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

Short communication: Effects of garlic (Allium sativum L) extract on growth, feed utilization and carcass composition in Mugil cephalus (Linnaeus, 1758) larvae

Various extracts from herbs and spices are reported to improve animal performance by stimulating action on gut secretions or by having a direct bactericidal effect on gut micro flora. Furthermore the active principles of the herb in the diets induce the secretion of the digestive enzymes and the growth promoter in herbs induces high protein synthesis. Garlic is an important medicinal herb extensively cultivated in many countries and has played an important dietary function as well as medicinal role for centuries. Several studies have demonstrated the positive effect of garlic inclusion in fish feed on the growth performance of various species. ... Until now, no trial has been conducted to study the effects of dietary garlic extract on growth of grey mullet (M. cephalus) This study was therefore designed to investigate the effects of garlic on growth, feed utilization and carcass composition of M. cephalus larvae with the aim of ascertaining the importance and level of garlic supplementation in fish feeds especially in M. cephalus

Risk assessment of noise pollution by analyzing the level of sound loudness resulting from central traffic in Shiraz

Background: Today, the effects of environmental pollution on human life and human needs, which reduces the level of community health caused by traffic noise in large cities, are clearly visible by creating irritation and pathogenic conditions. The aim of this study was to assess the risk of noise pollution resulted from central traffic in Shiraz by analyzing its indicators and related components. Methods: By specifying the high traffic jam in Shiraz, the sound and its frequency in 156 points of the city were analyzed using a sound analyzer (Tes-1358C model). The sound pressure levels (LA and LP) and the one and one-third octave band were continuously measured in A and C networks. Then, data were extracted and analyzed using Excel 2016 and Minitab 18.1. Eventually, phon and sone indexes were calculated for the heavy traffic jam in some of the central streets of Shiraz and the results were statistically calculated and their charts were prepared with comfort disturbance ranges. Results: The highest harmful frequency of traffic in Shiraz was 50 Hz and 83.3 dB. The sound pressure level ranged from 70 to 92.7 dB in network A and 87.8 dB in network C. The maximum sound level was 87 phon and the maximum sone was 26 at 14 stations. Conclusion: According to the results, the sound pressure levels exceeded the environmental standards of Iran and the values of phon and sone were higher than the standard of comfort at night and day. Keywords: Noise pollution, Environmental pollution, Loudness perception, Health risk assessment, Shiraz

Active tactile sensibility of three-unit implant-supported FPDs versus natural dentition

Splinting of the implants might improve the active tactile sensibility (ATS) of the pontic area due to cumulative effect of Osseo perception of two retainers; on the other hand, due to the lack of any supporting implant in the axis of occlusal force for the pontic area, ATS might be lower for this portion of FPDs. we evaluated the active tactile sensibility of natural teeth and three-unit implant-supported FPDs. The ATS of posterior 3-unit implant-supported FPD and contralateral teeth was measured in 50 patients, in a random order blinded to patients and assessor, carried out at two sessions. Based on the experimental range of 0 to 70 um, the sigmoid shape of psychometric curve was estimated to locate the 50% values as the ATS thresholds for each tooth or implant. Data were analyzed using unpaired t-tests. The ATS of the teeth and implants differed significantly and compared to teeth, implants exhibited significantly higher ATS thresholds in all the groups. The results of independent t-test showed the highest difference in the means of ATS between the pontic and the first molar tooth. Based on the equivalence testing approach, the 95% CIs indicated that the differences were clinically significant only in the Pontic/First Molar group. In multi-unit implant-supported prostheses the tactile perception of the prosthesis that are placed on fixtures is similar to the natural teeth. In pontic areas there are significant statistical and clinical differences, with much lower tactile sensibility in pontics compared to the natural teeth

Numerical modeling of a multi degree freedom system consisting of heave, pitch and surge motions for the conversion of sea wave energy

1813-1821In this study, we present a point absorber wave energy converter model of a multi degree freedom system. This converter uses heave, pitch, and surge motions in order to absorb energy. Given that the function of the point absorber converters is dependent on the frequency of the wave excitation, the maximum power is obtained when the frequency of the system and the wave frequency are equal so the greatest oscillation occurs in the system. Therefore, using several natural frequencies for the system can help achieve the resonance condition. For this purpose, in addition to heave motion mode, other motion modes can also be used in order to gain more power in the system. The process of modeling and analyzing of the system in the first step was only by using heave's motion mode. But in the next step, the effect of pitch and surge's motions were added. Finally, the power absorbed by the system in these two steps was compared with each other. Increasing the power absorbed by the system is one of the results of this study

The Sport Tourism Capabilities of the Hormozgan Province

ABSTRACT: The sport tourism is most important and most developed sector of tourism industry. The first step for development of this white industry is analyzing the potentials and capabilities. The present study has prioritized the sport tourism potentials of the Hormozgan Province. To achieve this purpose, a population of 150 people including tourism agencies experts (n = 50), sports experts (n=50) and sport tourists (n=50) were studied based on a five-choice Likert scale (very small= 1 to very much= 5). Accordingly, six dimensions of potentials with 22 subscales were examined using a researcher-made questionnaire. The validity and reliability of the questionnaire were confirmed by experts and Cronbach's alpha (α=0.81), respectively. According to the results of factor analysis, 79% of the subjects believed that beach and aqua sports (boating, swimming, diving and scuba diving, beach volleyball and futsal and surfing) have the capability of sport tourism development in the Hormozgan Province. Also, 77% of respondents believed that that desert trekking sport (motorcycle, car and truck rallies and camel riding) have the capability of sport tourism development considering the semi-arid climate of the Hormozgan Province. The results showed that the traditional sport of camel riding as major sport attractions has a high potential for the development of the sport tourism in Hormozgan Province

Efficiency enhancement of multiphase electric drives at light-load operation considering both converter and stator copper losses

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 ac-dc converter modules. For instance, they are becoming a serious option in the context of 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 paper 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