Indirect Rotor Field Oriented Control of Induction Motor With Rotor Time Constant Estimation

This thesis presents an estimation technique of the inverse rotor time constant for Indirect Rotor Field Oriented Control (IRFOC) induction motor application. In this estimation technique two different equations are used to estimate the rotor flux in the stator reference frame. One of the equations is a function of the rotor time constant, rotor angular velocity and the stator currents, and the other equation is a function of measured stator currents and voltages. The equation that uses the voltage and the current signals of the stator serves as reference model, while the other equation works as an adjustable model with respect to the variation of the rotor time constant. Measurements of two phases of the current, and speed using an optical encoder are required in this estimation technique. The stator phase voltages are estimated from the DC bus voltage and the switching commands signals with compensation of the dead time effect. Field oriented control of induction motor is gaining wides acceptance in high performance AC motor drive applications. Field oriented control, in its both forms as a direct or indirect, gives the AC motor dynamics that are equivalent to that of a DC motor. However, direct and indirect field oriented control suffer from specific theoretical and practical problems. The approach of direct field oriented control with Hall sensors for flux sensing has limitations governed by the physical structure of the machine itself. On the other hand, the approach of indirect field oriented control of induction machines is highly dependent on the rotor parameters, which are not easily accessible for measurements except for the rotor speed. In a DC motor, spatial relationship of the torque and flux is maintained by the physical construction of the motor armature and field circuits. However, in an induction motor such spatial relationship does not maintain as such machine has usually a single terminal where electric power is supplied. Therefore, such relationship is maintained by external control methods. In a basic IRFOC of an induction motor, speed and phase currents are sensed in order to control the stator current vector such a way so it can be resolved into two components, one is to control the rotor flux and the other to control the motor torque. Successful decomposition of stator current vector into these two components requires the knowledge of the instantaneous position, of the rotor flux vector. Since the position of the rotor flux vector is estimated in an IRFOC scheme, and is dependent on the motor model (more specifically the rotor parameters), these parameters must be obtained accurately and match the motor parameters at all times. Unfortunately, rotor parameters vary and are not easily accessible for measurements. Therefore, this uncertainty about the rotor flux vector position degrades the dynamic operation of the drive.Enormous efforts have been made to improve IRFOC complicated hardware and software in order to coixpensate for such imperfection. Hence, this work focuses on the Indirect Rotor Field Oriented Control of induction motors with estimation of the rotor time constant. A simple yet effective rotor time constant identification method is presented and used for updating the slip calculator used by the IRFOC algorithms. A complete simulation model of an induction motor and IRFOC scheme is presented and tested using SIMULINWMATLAB, and experimentally implemented on a DSP Board (MCK243j without any need for voltage phase sensors. Simulation and experimental results were presented and compared to verify the validity of the proposed estimator for different operating conditions

Recent changes in family structure and fertility in Jordan

This study seeks to make a contribution to the field of population studies by throwing some light on the explanation of fertility change in developing countries. It hopes to do this by investigating the role of the family and its structure in explaining fertility attitudes and behaviour in Jordan. Some of the causes - at the level of intermediate variables - of regional variations in fertility levels and fertility preferences in Jordan are examined. The study tries to analyse several aspects of change in the family system in Jordan: social, economic kin-relationships and wealth flow directions within the family. Also, fertility attitudes are examined in relation to contrasting social contexts. It is assumed that fertility decline will be the result of certain changes in the family's internal and external social and economic structure. In order to test this assumption it is necessary to examine the nature of internal and external family relationships in terms of the following five dimensions: a) the scale and character of mutual economic obligations (or feelings of financial responsibility) which exist within the families under study b) the nature of the family budget (to what extent it is a common budget or one divided into separate units related to individual wage earners) c) relations between the father and his children in terms of obedience and societal and family norms (even when the family is geographically separated as a result of migration) d) the coherence and structure of the family system (is it a closed or open nuclear family or does it still have elements of the extended family?), and women's roles and status within the family e) wealth flow direction and its relation to power structure within the family. Results suggest that changes in the family's internal and external social and economic structure have a significant influence on fertility attitudes which, in turn, tell that fertility decline is an outcome of family change

Students’ Perceptions of Their Teachers’ Performance in Teaching Engineering Drawing in Nigerian Tertiary Institutions

There have been concerns about the performance of Nigerian school teachers’ in delivering occupational related courses. However, there are currently limited empirical data on this phenomenon – in particular with respect to the teaching of engineering drawing – to justify further actions from educational managers and policy makers. The aim of this study was to assess teachers’ performance in teaching engineering drawing using students’ perception as indicator of teachers’ performance. The study utilized a cross-sectional research design method with the target population of technical education students drawn from four (4) Federal Colleges of education (Technical) in Northern Nigeria. Stratified proportionate sampling technique was used to arrive at the study sample of 253 technical education students. A specifically designed instrument, the Students’ Perceptions of Teachers’ Performance Scales (SPTPS) was used to gather data on the three performance dimensions namely contextual, task and adaptability performance. The exploratory factor analysis and confirmatory factor analysis methods were conducted to validate the performance constructs. The instrument has a high reliability of 0.90 based on the Cronbach Alpha method. The result of the analysis using estimation method indicates that students perceive their teachers’ performance to be at a slightly above average level (M= 3.51 ± 0.05 at the 95% confidence level). The teachers’ task performance, in particular, is found to be the least developed among the three dimension of performance while their adaptability performance is the highest while still being less than excellent. The data support the conclusion that there are aspects of teachers’ performance in teaching engineering drawing that is less than excellent and in need of further enhancements

The United Republic of Tanzania and Conventions on Carriage of Passengers, Cargo and Baggage by Air Aviation: A Historical Study

Transportation of both passengers and goods, in URT, has become a very important and paramount issue since the inception and commencement of the air aviation law in URT and the world in general. Several attempts have been made by partners’ states, that in the beginning, started and initiated a milestone journey to the point where the aviation law regime has reached today. The enactment of international laws governing the aviation industry had gone through several stages. With several challenges encountered and evidenced for several years, transportation of passengers and goods has become a must and paramount. URT as a party to several international air rules and Conventions, aircraft from within and outside URT, have utilized both domestic as well international conventions in ensuring that passengers and goods are transported within and all over the world and their safety and life are well safeguarded through air laws applicable within URT. This research article is aimed at examining various international conventions applicable to URT. The article generally attempts at showing the historical evidence on the carriage of passengers through various conventions to which URT is a party, and how transportation of passengers and goods has become possible. The research article also covers the issues of liabilities for air carriers operating in URT with a special focus on the Conventions that are applicable in URT and the extent of compensation that those Conventions guarantee as a result of personal or bodily injuries or loss of passengers’ goods that seem to be harmonized with current domestic aviation laws in URT.

Design and Construction of a DC-to-DC Converter for Electric Vehicle Application

A DC-to-DC converter has been designed to control the speed of a DC motor for electric vehicle application. The power circuit of the converter consists of transistorised power switches (IGBTs) to step-down the voltage to the level required by the speed and load demand. The series shunt resistor method is used to control the current and keep it below the maximum rate of the power transistors and the motor especially at the starting point. The transistor gate drive circuit was designed to provide the maximum isolation between the power and the control circuits. A controller chip originally used to control a three phase brushless DC motor is programmed and modified to control a brushed DC motor. This controller chip provides the pulse width modulation (PWM) control signal in order to drive the power switches at fixed frequency and variable duty cycle. More over using this chip a control over the current flow through the power circuit could be achieved, this will protect the circuit from any faulty conditions taking the benefit of Cycle-by-Cycle current detection

THE RELATIONSHIP BETWEEN SOCIAL RESPONSIBILITY AND ORGANIZATIONAL CITIZENSHIP BEHAVIOR IN 5 STARS HOTELS OPERATING IN PETRA CITY

This study explored the degree to which 5 stars hotels operating in Petra city are considered socially responsible, and the linkage between social responsibility activities of these organizations and the citizenship behavior of employees.A sample of 80 out of 200 employees working at 2 five stars hotels, were surveyed.Four dimensions of social responsibility (the economic, ethical, philanthropic, and the legal) with 5 dimensions of citizenship behavior (Altruism, Curtsey, Sportsmanship, Civic Virtue and conscientiousness) were correlated, the results bring to light the positive association between the examined variables, the strongest relationship was with the legal dimension followed by philanthropic, then with the ethical, and the weakest relationship was with the economic dimension

An Examination on Evolution of Accountability and Transparency Procurement Principles in Mainland Tanzania

Like in other African countries, the government of the United Republic of Tanzania has engaged and conducted a good number of procurement reforms. This has been carried out by the government since it attained its independence in 1961. It was an expectation of the public that all reforms that have taken place mainly aimed at ensuring that procurement system become robust and promising. This is because, in its day-to-day business, the government relies entirely on public purchasing in getting various commodities from bidders, both local and internationally. It is unfortunate, however, in all procurement reforms that have carried out by the government, with exception of 2016 procurement reforms, accountability and transparency procurement principles evolution was not given a deserving priority it deserved. Obviously, the 1977 Constitution of the United Republic of Tanzania, and all other previous Constitutions contained a provision relating to financial matters, yet it is unluckily that as of today, the same 1977 Constitution of the United Republic of Tanzania has not a single provision emphasizing or rather indicating on accountability and transparency procurement principles. This evidences clearly that procurement reforms seem to be not fruitful since accountability and transparency procurement principles evolution has slowly emerged and in previous procurement reforms, this was in fact, given little and less attention on various occasions when public procurement laws were reformed. In all procurement reforms, until 2016 procurement reforms that the government did, accountability and transparency procurement principles did not feature in any statute in Mainland Tanzania.