EFFICIENCY AND RELIABILITY ENHANCEMENT OF MULTIPHASE SYNCHRONOUS MOTOR DRIVES

Multiphase electric machines are attractive in comparison with three-phase ones due to advantages such as fault-tolerant nature, smaller rating per phase and lower torque ripple. More specifically, the machines with multiple three-phase windings are particularly convenient, because they are suitable for standard off-the-shelf three-phase dc/ac converter modules. For instance, they are becoming a serious option for applications such as electric vehicles and wind turbines. On the other hand, in these applications, operation at low power is often required for long time intervals; hence, improving the efficiency under such conditions is highly desired and could save a significant amount of energy in the long term. This dissertation proposes a method to enhance the efficiency of electric drives based on multiple three-phase windings at light load. The number of active legs is selected depending on the required torque at each instant. To ensure that the overall efficiency is effectively optimized, not only the converter losses, but also the stator copper losses, are taken into account. Experimental results verify the theoretical outcomes. Surface-mounted permanent-magnet synchronous motors (SPMSMs) require a position measurement to ensure a high-performance control. To avoid the cost and maintenance associated to position sensors, sensorless methods are often preferred. The approaches based on high-frequency signal injection are currently a well-established solution to obtain an accurate position estimation in SPMSMs. These techniques can be roughly divided into two groups: those based on sinusoidal or on square-wave high-frequency signals. The main drawback of the former is the limitation on the response speed, due to the presence of several low-pass filters (LPFs). On the other hand, the latter methods are sensitive to deadtime effects, and high-frequency closed-loop current control is required to overcome it. This dissertation proposes to improve the sensorless strategies based on sinusoidal high-frequency injection by simplifying the scheme employed to extract the information about the position error. Namely, two LPFs and several multiplications are removed. Such simplification does not only reduce the computational complexity, but also permits to obtain a faster response to the changes in the angle/speed, and hence, a faster closed-loop control. Experimental results based on a SPMSM prove the enhanced functionality of the proposed method with respect to the previous ones based on high-frequency sinusoidal signal injection

Modeling and Experimental Verification of Adaptive 100% Stator Ground Fault Protection Schemes for Synchronous Generators

Salient pole synchronous generators as the main component of an electricity generation station should be carefully maintained and their operation has to be monitored such that any damage on them is avoided. Otherwise, the generating station might experience frequent shut downs which results in electricity generation interruptions and high costs associated with repairing and compensation of lack of energy. In this sense, many protective schemes focusing on a variety of synchronous generator faults have already been proposed and are still modified and developed to further enhance the quality of protection. In this thesis, synchronous generator stator windings to ground fault is studied as one of the most common and crucial faults in these machines. Numerous methods of stator winding to ground fault protection schemes are also reported in the literature. Third harmonic differential voltage and sub-harmonic schemes are studied in this research. A novel adaptive scheme for both methods is modelled and implemented in a comprehensive lab scale set-up where a real generation unit is scaled down including all different components and apparatus. The simulation model is also established based on simultaneous finite element analysis (FEA) and coupled magnetic circuit to assist with system configuration design and parameter selections. The adaptive scheme is proved to be capable of detecting stator windings to ground faults based on actual experimental data. Finally, the proposed adaptive scheme is compared against other available non-adaptive protection schemes currently used in industrial relays. Several important performance evaluation criteria in protection schemes such as sensitivity and security of operation referred to as reliability are considered. It is shown that the adaptive scheme offers higher reliability than other schemes which emphasizes its credibility and applicability

EFFICIENCY AND RELIABILITY ENHANCEMENT OF MULTIPHASE SYNCHRONOUS MOTOR DRIVES

Multiphase electric machines are attractive in comparison with three-phase ones due to advantages such as fault-tolerant nature, smaller rating per phase and lower torque ripple. More specifically, the machines with multiple three-phase windings are particularly convenient, because they are suitable for standard off-the-shelf three-phase dc/ac converter modules. For instance, they are becoming a serious option for applications such as electric vehicles and wind turbines. On the other hand, in these applications, operation at low power is often required for long time intervals; hence, improving the efficiency under such conditions is highly desired and could save a significant amount of energy in the long term. This dissertation proposes a method to enhance the efficiency of electric drives based on multiple three-phase windings at light load. The number of active legs is selected depending on the required torque at each instant. To ensure that the overall efficiency is effectively optimized, not only the converter losses, but also the stator copper losses, are taken into account. Experimental results verify the theoretical outcomes. Surface-mounted permanent-magnet synchronous motors (SPMSMs) require a position measurement to ensure a high-performance control. To avoid the cost and maintenance associated to position sensors, sensorless methods are often preferred. The approaches based on high-frequency signal injection are currently a well-established solution to obtain an accurate position estimation in SPMSMs. These techniques can be roughly divided into two groups: those based on sinusoidal or on square-wave high-frequency signals. The main drawback of the former is the limitation on the response speed, due to the presence of several low-pass filters (LPFs). On the other hand, the latter methods are sensitive to deadtime effects, and high-frequency closed-loop current control is required to overcome it. This dissertation proposes to improve the sensorless strategies based on sinusoidal high-frequency injection by simplifying the scheme employed to extract the information about the position error. Namely, two LPFs and several multiplications are removed. Such simplification does not only reduce the computational complexity, but also permits to obtain a faster response to the changes in the angle/speed, and hence, a faster closed-loop control. Experimental results based on a SPMSM prove the enhanced functionality of the proposed method with respect to the previous ones based on high-frequency sinusoidal signal injection

The Comparison of Job Stress among Dental Professionals of Dentistry Faculty Members of Tabriz University

Several studies have so far focused on occupational stress among dentists and the results have shown that many factorscan cause stress. However, the level of stress among experts in the fields of dentistry has not yet been studied in Iran.The aim of this study is to examine the causes and levels of job stress among dental professionals in Tabriz University ofMedical Sciences. This cross-sectional study included all dental professionals of Dentistry Faculty; an overall of 55 subjectsin Tabriz were studied in this research and their level of stress was evaluated using “The Health and Safety ExecutiveManagement Standards Indicator Tool” (HSE stress questionnaire) from September up to October 2014. The level of stressin each dental specialty was examined descriptively (mean, standard deviation). Statistical analysis was performed usingSPSS 20. The findings of the study showed that the highest stress among dental professionals from different fields wasobserved in the field of oral and maxillofacial radiology; fields of oral medicine, endodontics, oral and maxillofacial surgeryand pediatric dentistry ranked later. The lowest stress was seen among orthodontics specialists. Based on the results of thepresent study, the rate of job stress varied significantly among dental professionals

Application of Discriminant Analysis for Studying the Source Rock Potential of Probable Formations in the Lorestan Basin, Iran

Understanding the performance and role of each formation in a petroleum play is crucial for the efficient and precise exploration and exploitation of trapped hydrocarbons in a sedimentary basin. The Lorestan basin is one of the most important hydrocarbon basins of Iran, and it includes various oil-prone potential source rocks and reservoir rocks. Previous geochemical studies of the basin were not accurate and there remain various uncertainties about the potential of the probable source rocks of the basin. In the present research, the geochemical characteristics of four probable source rocks of the Lorestan basin are studied using Rock-Eval pyrolysis and discriminant analysis. In achieving this goal, several discriminant functions are defined to evaluate the discriminant factor for the division of samples into two groups. The function with the highest discriminant factor was selected for the classification of probable source rocks into two groups: weak and strong. Among the studied formations, Garau and Pabdeh had the richest and poorest source rocks of the Lorestan basin, respectively. The comparison of the obtained results with the previous literature shows that the proposed model is more reliable for the recognition of the richness of source rock in the area

Comparison of Common Monogenic Defects in a Large Predominantly Antibody Deficiency Cohort

Background: Predominantly antibody deficiencies (PADs) are the most common primary immunodeficiencies, characterized by hypogammaglobulinemia and inability to generate effective antibody responses. Objective: We intended to report most common monogenic PADs and to investigate how patients with PAD who were primarily diagnosed as suffering from agammaglobulinemia, hyper-IgM (HIgM) syndrome, and common variable immunodeficiency (CVID) have different clinical and immunological findings. Methods: Stepwise next-generation sequencing and Sanger sequencing were performed for confirmation of the mutations in the patients clinically diagnosed as suffering from agammaglobulinemia, HIgM syndrome, and CVID. Results: Among 550 registered patients, the predominant genetic defects associated with agammaglobulinemia (48 Bruton's tyrosine kinase [BTK] and 6 μ heavy chain deficiencies), HIgM syndrome (21 CD40 ligand and 7 activation-induced cytidine deaminase deficiencies), and CVID (17 lipopolysaccharides-responsive beige-like anchor deficiency and 12 atypical Immunodeficiency, Centromeric instability, and Facial dysmorphism syndromes) were identified. Clinical disease severity was significantly higher in patients with μ heavy chain and CD40 ligand mutations compared with patients with BTK (P = .003) and activation-induced cytidine deaminase (P = .009) mutations. Paralysis following live polio vaccination was considerably higher in patients with μ heavy chain deficiency compared with BTK deficiency (P < .001). We found a genotype-phenotype correlation among patients with BTK mutations regarding clinical manifestation of meningitis and chronic diarrhea. Surprisingly, we noticed that first presentations in most patients with Immunodeficiency, Centromeric instability, and Facial dysmorphism were respiratory complications (P = .008), whereas first presentations in patients with lipopolysaccharides-responsive beige-like anchor deficiency were nonrespiratory complications (P = .008). Conclusions: This study highlights similarities and differences in the clinical and genetic spectrum of the most common PAD-associated gene defects. This comprehensive comparison will facilitate clinical decision making, and improve prognosis and targeted treatment

Comparison of Common Monogenic Defects in a Large Predominantly Antibody Deficiency Cohort

Predominantly antibody deficiencies (PADs) are the most common primary immunodeficiencies, characterized by hypogammaglobulinemia and inability to generate effective antibody responses