Parallel-Operating Three-Phase Voltage Source Inverters – Circulating CurrentModeling, Analysis and Mitigation

The maximum realizable power throughput of power electronic converters may be limited or constrained by technical or economical considerations. One solution to this problemis to connect several power converter units in parallel. The parallel connection can be used to increase the current carrying capacity of the overall system beyond the ratings of individual power converter units. Thus, it is possible to use several lower-power converter units, produced in large quantities, as building blocks to construct high-power converters in a modular manner. High-power converters realized by using parallel connection are needed for example in multimegawatt wind power generation systems. Parallel connection of power converter units is also required in emerging applications such as photovoltaic and fuel cell power conversion. The parallel operation of power converter units is not, however, problem free. This is because parallel-operating units are subject to overcurrent stresses, which are caused by unequal load current sharing or currents that flow between the units. Commonly, the term ’circulatingcurrent’ is used to describe both the unequal load current sharing and the currents flowing between the units. Circulating currents, again, are caused by component tolerances and asynchronous operation of the parallel units. Parallel-operating units are also subject to stresses caused by unequal thermal stress distribution. Both of these problemscan, nevertheless, be handled with a proper circulating current control. To design an effective circulating current control system, we need information about circulating current dynamics. The dynamics of the circulating currents can be investigated by developing appropriate mathematical models. In this dissertation, circulating current models aredeveloped for two different types of parallel two-level three-phase inverter configurations. Themodels, which are developed for an arbitrary number of parallel units, provide a framework for analyzing circulating current generation mechanisms and developing circulating current control systems. In addition to developing circulating current models, modulation of parallel inverters is considered. It is illustrated that depending on the parallel inverter configuration and the modulation method applied, common-mode circulating currents may be excited as a consequence of the differential-mode circulating current control. To prevent the common-mode circulating currents that are caused by the modulation, a dual modulator method is introduced. The dual modulator basically consists of two independently operating modulators, the outputs of which eventually constitute the switching commands of the inverter. The two independently operating modulators are referred to as primary and secondary modulators. In its intended usage, the same voltage vector is fed to the primary modulators of each parallel unit, and the inputs of the secondary modulators are obtained from the circulating current controllers. To ensure that voltage commands obtained from the circulating current controllers are realizable, it must be guaranteed that the inverter is not driven into saturation by the primary modulator. The inverter saturation can be prevented by limiting the inputs of the primary and secondary modulators. Because of this, also a limitation algorithm is proposed. The operation of both the proposed dual modulator and the limitation algorithm is verified experimentally.

Spare part business analysis and development

The purpose of this Thesis was to comprehensively analyze and develop the spare part business in Company Oy’s five biggest product groups by searching development issues related to single spare parts’ supply chains as well as the spare part business process, make implementation plans for them and implement the plans when possible. The items were classified based on special characteristics of spare parts and on their actual sales volumes. The created item classes were examined for finding improvement possibilities. Management strategies for classified items were suggested. Vendors and customers were analyzed for supporting the comprehensive supply network development work. The effectiveness of the current spare part business process was analyzed in co-operation with the spare part teams in three business unit locations. Several items were taken away from inventories as uselessly stocked items. Price list related to core items with one of the main product group’s core item manufacturer was suggested to be expanded in Town A. Refinement equipment seal item supply chain management was seen important to develop in Town B. A new internal business process model was created for minimizing and enhancing the internal business between Company’s business units. SAP inventory reports and several other features were suggested to be changed or developed. Also the SAP data material management was seen very important to be developed continuously. Many other development issues related to spare parts’ supply chains and the work done in the business process were found. The need for investigating the development possibilities deeper became very clear during the project.

The analysis and mitigation of risks in FMCG supply chain: the case of British American Tobacco Eastern Europe

This work investigates the Bullwhip Effect, which is one of the most important phenomena in contemporary supply chain management. The author uses most recent theoretical apparatus to analyze operational activities of a leading FMCG company British American Tobacco Eastern Europe. This paper investigates and describes the process in BAT supply chain management and considers the impact of the Bullwhip Effect together with the potential risks threatening company's operations. Emergence of the Bullwhip Effect leads to supply chain inefficiency. This paper contains methodological supply chain risk mitigation recommendations, description of a real case study and an analytical study of internal and external supply chain processes

Analysis and forecast of the storage needs of soybeans in Brazil

The existence of a minimum storage capacity of grains as a condition for the maintenance of regulator physical stocks has been used as a strategic factor in the agribusiness expansion. However, in Brazil the storage infrastructure has not followed the growth of the agricultural sector. This fact is evident in the case of soybeans that currently represent 49% of grain production in the country, whose volume production has been increasing significantly over the years. This study aimed to predict the futureneeds of static storage capacity of soybeans from historical data to estimate the investment needed to install storage units in Brazil for the next five years. A statistic analysis of collected data allowed a forecast and identification of the number of storage units that should be installed to meet the storage needs of soybeans in the next five years. It was concluded that by 2015 the soybean storage capacity should be 87 million tons, and to store 49% of soybeans produced, 1,104 storage units should be installed at a cost of R$ 442 million.

Application of morphometry, static DNA ploidy analysis, and steroid receptor expression in diagnosis and prognosis of Libyan breast cancer

The aim of this study was to describe the demographic, clinicopathological, biological and morphometric features of Libyan breast cancer patients. The supporting value of nuclear morphometry and static image cytometry in the sensitivity for detecting breast cancer in conventional fine-needle aspiration biopsies were estimated. The findings were compared with findings in breast cancer in Finland and Nigeria. In addation, the value of ER and PR were evaluated. There were 131 histological samples, 41 cytological samples, and demographic and clinicopathological data from 234 Libyan patients. The Libyan breast cancer is dominantly premenopausal and in this feature it is similar to breast cancer in sub-Saharan Africans, but clearly different from breast cancer in Europeans, whose cancers are dominantly postmenopausal in character. At presention most Libyan patients have locally advanced disease, which is associated with poor survival rates. Nuclear morphometry and image DNA cytometry agree with earlier published data in the Finnish population and indicate that nuclear size and DNA analysis of nuclear content can be used to increase the cytological sensitivity and specificity in doubtful breast lesions, particularly when free cell sampling method is used. Combination of the morphometric data with earlier free cell data gave the following diagnostic guidelines: Range of overlap in free cell samples: 55 μm2 -71 μm2. Cut-off values for diagnostic purposes: Mean nuclear area (MNA) >54 μm2 for 100% detection of malignant cases (specificity 84 %), MNA < 72 μm2 for 100% detection of benign cases (sensitivity 91%). Histomorphometry showed a significant correlation between the MNA and most clinicopathological features, with the strongest association observed for histological grade (p <0.0001). MNA seems to be a prognosticator in Libyan breast cancer (Pearson’s test r = - 0.29, p = 0.019), but at lower level of significance than in the European material. A corresponding relationship was not found in shape-related morphometric features. ER and PR staining scores were in correlation with the clinical stage (p= 0.017, and 0.015, respectively), and also associated with lymph node negative patients (p=0.03, p=0.05, respectively). Receptor-positive (HR+) patients had a better survival. The fraction of HR+ cases among Libyan breast cancers is about the same as the fraction of positive cases in European breast cancer. The study suggests that also weak staining (corresponding to as few as 1% positive cells) has prognostic value. The prognostic significance may be associated with the practice to use antihormonal therapy in HR+ cases. The low survival and advanced presentation is associated with active cell proliferation, atypical nuclear morphology and aneuploid nuclear DNA content in Libyan breast cancer patients. The findings support the idea that breast cancer is not one type of disease, but should probably be classified into premenopausal and post menopausal types.

Analysis and validation of space averaged drag model for numerical simulations of gas-solid flows in fluidized beds

This thesis presents an approach for formulating and validating a space averaged drag model for coarse mesh simulations of gas-solid flows in fluidized beds using the two-fluid model. Proper modeling for fluid dynamics is central in understanding any industrial multiphase flow. The gas-solid flows in fluidized beds are heterogeneous and usually simulated with the Eulerian description of phases. Such a description requires the usage of fine meshes and small time steps for the proper prediction of its hydrodynamics. Such constraint on the mesh and time step size results in a large number of control volumes and long computational times which are unaffordable for simulations of large scale fluidized beds. If proper closure models are not included, coarse mesh simulations for fluidized beds do not give reasonable results. The coarse mesh simulation fails to resolve the mesoscale structures and results in uniform solids concentration profiles. For a circulating fluidized bed riser, such predicted profiles result in a higher drag force between the gas and solid phase and also overestimated solids mass flux at the outlet. Thus, there is a need to formulate the closure correlations which can accurately predict the hydrodynamics using coarse meshes. This thesis uses the space averaging modeling approach in the formulation of closure models for coarse mesh simulations of the gas-solid flow in fluidized beds using Geldart group B particles. In the analysis of formulating the closure correlation for space averaged drag model, the main parameters for the modeling were found to be the averaging size, solid volume fraction, and distance from the wall. The closure model for the gas-solid drag force was formulated and validated for coarse mesh simulations of the riser, which showed the verification of this modeling approach. Coarse mesh simulations using the corrected drag model resulted in lowered values of solids mass flux. Such an approach is a promising tool in the formulation of appropriate closure models which can be used in coarse mesh simulations of large scale fluidized beds.

IgA production, coliforms analysis and intestinal mucosa morphology of piglets that received probiotics with viable or inactivated cells

Two types of probiotics were used in piglets. One product is a mixed culture of viable Lactobacillus acidophilus, Enterococcus faecium e Bifidobacterium bifidum. The second product is composed of inactivated Lactobacillus acidophilus cells. The piglets received two weekly oral doses for 30 days while a control group did not receive probiotics. All piglets were euthanized at the 30th day of life and the mesenteric lymph nodes, the small intestine, and blood samples were collected. The tissue samples were studied by light microscopy and the blood serum was analyzed by ELISA method. The treatment with the probiotic with viable cells produced higher serum levels of IgA (P<0.05) and more IgA expressing cells were found in the mesenteric lymph nodes than observed in the inactivated cells treatment or control groups (P<0.05). Also, intestinal villi were longer, crypts were deeper (P<0.05) and fecal coliform count was lower than found in the inactivated product (P<0.05). These results suggest that viable probiotics are more efficient than inactivated probiotics to induce immunostimulation and intestinal modifications in piglets, thus improving their health and development.

Evaluation of follicular lymphoid depletion in the Bursa of Fabricius: an alternative methodology using digital image analysis and artificial neural networks

Fifty Bursa of Fabricius (BF) were examined by conventional optical microscopy and digital images were acquired and processed using Matlab® 6.5 software. The Artificial Neuronal Network (ANN) was generated using Neuroshell® Classifier software and the optical and digital data were compared. The ANN was able to make a comparable classification of digital and optical scores. The use of ANN was able to classify correctly the majority of the follicles, reaching sensibility and specificity of 89% and 96%, respectively. When the follicles were scored and grouped in a binary fashion the sensibility increased to 90% and obtained the maximum value for the specificity of 92%. These results demonstrate that the use of digital image analysis and ANN is a useful tool for the pathological classification of the BF lymphoid depletion. In addition it provides objective results that allow measuring the dimension of the error in the diagnosis and classification therefore making comparison between databases feasible.

Identification of new flagellin-encoding fliC genes in Escherichia coli isolated from domestic animals using RFLP-PCR and sequencing methods

Identification of Escherichia coli requires knowledge regarding the prevalent serotypes and virulence factors profiles allows the classification in pathogenic/non-pathogenic. However, some of these bacteria do not express flagellar antigen invitro. In this case the PCR-restriction fragment length polymorphism (RFLP-PCR) and sequencing of the fliC may be suitable for the identification of antigens by replacing the traditional serology. We studied 17 samples of E. coli isolated from animals and presenting antigen H nontypeable (HNT). The H antigens were characterized by PCR-RFLP and sequencing of fliC gene. Three new flagellin genes were identified, for which specific antisera were obtained. The PCR-RFLP was shown to be faster than the serotyping H antigen in E. coli, provided information on some characteristics of these antigens and indicated the presence of new genes fliC.

Purchasing portfolio analysis and supplier classification

The purpose of the thesis is to classify suppliers and to enhance strategic purchasing in the case company. Supplier classification is conducted to fulfill the requirements of the company quality manual and international quality standards. To gain more benefit, a strategic purchasing tool, Kraljic’s purchasing portfolio and analytical hierarchy process are utilized for the base of supplier classification. Purchasing portfolio is used to give quick and easy visual insight on product group management form the viewpoint of purchasing. From the base on purchasing portfolio alternative purchasing and supplier strategies can be formed that enhance the strategic orientation of purchasing. Thus purchasing portfolio forces the company to orient on proactive and strategic purchasing. As a result a survey method for implementing purchasing portfolio in the company is developed that exploits analytical hierarchy process. Experts from the company appoint the categorization criteria and in addition, participate in the survey to categorize product groups on the portfolio. Alternative purchasing strategies are formed. Suppliers are classified depending on the importance and characteristics of the product groups supplied.

Object-oriented Programming Applied to the Development of Structural Analysis and Optimization Software

This paper presents the development of a two-dimensional interactive software environment for structural analysis and optimization based on object-oriented programming using the C++ language. The main feature of the software is the effective integration of several computational tools into graphical user interfaces implemented in the Windows-98 and Windows-NT operating systems. The interfaces simplify data specification in the simulation and optimization of two-dimensional linear elastic problems. NURBS have been used in the software modules to represent geometric and graphical data. Extensions to the analysis of three-dimensional problems have been implemented and are also discussed in this paper.

A Well Stated Time Domain Integral Representation for Elastodynamic Analysis and Applications

This article discusses three possible ways to derive time domain boundary integral representations for elastodynamics. This discussion points out possible difficulties found when using those formulations to deal with practical applications. The discussion points out recommendations to select the convenient integral representation to deal with elastodynamic problems and opens the possibility of deriving simplified schemes. The proper way to take into account initial conditions applied to the body is an interesting topict shown. It illustrates the main differences between the discussed boundary integral representation expressions, their singularities and possible numerical problems. The correct way to use collocation points outside the analyzed domain is carefully described. Some applications are shown at the end of the paper, in order to demonstrate the capabilities of the technique when properly used.