Archives of Electrical Engineering

The article proposes the method of synthesis of active elements with time-varying parameters R(t), C(t) and L(t). In order to construct the elements, it is necessary to use operational amplifiers, multipliers and classic RLC components. The variability in time of the elements results from applying voltage to control terminals. Assuming that the parameters of elements R(t), L(t), C(t) are exponentially varying, dependencies describing the control voltage waveforms which enable such a parameter variability were determined. The obtained results were illustrated with examples and PSpice simulations.

In order to control joints of manipulators with high precision, a position tracking control strategy combining fractional calculus with iterative learning control and sliding mode control is proposed for the control of a single joint of manipulators. Considering the coupling between joints of manipulators, a fractional-order iterative sliding mode cross-coupling control strategy is proposed and the theoretical proof of its progressive stability is given. The paper takes a two-joint manipulator as the research object to verify the control strategy of a single-joint manipulator. The results show that the control strategy proposed in this paper makes the two-joint mechanical arm chatter less and the tracking more accurate. The synchronous control of the manipulator is verified by a three-joint manipulator. The results show that the angular displacement adjustment times of the three-joint manipulator are 0.11 s, 0.31 s and 0.24 s, respectively. 3.25 s > 5 s, 3.15 s of a PD cross-coupling control strategy; 2.85 s, 2.32 s, 4.22 s of a PD iterative cross-coupling control strategy; 0.14 s, 0.33 s, 0.28 s of a fractional-order sliding mode cross-coupling control strategy. The root mean square error of the position error of the designed control strategy is 6.47 × 10-6 rad, 3.69 × 10-4 rad, 6.91 × 10-3 rad, respectively. The root mean square error of the synchronization error is 3.96 × 10-4 rad, 1.36 × 10-3 rad, 7.81 × 10-3 rad, superior to the other three control strategies. The results illustrate the effectiveness of the proposed control method.

One of the most critical systems of any satellite is the Electrical Power System (EPS) and without any available energy, the satellite would simply stop to function. Therefore, the presented research within this paper investigates the areas relating to the satellite EPS with the main focus towards the CubeSat platform. In this paper, an appropriate EPS architecture with the suitable control policy for CubeSat missions is proposed. The suggested control strategy combines two methods, the Maximum Power Point Tracking (MPPT) and the Battery Charge Regulation (BCR), in one power converter circuit, in order to extract the maximum power of the Photovoltaic (PV) system and regulate the battery voltage from overcharging. This proposed combined control technique is using a Fuzzy Logic Control (FLC) strategy serving two main purposes, the MPPT and BCR. Without an additional battery charger circuit and without switching technique between the two controllers, there are no switching losses and the efficiency of the charging characteristic can be increased by selecting this proposed combined FLC. By testing a space-based PV model with the proposed EPS architecture, some simulation results are compared to demonstrate the superiority of the proposed control strategy over the conventional strategies such as Perturb and Observe (P&O) and FLC with a Proportional Integral Derivative (PID) controller.

Afeeder automation (FA) system is usually used by electricity utilities to improve power supply reliability. The FA system was realized by the coordinated control of feeder terminal units (FTUs) in the electrical power distribution network. Existing FA testing technologies can only test basic functions of FTUs, while the coordinated control function among several FTUs during the self-healing process cannot be tested and evaluated. In this paper, a novel cloud-based digital-physical testing method is proposed and discussed for coordinated control capacity test of the FTUs in the distribution network. The coordinated control principle of the FTUs in the local-reclosing FA system is introduced firstly and then, the scheme of the proposed cloud-based digital-physical FA testing method is proposed and discussed. The theoretical action sequences of the FTUs consisting of the FTU under test and the FTUs installed in the same feeder are analyzed and illustrated. The theoretical action sequences are compared with the test results obtained by the realized cloud-based simulation platform and the digital-physical hybrid communication interaction. The coordinated control capacity of the FTUs can be evaluated by the comparative result. Experimental verification shows that the FA function can be tested efficiently and accurately based on our proposed method in the power distribution system inspection.

One of the least expensive and safest diagnostic modalities routinely used is ultrasound imaging. An attractive development in this field is a two-dimensional (2D) matrix probe with three-dimensional (3D) imaging. The main problems to implement this probe come from a large number of elements they need to use. When the number of elements is reduced the side lobes arising from the transducer change along with the grating lobes that are linked to the periodic disposition of the elements. The grating lobes are reduced by placing the elements without any consideration of the grid. In this study, the Binary Bat Algorithm (BBA) is used to optimize the number of active elements in order to lower the side lobe level. The results are compared to other optimization methods to validate the proposed algorithm.

In recent years, power systems have been pushed to operate above their limits due to the increase in the demand for energy supply and its usage. This increase is accompanied by various kinds of obstructions in power transmission systems. A power system is said to be secured when it is free from danger or risk. Power systems security deals with the ability of the system to withstand any contingencies without any consequences. Contingencies are potentially harmful disturbances which occur during the steady state operation of a power system. Load flow constitutes the most important study in a power system for planning, operation, and expansion. Contingency selection is performed by calculating two kinds of performance indices; an active performance index (PIP) and reactive power performance index (PIV) for a single transmission line outage. In this paper, with the help of the Newton Raphson method, the PIP and PIV were calculated with DIgSILENT Power Factory simulation software and contingency ranking was performed. Based on the load flow results and performance indexes, the Ethiopian Electric Power (EEP) North-West region network is recommended for an upgrade or the reactive power or series compensators should be constructed on the riskiest lines and substations.

Current networks are designed for peak loads leading to low utilization of power resources. In order to solve this problem, a heuristic energy-saving virtual network embedding algorithm based on the Katz centrality (Katz-VNE) is proposed. For solving an energy-saving virtual network embedding problem, we introduce the Katz centrality to represent the node influence. In order to minimize the energy consumption of the substrate network, the energy-saving virtual network embedding problem is formulated as an integer linear program, and the Katz-VNE is used to solve this problem. The Katz-VNE tries to embed the virtual nodes onto the substrate nodes with high Katz centrality, which is effective, and uses the shortest paths offering the best factor of bandwidths to avoid the hot nodes. The simulation results demonstrate that the long-term average energy consumption of the substrate network is reduced significantly, and the long-term revenue/cost ratio, the acceptance rate of virtual network requests, and the hibernation rate of substrate nodes as well as links are improved significantly.

The purpose of this paper is to show possibility and advantages of initial control plane reproduction for an adaptive fuzzy controller. Usually the fuzzy control is used when the object is not very well known. Yet the truth is, however, that some, at least general information about the object, is available. Usually, in such a case, optimization algorithms are used to tune the control structure. The purpose of this article is to show how to find a starting point that is closer to optimum than a statistically random point, and this way to obtain better results in a shorter time.

In this paper, a rotor current fault monitoring method is proposed based on a sliding mode observer. Firstly, the state-space model of the Double-Fed Induction Generator (DFIG) is constructed by vector transformation. Meanwhile, the stator voltage orientation vector control method is applied to decouple a stator and rotor currents, so as to obtain the correlation between the stator and rotor current. Furthermore, the mathematical model of stator voltage orientation is obtained. Then a state sliding mode observer (SMO) is established for the output current of the rotor of the DFIG. The stability and reachability of the system in a limited time is proved. Finally, the system state is determined by the residuals of the measured and estimated rotor currents. The simulation results show that the method proposed in this paper can effectively monitor the status: a normal state, voltage drop faults, short-circuit faults between windings, and rotor current sensor faults which have the advantages of fast response, high stability.

In this paper, a study of the lightning phenomenon and its harmful effect on Aqaba Thermal Power Station (ATPS), located in the south-western border of Jordan, is presented using the Electromagnetic Transients Program – Alternative Transients Program (EMTP- ATP). This study has been arisen due to an installation need of appropriate lightning arresters (LAs) for the 15/410 kV step-up transformers of the ATPS to eliminate the destructive effect of lightning. The simulation is carried out for two cases, once without using LAs and once more with using them. Two scenarios are applied for each of these cases, once when lightning strikes the primary side of the transformer and once more when it strikes the secondary side. The results obtained by the simulation indicate the necessity of LAs installation. This study, with using the EMTP-ATP program, is done for the first time with additional details that help researchers, designers, and engineers to get a broad overview of the ATPS in order to protect it against lightning.

With the availability of UHV engineering technology, the scale of the power network is expanding, and the level of the short-circuit current is getting higher, which brings hidden trouble to the safe and stable operation of the power network. Further this article issued a method that optimized the configuration of a current limiter based on the reliability of the power network. According to the reliability analysis under the influence of a short circuit, the quantitative evaluation of reliability of the power network is realized by the calculation of the short-circuit current.Aquantitative model is established among reliability evaluation and the short-circuit current as well as load loss, the candidate installation site of a current limiter can be determined according to reliability quantification results. This method uses the particle swarm optimization algorithm to optimize the distribution of the limiter, aiming at the reliability level and the minimum number of current limiters in the short circuit of a power grid. Finally, taking the actual power grid of a province as an example, the result shows that this method can reduce the search space of the optimal solution, optimize the configuration of the current limiter, and effectively limit the short-circuit current and improve the reliability of the power network.

The article presents studies on the electromechanical system of a metallurgical horizontal looper in the steelmaking industry. During the operation of this unit, parameters in the system changes due to variations of length and mass of the steel strip, these variations significantly change elastic properties and reduce moments of inertia. Various methods of combating elastic vibrations in electromechanical systems are analyzed in this article. The article presents a description of experiments with a horizontal looper. A mathematical model for two extreme positions of the unit was developed based on experimental results. Simulation experiments were made and their results are presented. A new control system structure is proposed to reduce vibrations in the electromechanical system of a horizontal looper. A power-up sensor, adjuster and velocity derivative feedback were added into the model structure. The proposed feedback link structure takes into account the change of steel strip length. From the experimental data it follows that the proposed system provides effective damping of mechanical vibrations in the steel strip if its length during operation is changed.

When a single line-to-ground fault occurs in the ungrounded distribution system, the steady-state fault current is relatively small for fault analysis and the transient fault current is observable, which can be used for faulted feeder identification and location. The principal frequency component retains most of the characteristics of the transient current. The principal frequency is related to the distance from the fault point to the substation and can be used for fault location. This paper analyzes the sequence network model of a single line-to-ground fault in the distribution network, and gives a method for principal frequency calculation. Depending on the characteristics of the maximum amplitude of the principal frequency component of the faulted feeder, the method of faulted feeder identification is given. Based on the complementary characteristics of the phase angle of the principal frequency component of the fault current and the phase angle at the substation bus, the faulted section location is carried out. MATLAB simulation is used to verify the effectiveness of the faulted feeder identification and location method.

The grid integration of large-scale wind and solar energy affects the power flow of wind-PV-thermal-bundled power transmission systems and may introduce an unpredicted threat to the power system’s small signal stability. Meanwhile, a power system stabilizer (PSS) and static synchronous series compensator (SSSC) play an important role in improving the static and dynamic stability of the system. Based on this scenario and in view of the actual engineering requirements, the framework of wind-PV-thermal-bundled power transmitted by an AC/DC system with the PSS and SSSC is established considering the fluctuation of wind and photovoltaic power output and the characteristics of the PSS and SSSC. Afterwards, the situation model is constructed in the IEEE 2-area 4-unit system, and the influence of the PSS and SSSC on the system stability under different operating conditions is analyzed in detail through eigenvalue analysis and time-domain simulation. Finally, an index named the gain rate is defined to describe the improvement of the stability limitations of various wind-PV-thermal operating conditions with the PSS and SSSC. The results indicate (K) that the damping characteristics, dynamic stability and stability limitations for various wind-PV-thermal operating conditions of the wind-PV-thermal-bundled power transmission system can be significantly improved by the interaction of the PSS and SSSC.

A lightning protection system (LPS) of an urban 110 kV substation is designed and analysed according to NFPA 780 and IEC 62305-3 standards. The analysis of the LPS is established on the value of risk assessment. The total area of the plant is described by one soil layer with uniform resistivity. This study aims to improve the understanding of an unexpected manner of the grounding system beneath lightning currents by clarifying the basic concepts of the lightning protection level and the new design procedure in this paper was clarified according to NFPA-780 level 1 for a lightning protection system. The program is integrated with the CDEGS software, which provides effective geometrical modeling with object and result visualization. Furthermore, module and automated fast Fourier transform (FFT) is implemented in this study to simulate electromagnetic fields in the time and frequency domains. These current values are compared to the desired protection levels within the standards. The study results show that for the improved protection of the system against lightning, the total power grid must be considered as a source of improvement for studying shielding influence and the protection levels provided inside this substation.

Large-signal input characteristics of three DC–DC converter types: buck, boost and flyback working in the continuous conduction mode (CCM), obtained by simulations and measurements are investigated. The results of investigations are presented in the form of the analytical formulas and the exemplary results of the measurements and two forms of simulations: based on the full description of the converter components and on the averaged models. The parasitic resistances of the converter components are included in the simulations and their influence on the simulation results is discussed.