher education are responding to this criticism by incorporating experiential service-learning in their curricula. One business course which is particularly appropriate for integrating service-learning into the curriculum is Strategic Management