Volume 59 (2022): Edizione 4 (August 2022)

The paper presents the results of the research, which was initiated in our previous publication. The main goal of the research is to develop and validate our own multi-objective simulation tool for determination of optimal mix and sizing of off-grid and grid-connected microgrid systems. The first version of the developed model was tailored specifically for simulation of household off-grid system, which consisted of solar photovoltaics (PV), micro wind turbine, electric batteries, and backup power generator. Proposed algorithms are based on simulation of mentioned resources and hourly electric loads of off-grid system with the objective to reduce unsupplied energy volumes and total system costs. Several alternatives were considered with different configurations of the off-grid system and dispatching strategies of available resources. The developed model was validated with calculations of real off-grid system and results were compared to those, which were made in the previous publication, using Homer Pro software.

The migration of elementary electronic excitations was studied in a single crystal of stishovite and compared with migration in a crystal of α-quartz and polycrystalline stishovite powder. The research method is based on comparing the transfer of absorbed energy to luminescence centers, used as detectors of quasiparticles, and the near-surface nonradiative annihilation of electronic excitations. A sign of migration is the appearance of some minima in the photoluminescence (PLE) excitation spectrum in the region of maxima in the intrinsic absorption spectrum. The PLE spectrum of stishovite contains the first minimum at 9.8 eV, indicating the migration of electronic excitations and the existence of an intrinsic absorption band in stishovite at 9.8 eV. In α-quartz, the first minimum in the PLE spectrum is located at 10.5 eV and corresponds well to the intrinsic absorption band of the exciton.

We report the measuring method of scattering type display liquid crystal layer thickness based on capacitance values suitable for inline production process control. The method is selected for its effectiveness and simplicity over spectroscopic methods as conventional methods for scattering type displays are not applicable. During the method approbation process, a novel diffuser liquid crystal mixture refractive index was determined based on liquid crystal layer thickness measurement data.

The paper describes the design and control method of the synchronous reluctance machine with improved efficiency compared to traction induction motor for electric vehicle application.

Magnetic field finite element modelling is used in the design process. The paper presents load characteristics calculation method for the design process, considering the cross magnetic saturation effect. Control algorithm with constant d-axis current control method is developed in the research. The prototype of the machine is constructed and tested.

Hydrogen is the most abundant chemical element on the Earth, and it has really a wide variety of applications, starting from use in refining, petrochemical industry, steel manufacturing, and ending with use in energy production and renewable gas (hereinafter – RG) blending for gradual replacement of natural gas in all sectors of the national economy. Being practically emission-free, if produced in sustainable way or from renewable energy sources (hereinafter – RES), hydrogen is regarded as one of the most promising energy sources for decarbonisation of practically the entire segment of industrial and energy production. Growing pressure of the European climate neutrality targets has triggered special interest in production, use, storage and transportation of hydrogen – especially the green one, which can be used in at least four fundamental ways: as a basic material, a fuel, an energy carrier and an energy storage medium. In the context of sector coupling, however, hydrogen facilitates decarbonisation of those industrial processes and economic sectors in which carbon dioxide (hereinafter – CO₂) emissions can either not be reduced by electrification or this reduction would be minimal and linked to very high implementation costs. At the same time, development of an extensive hydrogen economy is the key to the achievement of the European climate protection targets, with the European Commission’s (hereinafter – EC) Hydrogen Strategy, a framework created in 2020 to develop and promote sustainable hydrogen economy in the European Union (hereinafter – EU), in its centre.

Green hydrogen also will take its legitimate place in the gaseous fuel diversification risk management strategy, as this gaseous fuel is not only one of the most perspective future energy sources, but also one of the most volatile and demanding sources. In the process of gaseous fuel diversification in the EU and worldwide, new logistical chains and supply – demand networks of green hydrogen will emerge. Therefore, adequate addressing of potential challenges of this new regional and global production, delivery and consumption framework will be of utmost importance for secure, safe and predictable functioning of future energy systems.

Operational monitoring of large sea aquatorium areas with the aim of detecting and controlling oil pollution is now carried out using various technological systems, such as satellite remote sensing, sea-going vessels, various aircraft and remotely piloted aircraft (RPA). Currently, the use of RPA for the fulfilment of monitoring tasks in the aquatorium is being intensively developed and can eliminate problems of remote sensing performed by satellites and piloted aircraft, such as short presence in the monitoring area, very long delay of information (up to 48 hours) and low quality of imagery. This paper presents mathematical modelling of RPA multi-sensor pay-loads for oil spill detection, monitoring and control. Information obtained from payload sensors is critical for increasing effectiveness of detection and monitoring of oil spills. Nowadays, many types of sensors are used for oil spill detection and monitoring. The most common sensors for detection of oil pollution are optical, multispectral, hyperspectral, thermal and laser fluorometers. Some oil pollution detection sensors have limitations, such as false alarm, only daytime operation, weather restrictions. Airborne remote sensors cannot provide all information required for detection of and response to oil spills, and water quality monitoring in the spill area. A model for selecting sensors for multi sensor payload that will make it possible to optimize the application of RPA for oil spill detection was developed. The RPA payload can be increased/reduced to the greatest possible extent with the help of different types of equipment at various parameters. The mathematical model of the integrated payload considers detection capability of sensors, weather conditions, sensor characteristics, and false alarm rate. The optimal multi-sensor payload will optimize the application of RPA for oil spill detection and monitoring.

Throughout the centuries, Riga has been the city with dynamic development. Its territory has unceasingly expanded, whereby previously unused territories have been urbanized. Managers of the city understood already at the end of 19th century that unified geodetic network had great importance in the development of the city. Since then, Riga’s local geodetic network has evolved with the city, several coordinate and height systems have been replaced, but the task has remained the same – to provide a flawless, homogeneous geodetic foundation for various surveying activities. In 2018, the development of the local geodetic network in several parts of the city was completed, whereby the problem arose – altitude values of surveyed terrain points determined by using the improved geodetic network did not coincide with altitude values determined using the GNSS method. Considering the above-mentioned problem, the objectives of this study were set: to plan and carry out control measurements of the improved local geodetic network in the vicinity of Grizinkalns, to provide analysis of the obtained results and recommendations for further development of a local geodetic network. The difference between the heights determined by the geometric levelling method and the heights determined by the GNSS method shall not exceed 2 mm. According to the GNSS method, using the quasi-geoid model LV’14 v2, the determined heights of the geodetic grid points differ from the given ones by 0.062 m on average. The differences are systematic. To overcome these differences, the quasi-geoid model needs to be refined.