Reducing switching losses through MOSFET-IGBT combination

This paper introduces a configuration aimed at switching losses reduction trough a power leg constructed by combining a MOSFET and an IGBT. The combined use of these different switches leads to the turn-on losses reduction trough the use of the faster freewheeling diode of the IGBT, and the turn-off losses reduction trough use of the MOSFET’s lower losses because of the lack of tailing current, typical for IGBT’s. The introduced leg structure can be used to build single phase – full bridge invertors or three phase inverters. The proposed leg is realized, experimented and validated

Applications of combined MOSFET-IGBT power leg with reduced switching losses

This paper discusses power legs built upon the combination of a MOSFET and an IGBT. The suggested combined use of those different switches is intended to be applied in PWM controlled single and three phase inverters. The main advantage of the presented topology is the reduced switching losses in the overall inverter topology compared to the classical pure IGBT and MOSFET topologies. The paper presents and compares experimental results for the proposed power leg and the conventional pure IGBTs and pure MOSFETs legs. Realized applications of the proposed power leg are shown

Automated methodology for adjustment of component values in passive converter circuit for wind turbine generators

The current paper proposes an automated design approach for a previously developed passive converter circuits for wind turbine generators. This suggested approach allows to calculate the components for all passive converter circuits approved in European patent number PCT/EP2010/055637, where only minor changes in the source code of the mathematical and simulation software have to be made when different circuits are involved. An optimisation based on steepest descent method results in power/frequency (power/speed) curve that matches well the cubic dependence (Pwtmax~ω3) of the extracted power

Modelling, analysis and verification of a resonant llc converter as a power supply for the electromagnetic driving mechanism of an electromagnetic contactor

The paper presents model based analysis and experimental verification of a half-bridge resonant LLC converter for suppling power to the electromagnetic driving mechanism of an electromagnetic contactor. In the proposed application the convertor - powered either by AC or DC voltage - supplies the coil of the contactor with DC voltage. Analytical and experimental results presented, show several important advantages of the proposed topology: versatility in terms of input voltages – both AC and DC are accepted; stability over wide voltage range; omission of overvoltages – common to electromagnetic systems; reduced power consumption

Modelling, analysis and comparison of heatsink designs with improved natural convection

The paper presents FEM based study of various heatsink designs. The main aim of the study is to determine and evaluate solutions with improved heat dissipation by utilization of natural convection. Seventeen different cases both classical and proposed by the authors are studied, where each case is examined under three different heat source (in the case with the proposed study a transistor) powers. Results for temperature of the power source and velocity magnitudes in the studied volume are presented and comparted. Experimental verification of the modeling is presented for selected cases

Modelling, analysis and comparison of heat sink designs with improved natural convection

The paper presents FEM based study of various heatsink designs. The main aim of the study is to determine and evaluate solutions with improved heat dissipation by utilization of natural convection. Seventeen different cases both classical and proposed by the authors are studied, where each case is examined under three different heat source (in the case with the proposed study a transistor) powers. Results for temperature of the power source and velocity magnitudes in the studied volume are presented and comparted. Experimental verification of the modeling is presented for selected cases

Емпирично изследване на управлението на услугите на агроекосистемите в България

The study is a report from the second stage of the research project "Management of agro-ecosystem services", funded by the Agricultural Academy - https://maessbg.alle.bg The approach developed during the first stage for analysis, evaluation and improvement of the management system of the agro-ecosystem services in the country has been tested. A survey with agricultural producers identified the size and type of "produced" services of agro-ecosystems of different types, and the dominant forms, factors and efficiency of management of agro-ecosystem services. Primary micro-information was collected from managers of 162 "typical" farms of different legal type, size, production specialization, ecological and geographical location. The main agro-regions and basic agroecosystems (plain, mountainous, protected areas, non-favored areas, etc.) are covered, as well as 12 main specific agroecosystems and their agro-ecosystems - Western Stara Planina, Central Balkans, Danube Plain, Stara Planina, Northeast Fore-Balkans, Struma River Valley, Rhodopes, Pernik Basin, Radomir Field, Sredna Gora, Sub-Balkans, Thracian Lowland and Southeastern Bulgaria. By grouping and summarizing the collected primary information, the structure and volume of agro-ecosystem services in the country and in the main types of agro-ecosystems are identified - geographical, basic and specific ecosystems, subsectors of agricultural production, size and legal type of farming organization. Share of participating producers and degree of participation in storage and supply were used as proxy indicators for production volume of the respective types of holdings. The connection between the main characteristics of farm managers (gender, age, education, farming experience, etc.) and their knowledge and application of the concept of agro-ecosystem services has been established. The main domestic, market, contractual, collective, tripartite, etc. are identified. forms of management of agro-ecosystem services of different types in general and depending on the type of agro-ecosystem and the agricultural producer. An in-depth study of the predominant forms of management of basic agro-ecosystem services such as providing external access to the farm, biodiversity conservation, plant pollination, bioproduction, etc. has been established, and a link with specialization, location, etc. has been established. characteristics of holdings. The effectiveness of the various forms of management of agro-ecosystem services has been established by assessing the direct and additional costs associated with the supply and management of agro-ecosystem services, as well as the direct, additional and indirect effects of their supply. The main behavioral, economic, institutional, natural, etc. are identified. factors that stimulate or limit the "production" of agro-ecosystem services by farmers. The intentions of the agricultural producers related to the protection of ecosystems and ecosystem services in the near future have also been determined. An in-depth analysis of the development and efficiency of organic production as one of the main forms of supply of agro-ecosystem services by Bulgarian farms. A multifaceted analysis of soils has been made as part of Bulgaria's agri-environmental resource, on the example of rural areas in the South Central region. The possibilities for using the sludge from the wastewater treatment plants as a form of agro-eco-service in support of agriculture have been assessed. The use of the customer value category in the management of agro-ecosystem services is analyzed. Summarized conclusions and proposals for improving the approach to scientific analysis and guidelines for improving public policies and forms of public intervention, and individual, business and collective strategies and actions for effective management of agro-ecosystems and services of agro-ecosystems of different types have been prepared

Въпроси на конкурентоспособността на земеделските стопанства на България

A holistic approach for understanding, evaluating and improving the competitiveness of agricultural holdings in Bulgaria has been refined and applied. A multi-criteria assessment of the competitiveness of farms of different types is made by using survey information. A multi-criteria assessment of the level of competitiveness of agricultural holdings as a whole and with different types of product specialization was also made by using statistical data and applying the method of principal components. A comparative analysis of the level and dynamics of competitiveness of Bulgarian farms in general and with different specializations for the period 2010-2020 was also carried out. A comparative analysis of the results of the assessment of competitiveness based on survey and statistical data was made and the advantages and disadvantages of the various approaches. An assessment was made of the level and factors of competitiveness of agricultural holdings with organic production, the relationships with the main characteristics of the farmer (gender, age, etc.) were established, the most significant factors and political instruments affecting competitiveness were highlighted and the intentions were identified of organic farms in the near future. A model of CPR factor analysis and an index method for measuring competitiveness in the sheep meat sector were applied. The restructuring and diversification of agricultural cooperatives for the period after the country's integration into the EU was analyzed and a comparative assessment was made with other forms of business organizations in agriculture. The multi-criteria evaluation of alternative business models and strategies for managing the agricultural enterprise and risk was carried out, and the factors of the competitiveness of Bulgarian farms were identified. A theoretical analysis of the meso-economic level of management was made, the attitudes of alternative farmers in our country for the use of meso-institutions were established, and the relationship with agrarian competitiveness at the current stage of development of the industry was rethought. The development of agricultural holdings for the period 2007–2020 in the country was analyzed and the development of rural areas and the agrarian sector in the South Central region was compared with the general situation, by means of the Localization Index. The new trends in agricultural marketing (digitalization, intelligent marketing, etc.) are revealed, the impact on the relationship between agricultural producers and end users and the effect on the competitiveness of farms are assessed. An algorithm for the development and implementation of new models for innovative activity of small and medium-sized enterprises in agriculture is proposed, which allows effective management decisions at different levels, quantification of the index for innovative activity and easy adaptation when developing an automated system. General conclusions have been drawn up about the level, trends and factors of competitiveness of Bulgarian farms of different types and recommendations have been made for improving the scientific and evaluation methods, the system for gathering agro-information, public policies, programs and forms of intervention, and of farming strategies to improve competitiveness

Холистичен подход за дефиниране, оценяване и подобряване на конкурентоспособността на земеделските стопанства в България

The report presents the results of the first stage of the research project "Competitiveness of agricultural farms in Bulgaria" funded by the Agricultural Academy and implemented by a team from the Institute of Agrarian Economics, UNWE, NBU and IPAZR "N. Pushkarov ”in Sofia. A holistic framework for understanding, evaluating, and improving the competitiveness of agricultural holdings in Bulgaria has been elaborated. The achievements of the interdisciplinary New Institutional Economics, Theory of Economic Organizations, Theory of Competitiveness and other scientific methods such as: study of literature and experience, summary, synthesis, design, comparative and institutional analysis, multicriteria analysis, groupings, discrete structural analysis, value -measuring, qualitative analysis, expert evaluation, survey, Shift-share Analysis, VTOPSIS and statistical analysis, localization analysis, etc. Numerous publications and experience in the country and the world for understanding and assessing the competitiveness of agricultural holdings have been studied. On this basis, a (more) adequate definition of the competitiveness of the farm is given, it is justified that it has four equally important pillars (economic efficiency, financial capability, adaptability and sustainability), and a hierarchical system is developed to assess its level consisting of adequate criteria, indicators and reference values, and an approach to integration and interpretation. The new evaluation system is being experimented with, using survey information from managers of "typical" farms of different types, production specializations and geographical locations. The theoretical bases of business models are summarized and an innovative model of competitiveness of agricultural holdings is developed. An approach to assessing market and factor competitiveness has been adapted and tested in the dairy sector. The regional differences in the competitiveness of agriculture in the EU countries have been identified. The competitive positions and forms of management of alternative farms in the conditions of the Kovid pandemic are assessed. The peculiarities in determining the competitiveness of organic farms are highlighted. The advantages of strategic partnerships and network structures as a tool for increasing the competitiveness of small and medium farms were assessed. The possibilities of the "new" forms of marketing (green, niche, sustainable, etc.) and digitalization to increase the competitiveness of farms are assessed. A regional analysis of agricultural holdings and employees in the South Central region was made. Alternative forms of financing agriculture from banks and leasing companies to improve the competitiveness of farms have been assessed. Conclusions and recommendations for improving public policies and farming strategies have been prepared. The performed activity and the achieved results in terms of volume and quality fully correspond (and exceed) the planned for all tasks. More information can be obtained from the project website https://cfb.alle.bg