Multiport power electronics circuitry for integration of renewable energy sources in low power applications : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering at Massey University, Palmerston North, New Zealand

The increasing demand for electricity and the global concern about environment has led energy planners and developers to explore and develop clean energy sources. Under such circumstances, renewable energy sources (RES) have emerged as an alternative source of energy generation. Immense development has been made in renewable energy fields and methods to harvest it. To replace conventional generation system, these renewable energy sources must be sustainable, reliable, stable, and efficient. But these sources have their own distinguished characteristics. Due to sporadic nature of renewable energy sources, the uninterrupted power availability cannot be guaranteed. Handling and integration of such diversified power sources is not a trivial process. It requires high degree of efficiency in power extraction, transformation, and utilization. These objectives can only be achieved with the use of highly efficient, reliable, secure and cost-effective power electronics interface. Power electronics devices have made tremendous developments in the recent past. Numerous single and multi-port converter topologies have been developed for processing and delivering the renewable energy. Various multiport converter topologies have been presented to integrate RES, however some limitations have been identified in these topologies in terms of efficiency, reliability, component count and size. Therefore, further research is required to develop a multiport interface and to address the highlighted issues. In this work, a multi-port power electronics circuitry for integration of multiple renewable energy sources is developed. The proposed circuitry assimilates different renewable sources to power up the load with different voltage levels while maintaining high power transfer efficiency and reliability with a simple and reliable control scheme. This research work presents a new multiport non-isolated DC-DC buck converter. The new topology accommodates two different energy sources at the input to power up a variable load. The power sources can be employed independently and concurrently. The converter also has a bidirectional port which houses a storage device like battery to store the surplus energy under light load conditions and can serve as an input source in case of absence of energy sources. The new presented circuitry is analytically examined to validate its effectiveness for multiport interface. System parameters are defined and the design of different components used, is presented. After successful mathematical interpretation, a simulation platform is developed in MATLAB/Simscape to conduct simulations studies to verify analytical results and to carry out stability analysis. In the final stage, a low power, low voltage prototype model is developed to authenticate the results obtained in simulation studies. The converter is tested under different operating modes and variable source and load conditions. The simulation and experimental results are compiled in terms of converter’s efficiency, reliability, stability. The results are presented to prove the presented topology as a highly reliable, stable and efficient multiport interface, with small size and minimum number of components, for integration of renewable energy sources

Investigation of FACTS devices to improve power quality in distribution networks

Flexible AC transmission system (FACTS) technologies are power electronic solutions that improve power transmission through enhanced power transfer volume and stability, and resolve quality and reliability issues in distribution networks carrying sensitive equipment and non-linear loads. The use of FACTS in distribution systems is still in its infancy. Voltages and power ratings in distribution networks are at a level where realistic FACTS devices can be deployed. Efficient power converters and therefore loss minimisation are crucial prerequisites for deployment of FACTS devices. This thesis investigates high power semiconductor device losses in detail. Analytical closed form equations are developed for conduction loss in power devices as a function of device ratings and operating conditions. These formulae have been shown to predict losses very accurately, in line with manufacturer data. The developed formulae enable circuit designers to quickly estimate circuit losses and determine the sensitivity of those losses to device voltage and current ratings, and thus select the optimal semiconductor device for a specific application. It is shown that in the case of majority carrier devices (such as power MOSFETs), the conduction power loss (at rated current) increases linearly in relation to the varying rated current (at constant blocking voltage), but is a square root of the variable blocking voltage when rated current is fixed. For minority carrier devices (such as a pin diode or IGBT), a similar relationship is observed for varying current, however where the blocking voltage is altered, power losses are derived as a square root with an offset (from the origin). Finally, this thesis conducts a power loss-oriented evaluation of cascade type multilevel converters suited to reactive power compensation in 11kV and 33kV systems. The cascade cell converter is constructed from a series arrangement of cell modules. Two prospective structures of cascade type converters were compared as a case study: the traditional type which uses equal-sized cells in its chain, and a second with a ternary relationship between its dc-link voltages. Modelling (at 81 and 27 levels) was carried out under steady state conditions, with simplified models based on the switching function and using standard circuit simulators. A detailed survey of non punch through (NPT) and punch through (PT) IGBTs was completed for the purpose of designing the two cascaded converters. Results show that conduction losses are dominant in both types of converters in NPT and PT IGBTs for 11kV and 33kV systems. The equal-sized converter is only likely to be useful in one case (27-levels in the 33kV system). The ternary-sequence converter produces lower losses in all other cases, and this is especially noticeable for the 81-level converter operating in an 11kV network

The Negotiation of Religious Identity of Muslim Women in Leh District, Ladakh

This paper examines the negotiation of religious identity among Sunni Muslim women in Leh, Ladakh. Although Muslims in Leh share the same socio-cultural environment with Buddhists, the differences between the two communities have become more pronounced in recent decades. The assertion of religious identity and increasing religiosity in the form of vegetarianism among Buddhists and strict veiling among Muslim women are fairly visible. Changes are also seen in religious practices, including the imposition of a strict prohibition on dance, music, and alcohol consumption among Muslims. Here, I explore the manner in which religious identity is perceived and propagated among Muslim women in urban Leh. I discuss processes of identity formation and examine the emergence of religion as the most salient source of personal and social identity among Muslim women. The research addresses the question of how women use their agency for religious activities, institutional learning, choice of dress and mobility. Based on ethnographic fieldwork, I depict socio-religious changes among them with reference to dress, mobility and lay sermons. The study discusses the motivations behind these changes and the reasons for Muslim women’s focus on the collective identity that distinguishes them from the wider Ladakhi society

The psychometric impacts of Karasek's demands and control scale on employees' job dissatisfaction

The aim of this study was to provide the reliability and validity of job factors and to analyze its association with Demands-Control Model and job dissatisfaction in two time cross-sectional study of Distribution Companies of Water and Power Development Authority (WAPDA) in Pakistan. Two times self-reported cross-sectional surveys were conducted, the study samples consisting of 420 respondents at T1 and 388 respondents at T2. Appropriate internal consistencies of the four scales: demands, control, job satisfaction and social supports, were obtained. Zero-order correlation and linear and multiple regressions analysis replicated the theoretically assumed structure of the job factors and job satisfaction construct in men and women collectively. Evidence of criterion validity was obtained from cross-correlations of the scales and from their linear and multiple regression analysis. Finally, all four measures were associated with a highly significant ratio of job dissatisfaction (JD), and the effect was strongest for the JD ratio as predicted by fundamental theory of Karasek. The level of work related to their demands and the level of autonomy and control they enjoy in their work place directly results in satisfaction and wellbeing of employees. Based on the results of this study the four quadrant version of the DCM questionnaire is considered a reliable and valid instrument for measuring psychosocial pressure at work environment. These outcomes and measures are applicable to all services and manufacturing industries

A note on a characterization theorem for a certain class of domains

We have introduced and studied in [3] the class of Globalized multiplicatively pinched-Dedekind domains (GMPD domains). This class of domains could be characterized by a certain factorization property of the non-invertible ideals, (see [3, Theorem 4]). In this note a simplification of the characterization theorem [3, Theorem 4] is provided in more general form

Impact of Model Specification Decisions on Unit Root Tests

Performance of unit tests depends on several specification decisions prior to their application e.g., whether or not to include a deterministic trend. Since there is no standard procedure for making such decisions, therefore the practitioners routinely make several arbitrary specification decisions. In Monte Carlo studies, the design of DGP supports these decisions, but for real data, such specification decisions are often unjustifiable and sometimes incompatible with data. We argue that the problems posed by choice of initial specification are quite complex and the existing voluminous literature on this issue treats only certain superficial aspects of this choice. We also show how these initial specifications affect the performance of unit root tests and argue that Monte Carlo studies should include these preliminary decisions to arrive at a better yardstick for evaluating such tests.model specification, trend stationary, difference stationary

Design & development of a novel house hold compressing device for a wheelie bin

This project consists of researching, designing, developing, prototyping and testing a device that clamps onto a wheelie bin and easily compresses the waste inside. Once attached, by pulling on the lever, the device will compress the contents inside allowing for disposal of more waste. The design is easily assembled, light and sturdy enough so that any household individual can use it. Prototype testing was performed to identify the required forces necessary to compress a sufficient amount of waste and identifying which materials or types of waste can be compressed. The prototype testing showed that the device is capable of compressing the normal household wastes (compressing plastic bottles, cardboards, tin cartons) up to 45% off the original volume. The paper discusses the design, development and testing of this device to appreciate the proof of the concept as well as discussing it in terms of saving the cost of recycling as well

Most Stringent Test for Location Parameter of a Random Number from Cauchy Density

We study the test for location parameter of a random number from Cauchy density, focusing on point optimal tests. We develop analytical technique to compute critical values and power curve of a point optimal test. We study the power properties of various point optimal tests. The problem turned out to be different in its nature, in that, the critical value of a test determines the power properties of test. We found that if for given size  and any point m in alternative space, if the critical value of a point optimal test is 1, the test optimal for that point is the most stringent test.Cauchy density, Power Envelop, Location Parameter, Stringent Test