bluuebunny/crossref_metadata_2025 huggingface dataset:
Reinforcement learning‐based spectrum handoff scheme with measured PDR in cognitive radio networks
Authors: Shi Qianqian , Shao Wei , Fang Bing , Zhang Yan , Zhang Yunyang
Published: October 2019

Spectrum handoff plays an important role in cognitive radio networks (CRNs). Secondary users (SUs) use spectrum handoff to hold on the idle channel or to free the channel for primary users (PUs). Spectrum handoff scheme greatly affects the transmission quality and the success rate of SUs connection. In this Letter, a reinforcement learning‐based spectrum handoff scheme with the measured packet drop rate (PDR) for multimedia transmissions over CRNs is proposed. In a system model with multiple PUs and SUs, a new state space description method is designed and an observed state includes not only the status whether PUs arrive on each channel but also several other important factors. Also, the measured PDR, instead of the calculated one, is presented to update the mean opinion score, the Q‐table and the handoff policy. Compared with the existing schemes with the calculated PDR from the Quality‐of‐Experience model, the authors' proposed scheme can converge more rapidly in the dynamic radio environment, and reduce the PDR of SUs more significantly.
Performance enhancement of dual‐band antenna for internet of things applications using closed loops
Authors: Kim M. , Qu L. , Shin H. , Kim H.
Published: October 2019

In this Letter, a dual‐band antenna with improved performance is proposed by generating a stronger coupling with the ground plane using two closed loops. The antenna is designed in such a way that it is coupled with two orthogonal ground modes in the lower and higher bands. Two closed loops are attached at the end of the ground plane to control the frequencies of the two ground characteristic modes. Through simulation and experimental verification, the proposed antenna has obtained greatly improved performance in both bands compared to the reference antenna without closed loops.
Deep feature based efficient regularised ensemble for engagement recognition
Authors: Park Y.‐m. , Lee G.‐M. , Yang H.‐S.
Published: October 2019

Over the years, open education in online environments, such as Massive Online Open Courses, has grown rapidly. While the trend is expected to bridge the educational gap among students, the new environment has also created new challenges such as the lack of feedback and difficulties in interaction. The authors propose an automated engagement recognition system to alleviate this problem, driven by the recent developments in computer vision and artificial neural networks. The authors' proposed system extracts deep features from a facial image and employs a combination of multiple regularised shallow networks to recognise engagement. They verified the system in a public data set. The proposed system has faster learning speed and better accuracy than single deep network based approaches do.
Precise methods for distinguishing S‐box faults in laser injection attacks
Authors: Zhang Fan , Zhang Yiran , Jiang Huilong , Zhu Xiang , Lin Feng , Ren Kui
Published: October 2019

Fault attack is a type of active attack which retrieves the secret key by injecting computational faults. Laser is one of the most common fault injection methods. When attacking substitution‐permutation networks‐ciphers, S‐box is often chosen as the laser injection target. However, the adversary has to know whether the S‐box is corrupted or not after each injection, which was difficult in real‐world attacks. Two analysing methods to distinguish the S‐box faults for different ciphers is proposed in this Letter. A laser‐based physical experiment is carried out to verify the authors' methods on Advanced Encryption Standard and PRESENT ciphers on an ATmega163L microcontroller. Experimental results show that their methods can precisely distinguish S‐box faults merely using dozens of ciphertexts.
Understanding insulation failure of nanodielectrics: tailoring carrier energy
Authors: Li Shengtao , Xie Dongri , Lei Qingquan
Published: October 2019

Owing to the formation of interface and new feature of which, the properties of nanodielectrics can be improved. ‘Hard/soft interface’ and its trap distribution can be tailored by functionalised groups. Molecular simulation results show that the interaction energy and electrostatic potential are larger for the soft interface, which indicates the greater bonding strength with the polymer matrix and electrostatic force on charge carriers. Charge transport simulation indicates that the accumulation of homo‐charges would form a reverse electric field and distort electric field distribution. The injection depth would be restricted at the vicinity of sample/electrodes due to the greater trapping effect of deep traps, thus weakening the distortion in the sample bulk, thereby decreasing carrier energy and delaying the formation of impact ionisation. Based on the accumulation of carrier energy Φ = Eeλ, the idea of suppressing electron free path and carrier energy to enhance the insulation breakdown is confirmed. The classified effects of nanofillers during dc breakdown and corona‐resistant are further understood from carrier energy. The introduced interfacial trap is effective in trapping carriers due to the low carrier energy under dc voltage, while ineffective in blocking the energetic charges during corona‐discharge, but nanoparticles exert blocking and scattering effect against the energetic charges.
Wireless information and power transfer with optimal transmit antenna selection
Authors: Hayajneh Maymoona , Gulliver Thomas Aaron
Published: October 2019

A dual hop, half‐duplex amplify and forward (AF) relay is considered for a source equipped with multiple transmit antennas. A power splitter is employed at the relay to harvest energy from the signal received from the source. The outage probability (OP) is derived considering optimal antenna selection to maximise the end‐to‐end signal‐to‐noise ratio. It is shown that the performance of the proposed energy harvesting based scheme improves with the number of transmit antennas. The effect of the power splitting factor on the OP is studied for different relay locations. Further, the OP is examined for different distances between the source and relay.
Real‐valued off‐grid DOA estimation based on fourth‐order cumulants using sparse Bayesian learning in spatial coloured noise
Authors: Pan Meihong , Zhang Gong , Hu Zhentao , Zheng Qin
Published: October 2019

In this study, the authors address the problem of off‐grid sparsity‐inducing direction‐of‐arrival (DOA) estimation in the context of real‐valued fourth‐order cumulants (FOC) in the presence of spatially coloured noise. Firstly, a selection matrix is constructed to eliminate the redundant data of FOC and rearrange the data in the de‐redundant FOC matrix to facilitate real processing. Then a new virtual overcomplete dictionary is constructed with coupling symmetric property by linear transform with the selection matrix. Next, the FOC matrix is transformed into a real‐valued matrix via a unitary transformation which can be sparsely represented by a real‐valued virtual overcomplete dictionary. The real‐valued sparse model is vectorised for transforming to a single measurement vector (SMV) model, and the redundant data in the vector model is further removed by another selection matrix. Finally, an off‐grid sparse model based on the real‐valued SMV is established and solved by utilising the SBL strategy. The proposed method not only reduces the computational complexity but also obtains an extended‐aperture array with increased degrees of freedom which yields high resolution, and provides superiority in performance and robustness against coloured noise. The simulation results demonstrate the effectiveness of the proposed method.
Optimal power allocation for energy‐efficient full‐duplex cognitive relay networks under primary interference
Authors: Poornima S. , Babu A.V.
Published: October 2019

This study investigates optimal power allocation (OPA) for maximising the energy efficiency (EE) of dual‐hop underlay full‐duplex cognitive relay network, under the influence of interference from primary source. The OPA for the EE optimisation is constrained on the maximum transmit power of the secondary nodes and the interference threshold power which can be tolerated at the primary destination. The authors convert the initial non‐convex optimisation problem to a concave fractional programming form and propose an iterative algorithm using parametric transformation to find the OPA vector. Further, they prove that the point of convergence of the proposed iterative algorithm is a Karush–Kuhn–Tucker point of the initial non‐convex problem. They numerically demonstrate the EE improvement achieved by the proposed algorithms over equal power allocation strategy.
Non‐linear‐disturbance‐observer‐enhanced MPC for motion control systems with multiple disturbances
Authors: Yan Yunda , Yang Jun , Sun Zhenxing , Li Shihua , Yu Haoyong
Published: October 2019

This study addresses the optimised tracking problem for motion control systems with multiple disturbances by a non‐linear‐disturbance‐observer‐enhanced continuous‐time model predictive control (MPC) method. The core is to predict the future tracking error and desired control input (including the lumped effects of disturbances/uncertainties) in the receding‐horizon by a higher‐order sliding mode disturbance observer, which is designed based upon a rough nominal system. Different from the direct compensation approach in most existing composite MPC methods, disturbance estimates are taken full advantage in the optimisation. The explicit relationship between asymptotic stability and weights in the performance index is provided. Simulations on position control of the robot arm system and experiments on speed regulation of the permanent magnet synchronous motor servo system are both presented to demonstrate the workability.
Guaranteed cost control for Markovian jump systems with controller failures
Authors: Wang Guoliang , Xu Lei
Published: October 2019

This study focuses on the guaranteed control problem of continuous‐time Markovian jump systems. Different from the traditionally guaranteed controllers, a kind of failure‐tolerant controller is proposed. Particularly, the dwell times of controller suffering failures or not are constants. A Lyapunov function approach is used to analyse its stability, which could lead to convex conditions depending on such dwell times. Because of these conditions being LMIs, they could be tested and used to compute control gains easily. Two examples are used to demonstrate the effectiveness and superiority of the proposed methods.
Stochastic LQ control under asymptotic tracking for discrete systems over multiple lossy channels
Authors: Ling Rongyao , Feng Yu , Claveau Fabien , Chevrel Philippe
Published: October 2019

This study addresses the asymptotic tracking problem subjected to linear quadratic (LQ) constraints for linear discrete‐time systems, where packet dropout occurs in actuating channels. To solve this objective control problem, the controller‐coding co‐design approach is adopted, i.e. the controller, encoder and decoder are designed for taking full advantage of the network resource collaboratively, thereby achieving better transmission of control signals. A stabilisability condition in the mean square sense that reveals the fundamental limitation among the norm of the plant, data arrival rates and coding matrices is first derived. Then, a solvability condition is conducted to handle the additional stochastic LQ control objective by a modified discrete‐time algebraic Riccati equation, and an iterative algorithm is also given for designing the corresponding state feedback gain and coding matrices. Relied on such design, the asymptotic tracking constraint is further fulfilled through solving a Sylvester equation, and the feedforward gain related to tracking is parameterised. Finally, a simulation with the implementation of the design method on two cooperative robots is included to show the effectiveness of the current results.
Stability analysis of discrete‐time positive polynomial‐fuzzy‐model‐based control systems through fuzzy co‐positive Lyapunov function with bounded control
Authors: Li Xiaomiao , Mehran Kamyar , Lam Hak Keung , Xiao Bo , Bao Zhiyong
Published: October 2019

This study employs a novel fuzzy co‐positive Lyapunov function to investigate the stability of discrete‐time polynomial‐fuzzy‐model‐based control systems under positivity constraint. The fuzzy co‐positive Lyapunov function consists of a number of local sub‐Lyapunov function candidates which includes the positivity property of a non‐linear system and the contribution of each sub‐Lyapunov function candidates depends on the corresponding membership functions. Imperfect premise matching design concept is used for the design of a closed‐loop polynomial fuzzy controller based on the constructed polynomial fuzzy model. The bounded control signal conditions (upper and lower boundary demands on control signal) are included in the Lyapunov stability and positivity conditions, in which all are formulated in the form of sum‐of‐squares conditions. A numerical example is given to validate the proposed approach.
Zonotopic fault detection observer design for discrete‐time systems with adaptively adjusted event‐triggered mechanism
Authors: Wang Xudong , Fei Zhongyang , Wang Zhenhua , Yu Jinyong
Published: October 2019

This study addresses the event‐triggered fault detection for a class of discrete‐time systems with unknown but bounded external disturbance and measurement noise. In order to save limited network bandwidth, an adaptively adjusted event‐triggered scheme is designed by considering the probability of system failure and the fault detection progress. Based on the event‐triggered system output, an fault detection observer is well designed in finite frequency ranges, such that the generated residual is sensitive to injected faults and robust against disturbance and noise. Moreover, a novel zonotope‐based residual evaluation strategy is constructed to reduce conservatism by considering the impacts of external disturbance, measurement noise and measured error caused by event‐triggered scheme. Finally, simulation results are provided to demonstrate the effective performance of the proposed event‐triggered fault detection strategy.
Robustness of ToF and stereo fusion for high‐accuracy depth map
Authors: Bao Zhenshan , Li Bowen , Zhang Wenbo
Published: October 2019

A depth map can be used in many applications such as robotic navigation, driverless, video production and 3D reconstruction. Both passive stereo and time‐of‐flight (ToF) cameras can provide the depth map for the captured real scenes, but they both have innate limitations. Since ToF cameras and passive stereo are intrinsically complementary for certain scenes, it is desirable to appropriately leverage all the available information by ToF cameras and passive stereo. As a result, this study proposes an approach to integrate ToF cameras and passive stereo to obtain high‐accuracy depth maps. The main contributions are: the first step is to design an energy cost function to utilise the depth map from ToF cameras to guide the stereo matching of passive stereo and the second step is to design their weight function for depth maps pixel‐level fusion. The experiments show that the proposed approach achieves the improved results with high accuracy and robustness.
Partial bundle adjustment for accurate three‐dimensional reconstruction
Authors: Luo Keyang , Pan Hailong , Zhang Yang , Guan Tao
Published: October 2019

Structure from motion aims at estimating the cameras and sparse structure of the scene globally, but the approximation biases in bundle adjustment and the propagated errors among the registered cameras and triangulated points reduce the quality of the reconstruction. To improve the accuracy of the reconstruction, the authors present an efficient subgraph‐based approach to optimise the visibility graph locally. The central idea is to divide the visibility graph into well‐configuration subgraphs for partial bundle adjustment based on a Markov random field, reconstruct the dense local points via the subgraph‐based multi‐view stereo matching, and then merge them into a consistent scene to extract the complete surface. They evaluate the proposed algorithm on several real and synthetic datasets, and the results demonstrate that their algorithm can improve the reconstruction quality significantly and maintain an inexpensive computation cost in the meanwhile.
Moving vehicle tracking based on improved tracking–learning–detection algorithm
Authors: Dong Enzeng , Deng Mengtao , Tong Jigang , Jia Chao , Du Shengzhi
Published: October 2019

This study addresses the tracking–learning–detection (TLD) algorithm for long‐term single‐target tracking of moving vehicle from video streams. The problems leading to tracking failures in existing TLD methods are discovered, and an improved TLD (ITLD) tracking algorithm is proposed which is more robust to object occlusion and illumination variation. A square root cubature Kalman filter (SRCKF) is employed in the tracker of TLD to predict the position of the object when occlusion occurs. Besides, this study introduces fast retina keypoint (FREAK) feature into the tracker to alleviate the instability caused by illumination variation or scale variation. The overlap comparison and the normalised cross‐correlation coefficient (NCC) are introduced to the integrator of the TLD to obtain reliable bounding boxes with improved tracking precision. Experiments are conducted to compare the performance of the state‐of‐the‐art trackers and the proposed method, using the object tracking benchmark that includes 50 video sequences (OTB‐50) and TLD datasets. The experimental results show that the proposed ITLD outperforms on both tracking accuracy and robustness. The proposed method can track a moving vehicle even when it is temporally totally occluded.
HGR‐Net: a fusion network for hand gesture segmentation and recognition
Authors: Dadashzadeh Amirhossein , Targhi Alireza Tavakoli , Tahmasbi Maryam , Mirmehdi Majid
Published: October 2019

We propose a two‐stage convolutional neural network (CNN) architecture for robust recognition of hand gestures, called HGR‐Net, where the first stage performs accurate semantic segmentation to determine hand regions, and the second stage identifies the gesture. The segmentation stage architecture is based on the combination of fully convolutional residual network and atrous spatial pyramid pooling. Although the segmentation sub‐network is trained without depth information, it is particularly robust against challenges such as illumination variations and complex backgrounds. The recognition stage deploys a two‐stream CNN, which fuses the information from the red–green–blue and segmented images by combining their deep representations in a fully connected layer before classification. Extensive experiments on public datasets show that our architecture achieves almost as good as state‐of‐the‐art performance in segmentation and recognition of static hand gestures, at a fraction of training time, run time, and model size. Our method can operate at an average of 23 ms per frame.
Analysis of end effect in ironless stator AFPM machine via MEC model
Authors: Gao Huamin , Zhang Zhuoran , Wang Chen , Geng Weiwei , Liu Ye
Published: October 2019

The Halbach‐array permanent magnet (PM) rotors can achieve higher air‐gap flux density due to magnetic flux gathering effect, which contributes to the higher‐torque density improvement of the ironless stator axial flux PM (AFPM) machine. However, the end leakage fluxes of the ironless stator AFPM machine are serious due to the large magnetic resistance of the main flux loop in ironless stator machines. Circular arc straight line permeance model is adopted to calculate magnet‐to‐magnet and magnet‐to‐rotor end leakage fluxes based on the analysis of the relationship between end leakage fluxes and coils. A magnetic equivalent circuit (MEC) model is established considering end leakage fluxes. The leakage coefficients representing the ratio of end leakage fluxes to main flux and radial coefficients representing effective radial lengths of end leakage fluxes are analysed via the MEC model. The coefficients vary with machine parameters including PM thickness, rotor yoke thickness and air‐gap length. On the basis of the analysis results, the influence factors of end leakage fluxes are summarised and the 50 kW ironless stator AFPM machine is optimised. Finally, a 50 kW ironless stator AFPM machine with Halbach‐array PM rotors is prototyped to verify the results of the finite element analysis and MEC model.
Design methodology to optimise induction machines based stand‐alone electrical wind water pumping systems
Authors: Esmaeilian Hamidreza , Mohammadi Ebrahim , Fadaeinedjad Roohollah , Bakhshai Alireza , Rahnama Mohammad
Published: October 2019

A novel methodology for designing a wind‐electric water pumping system is developed in this study. The system employs a self‐excited induction generator (SEIG) driven by a wind turbine (WT) and an induction motor (IM) feeding a water pump. Selection of values and proper configuration of excitation capacitors for this system is the key factor which is performed by an optimisation algorithm. The methodology commences with the design of hydraulic system and choice of proper pump. Then, the gearbox ratio of the chosen WT is determined to coordinate the characteristic of the WT with that of the pump. The aim is operation of the system near the maximum power output of the WT in different wind speeds. Thereafter, the electrical system is designed by choosing the suitably rated powers for the SEIG and IM. The optimal capacitor values in various configurations, viz. the shunt, short shunt, long shunt, T, and Π, are calculated utilising the genetic algorithm and then, the best configuration considering the system operating conditions is introduced. The objective function is defined to regulate the IM operating point at the knee point of its magnetising characteristic under wind speed variations. The system performance is evaluated through simulation and experiment.
Analytical validation of novel consequent pole E‐core stator permanent magnet flux switching machine
Authors: Ullah Wasiq , Khan Faisal , Sulaiman Erwan , Umair Muhammad , Ullah Noman , Khan Bakhtiar
Published: October 2019

Flux switching machines (FSMs) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine. Permanent magnet FSM (PMFSM) is capable of high torque density and applicable for high‐speed application, however conventional PMFSM exhibits demerits of high PM volume, high torque ripples and significant stator flux leakage. In this paper, a novel consequent pole E‐core stator PMFSM is proposed and compared with conventional topology utilising 2D finite‐element analysis (2D‐FEA). Finite‐element analysis revealed that proposed design enhanced flux modulation effects by introducing flux bridges and flux barriers as a result reduced cogging torque by reducing 46.53% of the total PM volume, reduce torque ripples by reducing PM slot effects and reduce flux leakage utilising flux bridges in the stator. Furthermore, analytical model for flux linkages, cogging torque, mechanical torque, no load and on‐load magnetic flux density (MFD) is developed for initial design of conventional and proposed model. 2D analytical methodologies resolve equivalent magnetic circuits for open‐circuit flux linkages, Fourier analysis for cogging torque, Laplace equations for MFD and Maxwell stress tensor for mechanical torque. Finally, results obtained from 2D‐FEA and analytical methodologies are validated and compared.
Model‐based unified technique for identifying severities of stator inter‐turn and rotor broken bar faults in SCIMs
Authors: Sabouri Mehdi , Ojaghi Mansour , Faiz Jawad , Marques Cardoso Antonio J.
Published: October 2019

Condition monitoring is an essential technology for detecting various incipient defects in electrical machines. Stator inter‐turn and rotor broken bar faults are two major faults of the squirrel cage induction motors (SCIMs). Many attempts have been made to provide fault diagnosis systems for detecting the faults individually. This study proposes a novel unified fault diagnosis system for detecting the faults and identifying their exact severities. The system is based on a flexible model of the SCIM and can identify the severities of the faults even if they are presenting simultaneously. Robustness against the motor load change, the unbalance degree of the voltage supply and its distortion are the other merits of the proposed fault diagnosis system. Experimental results under various fault modes and operating conditions demonstrate the effectiveness of the proposed fault identification technique.
Segmented power supply control of double‐sided linear flux‐switching permanent magnet motor
Authors: Cao Ruiwu , Zhang Zheng , Lu Minghang , Jiang Ning
Published: October 2019

Current research shows that the double‐sided linear flux‐switching permanent magnet (DLFSPM) motor is suitable for electromagnetic launch systems, in which the armature windings and permanent magnets are set on the long primary stator, whereas the mover is only composed of yokeless iron. Thus, the DLFSPM motor incorporates the merits of high power density and efficiency of the linear permanent magnet synchronous motor and simple and robust structure of linear induction motor. To improve the power factor and decrease the inverter capacity, the segmented power supply control methods of the DLFSPM motor are investigated in this study. First, the structure, electromagnetic parameters, and the segmented power supply method of the DLFSPM motor are explored. Then, the mathematical models and the control strategies of the DLFSPM motor are deduced and proposed. Finally, the simulations and experiments of the DLFSPM motor are conducted to validate the study of segmented power supply method.
Parameter estimation of extended Jiles–Atherton hysteresis model based on ISFLA
Authors: Zou Mi
Published: October 2019

This study introduces an extended Jiles–Atherton (JA) hysteresis model, which considers dynamic loss and anisotropy. The two considerations facilitate an accurate non‐linearity representation of electromagnetic devices, thereby resulting in a precise agreement between the simulated and measured hysteresis loops. To achieve this goal, JA hysteresis model parameters must be estimated by an optimisation algorithm. Therefore, an improved shuffled frog‐leaping algorithm (ISFLA) is proposed in this study. Differential evolution (DE) mutation operator, adaptive step size factor, and inertia weight factor are considered. Then, the implementation of the ISFLA is discussed using MATLAB. The proposed ISFLA is verified by the measured hysteresis loops of grain‐oriented silicon toroidal core. The comparison between genetic algorithm, simulated annealing, DE, and ISFLA is discussed. Results show that the proposed ISFLA demonstrates better global optimum ability, lower computational burden, and faster convergence rate than the other three methods.
Investigation of linear synchronous reluctance motor for urban rail transit
Authors: Cao Ruiwu , Su Enchao , Lu Minghang , Si Jikai , Wang Kai
Published: October 2019

The long stator of linear synchronous reluctance motor (LSynRM) consists only of low‐cost permeable material. Hence, LSynRM has a good application prospect in long‐distance drive systems. What about the electromagnetic performance of LSynRM under the constraints of installation size of rail transit? What are the advantages of LSynRM compared with the existing linear induction motor (LIM)? Research is non‐existent in academic circles. The purpose of this study is to compare LSynRM with LIM used in rail transit and give a comprehensive evaluation. First, a LIM used in Guangzhou Metro was analysed. Second, the working principle of LSynRM was analysed, and the selection principles of key parameters were determined. On this basis, the relevant parameters were optimized by using two‐dimensional finite‐element analysis (FEA) software. Then, the output characteristics of LIM and LSynRM were compared. The influence of ferrite on LSynRM was explored in view of the low power factor. The influence of winding end effect is explored through three‐dimensional FEA. The thrust force and power factor of LSynRM are corrected and the model is adjusted. Finally, the system cost and energy consumption of the two motors based on Guangzhou Metro Line 4 were estimated and compared in detail.
Efficiency improvement and torque ripple minimisation of four‐phase switched reluctance motor drive using new direct torque control strategy
Authors: Reddy Pittam Krishna , Ronanki Deepak , Perumal Parthiban
Published: October 2019

The direct torque control (DTC) strategy is one of the most effective techniques, used to control the switched reluctance motor (SRM) with improved dynamic performance and reduced torque ripple. However, this approach draws a higher source current due to an extension of the phase current into the negative torque region, which lowers the net torque per ampere ratio. This study proposes a new DTC strategy for SRM to overcome this issue by modifying the partition of the sectors and appropriate voltage vector selection. Therefore, the proposed method improves the drive efficiency while minimising torque ripple. To implement this method, a non‐linear machine model is developed using the torque and flux characteristics obtained from experimental studies on a four‐phase 8/6 SRM. The proposed DTC scheme is implemented on a digital control platform and power loss calculations are performed to evaluate the drive efficiency. Test results show that the proposed DTC method has improved performance in terms of efficiency and torque ripple under various operating conditions in comparison to the conventional DTC strategy.
Design and analysis of a new partitioned stator flux‐modulation motor for direct drive applications
Authors: Zhu Xuhui , Zhao Wenxiang , Xu Liang , Ji Jinghua
Published: October 2019

In this study, in order to improve the torque density of the conventional permanent magnet (PM) motor, a flux‐modulation (FM) motor employing the magnetic gear effect is proposed. However, the FM motor has space conflict in the finite stator area, which limits the further improvement of torque density. Therefore, a new partitioned stator flux‐modulation (PSFM) motor with separated PM excitation and armature windings is artfully proposed. The main design parameters influence on the average electromagnetic torque in the proposed PSFM motor is investigated, together with the proposed FM motor. Furthermore, based on the optimal designs for the highest average electromagnetic torque in this study, the electromagnetic performances of the three motors, including back‐electromotive force performances, torque characteristics and several other performances with respect to speed are analysed by finite‐element method. Additionally in the PSFM motor, torque generation mechanism and the reduction method of torque ripple are theoretically analysed. Results show that the proposed PSFM motor exhibits 29.1% higher torque density than the FM motor and 87.6% higher than the conventional PM motor with reduced torque ripple and superior loss performance. Finally, the proposed PSFM motor is prototyped for verification.
Analytical model for magnetic‐geared double‐rotor machines and its d–q‐axis determination
Authors: Zhao Hang , Liu Chunhua , Song Zaixin , Liu Senyi , Lubin Thierry
Published: October 2019

This study presents an analytical sub‐domain model for the prediction of various electromagnetic parameters of magnetic‐geared double‐rotor machine (MGDRM). By dividing the MGDRM into six sub‐domains and solving the Maxwell equations in polar coordinates for each region, the vector magnetic potential distribution can be derived. Subsequently, the flux density distribution, back electromotive force, and output torque, can be calculated. Furthermore, based on the proposed model, the equivalent d–q‐axis is elaborated. Also, the corresponding d and q inductance can be obtained. It proves that the MGDRM can be regarded as a non‐salient‐pole synchronous machine. Besides, the power factor of the MGDRM under id = 0 control is deduced and optimised for the different thicknesses of modulators. In addition, the demagnetisation capability is analysed by adopting the sub‐domain model. Finally, the accuracy of proposed sub‐domain model for MGDRMs is validated via the finite‐element method (FEM).
Improving the performance of a lumped transmission line model used in electromagnetic transient analysis
Authors: Colqui Jaimis S.L. , de Araújo Anderson R.J. , Kurokawa Sérgio
Published: October 2019

A simplified methodology is proposed to reduce numerical oscillations in transient responses when transmission lines are represented by a lumped parameter approach employing a ‐circuit cascade. These oscillations cause erroneous peaks in electromagnetic transient simulations, which may lead to incorrect interpretations for users. A modified ‐circuit cascade, which consists of inserting a damping resistance in series to the capacitor in the traditional ‐circuit cascade, is a known topology in the literature, but its influence on transient responses has not been fully studied. In this study, a methodology is shown for selecting an appropriate adjustable factor to reduce the numerical oscillations for a given transmission line of length l without distorting the transient response. The proposed methodology is applied directly in line modelling, facilitating the selection of the damping resistance. The results obtained from the proposed methodology are compared with inverse numerical Laplace transform responses, which is a well‐established technique, and with the traditional lumped parameter model, showing an expressive attenuation of the numerical oscillations in the electromagnetic transient responses.
Modular multilevel converter based on arm transfer to clear dc fault
Authors: Wang Zhenhao , Liu Jie , Xiao Zhuang , Wang Chaobin , Li Guoqing
Published: October 2019

Modular multilevel converter (MMC) has great prospects in voltage source converter‐based high‐voltage direct current (HVDC) transmission. Although the typical half‐bridge MMC can bring huge economic benefits, it is unable to clear dc fault. An MMC based on arm transfer (AT‐MMC) and corresponding timing control are presented to effectively solve this drawback. Compared with the half‐bridge MMC, the AT‐MMC adds the arm‐transferring branch to the each phase unit of the converter and adds the current‐breaking branch and the energy‐absorbing branch to the dc line. Through these branches cooperating with each other, the fault current is cleared. Referring to the half‐bridge MMC with the same voltage grade, the AT‐MMC has a good economy and its additional device cost is low and additional conduction loss is very small. A model of 51‐level MMC–HVDC system is built in RT‐LAB OP5600 to verify the effectiveness of the proposed solution.
Early warning system for spatiotemporal prediction of fault events in a power transmission system
Authors: Sun Chenhao , Wang Xin , Zheng Yihui , Chen Shaoyi , Yue Yishi
Published: October 2019

Predictions of the spatiotemporal distribution of fault events help the management planning and the maintenance scheduling in power transmission systems. To this end, this study proposes an early warning system based on the exploration of cause‐attribute relationships. A comprehensive assessment of all the fault causes is conducted by incorporating entire available environmental attributes in the investigated system as inputs. To cope with the rarely occurred fault causes and environmental elements, a procedure of the weighted association rule mining is established. Then, a risk evaluation model is employed in evaluating the prediction performance and the risks of possible false predictions. Three requirements for the uncertainty are taken into account when this framework is applied in real use: technical reliability, internal reliability, and factitious effectiveness. An empirical study is conducted in a real power transmission system to verify the feasibility of the proposed framework, and the results prove that a flexible and robust prediction can be generated consequently.
Controlling a retailer's short‐term financial risk exposure using demand response
Authors: Brolin Magnus , Sandels Claes
Published: October 2019

The transition of the electric power system to reach sustainability goals leads to new market conditions with larger uncertainties. This constitutes new challenges and opportunities for new as well as for existing market players such as retailers. In a future more volatile and unpredictable market, financial risk management becomes an important element for such actors in order to achieve viable businesses. Different instruments can be applied for this purpose, where demand response can contribute in the short‐term to manage risks related to price variations and imbalance costs. This study contributes to the enhancement of retailer's businesses by presenting a stochastic optimisation model exploring the possibility to apply demand response to control financial risk exposure. The model considers trading and demand response scheduling for different customer clusters, generating optimal trading volumes for day‐ahead markets while also considering the possibility to trade intra‐day. The optimisation considers uncertainties in prices and loads as well as imbalance settlement costs. Risk management is integrated into the model by applying conditional value‐at‐risk as risk measures. The developed model has also been applied in a case study with data from the Swedish and Nordic electricity market together with simulated load profiles for different customer clusters.
Flexible feeder interconnections for increased penetration of renewables and improved volt/VAr control in distribution networks
Authors: Baghban‐Novin Salar , Golshannavaz Sajjad , Nazarpour Daryoush , Hamidi Amir
Published: October 2019

In this study, a daily distribution management system (DMS) is developed, which utilises the potential of soft open points (SOPs) to enhance the renewable share in power provision task. The active and reactive power contributions of SOPs, as a flexible interconnection, amend the voltage security issues due to high penetration of photovoltaics (PVs). A complete model for SOP is developed to address the conduction and switching losses that affect the technical and economic operation indices. The optimal scheduling framework of DMS is linearly modelled within mixed‐integer linear programming to lower the computational burden of the problem. Case studies are carried out on IEEE 33‐node system to illustrate and verify the effectiveness of the proposed model. The comparative analysis shows a lower operation cost besides the improved voltage profile and the reduced losses of the whole system. The effective collaboration of PVs and dispatchable distributed generations (DDGs) assisted by the SOPs power processes causes higher penetration of PVs and enhanced the exploitation of DDGs results in a 9.8% increment of PV power exploitation and improved power factor of DDGs operation.
HIF detection in distribution networks based on Kullback–Leibler divergence
Authors: Nezamzadeh‐Ejieh Shiva , Sadeghkhani Iman
Published: October 2019

A high‐impedance fault (HIF) is mostly associated with the arcing phenomenon, and its main features are low current, randomness, non‐linearity, and asymmetry. The low fault current of an HIF is a major challenge for overcurrent‐based protection system of distribution networks. Power loss, potential fire hazard, and electric shock are consequences of an undetected HIF. This study presents a time‐domain HIF detection algorithm based on monitoring the substation current waveform. Using the Kullback–Leibler divergence similarity measure, the non‐linearity, and asymmetry features of two subsequent half cycles of the current waveform are quantified as the HIF detection criterion. A time duration‐based criterion is also used to distinguish HIFs from the load, capacitor, feeder, and distributed energy resource switchings and the voltage sag and swell events. The proposed scheme satisfactorily works in the presence of non‐linear loads. Also, it does not require the training data set, transformation, and calculation of harmonic/sequence components. Extensive time‐domain simulation case studies using the IEEE 13 and 34 node test feeders demonstrate the merits of the proposed HIF detection algorithm.
Enhancing the distribution grid resilience using cyber‐physical oriented islanding strategy
Authors: An Yu , Liu Dong , Chen Bo , Wang Jianhui
Published: October 2019

The increasing penetration of distributed generations enables an innovative operation paradigm that allows islanded operation to enhance the resilience of the distribution grid. In this study, a cyber‐physical oriented islanding strategy is proposed by coordinating centralised and distributed control to achieve seamless islanding transition and operational flexibility in emergency conditions. A cyber‐physical control structure is developed to mitigate various disturbances (e.g. emergencies or fluctuations) according to different operation conditions. Specifically, the distributed fault isolation and seamless islanding transition are coordinated to mitigate the outage caused by unplanned islanding, while a secondary control is proposed to support primary control by reducing the power fluctuations during islanded operation. With a rapid response speed, the local cyber‐physical devices are coordinated to accomplish islanding separation by selecting a feasible islanded area even under an unplanned islanding situation. A field test was conducted on a practical distribution network in China, and the results demonstrated the effectiveness and feasibility of the proposed islanding strategy.
AC load bus frequency control of a DC microgrid based on DC voltage regulation using inertia emulation and economic power management
Authors: Samanta Soumya , Mishra Jyoti Prakash , Roy Binoy Krishna
Published: October 2019

The use of inertia emulation in a microgrid has been growing as a promising control approach to maintain the bus voltage and frequency. An inertia emulation‐based control technique is proposed for a DC microgrid supplying AC loads in this study. The proposed work includes: (i) the DC bus voltage regulation using virtual inertia control and economic power management by a current sharing algorithm in cascade with a restoration control; (ii) AC load bus voltage and frequency regulation using virtual excitation emulation and inertia emulated control that utilises the emulated inertia and DC bus voltage. Further, it also provides inertia support to the grid. The coordinated current sharing algorithm manages the current (power) sharing between the grid and battery pack of electric vehicles based on electricity price and state of charge of the battery. The cascaded restoration control eliminates the steady‐state error in the DC bus voltage. Finally, the DC microgrid is simulated under various operating conditions to verify the performance of the proposed control approach. The simulation results reveal that the objectives are achieved successfully.
Field and earth‐return impedance for conductors inside an elliptic tunnel
Authors: Luo Yao , Zhu Runhang
Published: October 2019

An electrodynamic boundary value problem is solved in the elliptic cylindrical coordinates to give the earth‐return impedance of conductors inside an elliptic tunnel. The authors commence the analysis with the eigenfunction expansion of the source in the elliptic cylindrical coordinates, and the series solutions are obtained from the field ansatzes consisting of the modified Mathieu functions Kem (ξ, q) and Kom (ξ, q) with imaginary q, for which the detailed descriptions of the numerical implementations are provided, especially for the sign determination rule of Fourier coefficients of the expressions of modified Bessel function products. The proposed method is verified by the numerical results compared with those of finite‐element method and good agreement is achieved in all cases. In addition, the presented method is further compared with those developed for the special cases in the literature, from which it is confirmed that proposed method is a valid generalisation of existing ones.
Integrated transmission and storage systems investment planning hosting wind power generation: continuous‐time hybrid stochastic/robust optimisation
Authors: Nikoobakht Ahmad , Aghaei Jamshid
Published: October 2019

In this study, a continuous‐time hybrid stochastic/robust optimisation is proposed for the integrated investment in transmission lines (TLs) and energy storage systems (ESSs) with high penetration of uncertain wind power generation (WPG) sources from a central planner viewpoint. The main objective of the problem is to achieve a simultaneous expansion of transmission assets, TLs and ESSs, whereas minimising the investment cost while taking the operational aspects of a power system into account to accommodate higher shares of uncertain and intermittent WPGs. However, the integrated expansion planning of joint TL and ESS to integrate WPGs via conventional hourly discrete time model can increase the operation cost and result in a non‐optimal sizing and siting of TLs and ESSs, hence, can impose an opposite effect on the favourite. Accordingly, a continuous‐time model is proposed to coordinate the expansion planning of both TL and ESS to deal with sub‐hourly uncertainty of WPGs. Also, the WPG uncertainty in expansion planning problem is characterised using a hybrid stochastic/robust optimisation framework. Numerical tests are implemented on a modified IEEE RTS 24‐bus system and the achieved results confirm the efficiency of the proposed model.
Rectangular branch‐based load flow
Authors: Adel Mohamed Amr , Venkatesh Bala
Published: October 2019

Power of constant impedance load is proportional to the square of bus voltage magnitude (SBVM). A solution space for a set of power balance equations (PBEs), constructed using SBVMs, has lower‐order terms and less non‐linearity. Such solution space yields faster solution. This work proposes a set of rectangular PBEs which uses SBVMs in conjunction with bus phase angles to relate branches power flow, a pair of real and reactive power equations for each branch for sending/receiving ends. Using an incidence matrix, branches power flows are related to bus powers with two set of equations for real and reactive powers. Another set of equations to relate rectangular form of voltages at generators to their voltage magnitudes, the total number of equations equals four times branches number, and two times buses number, less the two for unknown powers of slack bus. While the equations number is more than the node‐based PBEs, order of Jacobian's terms is significantly lower. Testing the proposed algorithm on numerous case studies, up to a 9241‐bus real system, showing the algorithm is precise, has superior convergence features, scales well for real systems and is up to thrice as fast as the rectangular node‐based load flow for some cases.