First-principles study on electronic and structural properties of Cu(In/Ga)Se alloys for solar cells

Thin-film photovoltaic solar cells based on the Cu(In1−xGax)Se2 (CIGS) alloys have attracted more and more attention due to their large optical absorption coefficient, long term stability, low cost, and high efficiency. Modern theoretical studies of this material with first-principles calculations can provide accurate description of the electronic structure and yield results in close agreement with experimental values, but takes a large amount of calculation time. In this work, we use first-principles calculations based on the computationally affordable meta- generalized gradient approximation of the density-functional theory to investigate electronic and structural properties of the CIGS alloys. We report on the simulation of the lattice parameters and band gaps, as a function of chemical composition. The obtained results were found to be in a good agreement with the available experimental data.

Power Electronic Converters in Low-Voltage Direct Current Distribution – Analysis and Implementation

Over the recent years, smart grids have received great public attention. Many proposed functionalities rely on power electronics, which play a key role in the smart grid, together with the communication network. However, “smartness” is not the driver that alone motivates the research towards distribution networks based on power electronics; the network vulnerability to natural hazards has resulted in tightening requirements for the supply security, set both by electricity end-users and authorities. Because of the favorable price development and advancements in the field, direct current (DC) distribution has become an attractive alternative for distribution networks. In this doctoral dissertation, power electronic converters for a low-voltage DC (LVDC) distribution system are investigated. These include the rectifier located at the beginning of the LVDC network and the customer-end inverter (CEI) on the customer premises. Rectifier topologies are introduced, and according to the LVDC system requirements, topologies are chosen for the analysis. Similarly, suitable CEI topologies are addressed and selected for study. Application of power electronics into electricity distribution poses some new challenges. Because the electricity end-user is supplied with the CEI, it is responsible for the end-user voltage quality, but it also has to be able to supply adequate current in all operating conditions, including a short-circuit, to ensure the electrical safety. Supplying short-circuit current with power electronics requires additional measures, and therefore, the short-circuit behavior is described and methods to overcome the high-current supply to the fault are proposed. Power electronic converters also produce common-mode (CM) and radio-frequency (RF) electromagnetic interferences (EMI), which are not present in AC distribution. Hence, their magnitudes are investigated. To enable comprehensive research on the LVDC distribution field, a research site was built into a public low-voltage distribution network. The implementation was a joint task by the LVDC research team of Lappeenranta University of Technology and a power company Suur-Savon S¨ahk¨o Oy. Now, the measurements could be conducted in an actual environment. This is important especially for the EMI studies. The main results of the work concern the short-circuit operation of the CEI and the EMI issues. The applicability of the power electronic converters to electricity distribution is demonstrated, and suggestions for future research are proposed.

Benefits and challenges of Enterprise Resource Planning for Pakistani SMEs

Enterprise resource planning (ERP) software is used to combine all the functions happening inside the organization with the help of one software. All the data is centralized which makes it easy to manage information for all participants. The literature on ERP is studied thoroughly the whole process of adoption till the implementation and final evaluations. But studies that focus on small and medium sized enterprises are limited in number when compared to the large scale enterprises. In case of Pakistan, research is very limited. In this thesis, the author tries to analyze the current status of SMEs usage of ERP system. The benefits obtained and challenges faced by SMEs of Pakistan are studied. Framework presented by Shang and Seddon (2000) is used to understand the benefits obtained by the SMEs in Pakistan. This is a comprehensive framework that classifies the benefits obtained by the ERP adoption, into five categories: operational benefits, managerial benefits, Strategic benefits, IT benefits, and Organizational benefits. The results show that SMEs of Pakistan are also getting many benefits after adoption of ERP. Most of the firms had implemented SAP software. Operational benefits were mentioned by all the firms. The most important benefits were report generation, quick access to critical information, better product and cost planning. Respondents also mentioned that they had reduced corruption as a result of ERP implementation. It is also an important benefit considering high corruption rate in Pakistan. Along with benefits, challenges faced by Pakistani SMEs included infrastructure problems like electricity, difficulties with integration of one module with other module, costs of adoption and lack of skilled ERP consultants. Further studies in this regard can be conducted on cloud based ERP which is fast growing all around the world.