Archives of Electrical Engineering

This paper deals with the finite element analysis of the demagnetization process of the line start permanent magnet synchronous motor. Special attention has been paid to demagnetization risk assessment after resynchronization during a short-term supply power outage. The current and torque waveforms have been determined assuming the difference depending initial rotor position angle. It has been demonstrated that the highest demagnetization risk occurs when resynchronization (motor reclosing) is performed whe induced electromotive forces are in anti-phase to the supply voltage waveforms. The effect of cage winding resistance on the risk of demagnetization is examined and discussed.

This paper presents an innovative solution for increasing life of lead-acid batteries used in a glider launcher. The study is focused on upgrading a charging system instead of a costly full replacement of it. Based on literature review, the advanced three-stage charging profile was indicated. The new topology of the power converter was proposed and a simulation model was developed. A simulation study was performed which leads to a conclusion that the suggested solution can be successfully applied to the studied device. As a result, the conclusion of this work is the recommendation for modification of the launching system with an additional converter enabling 3 stage charging.

Against the background of increasing installed capacity of wind power in the power generation system, high-precision ultra-short-term wind power prediction is significant for safe and reliable operation of the power generation system. We present a method for ultra-short-term wind power prediction based on a copula function, bivariate empirical mode decomposition (BEMD) algorithm and gated recurrent unit (GRU) neural network. First we use the copula function to analyze the nonlinear correlation between wind power and external factors to extract the key factors influencing wind power generation. Then the joint data composed of the key factors and wind power are decomposed into a series of stationary subsequence data by a BEMD algorithm which can decompose the bivariate data jointly. Finally, the prediction model based on a GRU network uses the decomposed data as the input to predict the power output in the next four hours. The experimental results show that the proposed method can effectively improve the accuracy of ultra-short-term wind power prediction.

Frequency regulation is in a first line of preference for an interconnected power system. Presence of nonlinearities in the generation systems further raises the complexity level of the problem. In this scenario, this article presents a robust Automatic Generation Control (AGC) mechanism to maintain the frequency and tie-line power of the power system to their nominal values. A Coefficient Diagram Method (CDM) based AGC mechanism including an AC/DC tie-line and Unified Power Flow Controller (UPFC) has been developed and the performance in handling the frequency regulation has been analyzed. The nonlinearities such as Governor Dead-Band (GDB) and Generation Rate Constraint (GRC) are included in the system to analyze the proposed AGC scheme in a more realistic approach. The AC/DC tie-line and UPFC which are included in the proposed AGC scheme provides an immense strength to handle the active power variation as-well-as frequency regulation. To develop a more effective AGC scheme, the parameters of an AC/DC tie-line and UPFC are optimized by successful implementation of the Fruit Fly Optimization Algorithm (FOA). The justification of the proposed AGC scheme has been carried out through a step by step verification such as justifying the CDM based controller, effectiveness of the proposed scheme and robustness of the system against parameters variation. The CDM based controller has been compared with the conventional controllers to elevate the effectiveness and the supremacy of the proposed AGC scheme has been examined by comparing with previously published work. The design and simulation of the work has been carried out by the MATLAB/Simulink® tool box.

The concentrated winding (CW) is obviously different from the traditional distributed winding (DW) in the arrangement of windings and the calculation of winding factors, which will inevitably lead to different performances of the permanent magnet synchronous motor (PMSM). In order to analyze the differences between the CW and the DW in the performance, a 3 kW, 1500 r/min PMSM is taken as an example to establish a 2-D finite element model. The correctness of the model is verified by comparing experimental data and calculated data. Firstly, the finite element method (FEM) is used to calculate the electromagnetic field of the PMSM, and the performance parameters of the PMSM are obtained. On this basis, the influences of the two winding structures on the performance are quantitatively analyzed, and the differences between the two winding structures on the performance of the PMSM will be determined. Finally, the differences of efficiency between the two winding structures are obtained. In addition, the influences of the winding structures on eddy current loss are further studied, and the mechanism of eddy current loss is revealed by studying the eddy current density. The analysis of this paper provides reference and practical value for the optimization design of the PMSM.

Accurate information on Induction Motor (IM) speed is essential for robust operation of vector controlled IM drives. Simultaneous estimation of speed provides redundancy in motor drives and enables their operation in case of a speed sensor failure. Furthermore, speed estimation can replace its direct measurement for low-cost IM drives or drives operated in difficult environmental conditions. During torque transients when slip frequency is not controlled within the set range of values, the rotor electromagnetic time constant varies due to the rotor deep-bar effect. The model-based schemes for IM speed estimation are inherently more or less sensitive to variability of IM electromagnetic parameters. This paper presents the study on robustness improvement of the Model Reference Adaptive System (MRAS) based speed estimator to variability of IM electromagnetic parameters resulting from the rotor deep-bar effect. The proposed modification of the MRAS-based speed estimator builds on the use of the rotor flux voltage-current model as the adjustable model. The verification of the analyzed configurations of the MRAS-based speed estimator was performed in the slip frequency range corresponding to the IM load adjustment range up to 1.30 of the stator rated current. This was done for a rigorous and reliable assessment of estimators’ robustness to rotor electromagnetic parameter variability resulting from the rotor deep-bar effect. The theoretical reasoning is supported by the results of experimental tests which confirm the improved operation accuracy and reliability of the proposed speed estimator configuration under the considered working conditions in comparison to the classical MRAS-based speed estimator.

This paper presents the application of an improved ant colony optimization algorithm called mixed integer distributed ant colony optimization to optimize the power flow solution in power grids. The results provided indicate an improvement in the reduction of operational costs in comparison with other optimization algorithms used in optimal power flow studies. The application was realized to optimize power flow in the IEEE 30 and the IEEE 57 bus test cases with the objective of operational cost minimization. The optimal power flow problem described is a non-linear, non-convex, complex and heavily constrained problem.

In the hybrid multiple H-bridge topology of beam supply, the load change of a DC/DC full-bridge converter can greatly affect the output voltage during onsite operation. An improved sliding mode control (SMC) strategy is thus proposed in this paper, where the rate of switching control is added to the law of system equivalent control to create a law that can realize a complete sliding mode control. Considering the special operating conditions of the load can have an influence on the performance of the controller, the impact of uncertainty existing in onsite conditions is suppressed with the proposed strategy utilized. The validity of the proposed strategy, finally, is verified by simulation, which proves the outperformance of the system in both robustness and dynamics.

Sections of the superconducting magnets of the SIS100 particle accelerator, under construction at the Facility for Antiproton and Ion Research (FAIR), the Society for Heavy Ion Research (GSI), Darmstadt, are going to be connected with the by-pass lines. Each line will be used to transfer a two-phase helium flow and an electric current. The electric current will be carried by four pairs of superconducting Nuclotron-type cables. Fast-ramping currents are expected to cause the generation of heat within the cables. In this work the results of a numerical thermal analysis of a bus-bar are presented. The amount of heat transferred from the environment was found based on geometric dimensions of the line and applied insulation. The amount of hysteresis loss, generated in the cable during the operation under most demanding regime of the operation of the accelerator, was calculated. According to the amount of the generated heat, the amount of the hysteresis loss is low in relation to the heat generated in the superconducting magnets. Also it was found that the cable used in the line still retains a large margin of current-carrying capacity.

Energy storage technology (EST) is an effectiveway to improve the power quality of renewable energy generation (such as solar energy and wind energy), but a single energy storage system (ESS) is difficult to meet the demand for the safe operation of the grid. According to the structure and operation characteristics of the existing battery/super-capacitor hybrid energy storage system (HESS), a battery/super-capacitor HESS is proposed. The working principle and three working modes (the super-capacitor pre-charging cold stand-by mode, the boost mode and buck mode) of the HESS are analyzed in detail. The state equations of the boost mode and buck mode are derived. The state space average method is used to establish the small signal equivalent model under the buck/boost mode. More-over, the charge and discharge control strategy of the HESS is obtained by combining the voltage closed-loop control. The simulation model is built in Matlab/Simulink to verify the effectiveness of the proposed HESS and its control strategy. The results show that the HESS and its control strategy can ensure the DC bus voltage has good stability and superior anti-interference, and it can simultaneously provide large current, increase the battery life, and improve the technical economy of energy storage.

Photovoltaic (PV) cells are very costly because of the silicon element which is not cheaply available. Usually, PV cells are preferred to be used at maximum efficiency. Therefore, PV plants are emphasized to extract maximum power from PVcells. When inertia free PV plants are integrated into the grid in large numbers, the problem of maintaining system stability subjected to load perturbation is quite difficult. In response to this, a control topology is being an approach to make available the PV cells in maintaining system stability by utilizing the system frequency deviation as feedback to the controller. To implement this, the PVs are operated at Maximum Power Point Tracking (MPPT). This allows the PV to operate at Pseudo Maximum Power Point tracking (PMPPT) which makes it possible to run the PV with reserve power capacity without employing a battery for storage. The control strategy has been implemented over a two-stage power conversion model of the PV system. The simulation results showed that the proposed control PMPPT topology is effective in frequency regulation capability as compared to the MPPT technique.

Circuit Breakers (CBs) play an important role in ensuring the safe operation of protection systems. Condition Monitoring (CM) devices are widely implemented to extend lifetime, and to improve the maintenance quality. The present paper proposes a cost-based prioritization approach for CBs in a network equipped withCMdevices. To this end, a mathematical formulation is developed for the categorization and modeling of equipment failures based on their severity. This formulation quantifies the effect of the CM devices on the outage rate of the equipment. The reliability parameters of the substations 400/132/20 KV, including the failure rate, λ, average repair time, r, average outage time, U, substations, in two status of without CM and with CM of the CBs are calculated. These parameters are calculated implementing a minimal cut-set method. The outage rate of equipment with and without the CM devices is used to determine the effect of the CM devices on the reliability of the network. Finally, the prioritization of substations to install theCMdevices on the CBs has been investigated in terms of the Expected Energy Not Supplied (EENS) and costs of CM. To verify the effectiveness and applicability of the method, the proposed approach is applied to the CBs in the power transmission network in the Khorasan Regional Electricity Company (KREC) in Iran.

In this article a three-dimensional mathematical model of radiofrequency ablation during open-heart surgery is presented. It was developed to study temperature field distribution into myocardial tissue. This model uses an anatomically correct 3D model for the left atrium, obtained by magnetic resonance imaging (MRI) processing of a patient; takes into account thermoelectric characteristic differences depending on the area of electric current application; considers cooling by the air flow. An ex-vivo experiment on the pig’s heart was performed where the depth of myocardium tissue damage was measured for the model validation. It was shown that the deviation of the model data from the experiment is within the limits of instrumental measurement error. The developed model is proposed to be used for heart ablation procedures planning, or new equipment development.

Wind and solar radiation are intermittent with stochastic fluctuations, which can influence the stability of operation of the hybrid system in the grid integrated mode of operation. In this research work, a smoothing control method for mitigating output power variations for a grid integrated wind/PV hybrid system using a battery and electric double layer capacitor (EDLC) is investigated. The power fluctuations of the hybrid system are absorbed by a battery and EDLC during wide variations in power generated from the solar and wind system, subsequently, the power supplied to the grid is smoothened. This makes higher penetration and incorporation of renewable energy resources to the utility system possible. The control strategy of the inverter is realized to inject the power to the utility system with the unity power factor and a constant DC bus voltage. Both photovoltaic (PV) and wind systems are controlled for extracting maximum output power. In order to observe the performance of the hybrid system under practical situations in smoothing the output power fluctuations, one-day practical site wind velocity and irradiation data are considered. The dynamic modeling and effectiveness of this control method

As for a single line-to-ground fault in an ungrounded distribution system, the power-frequency current is too low to detect the fault. The transient current is more palpable than that at a power-frequency of 50 or 60 Hz. It is an effective method to estimate the fault using the transient fault current. To analyze and calculate the transient current of single line-to-ground faults, an equivalent circuit is proposed in this paper. This model is based on distributed parameters of power lines. And it contains positive, negative and zero sequence information. The transient equivalent circuit consists of equivalent resistance, equivalent inductance and equivalent capacitance. And the method of calculation the equivalent ele- ments is also submitted.MATLAB simulation results showthat the newtransient equivalent circuit has higher accuracy and stronger adaptability compared with the traditional one.

This paper presents a review of the electromagnetic field and a performance analysis of a radial flux interior permanent magnet (IPM) machine designed to achieve 80 kW and 125 Nmfor an electric and hybrid traction vehicle. The motor consists of a 12-slot stator with a three-phase concentrated winding as well as an 8-pole rotor with V-shaped magnets. Selected motor parameters obtained from an IPM prototype were compared with the design requirements. Based on the electromagnetic field analysis, the authors have indicated the parts of the motor that should be redesigned, including the structure of the rotor core, aimed at enhancing the motor’s performance and adjusting segmentation for magnet eddy current loss reduction. In addition, iron and PM eddy current losses were investigated. Moreover, transient analysis of current peak value showed that the current may increase significantly compared to steady-state values.Amap of transient peak current load vs. torque load plotted against rotor speed was provided. Based on the numeric and analytical results of physical machine parameters, the authors indicate that collapse load during the motor’s operation may significantly increase the risk of permanent magnet (PM) demagnetization. It was also found that collapse load increases the transient torque, which may reduce the lifetime of windings.