Ilie Nuca

The main scope of this research was to complete and validate the analysis of stator winding topologies of six-phase AC machines using the winding quality factor by determining fault tolerance and validating it through experimental tests. This paper proposes a unified and practical methodology for evaluating the performance of stator windings in six-phase induction machines, with emphasis on magnetic field quality and fault-tolerant operation. The approach combines analytical modeling of the magnetomotive force (MMF) with its graphical representation using the MMF polygon, enabling an efficient assessment of harmonic content through a global indicator, referred to as the winding quality factor. Several representative winding topologies are analyzed within a common framework, including single-layer and double-layer configurations with full-pitch and short-pitch coils, suitable for generating homologous series of six-phase machines. The study considers both normal operating conditions and post-fault regimes, particularly operation with a single three-phase set. The results reveal the strong influence of winding topology on harmonic distortion and overall machine performance, highlighting the trade-offs between magnetic field quality and fault tolerance. It is shown that appropriate winding design can reduce spatial harmonics and improve robustness under degraded operating conditions. The theoretical findings are validated through experimental investigations, demonstrating good agreement between analytical predictions and measured data. A parallel analysis was performed between the theoretical findings and experimental data, and the results conform to the authors’ expectations.

The paper presents a detailed analysis of the external stakeholders' perception regarding the quality of the “Electromechanical Systems Engineering” study program at the Technical University of Moldova. Based on a structured questionnaire applied to experts from industry, research, and education, the study highlights relevant aspects concerning curriculum adequacy, teaching methods, and the relevance of the developed competencies. The results reveal a predominantly positive appreciation of the program, while also emphasizing the need for modernization of practical content and educational resources.

This paper presents a comparative study of several six-phase winding configurations, evaluated both through analytical calculations and a graphical assessment method based on the MMF diagram. The mathematical approach involves determining the winding quality factor for each configuration, taking into account the distribution of the magnetomotive force along the air gap, as well as the winding distribution and pitch factors. The graphical method provides a visual interpretation of winding performance, facilitating direct comparison between configurations, as well as highlighting practical engineering applications. The paper presents examples of basic topological structures of single-layer, double-layer, bipolar, and multipolar windings for the development of homologous series of six-phase induction machines. Both the nominal operating mode and operation under fault conditions are examined. The results enable the classification of winding variants into a quality-based hierarchy, offering valuable recommendations for selecting winding topologies in the design of high-performance six-phase machines. This combined analytical-graphical approach supports both theoretical research and practical engineering applications.

The paper explores the energy efficiency of general-purpose installations, particularly the equipment used in espresso coffee production, and the unique functions of hydraulic systems. By applying eco-design principles and innovative, efficient solutions, the negative impact on the environment can be significantly reduced, transforming citizens into eco-consumers. The study aimed to explore ways to decrease energy consumption in hydraulic systems of standard installations, particularly in heat transfer processes in solids and liquids, which account for up to 97% of energy consumption in such installations. An innovative solution is presented that converts electric energy into heat in liquids using inductive heat transfer. The instant heating inductive boiler, based on inductive heat transfer phenomena, eliminates the convective and conductive heat transfer losses associated with the operation of the boiler with the resistive heating element. The design methodology for dimensioning this type of equipment is provided, and the simulation model for necessary verifications in MatLab Simscape is created. With its practical benefits, the new inductive boiler reduces the preheating period to 7.5 s compared to the 90 s of systems with resistive heating elements, thereby eliminating the need to keep the coffee machine at operating temperatures during breaks and providing a reliable solution for energy efficiency.

Asynchronous motors with six and more phases (usually n-three-phase) are increasingly accepted in electric drive systems of road transport, marine and even aeronautical transport. Multiphase machines are credited with multiple advantages such as: less torque ripple, better power distribution per phase, higher efficiency and fault tolerance capability compared to traditional three-phase machines. There are many publications, but few of them are dedicated to the in-depth study of the multiphase motor (m>3) and especially of the magnetic field in its air gap. The purpose of the present paper: the development of the mathematical model of the magnetomotive force in the air gap of the six-phase asynchronous machines, which determines the fundamental properties of the machine, the structure of the magnetic field and the torque developed, the efficiency, the error tolerance. The research is based on analytical studies and the results of suitable experimental measurements. The paper presents the mathematical model for the harmonic analysis of the magnetomotive force in the air gap of six-phase machines with possible variants of windings on the stator. Based on this study, it was demonstrated that only n-three-phase machines with asymmetrically arranged stator windings have the ability to attenuate higher harmonics with a major negative effect on the developed torque, the applicability and efficiency of traditional tools for reducing higher harmonics in the case of six-phase machines was confirmed. The results of measurements carried out on samples of six-phase machines confirm the findings and conclusions formulated in the paper.

This paper contains the description of the solutions and tools for the implementation of this project. The proposed solutions are based on the implementation of new technologies in the technological part of water treatment and in the electromechanical part. New equipment and methods are selected based on the quantitative and qualitative analysis of the work front. Based on this design, a new water pumping and treatment network will be built for a city in the Republic of Moldova.

This paper focuses on the determination of the characteristics of refusals in low voltage electrical distribution systems. In order to solve this problem, the phenomena of occurrence of refusals in low-voltage electrical distribution systems, conditioned by different influencing factors, processed and mathematically modelled. The main results of the research consist in establishing the static characteristics of the refusals, the mathematical models that determine the occurrence of the cause phenomena and the parameters that characterize the distributions of the refusals, depending on the occurrence per system, depending on the occurrence per season, depending of interruptions duration and the number of affected consumers. The significance of the results obtained consists in solving a number of problems faced by the operating services of electrical distribution systems, concerning the assurance of reliability of operation, providing the possibility of forecasting and preventing the occurrence of the phenomena of occurrence of refusals, which enable the justified planning of prophylactic measures and ensuring the reliability level.

The work is a summary of the history of the industry and education development of electrotechnics in the Republic of Moldova during the independence period. With the national renaissance, the process of professional training in the electrotechnical field began to take on a natural national face - training in the Romanian language. Scientific research is determined by the subject of special submersible and permanent magnet electric machines, renewable energy sources, but also by new directions such as the development of adjustable electromechanical systems for the automation and efficiency of technological processes and traction systems of electric passenger vehicles.

The paper presents the current status and modernization of DC traction stations for powering trolleybuses. Most of the traction stations are over 50 years old and have a rigid structure, obsolete rectification equipment, and require colossal maintenance costs. Flexible power circuit structures, efficient electrical and electronic equipment, automated digital control systems, reactive energy compensation and trolleybus braking energy recovery have been proposed to modernise traction stations. The proposed modernization solutions will allow to increase the operating functionality and energy efficiency by about 30%, compatibility with the supplier’s electricity grid, reduction of operating costs of trolleybus traction stations.

The paper focuses on the development of hybrid battery charging systems for autonomous electric passenger vehicles. Aspects of elaboration and design methodology of the battery charging station are approached both from the three-phase electrical network, but also from a photovoltaic plant. A new structure of the battery charging station with power supply from a photovoltaic plant parallel to the public electricity grid was developed. The photovoltaic plant was dimensioned and the amount of electricity produced and consumed at the charging station was estimated. The excess of energy generated by the photovoltaic plant can be injected into the grid or, in offGrid mode, stored in buffer batteries.