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Preventing False Trips of Zone 3 Protection Relays in Smart Grid

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Tsinghua Science and Technology 2015年第2期20卷 142-154页

作者： Jiapeng Zhang Yingfei Dong department of electrical engineering University of Hawaii

While remote zone 3 protection relays are essential to power systems, their false trips are also one of main causes related to cascading blackouts. Although many methods have been developed on traditional power systems to address this issue, the past cascading failure events showed the ineffectiveness of these methods. With the development of Smart Grid （SG）, new agent-based methods have been proposed to address this issue by utilizing SG real-time communications. We found that these solutions simply assume ideal communication networks and do not consider the effect of practical network constraints and resource management. In this paper, we propose several solutions to address practical network resource management and constraints, and further improve the agent-based solutions in order to prevent the false tripping of zone 3 relays in various conditions. We also analyze the potential issues of these solutions, and point out the future investigation in this direction.

关键词： zone 3 relay cascading failure real-time communications smart grid

Domestic PV System with Feedback Linearization-based Control Strategy for Module-level MPPT under Partial Shading Condition

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Journal of Modern Power Systems and Clean Energy 2021年第6期9卷 1530-1539页

作者： Hamidreza Toodeji Shahram Aghaei department of electrical engineering Yazd University

A partial shading condition can adversely affect the energy conversion efficiency of domestic photovoltaic(PV) systems. Connecting each PV module to a microinverter and performing module-level maximum power point tracking(MPPT)are proposed as promising solutions. In this paper, a feedback linearization-based control strategy is designed for the nonlinear system by a novel straightforward approach. The obtained nonlinear control law can independently govern each microinverter, providing module-level MPPT for PV modules without DC optimizer. Moreover, PV modules can be easily connected or disconnected due to the lug-and-play ability of the proposed controller. As a result, the proposed PV system can be easily maintained and extended even by non-expert users. Moreover,any module failure in the proposed PV system can be tolerated without impacts on the normal operation of other PV *** advantages of the proposed control strategy are verified by the simulation of a test PV system in MATLAB/Simulink under various partial shading conditions as well as adding or removing PV modules.

关键词： Domestic photovoltaic(PV)system microinverter power optimizer module-level maximum power point tracking(MPPT) plug-and-play feedback linearization-based control strategy

Characterizing uniform discharge in atmospheric helium by numerical modelling

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Chinese Physics B 2009年第2期18卷 646-651页

作者：吕博王新新罗海云梁卓 department of electrical engineering Tsinghua University

One-dimensional fluid model of dielectric barrier discharge （DBD） in helium at atmospheric pressure was established and the discharge was numerically simulated. It was found that not only the spatial distributions of the internal parameters such as the electric field, the electron density and ion density are similar to those in a low-pressure glow discharge, but also the visually apparent attribute （light emission） is exactly the same as the observable feature of a low-pressure glow discharge. This confirms that the uniform DBD in atmospheric helium is a glow type discharge. The fact that the thickness of the cathode fall layer is about 0.5 mm, much longer than that of a normal glow discharge in helium at atmospheric pressure, indicates the discharge being a sub-normal glow discharge close to normal one. The multipulse phenomenon was reproduced in the simulation and a much less complicated explanation for this phenomenon was given.

关键词： dielectric barrier discharge atmospheric pressure glow discharge glow discharge numerical simulation

Analysis of transmitter-side control methods in wireless EV charging systems

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Science China(Technological Sciences) 2018年第10期61卷 1492-1501页

作者： LIU Fang CHEN KaiNan ZHAO ZhengMing LI Kai department of electrical engineering Tsinghua University

The wireless electric vehicle(EV) charging system is highly safe and flexible. To reduce the weight and cost of EVs, the wireless charging system, which simplifies the structure inside an EV and utilizes the transmitter-side control method, has become popular. This study investigates the transmitter-side control methods in a wireless EV charging system. First, a universal wireless charging system is introduced, and the function of its transfer power is derived. It is observed that the transfer power can be controlled by regulating either the phase-shift angle or the DC-link voltage. Further, the influence of the control variables is studied using numerical analysis. Additionally, the corresponding control methods, namely the phase-shift angle and the DC-link voltage control, are compared by calculation and simulation. It is found that:(1) the system efficiency is low with the phase-shift control method because of the converter switching loss;(2) the dynamic response is slow with the DC-link voltage control method because of the large inertia of the inductor and capacitor;(3) both the control methods have limitations in their adjustable power range. Therefore, a combined control method is proposed, with the advantages of high system efficiency, fast dynamic response, and wide adjustable power range. Finally, experiments are performed to verify the validity of the theoretical analysis and the effectiveness of the proposed method. This study provides a detailed and comprehensive analysis of the transmitter-side control methods in the wireless charging system, considering the sensitivity of parameters, converter losses, system efficiency,and dynamic performance, with the dead-time effect taken into consideration. Moreover, the proposed control method can be used to realize the optimal combination of the phase-shift angle and the DC-link voltage with good dynamic performance, and it is useful for the optimal operation of the wireless charging system.

关键词： clean-energy vehicles EV charging system wireless power transfer (WPT) transmitter-side control phase-shift control DC-link voltage control combined control method

An optimized encoding method for secure key distribution by swapping quantum entanglement and its extension

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Chinese Physics B 2015年第8期24卷 183-188页

作者：高干 department of electrical engineering Tongling University

Song [Song D 2004 Phys. Rev. A69034301] first proposed two key distribution schemes with the symmetry *** find that, in the schemes, the private channels which Alice and Bob publicly announce the initial Bell state or the measurement result through are not needed in discovering keys, and Song’s encoding methods do not arrive at the ***, an optimized encoding method is given so that the efficiencies of Song’s schemes are improved by 7/3 times. Interestingly, this optimized encoding method can be extended to the key distribution scheme composed of generalized Bell states.

关键词： quantum key distribution optimized encoding method entanglement swapping generalized Bell states

An analytical framework for the incorporation of non-orthogonal pilots in massive MIMO systems

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Digital Communications and Networks 2024年第5期10卷 1267-1279页

作者： Navid Pourjafari Jalil Seifali Harsini department of electrical engineering The University of Guilan

Training-based cellular communication systems use orthogonal pilot sequences to limit pilot ***,the orthogonality constraint imposes a certain pilot length,and therefore,in communication systems with a large number of users,time-frequency resources are wasted significantly in the training *** cellular massive MIMO systems,the time-frequency resources can be used more efficiently by replacing the orthogonal pilots with shorter non-orthogonal pilot sequences in such a way that more space is available for the transmission of additional data symbols,and thus achieving higher data *** course,the use of non-orthogonal pilots introduces additional pilot contamination,so the performance improvement could be achieved under certain system conditions,which are thoroughly investigated in this *** first provide a performance analysis framework for the uplink of cellular massive MIMO systems in which the effect of user pilot non-orthogonality has been analytically *** this framework,we derive analytical expressions for the channel estimation,user Signal-to-Interference-plus-Noise-Ratio(SINR),and the average channel capacity per *** then use the proposed framework to evaluate the achievable spectral efficiency gain obtained by replacing orthogonal pilots with non-orthogonal *** particular,the existing trade-off between pilot lengths and the additional data symbols that can be transmitted by reducing the number of pilot symbols,is numerically quantified over a wide range of system parameters.

关键词： Massive MIMO Non-orthogonal pilots Cellular systems Performance analysis

Numerical demonstration of three-dimensional terahertz metamaterials based on the causality principle

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Chinese Physics B 2014年第2期23卷 518-523页

作者： Saeid Jamilan Javad Nourinia Mohammad Naghi Azarmanesh department of electrical engineering Urmia University

A parameter retrieval algorithm based on the causality principle and Kramers-Kronig （KK） relations is employed to calculate the effective parameters of three-dimensional （3D） metamaterials. Using KK relations, the branch selecting problem, which is the challenge of effective parameter retrieval method, can be removed. To reveal the validity of the proposed algorithm, the constitutive refractive index of a homogeneous polymide cube is extracted. The result is in excellent agreement with the intrinsic refractive index of the polymide. Finally, the two terahertz metamaterials with 3D structures are designed and their effective parameters are then retrieved using the proposed algorithm. Numerical simulations are performed using the fuiI-wave electromagnetic solver, CST Microwave Studio.

关键词： metamaterial three-dimensional causality principle Kramers-Kronig relations

LC-Z-Source Inverter Design and Control

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Chinese Journal of Electronics 2020年第3期29卷 580-585页

作者： Asghar Taheri Jamal Abbasi Bolaghi Mohammad Hossein Babaei department of electrical engineering University of Zanjan

The paper presents a new Z-source inverter with a low-stress reduction in the voltage of capacitors compared to the traditional Z-source inverter with the same boost factor. The proposed structure reduces costs and weight by reducing voltage *** main difference between this inverter and the traditional Z-source inverter lies in the arrangement of the components. In addition, the superiority of the proposed inverter over the L-Z-source inverter is related to the use of two capacitors instead of two diodes, which increases the boost power factor and obviates the need for the snubber circuit. Furthermore, another advantage of the proposed inverter can be extended to n cases in cascade form and the proposed inverter is continues current. The analysis,derivation of boost factor, capacitor voltages, voltages gain,and switch stress of the proposed inverter topology are carried out and are compared with the similar *** advantages of the proposed structure are verified by simulation and implementation.

关键词： Z-source inverter Voltage stress Boost factor Modulation index

Faulty Phase Identification for Transmission Line with Metal Oxide Varistor-protected Series Compensator

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Journal of Modern Power Systems and Clean Energy 2021年第1期9卷 85-93页

作者： Mohammed Hussien Hassan Musa Ling Fu Zhengyou He Yumin Lei the electrical engineering department Southwest Jiaotong UniversityChengduChina the electrical engineering department College of EngineeringAlmughtarbeen UniversityKhartoumSudan

The nonlinear operation of metal oxide varistor(MOV)-protected series compensator in transmission lines introduces complications into fault detection approaches. The accuracy of a conventional fault detection schemes is adversely affected by continuous change of the system impedance and load current at the point of a series compensation unit. Thus, this study suggests a method for detecting the faulted phase in MOV-protected series-compensated transmission lines. Primarily, the fault feature is identified using the covariance coefficients of the current samples during the fault period and the current samples during the pre-fault period. Furthermore, a convenience fault detection index is established by applying the cumulative sum technique. Extensive validation through different fault circumstances is accomplished, including different fault positions,resistances, and inception times. The experimental results show that the proposed method performs well with high resistance or impedance faults, faults in noisy conditions, and close-in and far-end faults. The proposed method is simple and efficient for faulty phase detection in MOV-protected series-compensated transmission lines.

关键词： Cumulative approach covariance coefficient high-impedance fault response time