Typical Motion and Extinction Characteristics of the Secondary Arcs Associated with Half-Wavelength Transmission Lines

Secondary arc discharge is a complicated physical phenomenon and one of the key fundamental issues associated with ultra high voltage(UHV)half-wavelength transmission lines(HWTL).With the establishment of a physical simulation platform for the HWTLs,experiments were carried out regarding the motion and extinction characteristics of secondary arcs.The cathode arc root and the anode arc root were found to show an obvious polarity effect while the arc column was moving in a spiral,due to their different motion mechanisms.The extinction behavior was also recorded and experiments were designed with different compensation conditions.Results show that the arcing time can be greatly reduced if there exists an electrical compensation network.The research provides fundamentals for understanding the physics involved,especially the motion and extinction mechanisms of the secondary arcs.

Effect of TiO2 Nanoparticles on Charge Transportation in Mineral Oil and Natural Ester Based Nanofluid

TiO2 semiconductive nanoparticles are added into mineral and ester based transformer oil to form semiconductive nanofluids (SNFs) with the aim of enhancing the oil’s insulating performance. Charge accumulation and decay characteristics of both pure oils and SNFs are measured by pulse electroacoustic (PEA) technique. The result reveals that compared with pure oil, SNFs have more uniform in- ternal electric fields with voltage applied and higher charge decay rate after removing the applied voltage. This is caused by the increase of shallow trap density in SNFs, due to the test results of thermally stimulated current (TSC). It is proposed that the electron trapping and de-trapping processes in shallow traps could be the main charge transport processes in the nanofluid transformer oil.

Controlling chaos to unstable periodic orbits and equilibrium state solutions for the coupled dynamos system

In the case where the knowledge of goal states is not known, the controllers are constructed to stabilize unstable steady states for a coupled dynamos system. A delayed feedback control technique is used to suppress chaos to unstable focuses and unstable periodic orbits. To overcome the topological limitation that the saddle-type steady state cannot be stabilized, an adaptive control based on LaSalle's invariance principle is used to control chaos to unstable equilibrium (i.e. saddle point, focus, node, etc.). The control technique does not require any computer analysis of the system dynamics, and it operates without needing to know any explicit knowledge of the desired steady-state position.

Effect of Barrier Materials on Discharge Properties in Air at Low Pressure

Dielectric barrier discharge(DBD) is widely investigated in order to obtain uniform low-temperature plasma.Many studies have proved that some barrier materials,especially electrets,can improve the uniformity of discharge.It is regarded as an available way to get atmospheric pressure glow discharge(APGD).In this paper,discharge forms with 4 different barrier materials(alumina,quartz,PTFE and PET) are investigated,and the transition of discharge form depending on the air pressure are recorded to estimate the influence of barrier materials on discharge.By using electrets as barrier materials,homogeneous discharges can be obtained in a more wide pressure range.Under the same experimental conditions,discharges with electrets are more uniform or have larger uniform areas due to the storage and desorption of charges on the surface of electrets.The electrons deposited in the surface layer can be released on next half cycle when the polarity of the applied voltage changes,and provide a number of seed electrons,which makes the discharge more homogeneous.The capacitance and the permittivity of barrier materials have no effect on the discharge form directly.

POSSIBLE EXPLANATION OF THE PLATEAU WIDTH IN THE QUANTUM HALL EFFECT AT FINITE TEMPERATURE

The finite width of the plateau in the Hall resistance is studied quantitatively.If we give a filling factor v,the ratio of the plateau widthΔB to the center of the plateau BH square is constant for all other filling factors v'if v'=v+m with m any integer.The temperature dependence of the plateau width is also studied.Theoretical results are in good agreement with the data obtained from experiment.

Special issue on the 70th anniversary of HUST

Huazhong University of Science and Technology (HUST) celebrates its 70th anniversary in 2022.It was transferred to a comprehensive and modern university on the international level in the 1980s from its traditional engineering predecessor,Huazhong Institute of Technology,founded in the early 1950s as part of China’s academic institution reorganization.

Improved Unit Commitment with Accurate Dynamic Scenarios Clustering Based on Multi-Parametric Programming and Benders Decomposition

Stochastic unit commitment is one of the most powerful methods to address uncertainty. However, the existingscenario clustering technique for stochastic unit commitment cannot accurately select representative scenarios,which threatens the robustness of stochastic unit commitment and hinders its application. This paper providesa stochastic unit commitment with dynamic scenario clustering based on multi-parametric programming andBenders decomposition. The stochastic unit commitment is solved via the Benders decomposition, which decouplesthe primal problem into the master problem and two types of subproblems. In the master problem, the committedgenerator is determined, while the feasibility and optimality of generator output are checked in these twosubproblems. Scenarios are dynamically clustered during the subproblem solution process through the multiparametric programming with respect to the solution of the master problem. In other words, multiple scenariosare clustered into several representative scenarios after the subproblem is solved, and the Benders cut obtainedby the representative scenario is generated for the master problem. Different from the conventional stochasticunit commitment, the proposed approach integrates scenario clustering into the Benders decomposition solutionprocess. Such a clustering approach could accurately cluster representative scenarios that have impacts on theunit commitment. The proposed method is tested on a 6-bus system and the modified IEEE 118-bus system.Numerical results illustrate the effectiveness of the proposed method in clustering scenarios. Compared withthe conventional clustering method, the proposed method can accurately select representative scenarios whilemitigating computational burden, thus guaranteeing the robustness of unit commitment.

Future evolution of automated demand response system in smart grid for low-carbon economy

Smart grid construction is an important carrier and an effective way to promote the development of lowcarbon economy.Demand response(DR)is commonly regarded as an important core technology in smart grid field,and it reflects the flexible and interactive features of the core business in smart electricity.It is the developing direction of automated demand response(ADR)technology,and its main features are the standardization of information exchange,together with the intelligence of decision-making and the automation of implementations.ADR technology can improve the efficiency of the whole power system and enhance the ability to accept new energy sources.This paper analyzes the role of demand response in improving efficiency and low-carbon energy saving power systems.The automated demand response system architecture is investigated,and the ADR roadmap of commercial/industrial and residential customer is proposed.The key technologies for ADR system are analyzed,including demand response strategy,information exchanging model,measurement and verification techniques,and multi-agent scheduling techniques.To ensure the interoperability between the grid side and the user side,the ADR business in smart grid user interface standards is concluded to support further demand side management project.

Time-stepping finite element analysis on the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors

To study the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors,a 5.5-kW motor was taken as an example and the multi-sliced field-circuit coupled time stepping finite element method(T-S FEM)was used to analyze the axially non-uniform fundamental and harmonic field distribution characteristics at typical locations in the stator and rotor cores.The major conclusions are:firstly the skewed rotor exhibits a decrease in the harmonic copper losses caused by slot harmonic currents in the stator winding and rotor bars.Secondly,the skewed rotor shifts the non-uniform distribution of field in the axial direction,which leads to more severe saturation and an increase in iron losses.The heavier the load,the more pronounced the increase in iron losses.Furthermore,the influences of different skew angles on motor losses are studied systematically,with skew angles from 0.5 to 1.5 stator tooth pitch.It is found that the lowest total loss occurs at 0.8 stator tooth pitch,and the slot harmonics can be decreased effectively.

Development and prospect of direct‐current circuit breaker in China

The direct‐current circuit breaker(DCCB)is the most ideal choice for DC fault isolation in DC grids.Despite a late start,China's research and development on the DCCB have made outstanding achievements.This article provides a brief glance of current China's DCCB development status.It begins by sorting out the technical route according to the topology of DCCB.Then it systematically summarises both mechanical and hybrid DCCBs with focussing on the aspects of topology structure and principle,key technology and characteristics,prototype development and application.It is apparent that Chinese scientists and engineers confronted the worldwide problem of large capacity DC breaking,and put forward a comprehensive solution which consists of an innovative topology structure based on coupled negative voltage circuit,breaking throughs on the key technologies such as highly controllable and reliable fault current commutation,millisecond‐level ultra‐fast and efficient electromagnetic repulsion mechanism,high tolerance and high stability power electronic switch,low residual voltage and fast response energy consumption device,etc.The article states that the world's first set of hybrid high‐voltage(HV)DCCB,and the first set of mechanical HV DCCB have been developed.These DCCBs will soon be deployed to the DC grids which have the highest voltage levels therefore require the strongest breaking capacity.These achievements are leading the world in the development and application of DCCB.The article also discusses the overall development trends of DCCB in the areas of new topologies,key techno-logical breakthroughs and application scenarios,etc.These discussions serve as references for DCCB's future technological advancement and its ever‐expanding applications.

TD-SCDMA中基于信息融合技术的外环功率控制算法(英文)

An outer loop power control algorithm based on triangle norm(t-norm) information fusion technology is proposed in this paper.According to the difference between block error rate and bit error rate with target values,the membership function calculation and level dividing of the two differences are dealt with.And then t-norm operator is used to fuse the two membership function values to determine the adjustment step-size.The algorithm can acquire the optimal adjustment step-size in the light of the channel status and avoid the overshoot phenomenon of the existing outer power control methods.As a result,the block error rate can converge to the target value quickly.Experiment results verify the excellent property of the algorithm.

A universal method for rapid and large‐scale growth of layered crystals

Layered van der Waals(vdW)materials,consisting of atomically thin layers,are of paramount importance in physics,chemistry,and materials science owing to their unique properties and various promising applications.However,their fast and large‐scale growth via a general approach is still a big challenge,severely limiting their practical implementations.Here,we report a universal method for rapid(~60 min)and large‐scale(gram scale)growth of phase‐pure,high‐crystalline layered vdW materials from their elementary powders via microwave plasma heating in sealed ampoules.This method can be used for growth of 30 compounds with different components(binary,ternary,and quaternary)and properties.The ferroelectric and transport properties of mechanically exfoliated flakes validate the high crystal quality of the grown materials.Our study provides a general strategy for the fast and large‐scale growth of layered vdW materials with appealing physiochemical properties,which could be used for various promising applications.

Mesoscopic superelasticity,superplasticity,and superrigidity

Atomic-undercoordination-induced local bond contraction,bond strength gain,and the associated temperature (T)-dependent atomic-cohesive-energy and binding-energy-density are shown to originate intrinsically the exotic paradox of superplasticity,superelasticity,and superrigidity demonstrated by solid sizing from monatomic chain to mesoscopic grain.The paradox follows these relationships:(ε(K,T)y(K,T)σ(K,T))∝(exp(B/△T_(mk)),(η_1△T_(mk))d～(-3),[1+AK～(-2/2)exp(△T_(mk)/T)]△T_(mk)d～(-3)),(Plastic strain)(Elastic modulus)(Yield stress,IHPR)where A,B,η1,d and△T_(mk)=Tm(K) Tare size (K)-dependent physical parameters.Tm (K) is the melting point.Mechanical work hardening during compressing and self-heating during stretching modulate the measured outcome extrinsically.Superplasticity dominates in the solid-quasimolten-liquid transition state.The competition between the accumulation and annihilation of dislocations activates the inverse Hall-Petch relationship.Therefore,it is essential for one to discriminate the intrinsic competition between the local bond energy density gain and the atomic cohesive energy loss from the extrinsic factors of pressure and temperature in dealing with atomistic mechano-thermo dynamics.

A novel FBG velocimeter with wind speed and temperature synchronous measurement

Based on frequency demodulation method, a novel fiber Bragg grating(FBG) velocimeter which can achieve wind speed and temperature synchronous measurement is proposed in this paper. The wind speed and temperature synchronous measurement is realized by cup anemometer(CA) signal modulation and Hilbert-Huang transformation(HHT) signal processing. The working principle of the novel FBG velocimeter is demonstrated and its theory calculation model is also set up by using basic mechanical knowledge and blade element momentum(BEM). Further, calibration experiment is carried out on one prototype of the FBG velocimeter to obtain its measurement performance. HHT is introduced to deal with calibration experiment data. After data analyses, the results show that the novel FBG velocimter can achieve high-precision wind speed measurement of 0.012 m/s with minimum detection limit of 0.41 m/s, and its temperature detection precision is 10.6 pm/°C.

S-band low noise amplifier using 1μm InGaAs/InAlAs/InP pHEMT

This paper discusses the design of a wideband low noise amplifier(LNA) in which specific architecture decisions were made in consideration of system-on-chip implementation for radio-astronomy applications.The LNA design is based on a novel ultra-low noise InGaAs/InAlAs/InP pHEMT.Linear and non-linear modelling of this pHEMT has been used to design an LNA operating from 2 to 4 GHz.A common-drain in cascade with a common source inductive degeneration,broadband LNA topology is proposed for wideband applications.The proposed configuration achieved a maximum gain of 27 dB and a noise figure of 0.3 dB with a good input and output return loss(S_(11)<—10 dB,S_(22)<—11 dB).This LNA exhibits an input 1-dB compression point of-18 dBm,a third order input intercept point of 0 dBm and consumes 85 mW of power from a 1.8 V supply.

Network Lifetime Global Optimization for Multi-Source and Single-Sink Topology in Wireless Sensor Networks

The multi-source and single-sink(MSSS) topology in wireless sensor networks(WSNs) is defined as a network topology,where all of nodes can gather,receive and transmit data to the sink.In energy-constrained WSNs with such a topology,the joint optimal design in the physical,medium access control(MAC) and network layers is considered for network lifetime maximization(NLM).The problem of integrating multi-layer information to compute NLM,which involves routing flow,link schedule and transmission power,is formulated as a nonlinear optimization problem.Specially under time division multiple access(TDMA) scheme,this problem can be transformed into a convex optimization problem.To solve it analytically we make use of the property that local optimization is global optimization in convex problem.This allows us to exploit the Karush-Kuhn-Tucker (KKT) optimality conditions to solve it and obtain analytical solution expression,i.e.,the globally optimal network lifetime(NL).NL is derived as a function of number of nodes,their initial energy and data rate arrived at them. Based on the analysis of analytical approach,it takes the influence of data rates,link access and routing method over NLM into account.Moreover,the globally optimal transmission schemes are achieved by solution set during analytical approach and applied to algorithms in TDMA-based WSNs aiming at NLM on OMNeT++ to compare with other suboptimal schemes.

Reverse Droop Control-based Smooth Transfer Strategy for Interface Converters in Hybrid AC/DC Distribution Networks

Hybrid AC/DC distribution networks are promising candidates for future applications due to their rapid advancement in power electronics technology.They use interface converters(IFCs)to link DC and AC distribution networks.However,the networks possess drawbacks with AC voltage and frequency offsets when transferring from grid-tied to islanding modes.To address these problems,this paper proposes a simple but effective strategy based on the reverse droop method.Initially,the power balance equation of the distribution system is derived,which reveals that the cause of voltage and frequency offsets is the mismatch between the IFC output power and the rated load power.Then,the reverse droop control is introduced into the IFC controller.By using a voltage-active power/frequency-reactive power(U-P/f-Q)reverse droop loop,the IFC output power enables adaptive tracking of the rated load power.Therefore,the AC voltage offset and frequency offset are suppressed during the transfer process of operational modes.In addition,the universal parameter design method is discussed based on the stability limitations of the control system and the voltage quality requirements of AC critical loads.Finally,simulation and experimental results clearly validate the proposed control strategy and parameter design method.

Aluminum Alloy Material Structure Impact Localization by Using FBG Sensors

铝合金结构影响本地化系统由用纤维布拉格，栅栏(FBG ) 传感器和影响本地化算法被调查。察觉到网络的 four-FBG 被建立。并且力量紧张解调方法被初始化采用狭窄乐队的悦耳的激光。小浪变换被用来削弱影响信号噪音。并且影响信号时差被提取造时差本地化算法。最后，一个纤维布拉格栅栏影响本地化系统被建立并且试验性地验证了。试验性的结果与影响横座标本地化错误是的 500 公里 *500 公里 *2 公里测试区域，最大值和一般水准在铝合金板中显示出那 11 公里和 6.25 公里，和最大值和一般水准影响纵标本地化错误分别地是 9 公里和 4.25 公里。纤维布拉格栅栏传感器和解调系统是可行的认识到航空铝合金材料结构影响本地化。研究结果为铝合金材料结构影响本地化提供一个可靠方法。