Sebastijan Seme

Maximum Efficiency Trajectories of a Two-Axis Sun Tracking System Determined Considering Tracking System Consumption

This paper deals with the two-axis sun tracking system for a photovoltaic system. The trajectories of the sun tracking system are determined in an optimization procedure. The optimization goal is maximization of an electric energy production in the photovoltaic system considering the tracking system consumption. Determination of the tilt angle and azimuth angle trajectories is described as a nonlinear and bounded optimization problem, where the objective function is not available in the explicit form. A stochastic search algorithm called Differential Evolution is used as an optimization tool. In the optimization procedure, the objective function is evaluated by using the models of available solar radiation, tracking system consumption, and the efficiency of solar cells with the appropriate dc/dc converters. The problem bounds are given in the form of lower and upper bounds for both angles and time and angle quantization. The results presented in the paper show, that the optimal trajectories for the tilt and azimuth angle depend on the available solar radiation, solar cell efficiency, tracking system consumption and the optimization bounds.

Determining Magnetically Nonlinear Characteristics of Transformers and Iron Core Inductors by Differential Evolution

This paper deals with the differential evolution (DE)-based method for determining the magnetically nonlinear iron core characteristics of transformers and iron core inductors. The unknown iron core characteristic, approximated by the sum of exponential functions, is included in a dynamic model of the tested device. The approximation function parameters are determined by DE. The optimization objective is the best possible agreement between the measured and the dynamic model calculated currents in the time and frequency domains. Using the measured inrush currents and corresponding voltages, the magnetically nonlinear characteristic can be determined over a broad operational range. The inclusion of iron core characteristic, as determined by the proposed method, in the transformer dynamic model gives very good agreement between the measured and calculated currents in both transient and steady states.

Generalization of Methods for Voltage Sag Source Detection Using Vector Space Approach

This paper discusses methods for voltage sag source detection, which are based either on energy, current or impedance criteria. It is shown that methods known from the literature do not work well, particulary in cases of asymmetrical voltage sags. Therefore generalized methods for voltage sag source detection are proposed, using a vector space approach. All the discussed methods, both the already known and proposed ones, were tested by applying extensive simulations, as well as laboratory and field tests. The correctness of the proposed generalized methods was verified in this way. The obtained results show, that all the proposed methods are highly effective in all cases of voltage sags, whereas the overall effectiveness of those methods known from literature is mainly unacceptable.

The efficiency of different orientations of photovoltaic systems

This paper compares the efficiency of different orientations of photovoltaic systems under outdoor conditions over the five-year period in Slovenia. The four different photovoltaic systems were analysed with the same mono-crystalline silicon solar modules. The impact of orientation and inclination on efficiency are evaluated. The analysis of the data obtained shows that the efficiency of the photovoltaic systems depends on the solar irradiation and temperature of solar modules. Based on the analysis and measurements for different photovoltaic systems, the optimal orientation and inclination are presented. Streszczenie. W artykule porównano wydajność systemów fotowoltaicznych o różnej orientacji w warunkach pracy zewnętrznej podczas pięcioletniej ich aktywności na terenie Słowenii. Badano cztery różne systemy fotowoltaiczne z tym samym monokrystalicznym modułem krzemowym. Wpływ orientacji i odchylenia na wydajność tych systemów zostały poddane ewaluacji. Analiza otrzymanych danych pokazuje, że wydajność systemów fotowoltaicznych zależy od promieniowania słonecznego i temperatury modułów. Bazując na analizie i pomiarach czterech systemów fotowoltaicznych wyznaczono optymalną orientację i odchylenie. (Wydajność systemów fotowoltaicznych w różnych ukierunkowaniach )

Monitoring of the solar power plants and performance ratio

This paper deals with monitoring of solar power plants. We can observe solar power plants with energy yield, monitoring or performance ratio. All these approaches of monitoring solar power plants have their advantages and disadvantages. The procedures of monitoring different solar power plants in Slovenia will be presented and evaluated in the paper. It turns out that energy yield and monitoring of solar power plants don’t give enough necessary information concerning proper operation. Energy yield is the ratio between the energy produced and the nominal power of the solar power plant. Energy yield is dependent on the intensity of solar radiation and temperature. It appears that proper operation of solar power plants is best described with the performance ratio, which is the ration between the energy produced and the energy that would be produced at nominal yield. Performance ratio considers the intensity of solar radiation and/or temperature. The results show that the proper operation of the solar power plants is mostly affected by appropriate installation and orientation of solar modules.This paper deals with monitoring of solar power plants. We can observe solar power plants with energy yield, monitoring or performance ratio. All these approaches of monitoring solar power plants have their advantages and disadvantages. The procedures of monitoring different solar power plants in Slovenia will be presented and evaluated in the paper. It turns out that energy yield and monitoring of solar power plants don’t give enough necessary information concerning proper operation. Energy yield is the ratio between the energy produced and the nominal power of the solar power plant. Energy yield is dependent on the intensity of solar radiation and temperature. It appears that proper operation of solar power plants is best described with the performance ratio, which is the ration between the energy produced and the energy that would be produced at nominal yield. Performance ratio considers the intensity of solar radiation and/or temperature. The results show that the proper operation of the solar power p...

The classification of explosion-proof protected induction motor into adequate temperature and efficiency class

This article deals with the classification of explosion-proof protected induction motors, which are used in hazardous areas, into adequate temperature and efficiency class. Hazardous areas are defined as locations with a potentially explosive atmosphere where explosion may occur due to present of flammable gasses, liquids or combustible dusts (industrial plants, mines, etc.). Electric motors and electrical equipment used in such locations must be specially designed and tested to prevent electrical initiation of explosion due to high surface temperature and arcing contacts. This article presents the basic tests of three-phase explosion-proof protected induction motor with special emphasis on the measuring system and temperature rise test. All the measurements were performed with high-accuracy instrumentation and accessory equipment and carried out at the Institute of energy technology in the Electric machines and drives laboratory and Applied electrical engineering laboratory.

Comparison of the Shading Influence on PV Modules of Different Technologies

The characteristics of different PV modules are provided in this paper. The influence of shading on PV module characteristics of different technologies (different crystalline silicon and thin film technologies) is investigated. The study also took into account the orientation of PV modules (portrait or landscape), a by-pass diode number and a type of connections. An inter-row shading factor for different PV modules has also been determined. A comparison of shading influence on PV module characteristics of different technologies has been drawn. A shading factor comparison of different technology PV modules has also been made. The influence of shading on PV system electricity production has been modelled based on a study which examined the influence of shading on characteristics of different technology PV modules.