- نمایش 15 محصول در هر صفحه
Coordinated control for voltage regulation of distribution network voltage regulation by distributed energy storage systems
0 تومانWith more and more distributed photovoltaic (PV) plants access to the distribution system, whose structure is changing and becoming an active network. The traditional methods of voltage regulation may hardly adapt to this new situation. To address this problem, this paper presents a coordinated control method of distributed energy storage systems (DESSs) for voltage regulation in a distribution network. The influence of the voltage caused by the PV plant is analyzed in a simple distribution feeder at first. The voltage regulation areas corresponding to DESSs are divided by calculating and comparing the voltage sensitivity matrix. Then, a coordinated voltage control strategy is proposed for the DESSs. Finally, the simulation results of the IEEE 33-bus radial distribution network verify the effectiveness of the proposed coordinated control method.
Design and analysis of a full bridge LLC DC-DC converter for auxiliary power supplies in traction
0 تومانThis paper focuses on an 8 kW LLC resonant full bridge DC-DC converter topology using a high frequency transformer for auxiliary power supply systems in traction. The full bridge DC-DC converter with the LLC resonant network has been tested under hard switching and zero current switching conditions with 100 kHz switching frequency. In addition to this, an observation made for the effect of dead time variation of the power switches to improve the overall system efficiency. This paper describes the efficiency of the ZCS full bridge converter by considering different input power levels and also compared with hard switched topology. This paper presents the operating principles, simulation analysis, and experimental verification for 3 kW to 8 kW LLC resonant full bridge converter with 1200 V/40 A IGBTs, and its efficiency comparison.
Design of integral sliding mode control for DC-DC converters
0 تومانThe development and implementation of an integral sliding mode control algorithm for closed loop control of a DC-DC buck converter is presented in this paper. Integral sliding mode controller (ISMC) is formulated to tackle the variable switching frequency problem faced during load and supply variations in conventional sliding mode controlled buck converters. Variable switching frequency is undesirable as it leads to complications while designing filters for the system. ISMC aims to alleviate this problem through appropriate transformation of the sliding mode control lawmaking use of pulse width modulation scheme. The control algorithm is validated through detailed simulation studies in MATLAB/Simulink environment. Comprehensivecomparative assessment of the converter control system using ISMC is carried out with conventional sliding mode control (SMC) scheme which reveals the fixed frequency functioning of ISMC under diverse operating conditions.
Evaluation of high-voltage AC cable grounding systems based on the real-time monitoring and theoretical calculation of grounding currents
0 تومانFor high-voltage (HV) AC cable transmission systems, the metal sheaths of three separate single-core cables are cross-bonded at each end of the cable section, to suppress the induced voltages in sheaths. The status of HV cable grounding systems is, therefore, an important consideration for power utilities. This study presents the status evaluations of 93 cable grounding systems in Beijing, obtained using the standards established by State Grid Corporation of China. As a result, 13 of these systems were classified as abnormal or defective. Additionally, a theoretical calculation of grounding currents was proposed and these 13 systems are re-evaluated by comparing the calculated and measured values of certain parameters. Based on this work, the authors propose a modified evaluation standards. It is indicated that the absolute value of grounding current (|I|) during a given 24-hr period has no relationship with the status of grounding system, and the ratio of grounding current to load current (K) at the time of maximum load current could be used as a status indicator instead of K at some other time, in order to avoid possible incorrect evaluations due to light load conditions.
Flexible IR-HARQ Scheme for Polar-Coded Modulation
0 تومانA flexible incremental redundancy hybrid automated repeat request (IR-HARQ) scheme for polar codes is proposed based on dynamically frozen bits and the quasi-uniform puncturing (QUP) algorithm. The length of each transmission is not restricted to a power of two. It is applicable for the binary input additive white Gaussian noise (biAWGN) channel as well as higher-order modulation. Simulation results show that this scheme has similar performance as directly designed polar codes with QUP and outperforms LTE-turbo and 5G-LDPC codes with IR-HARQ.
Machine Learning for Electroencephalography Decoding and Robotics Dextrous Hands Movement
0 تومانThis work focuses on using machine learning (data analysis) for interpretation and understanding of brainwaves resulting from electroencephalography during a grasping task. Electroencephalography – EEG – was used for acquisition of brain neural signals thought activity, hence to layout a control strategy for robotic hand and fingers movements. This is done via decoding, in real-time, the neural activity associated with fingers motions. Results are used for training robotics dexterous hands, and might allow people with spinal cord injury, rainstem stroke, and ALS (amyotrophic lateral sclerosis) to control a robotic-prosthetic by thinking about movements. The project is novel in a sense, it relies on detecting grasping features for a human grasping using Principle Component Analysis (PAC), hence to learn these features for recognitions applications.
Reliability study of high gain DC-DC converters based on RRPP I-IIA configuration for shipboard power system
0 تومانThis paper examines the family of high gain DC-DC converter derived from I-IIA configuration, primarily based on Reduced Redundant Power Processing (RRPP). The primary intention of this study is to determine the best topology for high voltage applications. The steady-state analysis of the proposed topologies is investigated and verified. The denominators of the voltage conversion ratio are observed to be similar for all the derived topologies, and they are in quadratic form. A comprehensive assessment is done based on voltage gain,voltage stress across storage element, switch stress voltage, switch utilization factor and inductor value. The best topology is identified and analyzed thoroughly in Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). Also, its performance evaluation and reliability study are also carried out. The advantage of that topology is validated using theoretical and simulation results. Finally, 40 W prototype is developed to verify the results.
Thermal Optimization of Electronic Devices on PCB Based on the Ant Colony Algorithm
0 تومانWith the integration of the electronic devices on the printed circuit board, the heat flux density in narrow spaces isincreasing rapidly. The placement of electronic devices can affect the temperature of the overall circuit board. In addition, some special devices usually need to meet many location requirements. For example, the devices such as FPGAs, ARMs and MCUs need to be placed in the central position of the PCB for the use of multiple peripheral circuits. In order to optimize the temperature of devices with a priori layout requirement, this paper uses the micro-element thermal equilibrium method to establish the temperature field model and then the ant colony algorithm with classified compensation is used to search optimized position of all components. Simulation experiment results show that the proposed algorithm can effectively reduce the maximum temperature of devices in the case of the electronic devices meet the needs of the circuit function.
۹Round Attack on AES-256 by a 6-round property
0 تومانIn this paper, we propose a new 6-round Related Key Impossible Differential property of AES-256 and two related key impossible differential attacks on 7 and 9 round AES-256 based on the proposed property. The overall complexity of the the first time that a Related-Key Impossible Differential attack on 9- round AES-256 is successful. Also this is the first related-key attack on 9-round AES-256 that needs only 2 keys. Although the data and time complexities of the attack are approximately code book and exhaustive search, but we think the proposed property will be useful in future research like boomerang and rectangle attacks.
A DC to 20 GHz Ultra-Broadband High-Gain-Linear Distributed Power Amplifier with 19.5% Drain Efficiency
0 تومانIn this paper an ultra-broadband linear distributed power amplifier (DPA) is presented. This amplifier consumes only 100 mW DC power and amplifies input powers up to -3.7 dBm with a power gain of 16.7 dB linearly. Output power at 1-dB compression point is 13 dBm in the linear-mode. By increasing the level of input ower, the amplifier no longer works in the linear-mode, drain efficiency and non-linear distortions are increased, and power consumption is decreased to 90 mW. S21 parameter is 18±0.9 dB over DC to 20 GHz. The architecture of all power gain cells (including three stages) is cascade of inductively coupled common source. This amplifier is simulated in a 0.13 um CMOS technology.
A dual mode step-down switched-capacitor DC-DC converter with adaptive switch width modulation
0 تومانThis paper proposes a step-down switched-capacitor (SC) DC-DC converter with pulse frequency modulation (PFM) and burst mode. This design proposes a novel dual mode control strategy to achieve high performance over a wide load range. PFM is adopted at heavy load to achieve the small output voltage ripple while burst mode is adopted at light load to improve transient response and power efficiency. To further improve the efficiency, an adaptive switch width modulation (ASWM) is proposed to reduce switching losses. The measured results show that the proposed four conversion ratios converter can operate with a 2.0–3.6 V input voltage range, load current from 0 to 2 mA at the output voltage of 1.2 V. The peak power efficiency is up to 84.2% from a 2.7 V input voltage supply at a load current of 2 mA. At a load of 60 μA, the burst mode achieves an 11% maximum efficiency .improvement, and the average efficiency improvement of 6% is achieved with ASWM.
A Fast Hybrid Approach for Approximating a ThinPlate Spline Surface
0 تومانThin-plate spline (TPS) is a common method to smooth interpolation of bivariate scattered data. However, this method has been associated with very high computational cost, particularly when number of scattered data becomes large and interpolation function must be evaluated on a large grid. This paper describes a hybrid approach for computing a C2– continuous surface using combination of thin-plate spline and cubic spline interpolation that approximates the thin-plate spline interpolation function. Experimental results show that this method significantly speeds up the evaluation of thin-plate spline interpolation function in comparison with direct evaluation, particularly in the cases that interpolation function must be evaluated on a large grid.
A high frequency model for predicting the behavior of lithium-ion batteries connected to fast switching power electronics
0 تومانBattery powered energy systems such as electric vehicles utilize power electronics for controlling energy flows between the battery and the load or generation, respectively. Therefore, the battery is under high frequency stress due to fast switching power electronic devices. However, most battery models throughout the literatureare not able to cope with high frequency excitation. This paper proposes an easy to implement equivalent circuit model that covers aforementioned frequency regions with a series of inductors that are each connected in parallel with an ohmic resistance. This circuit is parameterized by electrochemical impedance spectroscopy (EIS) up to 100 kHz. For further regions that reach regions of megahertz a skin effect model is investigated and compared to the RL-model. It is shown that such semi-empirical models can be motivated by geometrical considerations that can be found in the literature. Moreover, the proposed model is validated by simulating the voltage response from an input current that originates from an actual back-to-back half bridge DC/DC converter.The promising results indicate that such models might be implemented in future battery energy systems to improve insights on how batteries react to perturbations such as EMI noise or high frequency current ripple.
A Markovian model for power transformer maintenance
0 تومانThe condition of the insulation paper is one of the key determinants of the lifetime of a power transformer. The winding insulation paper may deteriorate aggressively and result in the unexpected failure of power transformers, especially under the presence of high moisture, oxygen, and metal contaminants. Such types of scenarios can be prevented if the deterioration is detected on time. Various types of condition monitoring techniques have been developed to detect transformer condition such as dissolved gas analysis (DGA) and frequency esponseanalysis (FRA). They are non-intrusive and provide early warning of accelerated deterioration both chemically and mechanically. However, the accuracy of those techniques is imperfect, which means periodic inspection is still indispensable. In this paper, we discuss the value of continuous condition monitoring for power transformers and present a way to estimate this value. Towards this, a continuous-time Markov decision model is presented to optimize periodic inspections, so that the cost is minimized and the availability is maximized. We then analyze the performance based on the information from both discrete inspection and continuous condition monitoringusing DGA and FRA. The result shows the dissolved gas analysis can improve the availability and operation cost,while frequency response analysis can only improve the availability of power transformers.
A modular mobile robotic architecture for defects detection and repair in narrow tunnels of CFRP aeronautic components
0 تومانAdvanced composite structural components in aeronautics are characterized by very high production costs because of their dimensions, complex shapes and expensive forming equipment. For these components, such as horizontal stabilizers and wings, a defect occurrence is often critical because large part of inner surfaces, made of long and tapered narrow tunnels, are not reachable for repair operations. In these cases, the part is rejected with a relevant economic loss and high production costs. For this reason, aircraft constructors plan huge investments for defects avoidance during the forming processes of CFRP and to develop effective, robust and reliable repair tools and methods. Mobile robotics can play an important role, with specific systems capable of moving into narrow channels of wings structures (i.e. multi spar boxes) and repair it in accordance to technical standards. This paper describes an innovative mobile robot architecture for bonded repair scarfing operations on CFRP components. Targeting and responding to the demanding machining requirements, the functional-oriented design approach clearly highlights the advantages of a modular robotic solution. The mobile robotic architecture can be also applied in other fields with similar challenging manufacturing operations for further inspection, detection and machining operations.
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