XJTLU Research Repository

1. Minimize Reactive Power Losses of Dual Active Bridge Converters using Unified Dual Phase Shift Control

Author:Wen, HQ;Su, B

Source:JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY,2017,Vol.12

Abstract:This paper proposed an unified dual-phase-shift (UDPS) control for dual active bridge (DAB) converters in order to improve efficiency for a wide output power range. Different operating modes of UDPS are characterized with respect to the reactive current distribution. The proposed UDPS has the same output power capability with conventional phase-shift (CPS) method. Furthermore, its implementation is simple since only the change of the leading phase-shift direction is required for different operating power range. The proposed UDPS control can minimize both the inductor rms current and the circulating reactive current for various voltage conversion ratios and load conditions. The optimal phase-shift pairs for two bridges of DAB converter are derived with respect to the comprehensive reactive power loss model, including the reactive components delivered from the load and back to the source. Simulation and experimental results are illustrated and explained with details. The effectiveness of the proposed method is verified in terms of reactive power losses minimization and efficiency improvement.

2. Impact of Parasitic Elements on RF Performance of Nanometre-Scale MOSFET Structures

Author:Lam, S

Source:2013 IEEE INTERNATIONAL CONFERENCE OF ELECTRON DEVICES AND SOLID-STATE CIRCUITS (EDSSC),2013,Vol.

Abstract:A recently reported nanometre-scaled MOSFET structure with regrown source and drain is examined. The parasitic circuit elements are identified and quantitatively determined to estimate their impact on the transistor's RF performance. Due to the relatively large lateral parasitic capacitances from the gate electrode to the regrown source and drain regions, the current gain cut-off frequency f(T) of such a transistor is optimistically estimated to be 184 GHz which is not impressive for nanoelectronic devices with an effective gate length of 30 nm. However, with the significantly reduced parasitic series resistances due to the regrown source and drain structures together with the use of the metal gate, the maximum frequency of oscillation f(max) can attain to 820 GHz. This brings about an implication that device structure optimization to reduce the parasitic resistances has a dominant beneficial effect on the RF performance over the negative impact caused by the increased parasitic capacitances.

3. Robust Localisation of Pedestrians with Cast Shadows Using Homology in A Monocular View

Author:Xu, M;Jia, TY;Lu, L;Smith, JS

Source:PROCEEDINGS 2012 IEEE INTERNATIONAL CONFERENCE ON SYSTEMS, MAN, AND CYBERNETICS (SMC),2012,Vol.

Abstract:In this paper an object detection algorithm is proposed, which is robust in the presence of cast shadows and is based on geometric projections. The novelty of the work lies in the use of homology mapping of the foreground regions between different parallel planes within a monocular view, unlike some existing algorithms which depend on the use of multiple cameras. The results on an open video dataset are provided.

4. Operation of 8-wavelength-radius 2-layer lenses

Author:Gray, D;Nikolic, N;Thornton, J

Source:2015 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING,2015,Vol.2015-October

Abstract:Two competing 8-wavelength-radius 2-layer lens designs were identified in the literature. Both were analyzed by ray tracing and full wave simulation, as an initial step toward production by additive manufacturing for use at mm-wave frequencies. The conclusion of this initial study is that the relative permittivity 1.68 - 1.6 design appears to be best suited to production by laser sintering.

5. Moving shadow detection via binocular vision and colour clustering

Author:Lu, L;Xu, M;Smith, JS;Yan, YY

Source:IET COMPUTER VISION,2020,Vol.14

Abstract:A pedestrian segmentation algorithm in the presence of cast shadows is presented in this study. The novelty of this algorithm lies in the fusion of multi-view and multi-plane homographic projections of foregrounds and the use of the fused data to guide colour clustering. This brings about an advantage over the existing binocular algorithms in that it can remove cast shadows while keeping pedestrians' body parts, which occlude shadows. Phantom detection, which is inherent with the binocular method, is also investigated. Experimental results with real-world videos have demonstrated the efficiency of this algorithm.

6. An Improved Brain Storm Optimization with Differential Evolution Strategy for Applications of ANNs

Author:Cao, ZJ;Hei, XH;Wang, L;Shi, YH;Rong, XF

Source:MATHEMATICAL PROBLEMS IN ENGINEERING,2015,Vol.2015

Abstract:Brain Storm Optimization (BSO) algorithm is a swarm intelligence algorithm inspired by human being's behavior of brainstorming. The performance of BSO is maintained by the creating process of ideas, but when it cannot find a better solution for some successive iterations, the result will be so inefficient that the population might be trapped into local optima. In this paper, we propose an improved BSO algorithm with differential evolution strategy and new step size method. Firstly, differential evolution strategy is incorporated into the creating operator of ideas to allow BSO jump out of stagnation, owing to its strong searching ability. Secondly, we introduce a new step size control method that can better balance exploration and exploitation at different searching generations. Finally, the proposed algorithm is first tested on 14 benchmark functions of CEC 2005 and then is applied to train artificial neural networks. Comparative experimental results illustrate that the proposed algorithm performs significantly better than the original BSO.

7. Cascode GaN Power Device and Its Application in Wireless Power Transmission System

Author:Qian Hongtu;Zhu Yongsheng;Deng Guangmin;Liu Wen;Chen Dunjun;Pei Yi

Source:Journal of Power Supply,2019,Vol.17

Abstract:To achieve a higher power conversion efficiency, a cascode structure based on 650 V gallium nitride high electron mobility transistor(GaN HEMT) was introduced, together with its applications in wireless power transmission. From the aspect of GaN HEMT design, the effects of field plate design on capacitance and electric field were discussed through simulations. The fabricated cascode device had a leakage current of 2 muA at drain-source voltage of 650 V. At 400 V, the input capacitance C_(iss), the output capacitance C_(oss) and the reverse transfer capacitance Crss were 1 500 pF, 32 pF and 12 pF, respectively, and the dynamic on-resistance increased by about 16%%. Based on the design of this cascode device, a wireless charging prototype with operation frequency of 240~320 kHz and full-load power of 1 kW was designed and presented. Compared with the equivalent Si device, its efficiency was obviously higher within the load range of 200~1 000 W, with the peak efficiency higher than 95%%.

8. AlGaN/GaN Metal-Insulator-Semiconductor (MIS)-HFETs Based DC-DC Boost Converters with Integrated Gate Drivers

Author:Cui, M;Bu, QL;Cai, YT;Sun, RZ;Liu, W;Wen, HQ;Lam, S;Liang, YC;Mitrovic, IZ;Taylor, S;Chalker, PR;Zhao, CZ

Source:2019 10TH INTERNATIONAL CONFERENCE ON POWER ELECTRONICS AND ECCE ASIA (ICPE 2019 - ECCE ASIA),2019,Vol.

Abstract:This study proposed a 100 kHz, 5V/11V boost converter with an integrated gate driver for a power switching device using recessed E-mode MIS-HFETs. The integrated gate driver consisting of multi-stages DCFL (Direct-Coupled FET Logic) inverters and a buffer stage, has large input swing (up to 10 V) and wide noise margin with gate dielectric, which benefits applications requiring large gate swing without any additional drivers or level shifters. The impact of transistor size on rise times and fall times have been studied. Either buffer stage or larger width of DCFL inverter can reduce rise times from 2.4 mu s to less than 0.5 mu s at 100 kHz, so the output voltage of boost converter is increased by 10 %% at a duty cycle of 0.7. However, large buffer width can result in high gate overshoot and oscillation, indicating careful design to balance switching speed and oscillation.

9. The design and simulation of p-type Si/SiGe Terahertz quantum cascade lasers

Author:Chen, QY;Wu, JJ;Fang, Z;Zhao, CZ

Source:OPTICS AND LASER TECHNOLOGY,2014,Vol.57

Abstract:To prolong upper state lifetime in p-type Si/Si1-xGex Terahertz quantum cascade lasers, a new active region is designed in this work. Using 6 x 6 k . p theory, the eigenvalues and wavefunctions of heavy holes and light holes are firstly calculated in a single SiGe quantum well. The design in the active region of this THz Si/Si1-xGex quantum cascade lasers is then investigated. This work presents a SiGe quantum cascade laser with about 6.84 THz emission in the diagonal transition. The calculations show that about 32 ps of the upper state lifetime and about 9 cm(-1) of optical gain are obtained, which are enhanced when compared to previous designs. (C) 2013 Elsevier Ltd. All rights reserved.

10. FMCW Rail-mounted SAR: porting spotlight SAR imaging from MATLAB to FPGA

Author:Melnikov, A;Le Kernec, J;Gray, D

Source:2014 IEEE INTERNATIONAL CONFERENCE ON SIGNAL PROCESSING, COMMUNICATIONS AND COMPUTING (ICSPCC),2014,Vol.

Abstract:In this work, a low-cost laptop-based radar platform derived from the MIT open courseware has been implemented. It can perform ranging, Doppler measurement and SAR imaging using MATLAB as the processor. In this work, porting the signal processing algorithms onto a FPGA platform will be addressed as well as differences between results obtained using MAT LAB and those obtained using the FPGA platform. The target FPGA platforms were a Virtex6 DSP kit and Spartan3A starter kit, the latter was also low-cost to further reduce the cost for students to access radar technology.

11. Advances of RRAM Devices: Resistive Switching Mechanisms, Materials and Bionic Synaptic Application

Author:Shen, ZJ;Zhao, C;Qi, YF;Xu, WY;Liu, YN;Mitrovic, IZ;Yang, L;Zhao, CZ

Source:NANOMATERIALS,2020,Vol.10

Abstract:Resistive random access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, good scalability potential and so on, and are currently considered to be one of the next-generation alternatives to traditional memory. In this review, an overview of RRAM devices is demonstrated in terms of thin film materials investigation on electrode and function layer, switching mechanisms and artificial intelligence applications. Compared with the well-developed application of inorganic thin film materials (oxides, solid electrolyte and two-dimensional (2D) materials) in RRAM devices, organic thin film materials (biological and polymer materials) application is considered to be the candidate with significant potential. The performance of RRAM devices is closely related to the investigation of switching mechanisms in this review, including thermal-chemical mechanism (TCM), valance change mechanism (VCM) and electrochemical metallization (ECM). Finally, the bionic synaptic application of RRAM devices is under intensive consideration, its main characteristics such as potentiation/depression response, short-/long-term plasticity (STP/LTP), transition from short-term memory to long-term memory (STM to LTM) and spike-time-dependent plasticity (STDP) reveal the great potential of RRAM devices in the field of neuromorphic application.

12. Multiple strategies based orthogonal design particle swarm optimizer for numerical optimization

Author:Qin, QD;Cheng, S;Zhang, QY;Wei, YM;Shi, YH

Source:COMPUTERS & OPERATIONS RESEARCH,2015,Vol.60

Abstract:In the canonical partide swarm optimization (PSO), each particle updates its velocity and position by taking its historical best experience and its neighbors' best experience as exemplars and adding them together. Its performance is largely dependent on the employed exemplars. However, this learning strategy in the canonical PSO is inefficient when complex problems are being optimized. In this paper, Multiple Strategies based Orthogonal Design PSO (MSODPSO) is presented, in which the social-only model or the cognition-only model is utilized in each particle's velocity update, and an orthogonal design (OD) method is used with a small probability to construct a new exemplar in each iteration. In order to enhance the efficiency of OD method and obtain more efficient exemplar, four auxiliary vector generating strategies are designed. In addition, a global best mutation operator including non-uniform mutation and Gaussian mutation is employed to improve its global search ability. The MSODPSO can be applied to PSO with the global or local structure, yielding MSODPSO-G and MSODPSO-L algorithms, respectively. To verify the effectiveness of the proposed algorithms, a set of 24 benchmark functions in 30 and 100 dimensions are utilized in experimental studies. The proposed algorithm is also tested on a real-world economic load dispatch (ELD) problem, which is modelled as a non-convex minimization problem with constraints. The experimental results on the benchmark functions and ELD problems demonstrate that the proposed MSODPSO-G and MSODPSO-L can offer high-quality solutions. (C) 2015 Elsevier Ltd. All rights reserved.

13. Effects of Biased Irradiation on Charge Trapping in HfO2 Dielectric Thin Films

Author:Mu, YF;Zhao, CZ;Lu, QF;Zhao, C;Qi, YF;Lam, S;Mitrovic, IZ;Taylor, S;Chalker, PR

Source:4TH INTERNATIONAL CONFERENCE ON THE ADVANCEMENT OF MATERIALS AND NANOTECHNOLOGY (ICAMN IV 2016),2017,Vol.1877

Abstract:This paper reports the low-dose-rate radiation response of Al-HfO2/SiO2-Si MOS devices, in which the gate dielectric was formed by atomic layer deposition (ALD) with 5-nm equivalent oxide thickness. The degradation of the devices was characterized by a pulse capacitance-voltage (CV) and on-site radiation response technique under continuous gamma (gamma) ray exposure at a relatively low dose rate of 0.116 rad (HfO2)/s. Compared with conventional CV measurements, the proposed measurements extract significant variations of flat-band voltage shift of the hafnium based MOS devices. The large flat-band voltage shift is mainly attributed to the radiation-induced oxide trapped charges, which are not readily compensated by bias-induced charges produced over the measurement timescales (for timescales less than 5 ms). A negative flat-band voltage shift up to -1.02 V was observed under a positive biased irradiation with the total dose up to 40 krad (HfO2) and with the electric field of 0.5 MV/cm. This is attributed to net positive charge generation in the HfO2 oxide layer. The generated charges are transported towards the HfO2/SiO2 interface, and then form effective trapped holes in the HfO2. Similarly, a positive flat-band voltage shift up to 1.1 V was observed from irradiation under negative bias with an electric field of -0.5 MV/cm. The positive shift is mainly due to the accumulation of trapped electrons. Analyses of the experimental results suggest that both hole and electron trapping can dominate the radiation response performance of the HfO2-based MOS devices depending upon the applied bias. It was also found there was no distinct border traps with irradiation in all cases.

14. Artificial Bee Colony Algorithm with Time-Varying Strategy

Author:Qin, QD;Cheng, S;Zhang, QY;Li, L;Shi, YH

Source:DISCRETE DYNAMICS IN NATURE AND SOCIETY,2015,Vol.2015

Abstract:Artificial bee colony (ABC) is one of the newest additions to the class of swarm intelligence. ABC algorithm has been shown to be competitive with some other population-based algorithms. However, there is still an insufficiency that ABC is good at exploration but poor at exploitation. To make a proper balance between these two conflictive factors, this paper proposed a novel ABC variant with a time-varying strategy where the ratio between the number of employed bees and the number of onlooker bees varies with time. The linear and nonlinear time-varying strategies can be incorporated into the basic ABC algorithm, yielding ABC-LTVS and ABC-NTVS algorithms, respectively. The effects of the added parameters in the two new ABC algorithms are also studied through solving some representative benchmark functions. The proposed ABC algorithm is a simple and easy modification to the structure of the basic ABC algorithm. Moreover, the proposed approach is general and can be incorporated in other ABC variants. A set of 21 benchmark functions in 30 and 50 dimensions are utilized in the experimental studies. The experimental results show the effectiveness of the proposed time-varying strategy.

15. A Centralized Reactive Power Compensation System for LV Distribution Networks

Author:Chen, SX;Eddy, YSF;Gooi, HB;Wang, MQ;Lu, SF

Source:IEEE TRANSACTIONS ON POWER SYSTEMS,2015,Vol.30

Abstract:A centralized reactive power compensation system is proposed for low voltage (LV) distribution networks. It can be connected with any bus which needs reactive power. The current industry practice is to locally install reactive power compensation system to maintain the local bus voltage and power factor. By centralizing capacitor banks together, it can help to maintain bus voltages and power factors as well as reduce the power cable losses. Besides, the centralized reactive power system can be easily expanded to meet any future load increase. A reasonably sized centralized reactive power compensation system will be capable of meeting the requirements of the network and the optimization algorithm proposed in this paper can help to find this optimal size by minimizing the expected total cost (ETCH). Different load situations and their respective probabilities are also considered in the proposed algorithm. The concept of the centralized reactive power compensation system is applied to a local shipyard power system to verify its effectiveness. The results show that an optimally sized centralized reactive power system exists and is capable of maintaining bus voltages as well as reducing the power losses in the distribution network. A significant power loss reduction can be obtained at the optimal capacity of the centralized reactive power compensation system in the case study.

16. Segregated Lightweight Dynamic Rate (SLDR) control scheme for efficient internet communications

Author:Ting,T. O.;Ting,H. C.;Lee,Sanghyuk

Source:Lecture Notes in Electrical Engineering,2013,Vol.235 LNEE

Abstract:This paper proposes an effective Segregated Lightweight Dynamic Rate Control Scheme (SLDRCS) over the internet. Based on the feedback analysis of the current approaches, we found that the indicator of the congestion is only the queue length. It only captures a partial indicator of delay and loss in feedback mechanism. This may result in an ineffective way in controlling the network when congestion control occurs. Therefore, we suggest multiple congestion indicators to adapt inside this scheme to fully control the average delay and loss from bidirectional of sender to receiver. The behavior of next event packet being control using discrete event simulation tool with First Come First Serve (FCFS) scheduling policy and we code this algorithm into C programming language. Through the simulation results, our Segregated Lightweight Dynamic Rate Control Scheme (SLDRCS) guaranteed high improvement in packet drop and average delay under various congestion level and traffic load conditions compare with the current approach. © 2013 Springer Science+Business Media Dordrecht.

17. Dielectric relaxation of high-k oxides

Author:Zhao, C;Zhao, CZ;Werner, M;Taylor, S;Chalker, P

Source:NANOSCALE RESEARCH LETTERS,2013,Vol.8

Abstract:Frequency dispersion of high-k dielectrics was observed and classified into two parts: extrinsic cause and intrinsic cause. Frequency dependence of dielectric constant (dielectric relaxation), that is the intrinsic frequency dispersion, could not be characterized before considering the effects of extrinsic frequency dispersion. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which depended on the structure of the high-k material. It was attributed to the enhancement of the correlations among polar nanodomain. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain due to its higher concentration of grain boundary.

18. Hydrogen Consumption Minimization for Fuel Cell Trains Based on Speed Trajectory Optimization

Author:Huang, Zheng ; Wu, Chaoxian ; Lu, Shaofeng ; Xue, Fei

Source:Lecture Notes in Electrical Engineering,2020,Vol.638

Abstract:To make rail transport much greener, the fuel cell system has been applied in some train vehicles. The paper is aimed at establishing an integrated mixed-integer linear programming (MILP) model to optimize operations of the trains with the fuel cell system. Train motion analysis and physical constraints setup are given to illustrate the model. The main power-efficiency characteristic of the fuel cell system is also modeled in the research. The optimal train speed trajectory is obtained by applying the proposed approach, where the hydrogen consumption of the fuel cell is minimized. To prove the robustness of the model, the power profiles of scenarios with normal and extreme power-efficiency characteristics are compared, and the results show influences of these characteristics on the train operations. © Springer Nature Singapore Pte Ltd. 2020.

19. Emerging research on swarm intelligence and algorithm optimization

Author:Shi, Yuhui

Source:Emerging Research on Swarm Intelligence and Algorithm Optimization,2014,Vol.

Abstract:Throughout time, scientists have looked to nature in order to understand and model solutions for complex real-world problems. In particular, the study of self-organizing entities, such as social insect populations, presents a new opportunity within the field of artificial intelligence. Emerging Research on Swarm Intelligence and Algorithm Optimization discusses current research analyzing how the collective behavior of decentralized systems in the natural world can be applied to intelligent system design. Discussing the application of swarm principles, optimization techniques, and key algorithms being used in the field, this publication serves as an essential reference for academicians, upper-level students, IT developers, and IT theorists. © 2015 by IGI Global. All rights reserved.

20. Effect of Annealing Temperature for Ni/AlOx/Pt RRAM Devices Fabricated with Solution-Based Dielectric

Author:Shen, ZJ;Qi, YF;Mitrovic, IZ;Zhao, CZ;Hall, S;Yang, L;Luo, T;Huang, YB;Zhao, C

Source:MICROMACHINES,2019,Vol.10

Abstract:Resistive random access memory (RRAM) devices with Ni/AlOx/Pt-structure were manufactured by deposition of a solution-based aluminum oxide (AlOx) dielectric layer which was subsequently annealed at temperatures from 200 degrees C to 300 degrees C, in increments of 25 degrees C. The devices displayed typical bipolar resistive switching characteristics. Investigations were carried out on the effect of different annealing temperatures for associated RRAM devices to show that performance was correlated with changes of hydroxyl group concentration in the AlOx thin films. The annealing temperature of 250 degrees C was found to be optimal for the dielectric layer, exhibiting superior performance of the RRAM devices with the lowest operation voltage (<1.5 V), the highest ON/OFF ratio (>10(4)), the narrowest resistance distribution, the longest retention time (>10(4) s) and the most endurance cycles (>150).

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