Two kinds of wavelet-based elements have been constructed to analyze the stability of plates and shells and the static displacement of 3D elastic problems.The scaling functions of B-spline wavelet on the interval（BSW...Two kinds of wavelet-based elements have been constructed to analyze the stability of plates and shells and the static displacement of 3D elastic problems.The scaling functions of B-spline wavelet on the interval（BSWI） are employed as interpolating functions to construct plate and shell elements for stability analysis and 3D elastic elements for static mechanics analysis.The main advantages of BSWI scaling functions are the accuracy of B-spline functions approximation and various wavelet-based elements for structural analysis.The performances of the present elements are demonstrated by typical numerical examples.展开更多
This paper provides an asymptotic expansion for the mean integrated squared error （MISE） of nonlinear wavelet-based mean regression function estimators with long memory data. This MISE expansion, when the underlying...This paper provides an asymptotic expansion for the mean integrated squared error （MISE） of nonlinear wavelet-based mean regression function estimators with long memory data. This MISE expansion, when the underlying mean regression function is only piecewise smooth, is the same as analogous expansion for the kernel estimators.However, for the kernel estimators, this MISE expansion generally fails if the additional smoothness assumption is absent.展开更多
A wavelet-based boundary element method is employed to calculate the band structures of two-dimensional phononic crystals,which are composed of square or triangular lattices with scatterers of arbitrary cross sections...A wavelet-based boundary element method is employed to calculate the band structures of two-dimensional phononic crystals,which are composed of square or triangular lattices with scatterers of arbitrary cross sections.With the aid of structural periodicity,the boundary integral equations of both the scatterer and the matrix are discretized in a unit cell.To make the curve boundary compatible,the second-order scaling functions of the B-spline wavelet on the interval are used to approximate the geometric boundaries,while the boundary variables are interpolated by scaling functions of arbitrary order.For any given angular frequency,an effective technique is given to yield matrix values related to the boundary shape.Thereafter,combining the periodic boundary conditions and interface conditions,linear eigenvalue equations related to the Bloch wave vector are developed.Typical numerical examples illustrate the superior performance of the proposed method by comparing with the conventional BEM.展开更多
This letter proposes an efficient wavelet-based Fine Granularity Scalable (FGS)coding scheme, where the base layer is encoded with a newly designed wavelet-based coder, and the enhancement layer is encoded with Progre...This letter proposes an efficient wavelet-based Fine Granularity Scalable (FGS)coding scheme, where the base layer is encoded with a newly designed wavelet-based coder, and the enhancement layer is encoded with Progressive Fine Granularity Scalable (PFGS) coding.This algorithm involves multi-frame motion compensation, rate-distortion optimizing strategy with Lagrangian cost function and context-based adaptive arithmetic coding. In order to improve efficiency of the enhancement layer coding, an improved motion estimation scheme that uses both information from the base layer and the enhancement layer is also proposed in this letter. The wavelet-based coder significantly improves the coding efficiency of the base layer compared with MPEG-4 ASP (Advanced Simple Profile) and H.26L TML9. The PFGS coding is a significant improvement over MPEG-4 FGS coding at the enhancement layer. Experiments show that single layer coding efficiency gain of the proposed scheme is about 2.0-3.0dB and 0.3-1.0dB higher than that of MPEG-4 ASP and H.26L TML9, respectively. The overall coding efficiency gain of the proposed scheme is about 4.0-5.0dB higher than that of MPEG-4 FGS.展开更多
The phasor data concentrator placement(PDCP)in wide area measurement systems(WAMS)is an optimization problem in the communication network planning for power grid.Instead of using the traditional integer linear program...The phasor data concentrator placement(PDCP)in wide area measurement systems(WAMS)is an optimization problem in the communication network planning for power grid.Instead of using the traditional integer linear programming(ILP)based modeling and solution schemes that ignore the graph-related features of WAMS,in this work,the PDCP problem is solved through a heuristic graphbased two-phase procedure(TPP):topology partitioning,and phasor data concentrator(PDC)provisioning.Based on the existing minimum k-section algorithms in graph theory,the k-base topology partitioning algorithm is proposed.To improve the performance,the“center-node-last”pre-partitioning algorithm is proposed to give an initial partition before the k-base partitioning algorithm is applied.Then,the PDC provisioning algorithm is proposed to locate PDCs into the decomposed sub-graphs.The proposed TPP was evaluated on five different IEEE benchmark test power systems and the achieved overall communication performance compared to the ILP based schemes show the validity and efficiency of the proposed method.展开更多
Flat lenses,including metalenses and diffractive lenses,have attracted considerable attention for enabling miniaturized optical systems.However,achieving large-scale flat lenses with both a large numerical aperture(NA...Flat lenses,including metalenses and diffractive lenses,have attracted considerable attention for enabling miniaturized optical systems.However,achieving large-scale flat lenses with both a large numerical aperture(NA)and high achromatic performance remains a significant challenge.In this work,we propose a structural height optimization method named focal phasor matching to achieve high-performance designs for large apertures.展开更多
Owing to the large-scale grid connection of new energy sources, several installed power electronic devices introduce sub-/supersynchronous inter-harmonics into power signals, resulting in the frequent occurrence of su...Owing to the large-scale grid connection of new energy sources, several installed power electronic devices introduce sub-/supersynchronous inter-harmonics into power signals, resulting in the frequent occurrence of subsynchronous oscillations(SSOs). The SSOs may cause significant harm to generator sets and power systems;thus, online monitoring and accurate alarms for power systems are crucial for their safe and stable operation. Phasor measurement units(PMUs) can realize the dynamic real-time monitoring of power systems. Based on PMU phasor measurements, this study proposes a method for SSO online monitoring and alarm implementation for the main station of a PMU. First, fast Fourier transform frequency spectrum analysis is performed on PMU current phasor amplitude data to obtain subsynchronous frequency components. Second, the support vector machine learning algorithm is trained to obtain the amplitude threshold and subsequently filter out safe components and retain harmful ones. Finally, the adaptive duration threshold is determined according to frequency susceptibility, amplitude attenuation, and energy accumulation to decide whether to transmit an alarm signal. Experiments based on field data verify the effectiveness of the proposed method.展开更多
This paper proposes a new algorithm for High Impedance Fault (HIF) detection using Phasor Measurement Unit (PMU). This type of faults is difficult to detect by over current protection relays because of low fault curre...This paper proposes a new algorithm for High Impedance Fault (HIF) detection using Phasor Measurement Unit (PMU). This type of faults is difficult to detect by over current protection relays because of low fault current. In this paper, an index based on phasors change is proposed for HIF detection. The phasors are measured by PMU to obtain the square summation of errors. Two types of data are used for error calculation. The first one is sampled data and the second one is estimated data. But this index is not enough to declare presence of a HIF. Therefore another index introduces in order to distinguish the load switching from HIF. Second index utilizes 3rd harmonic current angle because this number of harmonic has a special behaviour during HIF. The verification of the proposed method is done by different simulation cases in EMTP/MATLAB.展开更多
The synchronizing torque of a power system may be weakened by increasing installation of static power converters accompanied by renewable energy resources because they used to trade their favorable active power by syn...The synchronizing torque of a power system may be weakened by increasing installation of static power converters accompanied by renewable energy resources because they used to trade their favorable active power by synchronizing their output voltage with the one at the point of common coupling. In the circumstances, a concept of Virtual Synchronous Machine (VSM) is proposed, where the self-commutated power converters are emulating synchronous generators. This paper describes a converter control to contribute to enhancing the synchronizing torque. The proposed control is similar to the VSM but it simply realizes active power trades among power generation units including converter-based generators by modulating phase angles of their output voltages. Therefore, it can provide an effective support to regulate the system frequency where the total rated power of the converter-based generators increases as much as the one of conventional rotating generators like a microgrid. This paper especially focuses on its robustness where the number of converter-based generators is increased or they are dispersed in the power network. The effectiveness is verified by simulation study based on instantaneous values.展开更多
Phasor Measurement Units(PMUs)provide Global Positioning System(GPS)time-stamped synchronized measurements of voltage and current with the phase angle of the system at certain points along with the grid system.Those s...Phasor Measurement Units(PMUs)provide Global Positioning System(GPS)time-stamped synchronized measurements of voltage and current with the phase angle of the system at certain points along with the grid system.Those synchronized data measurements are extracted in the form of amplitude and phase from various locations of the power grid to monitor and control the power system condition.A PMU device is a crucial part of the power equipment in terms of the cost and operative point of view.However,such ongoing development and improvement to PMUs’principal work are essential to the network operators to enhance the grid quality and the operating expenses.This paper introduces a proposed method that led to lowcost and less complex techniques to optimize the performance of PMU using Second-Order Kalman Filter.It is based on the Asyncrhophasor technique resulting in a phase error minimization when receiving the signal from an access point or from the main access point.The MATLAB model has been created to implement the proposed method in the presence of Gaussian and non-Gaussian.The results have shown the proposed method which is Second-Order Kalman Filter outperforms the existing model.The results were tested usingMean Square Error(MSE).The proposed Second-Order Kalman Filter method has been replaced with a synchronization unit into thePMUstructure to clarify the significance of the proposed new PMU.展开更多
To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient...To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient and dynamic phasors. Based on a demonstration of the concepts and properties of dynamic phasors, the models of single-phase and three-phase inverters described by dynamic phasors are established first. Considering the numerical compatibility problem between dynamic phasors and instantaneous values, an interface scheme between dynamic phasors and instantaneous values is designed, and the efficiency and precision differences of various transformation methods are compared in detail.Finally, by utilizing MATLAB/Simulink, a hybrid simulation platform of a multi-inverter grid-connected system is built, and the efficiency and accuracy of the hybrid simulation are validated via comparison with the full electromagnetic transient simulation.展开更多
With the advent of phasor measurement unit (PMU) technology, the grid observability has got a new dimension. This facet of technology helps in getting the real-time and dynamic scenario of the grid operations which wa...With the advent of phasor measurement unit (PMU) technology, the grid observability has got a new dimension. This facet of technology helps in getting the real-time and dynamic scenario of the grid operations which was a remote possibility some decades before. Achieving this level of observability puts us at an advantage of responding to the system faults with reduced response time, and helps in restoring the grid stability within fraction of second. This paper demonstrates the detailed fault characterization from the PMU inputs, after illustrations from various real-time examples and different faults occurred in India. This paper tries to shed some light on areas where the accurate fault characterization can help the operator in taking the right decision for reliable grid operations.展开更多
This paper proposes a method for optimal placement of synchronized PMUs （phasor measurement units） in electrical power systems using a MCGA （modified canonical genetic algorithm）, which the goal is to determine th...This paper proposes a method for optimal placement of synchronized PMUs （phasor measurement units） in electrical power systems using a MCGA （modified canonical genetic algorithm）, which the goal is to determine the minimum number of PMUs, as well as the optimal location of these units to ensure the complete topological observability of the system. In case of more than one solution, a strategy of analysis of the design matrix rank is applied to determine the solution with the lower number of critical measurements. In the proposed method of placement, modifications are made in the crossover and mutation genetic operators, as well as in the formation of the subpopulation, and are considered restrictive hypotheses in the search space to improve the performance in solving the optimization problem. Simulations are performed using the IEEE 14-bus, IEEE 30-bus and New England 39-bus test systems. The proposed method is applied on the IEEE 118-bus test system considering the presence of observable zones formed by conventional measurements.展开更多
远程终端单元(remote terminal unit, RTU)是当前电网中最主要的测量终端,但是其量测量没有统一时标,更新频率低,而且存在不确定性的传输时延。而同步相量测量单元(phasor measurement unit, PMU)具有高同步、高精度等特点,成为电力系...远程终端单元(remote terminal unit, RTU)是当前电网中最主要的测量终端,但是其量测量没有统一时标,更新频率低,而且存在不确定性的传输时延。而同步相量测量单元(phasor measurement unit, PMU)具有高同步、高精度等特点,成为电力系统中重要的数据采集装置。为协调利用这两种测量数据,首先归纳出RTU量测非同步的来源,分析了量测数据不同步对状态估计和潮流计算的影响,并给出了相关的验证结果。并提出基于能量交互算子的量测数据相关性分析方法。该方法应用同步数据间相关性最大的原理,利用PMU所产生的精确数据来同步RTU数据,为混合测量系统确定测量基准时刻。通过对IEEE39节点电网和广东83节点实际电网的仿真,结果表明该方法能有效校正量测数据非同步以及改善状态估计和潮流计算精度。展开更多
基金supported by the National Natural Science Foundation of China (No. 50805028)the Key Project of Chinese Ministry of Education (No. 210170)+1 种基金Guangxi key Technologies R & D Program of China (Nos. 1099022-1 and 0900705 003)supported in part by the Excellent Talents in Guangxi Higher Education Institutions of China
文摘Two kinds of wavelet-based elements have been constructed to analyze the stability of plates and shells and the static displacement of 3D elastic problems.The scaling functions of B-spline wavelet on the interval（BSWI） are employed as interpolating functions to construct plate and shell elements for stability analysis and 3D elastic elements for static mechanics analysis.The main advantages of BSWI scaling functions are the accuracy of B-spline functions approximation and various wavelet-based elements for structural analysis.The performances of the present elements are demonstrated by typical numerical examples.
文摘This paper provides an asymptotic expansion for the mean integrated squared error （MISE） of nonlinear wavelet-based mean regression function estimators with long memory data. This MISE expansion, when the underlying mean regression function is only piecewise smooth, is the same as analogous expansion for the kernel estimators.However, for the kernel estimators, this MISE expansion generally fails if the additional smoothness assumption is absent.
基金This work is supported by the National Natural Science Foundation of China(Nos.U1909217,U1709208)Zhejiang Special Support Program for High-level Personnel Recruitment of China(No.2018R52034).
文摘A wavelet-based boundary element method is employed to calculate the band structures of two-dimensional phononic crystals,which are composed of square or triangular lattices with scatterers of arbitrary cross sections.With the aid of structural periodicity,the boundary integral equations of both the scatterer and the matrix are discretized in a unit cell.To make the curve boundary compatible,the second-order scaling functions of the B-spline wavelet on the interval are used to approximate the geometric boundaries,while the boundary variables are interpolated by scaling functions of arbitrary order.For any given angular frequency,an effective technique is given to yield matrix values related to the boundary shape.Thereafter,combining the periodic boundary conditions and interface conditions,linear eigenvalue equations related to the Bloch wave vector are developed.Typical numerical examples illustrate the superior performance of the proposed method by comparing with the conventional BEM.
基金Supported partially by the National Natural Science Foundation of China(No.69973018)and Natural Science Foundation of Hubei Province(No.99J009)
文摘This letter proposes an efficient wavelet-based Fine Granularity Scalable (FGS)coding scheme, where the base layer is encoded with a newly designed wavelet-based coder, and the enhancement layer is encoded with Progressive Fine Granularity Scalable (PFGS) coding.This algorithm involves multi-frame motion compensation, rate-distortion optimizing strategy with Lagrangian cost function and context-based adaptive arithmetic coding. In order to improve efficiency of the enhancement layer coding, an improved motion estimation scheme that uses both information from the base layer and the enhancement layer is also proposed in this letter. The wavelet-based coder significantly improves the coding efficiency of the base layer compared with MPEG-4 ASP (Advanced Simple Profile) and H.26L TML9. The PFGS coding is a significant improvement over MPEG-4 FGS coding at the enhancement layer. Experiments show that single layer coding efficiency gain of the proposed scheme is about 2.0-3.0dB and 0.3-1.0dB higher than that of MPEG-4 ASP and H.26L TML9, respectively. The overall coding efficiency gain of the proposed scheme is about 4.0-5.0dB higher than that of MPEG-4 FGS.
基金supported by the National Key Research and Development Program of China(2023YFB 2906403).
文摘The phasor data concentrator placement(PDCP)in wide area measurement systems(WAMS)is an optimization problem in the communication network planning for power grid.Instead of using the traditional integer linear programming(ILP)based modeling and solution schemes that ignore the graph-related features of WAMS,in this work,the PDCP problem is solved through a heuristic graphbased two-phase procedure(TPP):topology partitioning,and phasor data concentrator(PDC)provisioning.Based on the existing minimum k-section algorithms in graph theory,the k-base topology partitioning algorithm is proposed.To improve the performance,the“center-node-last”pre-partitioning algorithm is proposed to give an initial partition before the k-base partitioning algorithm is applied.Then,the PDC provisioning algorithm is proposed to locate PDCs into the decomposed sub-graphs.The proposed TPP was evaluated on five different IEEE benchmark test power systems and the achieved overall communication performance compared to the ILP based schemes show the validity and efficiency of the proposed method.
基金National Natural Science Foundation of China(62125504,62405288)Natural Science Foundation of Zhejiang Province(LQN25F050005)National Key Research and Development Program of China(2021YFF0502700)。
文摘Flat lenses,including metalenses and diffractive lenses,have attracted considerable attention for enabling miniaturized optical systems.However,achieving large-scale flat lenses with both a large numerical aperture(NA)and high achromatic performance remains a significant challenge.In this work,we propose a structural height optimization method named focal phasor matching to achieve high-performance designs for large apertures.
基金supported by the National Key R&D Pro gram (2017YFB0902901)National Nature Science Founda tion of China (51725702, 51627811, 51707064)。
文摘Owing to the large-scale grid connection of new energy sources, several installed power electronic devices introduce sub-/supersynchronous inter-harmonics into power signals, resulting in the frequent occurrence of subsynchronous oscillations(SSOs). The SSOs may cause significant harm to generator sets and power systems;thus, online monitoring and accurate alarms for power systems are crucial for their safe and stable operation. Phasor measurement units(PMUs) can realize the dynamic real-time monitoring of power systems. Based on PMU phasor measurements, this study proposes a method for SSO online monitoring and alarm implementation for the main station of a PMU. First, fast Fourier transform frequency spectrum analysis is performed on PMU current phasor amplitude data to obtain subsynchronous frequency components. Second, the support vector machine learning algorithm is trained to obtain the amplitude threshold and subsequently filter out safe components and retain harmful ones. Finally, the adaptive duration threshold is determined according to frequency susceptibility, amplitude attenuation, and energy accumulation to decide whether to transmit an alarm signal. Experiments based on field data verify the effectiveness of the proposed method.
文摘This paper proposes a new algorithm for High Impedance Fault (HIF) detection using Phasor Measurement Unit (PMU). This type of faults is difficult to detect by over current protection relays because of low fault current. In this paper, an index based on phasors change is proposed for HIF detection. The phasors are measured by PMU to obtain the square summation of errors. Two types of data are used for error calculation. The first one is sampled data and the second one is estimated data. But this index is not enough to declare presence of a HIF. Therefore another index introduces in order to distinguish the load switching from HIF. Second index utilizes 3rd harmonic current angle because this number of harmonic has a special behaviour during HIF. The verification of the proposed method is done by different simulation cases in EMTP/MATLAB.
文摘The synchronizing torque of a power system may be weakened by increasing installation of static power converters accompanied by renewable energy resources because they used to trade their favorable active power by synchronizing their output voltage with the one at the point of common coupling. In the circumstances, a concept of Virtual Synchronous Machine (VSM) is proposed, where the self-commutated power converters are emulating synchronous generators. This paper describes a converter control to contribute to enhancing the synchronizing torque. The proposed control is similar to the VSM but it simply realizes active power trades among power generation units including converter-based generators by modulating phase angles of their output voltages. Therefore, it can provide an effective support to regulate the system frequency where the total rated power of the converter-based generators increases as much as the one of conventional rotating generators like a microgrid. This paper especially focuses on its robustness where the number of converter-based generators is increased or they are dispersed in the power network. The effectiveness is verified by simulation study based on instantaneous values.
文摘Phasor Measurement Units(PMUs)provide Global Positioning System(GPS)time-stamped synchronized measurements of voltage and current with the phase angle of the system at certain points along with the grid system.Those synchronized data measurements are extracted in the form of amplitude and phase from various locations of the power grid to monitor and control the power system condition.A PMU device is a crucial part of the power equipment in terms of the cost and operative point of view.However,such ongoing development and improvement to PMUs’principal work are essential to the network operators to enhance the grid quality and the operating expenses.This paper introduces a proposed method that led to lowcost and less complex techniques to optimize the performance of PMU using Second-Order Kalman Filter.It is based on the Asyncrhophasor technique resulting in a phase error minimization when receiving the signal from an access point or from the main access point.The MATLAB model has been created to implement the proposed method in the presence of Gaussian and non-Gaussian.The results have shown the proposed method which is Second-Order Kalman Filter outperforms the existing model.The results were tested usingMean Square Error(MSE).The proposed Second-Order Kalman Filter method has been replaced with a synchronization unit into thePMUstructure to clarify the significance of the proposed new PMU.
基金supported by the State Grid Science and Technology Project (grant no. KJ2021-069)。
文摘To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient and dynamic phasors. Based on a demonstration of the concepts and properties of dynamic phasors, the models of single-phase and three-phase inverters described by dynamic phasors are established first. Considering the numerical compatibility problem between dynamic phasors and instantaneous values, an interface scheme between dynamic phasors and instantaneous values is designed, and the efficiency and precision differences of various transformation methods are compared in detail.Finally, by utilizing MATLAB/Simulink, a hybrid simulation platform of a multi-inverter grid-connected system is built, and the efficiency and accuracy of the hybrid simulation are validated via comparison with the full electromagnetic transient simulation.
文摘With the advent of phasor measurement unit (PMU) technology, the grid observability has got a new dimension. This facet of technology helps in getting the real-time and dynamic scenario of the grid operations which was a remote possibility some decades before. Achieving this level of observability puts us at an advantage of responding to the system faults with reduced response time, and helps in restoring the grid stability within fraction of second. This paper demonstrates the detailed fault characterization from the PMU inputs, after illustrations from various real-time examples and different faults occurred in India. This paper tries to shed some light on areas where the accurate fault characterization can help the operator in taking the right decision for reliable grid operations.
文摘This paper proposes a method for optimal placement of synchronized PMUs （phasor measurement units） in electrical power systems using a MCGA （modified canonical genetic algorithm）, which the goal is to determine the minimum number of PMUs, as well as the optimal location of these units to ensure the complete topological observability of the system. In case of more than one solution, a strategy of analysis of the design matrix rank is applied to determine the solution with the lower number of critical measurements. In the proposed method of placement, modifications are made in the crossover and mutation genetic operators, as well as in the formation of the subpopulation, and are considered restrictive hypotheses in the search space to improve the performance in solving the optimization problem. Simulations are performed using the IEEE 14-bus, IEEE 30-bus and New England 39-bus test systems. The proposed method is applied on the IEEE 118-bus test system considering the presence of observable zones formed by conventional measurements.
文摘远程终端单元(remote terminal unit, RTU)是当前电网中最主要的测量终端,但是其量测量没有统一时标,更新频率低,而且存在不确定性的传输时延。而同步相量测量单元(phasor measurement unit, PMU)具有高同步、高精度等特点,成为电力系统中重要的数据采集装置。为协调利用这两种测量数据,首先归纳出RTU量测非同步的来源,分析了量测数据不同步对状态估计和潮流计算的影响,并给出了相关的验证结果。并提出基于能量交互算子的量测数据相关性分析方法。该方法应用同步数据间相关性最大的原理,利用PMU所产生的精确数据来同步RTU数据,为混合测量系统确定测量基准时刻。通过对IEEE39节点电网和广东83节点实际电网的仿真,结果表明该方法能有效校正量测数据非同步以及改善状态估计和潮流计算精度。
