Electrical Engineering & Electromechanics

Comparative analysis of principal modulation techniques for modular multilevel converter and a modified reduced switching frequency algorithm for nearest level pulse width modulation

M. Benboukous — 2025-07-02

Introduction. The Modular Multilevel Converter (MMC) is an advanced topology widely used in medium and high-power applications, offering significant advantages over other multilevel converters, including high efficiency and superior output waveform quality. Problem. The modulation techniques and submodule capacitor voltage balancing significantly affect the performance of the MMC, influencing output voltage and current quality, capacitor voltage balancing, and power losses. Goal. This study presents a comparative analysis of 3 modulation techniques for a 3-phase MMC: Level-Shifted Pulse Width Modulation (LS-PWM), Nearest Level Control (NLC), and hybrid Nearest Level Pulse Width Modulation (NL-PWM). In addition, this study proposes a modification to the Reduced Switching Frequency (RSF) capacitor voltage balancing algorithm to adapt it for use with the NL-PWM technique. Methodology. The performance of each modulation technique is evaluated through simulations using MATLAB/Simulink software, in terms of output signal quality, capacitor voltage balancing, converter losses, and behavior under a line-to-ground fault. Results. The results show that both LS-PWM and NL-PWM generate lower harmonic content compared to NLC. However, the NLC technique presents the lowest switching losses, followed by NL-PWM and LS-PWM. The NL-PWM technique shows intermediate performance, making it more appropriate for medium-voltage applications. The results also confirm the proposed modifications to the RSF capacitor voltage balancing algorithm. Additionally, the LS-PWM technique shows greater robustness under fault conditions compared to the other techniques. Originality. For the first time, a comparative analysis of 3 modulation techniques for the MMC, LS-PWM, NLC, and NL-PWM has been conducted, highlighting their performance under different operating conditions. The study also proposes a modified RSF capacitor voltage balancing algorithm specifically for NL-PWM, which has not been previously explored in the literature. Practical value. The results of this study contribute to the selection of the most suitable modulation technique for MMC for specific applications. References 34, table 5, figures 17.

Experimental analysis of the effects of potential-induced degradation on photovoltaic module performance parameters

Z. Khammassi — 2025-07-02

Introduction. Photovoltaic (PV) power plants are subject to various forms of degradation that can impair their performance and lead to significant faults within PV systems. Among these, Potential-Induced Degradation (PID) stands out as one of the most severe, impacting the efficiency and output of PV generators while shortening their lifespan. Problem. This phenomenon is the result of a decrease in the shunt resistance of the cells encapsulated within the PV module, directly associated with a reduction in its insulation resistance. Although extensive research has been conducted in this area, our understanding of the factors contributing to PID, as well as its detection and effects on PV systems, remains incomplete. The goal of this work is to investigate the variations in insulation resistance at the module’s glass and frame, and to map the changes in shunt resistance at the module level to identify the most vulnerable areas, characterized by lower insulation resistance values and significantly affected by PID. Methodology. This study utilizes a comparative experimental method to investigate the behavior of two identical PV modules under similar climatic conditions, where one module is exposed to voltage stress while the other remains unstressed. A high-voltage insulation resistance tester was employed to apply voltage stress between the terminals of the stressed module and its metal frame, with insulation resistance systematically measured at various points to analyze changes in electrical properties. The originality of this study lies in the estimation of the shunt resistance based on the operating voltage of the PV string, which depends on the types of grounding, climatic conditions such as temperature and humidity, as well as the position of the cell within the PV module. This estimation is correlated with the I-V characteristic curves of two PV modules, one of which is subjected to operating voltages under well-controlled environmental conditions. The results reveal that an increase in the test voltage leads to a reduction in insulation resistance, a phenomenon that becomes more pronounced in humid environments. This highlights the vulnerability of PV modules to PID, which can significantly affect their lifespan and performance, particularly through the reduction of shunt resistance and the distortion of the characteristic curve of the stressed module affected by this phenomenon, thereby causing increased difficulty in extracting its maximum power. References 30, table 3, figures 17.

Designing the optimal number of active branches in a multi-branch buck-boost converter

I. Kovacova — 2025-07-02

Introduction. Multi-branch buck-boost converters, widely used in energy conversion from alternative sources, offer significant advantages over single-branch configurations. Critical, however, is the question of the appropriate number of branches for optimal efficiency and the given output power of the converter. The novelty of the proposed work consists in the development of a precise method for determining the optimal number of branches in a multi-branch buck-boost converter for a specified output power. Additionally, the findings enable the development of adaptive control strategies that dynamically adjust the number of active branches based on the converter’s instantaneous power. This approach enhances the overall efficiency of the converter. Goal. The study aims to analyze the efficiency of multi-branch buck-boost converters, focusing on the optimal number of branches and the required output power. Methods. The problem was addressed through a theoretical analysis of the converter’s electrical equivalent circuit. The theoretical results were validated through practical measurements conducted on a prototype converter. Results. A detailed equivalent circuit for the converter was developed and analyzed for various operational modes. Based on this analysis, the converter’s losses were quantified, and a relationship was derived to determine the optimal number of parallel branches, taking into account the desired output power. Practical value. The findings provide guidelines for selecting the optimal number of branches in a multi-branch buck-boost converter based on the desired output power. Furthermore, they enable the implementation of adaptive switching strategies to maximize the converter’s efficiency. References 22, table 2, figures 20.

Improving the operation of an asymmetric inverter with magnetically coupled inductors for energy storage systems

D. V. Martynov — 2025-07-02

Introduction. Bidirectional DC-DC converters are widely used in energy storage systems for efficient energy transfer. One of the effective converters for such systems is the asymmetric inverter with a magnetically coupled inductors. To enhance the efficiency of this converter for energy storage applications, it is necessary to optimize its parameters. Objective. The objective is to develop a mathematical model of an asymmetric inverter with magnetically coupled inductors and based on this model, to establish the conditions for improving the energy efficiency of the inverter in energy storage systems. Methods. The study uses the state-space averaging method and simulation modelling to analyse operational processes. Results. Analytical expressions were derived for calculating current parameters of the magnetically coupled inductor within switching intervals. A correlation was identified between the inductor’s inductance and power source parameters under conditions that eliminate circulating currents, thus reducing static energy losses in the inverter. Novelty. Based on these expressions, new analytical and graphical dependencies were established, illustrating relationships between the inductor parameters and the magnetic coupling coefficient of its windings. These dependencies determine the boundaries of the discontinuous conduction mode for the asymmetric inverter with a magnetically coupled inductors within its switching range. Practical value. The application of these dependencies during the design phase allows for a reduction in both static and dynamic energy losses in the inverter using discontinuous conduction mode. This will also improve the dynamics of transient processes during changes in the direction of energy flow, which is a significant advantage in the development of hybrid power systems for electric vehicles. References 19, figures 9.

Control of an autonomous wind energy conversion system based on doubly fed induction generator supplying a non-linear load

M. L’Hadj Said — 2025-07-02

Introduction. Nowadays, many researches are being done on wind turbines providing electrical energy to a stable power grid by via a doubly fed induction generator (DFIG), but the studies on the autonomous networks are rare, due the difficulty of controlling powers often close to the nominal power of the generator. Goal. This paper presents a variable speed constant frequency (VSCF) autonomous control system to supply isolated loads (linear or non-linear). The main objective is the design of an effective strategy to reduce harmonic currents induced via the non-linear loads such as rectifier bridge with 6 diodes. The novelty of the work consists in study of system composed of a DFIG providing energy by his stator to a stand-alone grid. It uses a static converter connected to the rotor allowing operation in hypo and hyper synchronism. A permanent magnet synchronous machine (PMSM) connected to a wind turbine supplies this converter, that is sized proportionately to the variation range of the necessary rotational speed. In the case of linear loads there is no problem, all desired parameters are well controlled but in the non-linear loads case such as rectifier bridge with 6 diodes there is the harmonic problem. For this purpose, to reduce this harmonic, the proposed solution is the installation of a LC filter. Methods. The DFIG is controlled to provide a constant voltage in amplitude and frequency independently of the grid load or the drive turbine speed. This command is vector control in a reference related to the stator field. The stator flux is aligned along the d axis of this landmark allowing thus the decoupling of the active and reactive stator powers of DFIG. The DFIG is controlled by an internal control loop of rotor flux and an external control loop of output stator voltage. We present also the control of the PMSM and the DC bus of the converter. The PMSM is controlled by an internal control loop of the current and an external control loop of the continuous bus of the converter according to its nominal value. The control system of wind generator based on the maximum power point tracking and the control of bus continuous at output rectifier knowing that the non-linear loads introduce high harmonic currents and disrupt the proper functioning of the system. The installation of a LC filter between the stator and the network to be supplied reduce harmonics. Results. Simulation results carried out on MATLAB/Simulink show that this filter allows obtaining a quasi-sinusoidal network voltage and it also has the advantage of a simple structure, a good efficiency and a great performance. This proves the feasibility and efficiency of the proposed system for different loads (linear or non-linear). Practical value. This proposed system is very performing and useful compared to others because it ensures the permanent production of electricity at VSCF to feed isolated sites, whatever the load supplied (linear or non-linear), without polluting the environment so that the use of wind energy is very important to reduce the greenhouse effect. References 34, figures 9.

The complex influence of external and internal electricity networks on the magnetic field level in residential premises of buildings

V. Yu. Rozov — 2025-07-02

The problem of determining the complex influence of a group of electricity networks (external electricity networks, built-in transformer substations, cable electric heating systems, etc.) on the magnitude of the summary magnetic field (MF) in a residential premise of a building has not been sufficiently researched. This results in an overestimation of the assess the magnitude of the summary MF, generated by the group of electricity networks, as well as to the use of technical measures to reduce this MF, which have excessive efficiency and are accompanied by excessive expenses. The goal of the work is to investigate of the complex influence of external and internal electricity networks on the MF level in residential premises of buildings and definition of conditions, which provide the minimum necessary limitations on the MF flux density of individual electricity networks, at which the summary level of MF in residential premises, does not exceed the normative level of 0.5 μT. The methodology of determining the complex influence of the group of electricity networks on the level of MF in residential premises is based on the Biot-Savart’s law and the principle of superposition and allows determining the functional dependence between the instantaneous values of currents in electricity networks, their geometrical and physical parameters, and the summary effective value of MF flux density in the premise. Scientific novelty. For the first time, the methodology for determining the complex influence of the group of external and internal electricity networks on the level of MF in residential premises is proposed. Practical significance. The implementation of the proposed methodology will allow to reduce the calculated coefficient of normalization of the MF of individual electricity networks by 25–50 %, which, in turn, will contribute to the reduction of economic costs for engineering means of normalizing the summary MF in residential premises, caused by the influence of the group of electricity networks. References 56, tables 4, figures 8.

Robust control of single input multi outputs systems

D. Zehar — 2025-07-02

Introduction. Most of mechanical systems are nonlinear and complex, the complexity of these latter lies on highly nonlinear characteristics, or on dynamics that stimulate the development or change of the process through an applied force in a disturbed environment. Single input multi outputs (SIMO) systems, which are structured into subsystems, are considered as complex systems. The task to control their degrees of freedom is more complicated, and it is not easily reachable, due to the fact that nonlinear laws are not directly applicable to those systems, which requires to trait them in a particular way. Problem. First order sliding mode control (FOSMC) has already been applied in several previous works to this kind of systems, and due to its robustness property, this control gave good results in term of stabilization and tracking, but the chattering phenomenon remains a big problem, which affects the control structure and the actuators. Purpose. In order to address the problem of chattering encountered when applying the FOSMC to a category of second order subsystems, a second order sliding mode control (SOSMC) is designed. Methods. This work consists of developing an appropriate second order system structure, which can go with the sliding control expansion, and then studying the SOSMC for this chosen system. The hierarchical structure of the sliding surface which is made using a linear combination between subsurfaces, according to the system structure, allows the only control input to affect subsystems in graded manner from the last one to the first one. Results. We have applied the constructed control law to a SIMO system for two cases with and without disturbances. Simulation results of the application have shown the effectiveness and the robustness of the designed controller. References 30, figures 10.

The main characteristics of the leader channel during breakdown of a long air gap by high pulse voltage

M. I. Baranov — 2025-07-02

Goal. Calculation-experimental determination of basic descriptions of plasma channel of leader at an electrical breakdown of long air gap in the double-electrode discharge system (DEDS) «edge-plane» by artificial electricity of high pulse voltage of positive polarity. Methodology. Bases of the theoretical electrical engineering and electrophysics, electrophysics bases of technique of high and extra-high voltage, large pulse currents and high electromagnetic fields, basis of high-voltage pulse and measuring technique. Results. The simplified electrophysics model of origin and development of positive leader is offered in the long air gap of probed DEDS, which the followings descriptions of plasma channel of this positive leader were found on the basis of: a closeness of n_eL charge and electric potential U_eL in the head of leader; linear charge q_Ll of leader of plasma channel; closeness δ_eL of electron current i_eL and this current i_eL in the channel of leader; strength of high electric field outside E_Le and inwardly E_Li of the channel of leader; length l_s of streamer area before the head of leader; maximal electron temperature T_mL in plasma of channel of leader; linear active resistance R_Ll and active resistance R_Lc of channel of leader. Executed on a domestic powerful over-high voltage electrical equipment outdoors in the conditions of electrophysics laboratory high-voltage experiments with the use of standard interconnect aperiodic pulse of voltage U_e(t) of temporal shape of T_m/T_p≈200 μs/1990 μs of positive polarity for probed DEDS at a change in it of minimum length l_min of its discharge in air gap in the range of 1 m≤l_min≤4 m confirmed power and authenticity of row of the got calculation correlations for the indicated descriptions of plasma channel of positive leader which is formed and develops in this DEDS. Originality. In a complex kind calculation-experimental way the indicated basic descriptions of plasma channel of positive leader are certain in probed DEDS. By calculation way it is first rotined that on the stage of development of positive leader in atmospheric air of indicated DEDS high electric potential U_eL of his spherical head with the charge of q_eL≈58,7 nC has a less value (for example, U_eL≈605 kV for length of his channel of l_L=0,395 m at l_min=1,5 m) the radius of R_eL≈0,5 mm, what high potential U_e(t)≈U_e(T_d)≈611,6 kV its active metallic electrode-edge. Obtained result for the maximal electron temperature T_mL≈1,639·10⁴ K in plasma of the probed leader testifies that this plasma is thermo-ionized. Practical value. Practical application in area of industrial electrical power engineering, high-voltage pulse technique, techniques of high and extra-high voltage of the obtained new results in area of physics of gas discharge allows not only to deepen our electrophysics knowledges about a leader discharge in atmospheric air but also more grounded to choose the air insulation of power high and over-high voltage electrical power engineering and electrical engineering equipment, and also to develop different new electrical power engineering and electrophysics devices in area of industrial electrical power engineering and powerful pulse energy with enhanceable reliability and safety of their operation in the normal and emergency modes. References 49, figures 7.

Determination of parameters of an autonomous source of a constant magnetic field for a portable electromagnetic-acoustic transducer

V. F. Bolyukh — 2025-07-02

Purpose. Determination of rational parameters of an autonomous source of constant magnetic field, ensuring the efficiency of using portable electromagnetic-acoustic transducers (EMAT) for diagnostics of remote ferromagnetic objects. Methodology. An analysis of the parameters of an autonomous magnetic field source consisting of a permanent magnet and a ferromagnetic screen magnetizing a ferromagnetic object with a flat surface, providing a central magnetic field along the magnet axis above 0.3 T, was carried out. Results. The results of experimental studies on a sample of an autonomous source, which contained 6 sections of a permanent magnet made of NeFeB ceramics with dimensions of 50´50´10 mm³, correspond to the results of calculating the magnetic field on the surface of a ferromagnetic sample with an error of up to 9 %. Experimental studies were carried out for EMAT with two magnetic field sources containing rectangular permanent magnets of the same height but different widths. Novelty. It has been established that in order to select rational parameters of an autonomous source of magnetic field, it is necessary to use an integral criterion that takes into account the magnetic field in the surface layer of a ferromagnetic object, the magnetic scattering field, the volume of a permanent magnet, which determines the mass and size indicators and cost of the source, and the force of attraction to the ferromagnetic object. Practical value. For portable EMAT, increasing the magnetic field in a remote ferromagnetic object either by increasing the volume of a permanent magnet or by decreasing the air gap between the magnetic field source and the ferromagnetic object provides increased EMAT efficiency by increasing the ratio of the amplitude of the received ultrasonic bottom pulses to the noise amplitude. References 27, figures 14.

Application of the multilayer soil equivalence method in determining the normalized parameters of the grounding system

D. G. Koliushko — 2025-07-02

Introduction. Normalized parameters of the grounding system, such as touch voltage and resistance, are critically important for ensuring electrical safety and reliability of power plants and substations. The complexity of the multi-layered soil structure makes it difficult to determine mentioned parameters. This is due to the fact that real soils on the territory of energy facilities of Ukraine have three or more layers, and the specified parameters are determined by software with two-layer calculation models. Therefore, the need to provide multilayer geoelectric structures into equivalence two-layer models for practical application is an urgent task. Goal. Determination of the application limits of the multilayer soils equivalence method based on the calculating results analysis of the grounding system normalized parameters. Methodology. The study considered a three-layer model for four soil types (A, H, Q, K) common in Ukraine. The calculations were performed using the LiGro software package, which is based on the method of integro-differential equations, applied to the analytical solution of the problem of the electric field potential of a point current source in a three-layer conducting half-space. As a criterion for the possibility of applying the equivalence method, a relative error value of 10 % was chosen when determining the normalized parameters of a grounding system of the given topology and soil type. When determining the error, the calculation results in the original three-layer soil structure for the given topology of the grounding system were taken as the true value. The results show that the effectiveness of equivalent technique significantly depends on the type of soil and the area of the grounding system. In particular, for soil type A, replacing the upper and middle layers with the equivalent first layer (the lower layer with the second) provides a smaller error in the calculations of the grounding resistance than representing the upper layer as the first, and the middle and lower layers as the second equivalent layer. At the same time, there is a tendency for the error to decrease with increasing area of the object: from 225 m² to 14400 m², for the first case, the error decreased from –14.6 % to –2.6 %, and for the second case, it changed from –9.3 % to 14.6 %, respectively. Originality. For the first time, the results of the methodical error evaluation of the equivalence techniques of multilayered soils of different types when calculating the normalized parameters of grounding system are presented. Practical value. Determination of the conditions and limits of the use of the equivalence method when calculating the normalized parameters of grounding system by software complexes can be used in the design of new or reconstruction of existing energy facilities of Ukraine. References 20, tables 5, figures 4.