Oleksii Duniev

This study explores heat and mass transfer processes in the structural elements of an umbrella-type hydrogenerator, as well as the ventilation and cooling system in the active components of the hydrogenerator. A vertical synchronous air-cooled hydrogenerator with a rated capacity of 60 MW has been investigated. The task addressed relates to the cooling efficiency of generator components. Conventional analytical calculation methods do not make it possible to identify local overheating zones and pressure distribution in complex ventilation channels. Therefore, it becomes necessary to use numerical methods and algorithms to calculate and analyze the cooling efficiency of the generator’s active parts. The main result of this study is the designed structure of the guide channels (blades) of the rotor, which provides the required air flow rate of 45 m3/s. At the same time, the maximum values of the winding temperature do not exceed the permissible values for class F insulation. The CFD calculation detailed the action of the superchargers and showed the real pressure in the channels and the volume of air passing through each section of the generator. The error between the results from CFD modeling and analytical calculations is less than 3%. The results are attributed to the detailed reproduction of the geometry of the ventilation channels in the 3D model, which made it possible to determine the real aerodynamic resistance and cooling medium consumption. The proposed method uses the boundary conditions of the third kind for a comprehensive calculation of the conjugate heat and mass transfer. The proposed structure could be implemented in the design and modernization of air-cooled hydrogenerators.

Introduction. The growing demand for clean and stable electrical energy stimulates the development of new renewable energy sources, among which wave energy stands out due to its high energy density and potential to cover a significant share of global electricity consumption. One of the most promising technical solutions for converting wave energy is the use of direct-drive systems based on permanent-magnet linear generators, which eliminate the need for complex mechanical transmissions and reduce operational costs. Purpose. The purpose of this article is to review typical designs of permanent-magnet linear generators used in wave power plants and to identify their key advantages, disadvantages, and development prospects. Methods. The study is conducted as a review of contemporary scientific publications and technical solutions related to the design and operating principles of linear generators in wave energy systems. Results. The main structural varieties of linear generators are analyzed, including cylindrical and flat topologies, different permanent-magnet arrangements-embedded, surface-mounted, and Halbach arrays - as well as the use of iron-core and air-core configurations. Machines with longitudinal and transverse magnetic flux paths are examined separately, and their comparative characteristics are presented. Conclusion. The review shows that improving the designs of transverse-flux linear generators is the most promising direction for further research aimed at enhancing the efficiency and reliability of wave power plants, as these designs allow for the minimization of mechanical loads and the increase of the overall performance of the system.

This study explores new designs of linear generators intended for wave energy conversion systems based on transverse magnetic flux machines (TFM) with permanent magnets. The main focus is on developing new, highly efficient designs of linear generators for wave energy, operating at low speeds. The developed wave energy converters function as direct-drive machines, where the generator's translator is directly connected to the buoy. The working element performs a reciprocating motion, converting wave energy into mechanical energy, which is then transferred to the generator. As a result, the multi-pole TFM generator demonstrates high energy conversion efficiency even at low speeds. This eliminates the need for complex and unreliable hydraulic systems with compressors, simplifying the wave energy conversion system's design and improving its overall reliability. Based on previous research on cylindrical transverse magnetic flux machines with a disk structure, conducted in close collaboration with Germany's Otto-von-Guericke University, a theoretical analysis was performed and successfully validated through laboratory experiments. The experimental data confirmed the efficiency of the proposed generator concept. The findings from previous research were applied to linear types of electric machines, which were proposed and improved in the current study for use in wave energy conversion systems. One of the key achievements of this study was the introduction of a generator design that replaced the I-shaped core (the stator magnetic shunt) with an additional E-shaped core. This allowed the use of a double translator, located both inside and outside the stator core. This double translator and stator core design makes the generator more compact and increases the machine's power. The study also determined the optimal number, size and shape of stator cores to achieve the best magnetic field saturation, which further increased the generator's specific power. As a result, a new, promising design for a three-phase linear direct-drive generator with a nominal power of 2.3 kW and a translator speed of 1 m/s was designed. The generator's magnetic system has an outer diameter of 220 mm and a stator core length of 1 meter. At this translator speed, the system efficiency reached approximately 80%, which is a significant improvement compared to traditional high-speed hydraulic systems. The study's results also confirmed the scalability of the proposed generator design for use in high-power wave energy conversion systems. Such systems can be decentralized and operate in parallel along the shoreline, creating a network for converting ocean wave energy. Moreover, this research significantly contributes to the development of sustainable energy systems, offering an efficient, scalable, and innovative approach to harnessing wave energy. The new linear direct-drive generator designs not only reduce energy conversion losses compared to high-speed hydraulic indirect-drive systems but also promote decentralized production and the advancement of renewable energy sources. The research project results described above have received funding through the EURIZON project, which is funded by the European Union under grant agreement No.871072.

The electric power industry impacts each state’s economy significantly, driven by increasing electricity consumption that necessitates expanding power plants and finding alternative energy sources. Among alternative energy sources, ocean and sea wave energy converters can be distinguished as a separate class. Wave energy converters transform wave energy into mechanical and then electrical energy. The purpose of the study is to analyze and optimize the magnetic system of a transverse flux machine (TFM) linear generator and to determine the influence of the distance between the stator cores on the efficiency of the generator. This research included conducting 3D modeling and analysis to identify this rational distance. The methods for investigating the magnetic system and calculating the magnetic field pattern are divided into analytical and numerical. Thanks to advanced software for solving such tasks, numerical calculation methods based on the finite element method play a decisive role. Meanwhile, analytical calculations of the magnetic circuit are performed using Kirchhoff’s second law for preliminary analysis. The article discusses a two-phase linear TFM generator with a U-shaped core and permanent magnets. The results of numerical modeling show that the distance between the stator cores should have a specific size and requires detailed selection when designing the magnetic system in each particular case. In the design studied, it was calculated that 6 mm between the stator cores increases the machine’s performance. 3D modeling is necessary for accurate analysis, considering the axial magnetic flux to minimize stray fields and their mutual demagnetization. Future research will explore an E-shaped core TFM design.

The paper is devoted to finding the set value of the torque of an electromechanical energy converter with a solid rotor by solving an optimization problem in the Optimetrics module of the Ansys Maxwell software. A feature of the material described in the paper is the simultaneous optimization solution using the Sequential Nonlinear Programming (Gradient) algorithm and the solution of the field problem using the finite element method to determine the torque at each step of the iteration. The paper describes in detail the setting of the research tasks, the basic model of the electromechanical energy converter with a solid rotor in Ansys Maxwell 2D, the settings of the Optimetrics module, the task of the objective function and varied parameters, the convergence task with respect to the magnitude of the rotation torque, and the derivation and analysis of the results obtained during the optimization. The techniques described in this paper can be applied to any other type of electric machines.

The paper shows the implementation of simulation models of an electromechanical energy converter on the example of an induction motor with a squirrel-cage rotor in the SciLab environment and its graphic library Xcos for building structural diagrams. Despite the existence of simulation programs such as Simulink and ANSYS Twin Builder, SciLab is completely free, which is an advantage for use in an academic environment and in scientific research. Despite SciLab being free and significantly different from existing paid software, this program allows to create complex models and has a powerful built-in programming language. This paper shows how, using SciLab blocks, to build a simulation model of an induction motor with a squirrel-cage rotor, based on the differential equations of electromagnetic transients. The construction of models for the mode of direct start from a source of stable three-phase power supply is considered. An example of a code program in SciLab for determining the parameters of an induction motor with a squirrel-cage rotor, necessary for simulation, only from the motor rated data, is shown separately. The work will be useful to researchers who intend to use free software to solve complex problems.

The paper is devoted to solving the problem of building a control system for a special electromechanical energy converter, which is due to the inverted structure of the stator and the presence of a solid hollow rotor made of ferromagnetic steel. The task of the control system is to ensure the speed of the rotor's run-up to a given value in a certain time and then maintain it regardless of load fluctuations. The task was solved due to the implementation of Field Oriented Control (FOC) vector control with speed and current controllers and a phase locked loop (PLL). Despite the fact that from the point of view of the electric drive theory, the given task is not new, its solution using only ANSYS Twin Builder blocks is being solved for the first time. The peculiarity of this work is that the electromechanical converter in ANSYS Twin Builder is not presented in the form of a mathematical model and electric machine blocks built into the Twin Builder library, but through the solution of the ANSYS Maxwell 2D/3D coupling project and the ANSYS Twin Builder solver with co simulation, which significantly increases the quality of calculations. The obtained results will be useful for solving similar problems for other types of electric machines, not only for the considered electromechanical converter of the asynchronous type with a solid rotor.