Search

The issue of the atmosphere gases concentration decrease, generated by the human activities, was the key point for integrating renewable energy sources into the electricity grid. Thus, consumers became prosumers, allowing energy consumers not only to use, but also to generate energy, the surplus being sold on the electrical network. The support of prosumers in the countries of the European Union has registered significant growth rates, especially regarding the energy produced from photovoltaic panels in households or in commercial spaces. Romania will promote the distributed generation from renewable sources with installed power between 3 kW and 100 kW (most recently, starting form 4th of December 2020), the on-grid installations being subsidized through the financial support of the Environmental Fund Administration (3 kW for residential prosumers) with ,,photovoltaic green house,, program and Ministry of Economy, Energy and Business Environment with the ,,Electric Up,, program ( between 27 kW - 100 kW power for commercial prosumers). This paper proposes an analysis of a Romanian prosumers with a specific case study, comprise of a comparative analysis for an integrated 3kW (residential) energy user versus a smart prosumer, and their subsequent energy curves, in order to reduce the energy consumption with a management system for the optimal coordination of the energy to the owner’s need, also the rentability of the system and a minimum disturbance of the electricity grid.

Optimal dispatching of the thermal power plants which produce simultaneously heat and electricity (the cogeneration units) represents an important economical issue in power systems. To approach this problem it is necessary to establish the parameters for fuel-cost function as accurate as possible, these parameters showing the link between production costs of one unit, electrical power and amount of heat produced. In this paper, an enhanced crow search (ECS) algorithm is applied to estimate the fuel-cost parameters of the thermal units which produce only heat or operate in cogeneration mode. The ECS algorithm has the same framework as the original crow search (CS) algorithm, but it introduces a different relation to modify the solutions from the search space. The effectiveness of the ECS and CS is verified on a three-unit thermal system. The results obtained by the ECS and CS algorithms are compared with those obtained by other well-known algorithms.

Entrepreneurship is the force that drives economic, social and technical progress. A small percentage of firms (5%) is responsible for a disproportionately large amount of net job creation (>50%). Named high growth firms, these successful enterprises have been in the spotlight of research looking into the key drivers of firm growth and growth policy. This dissertation explores high growth from multiple perspectives: at the level of the firm, by understanding how the definition of a high growth firm impacts its characteristics and expected performance over time; at the local level, by isolating the effect of political connections of firm performance and firm entry; and at the macro level, by observing the evolution of entrepreneurship during transition. The first study finds that most HGFs are unable to maintain high growth rates for long, but do register lower volatility in growth rates and a higher chance of survival. Results on growth volatility and persistence vary significantly with the specific definition of “high growth” used as well as with the specific variable used to measure growth (e.g., revenue, employees, profit, productivity). These findings have direct implications for growth policies and programs that depend on identifying HGFs. The second study indicates a strong significant effect of political alignment on revenue growth and firm entry. Larger firms take advantage of political connections for performance gains, while small firms are negatively impacted. Furthermore, alignment reduces entry into entrepreneurship by 8-11%. These findings establish political alignment and local-level business-politics collusion as important dynamics to consider when evaluating entrepreneurship policy in developing countries. The third study describes the interdependence between entrepreneurship, institutions, and transitions. The case of Romania shows that the beginning of transition was characterized by an initial explosion of newly created private enterprises, followed by a declining trend in enterprise creation and, recently, by a new increase in entrepreneurship activity. To conclude, this work contributes new perspectives towards a better understanding of high growth firms and growth policy. Policy implications are targeted towards transition and developing economies that have seen little representation in literature. The goal is to enable successful high growth policies across multiple levels.

The present paper investigates the influence of magnetic saturation on the rotor position and speed estimators and the machine behavior during transients and short-circuit faults for a doubly-fed induction generator (DFIG) connected to the power grid. The DFIG is considered driven by a wind turbine whose torque vs. generator speed at different wind speed is optimised. The DFIG is connected to the grid, at a certain initial speed, simultaneously in the stator and in the rotor for given values of active and reactive stator power references. Subsequently a sudden three-phase short-circuit at the middle of a typical local power grid is investigated. A computer program in Matlab-Simulink package for the whole system has been developed and applied to simulate transients as described above with and without considering the magnetic saturation in the machine. It is shown by digital simulations that during short-circuit the sensorless control fails without considering the magnetic saturation and even during the sudden connection to the grid the errors in position and speed estimation and in the transient description are notable.