电力电子电源场站与交流电力系统及其他电力电子电源场站间的复杂交互作用,使得基于单机和单场站思想的稳定性评估方法存在失效风险,引发了电网稳定运行的安全隐患。针对上述问题,提出一种对高比例电力电子电力系统中区域稳定性评估的...电力电子电源场站与交流电力系统及其他电力电子电源场站间的复杂交互作用,使得基于单机和单场站思想的稳定性评估方法存在失效风险,引发了电网稳定运行的安全隐患。针对上述问题,提出一种对高比例电力电子电力系统中区域稳定性评估的统一性稳定判据。首先,该文提出区域动态统一性稳定指标(unification stability index of dynamic state,USI_(1))和区域静态统一性稳定指标(unification stability index of static state,USI_(2))的定义与计算方法,并详细论述了其理论依据与物理含义;其次,提出基于相对增益矩阵(relative gain array,RGA)理论和统一性稳定指标的高比例电力电子电力系统稳定性评估方法;再次,提出由USI_(1)、USI_(2)和R_(RGA)组成的稳定性评估指标体系,构建了从场站扩展到区域、进而延伸到电力系统的稳定性评估框架;最后,实例验证了该文方法在高比例电力电子电力系统稳定性评估中的有效性。展开更多
On the basis of the theoretical analysis of a single-machine infinite-bus （SMIB）, using the modified linearized Phil- lips-Heffron model installed with unified power flow controller （UPFC）, the potential of the UP...On the basis of the theoretical analysis of a single-machine infinite-bus （SMIB）, using the modified linearized Phil- lips-Heffron model installed with unified power flow controller （UPFC）, the potential of the UPFC supplementary controller to enhance the dynamic stability of a power system is evaluated by measuring the electromechanical controllability through singular value decomposition （SVD） analysis. This controller is tuned to simultaneously shift the undamped electromeehanical modes to a prescribed zone in the s-plane. The problem of robust UPFC based damping controller is formulated as an optimization problem according to the eigenvalue-based multi-objective function comprising the damping factor, and the damping ratio of the undamped electromechanical modes to be solved using gravitational search algorithm （GSA） that has a strong ability to find the most optimistic results. The different loading conditions are simulated on a SMIB system and the rotor speed deviation, internal voltage deviation, DC voltage deviation and electrical power deviation responses are studied with the effect of this flexible AC transmission systems （FACTS） controller. The results reveal that the tuned GSA based UPFC controller using the proposed multi-objective function has an excellent capability in damping power system with low frequency oscillations and greatly enhances the dynamic stability of the power systems.展开更多
This paper obtained some theorems that can ascertain the zero solution of functional differential equations are extremely uniformly stable, extremely asymptotically stable or extremely uniformly asymptotically stable....This paper obtained some theorems that can ascertain the zero solution of functional differential equations are extremely uniformly stable, extremely asymptotically stable or extremely uniformly asymptotically stable. In the obtained theorems, the derivative of Liapunov function on t along the solutions of functional differential equations is not required to be always negative, especially, it may be even positive.展开更多
Lattice constants, total energies and densities of states of transition metals Fe, Ru and Os with BCC, FCC and HCP structures were calculated by the GGA+PBE functional and the ultrasoft pseudo-potential plane wave met...Lattice constants, total energies and densities of states of transition metals Fe, Ru and Os with BCC, FCC and HCP structures were calculated by the GGA+PBE functional and the ultrasoft pseudo-potential plane wave method, and compared with those of the first-principles projector augmented wave (PAW) method, CALPHAD method and experimental data. The results show that the lattice stability of this work is △GBCC-HCP>△GFCC-HCP>0, agreeing well with those of PAW method in the first-principles and CALPHAD method except for BCC-Fe. And the densities of state of HCP-Ru and Os have an obvious character of stable phase, agreeing completely with the results of the total energy calculations. Further analyses of atomic population show that the transition rate of electrons from s to p state for HCP, FCC and BCC crystals increases from Fe to Os, and a stronger cohesion, a higher cohesive energy or a more stable lattice between atoms of heavier metals are formed.展开更多
In this paper, the nonlinear singular stabilization, H∞ control problem of systems with ordinary homogeneous properties is considered. At first, we discuss the stabilization problems of nonlinear systems with homogen...In this paper, the nonlinear singular stabilization, H∞ control problem of systems with ordinary homogeneous properties is considered. At first, we discuss the stabilization problems of nonlinear systems with homogeneous. Secondly, by vitue of Hamilton-Jacobi-Isaacs equations or inequalities, we solve regular H∞ of nonlinear systems with homogeneous properties. To overcome the H∞ problem of singular nonlinear system, we try to transform inputs of the singular nonlinear system into two parts： regular part input and singular part input. Following the previous results, we solve the singular nonlinear system H∞ control, we give the Lyapunov function and the state feedback controller of the singular nonlinear systems with homogeneous properties.展开更多
This paper studies the existence, uniqueness, and stability of solutions for stochastic impulsive systems. By employing Lyapunov-like functions, some sufficient conditions of the global existence, uniqueness, and stab...This paper studies the existence, uniqueness, and stability of solutions for stochastic impulsive systems. By employing Lyapunov-like functions, some sufficient conditions of the global existence, uniqueness, and stability of solutions for stochastic impulsive systems are established. Furthermore, the results are specialized to the case of linear stochastic impulsive systems. Finally, some examples are given to illustrate the applications of our theory.展开更多
This paper shows how the so called von Karman model can be obtained as a singular limit of a modified Mindlin-Timoshenko system when the modulus of elasticity in shear κ tends to infinity, provided a regularizing ter...This paper shows how the so called von Karman model can be obtained as a singular limit of a modified Mindlin-Timoshenko system when the modulus of elasticity in shear κ tends to infinity, provided a regularizing term through a fourth order dispersive operator is added. Introducing damping mechanisms, the authors also show that the energy of solutions for this modified Mindlin-Timoshenko system decays exponentially, uniformly with respect to the parameter k. As κ→∞, the authors obtain the damped von Karman model with associated energy exponentially decaying to zero as well.展开更多
The polarizabilities and hyperpolarizabilities of the tetrahydropyrrole diradical in different electronic states have been investigated using ab initio and density functional theory （DFT） methods combined with the f...The polarizabilities and hyperpolarizabilities of the tetrahydropyrrole diradical in different electronic states have been investigated using ab initio and density functional theory （DFT） methods combined with the finite field （FF） approach. The polarizability average value as is a maximum for the singlet state, while that for the closed-shell is a minimum. The trend in second hyperpolarizability average value yis in good agreement with that for as The yvalues of the singlet and triplet states are, respectively, about 3 and 2 times larger than that of the closed-shell. The order of the first hyperpolarizability total effective value βtot is βot （closed shell） βtot （singlet） 〉 βtot （triplet）. The as, βtot, and 7 values of different electronic states obtained using the B3LYP and MP4SDQ methods are close to those obtained using the reliable CCSD method. The nonlinear optical （NLO） properties of two systems isoelectronic with the tetrahydropyrrole diradical-cyclopentane and tetrahydrofuran diradicalsshow that the polarizabilities and hyperpolarizabilities of these systems are all smaller than those of the tetrahydropyrrole diradical in the three electronic states.展开更多
文摘电力电子电源场站与交流电力系统及其他电力电子电源场站间的复杂交互作用,使得基于单机和单场站思想的稳定性评估方法存在失效风险,引发了电网稳定运行的安全隐患。针对上述问题,提出一种对高比例电力电子电力系统中区域稳定性评估的统一性稳定判据。首先,该文提出区域动态统一性稳定指标(unification stability index of dynamic state,USI_(1))和区域静态统一性稳定指标(unification stability index of static state,USI_(2))的定义与计算方法,并详细论述了其理论依据与物理含义;其次,提出基于相对增益矩阵(relative gain array,RGA)理论和统一性稳定指标的高比例电力电子电力系统稳定性评估方法;再次,提出由USI_(1)、USI_(2)和R_(RGA)组成的稳定性评估指标体系,构建了从场站扩展到区域、进而延伸到电力系统的稳定性评估框架;最后,实例验证了该文方法在高比例电力电子电力系统稳定性评估中的有效性。
文摘On the basis of the theoretical analysis of a single-machine infinite-bus （SMIB）, using the modified linearized Phil- lips-Heffron model installed with unified power flow controller （UPFC）, the potential of the UPFC supplementary controller to enhance the dynamic stability of a power system is evaluated by measuring the electromechanical controllability through singular value decomposition （SVD） analysis. This controller is tuned to simultaneously shift the undamped electromeehanical modes to a prescribed zone in the s-plane. The problem of robust UPFC based damping controller is formulated as an optimization problem according to the eigenvalue-based multi-objective function comprising the damping factor, and the damping ratio of the undamped electromechanical modes to be solved using gravitational search algorithm （GSA） that has a strong ability to find the most optimistic results. The different loading conditions are simulated on a SMIB system and the rotor speed deviation, internal voltage deviation, DC voltage deviation and electrical power deviation responses are studied with the effect of this flexible AC transmission systems （FACTS） controller. The results reveal that the tuned GSA based UPFC controller using the proposed multi-objective function has an excellent capability in damping power system with low frequency oscillations and greatly enhances the dynamic stability of the power systems.
基金National Natural Science Foundation ofChina( No.1983 10 3 0 )
文摘This paper obtained some theorems that can ascertain the zero solution of functional differential equations are extremely uniformly stable, extremely asymptotically stable or extremely uniformly asymptotically stable. In the obtained theorems, the derivative of Liapunov function on t along the solutions of functional differential equations is not required to be always negative, especially, it may be even positive.
基金Project(20070533118) supported by the Doctoral Discipline Foundation of Ministry of Education of ChinaProjects(50471058, 50271085) supported by the National Natural Science Foundation of ChinaProject supported by the Postdoctoral Foundation of Central South University, China
文摘Lattice constants, total energies and densities of states of transition metals Fe, Ru and Os with BCC, FCC and HCP structures were calculated by the GGA+PBE functional and the ultrasoft pseudo-potential plane wave method, and compared with those of the first-principles projector augmented wave (PAW) method, CALPHAD method and experimental data. The results show that the lattice stability of this work is △GBCC-HCP>△GFCC-HCP>0, agreeing well with those of PAW method in the first-principles and CALPHAD method except for BCC-Fe. And the densities of state of HCP-Ru and Os have an obvious character of stable phase, agreeing completely with the results of the total energy calculations. Further analyses of atomic population show that the transition rate of electrons from s to p state for HCP, FCC and BCC crystals increases from Fe to Os, and a stronger cohesion, a higher cohesive energy or a more stable lattice between atoms of heavier metals are formed.
基金Supported by the Education Department of Henan Province(200511517007)
文摘In this paper, the nonlinear singular stabilization, H∞ control problem of systems with ordinary homogeneous properties is considered. At first, we discuss the stabilization problems of nonlinear systems with homogeneous. Secondly, by vitue of Hamilton-Jacobi-Isaacs equations or inequalities, we solve regular H∞ of nonlinear systems with homogeneous properties. To overcome the H∞ problem of singular nonlinear system, we try to transform inputs of the singular nonlinear system into two parts： regular part input and singular part input. Following the previous results, we solve the singular nonlinear system H∞ control, we give the Lyapunov function and the state feedback controller of the singular nonlinear systems with homogeneous properties.
基金This research is supported by the National Natural Science Foundation of China under Grant No. 60274007, and the Post Doctoral Foundation of China and the Excellent Young Program of the Education Department of Hunan Province under Grant No. 04B068, and the NSERC-Canada.
文摘This paper studies the existence, uniqueness, and stability of solutions for stochastic impulsive systems. By employing Lyapunov-like functions, some sufficient conditions of the global existence, uniqueness, and stability of solutions for stochastic impulsive systems are established. Furthermore, the results are specialized to the case of linear stochastic impulsive systems. Finally, some examples are given to illustrate the applications of our theory.
基金supported by INCTMat, FAPESQ-PB, CNPq (Brazil) under Grant Nos. 308150/2008-2 and 620108/2008-8the MICINN (Spain) under Grant No. MTM2008-03541+1 种基金the Advanced Grant FP7-246775 NUMERIWAVES of the ERCthe Project PI2010-04 of the Basque Government
文摘This paper shows how the so called von Karman model can be obtained as a singular limit of a modified Mindlin-Timoshenko system when the modulus of elasticity in shear κ tends to infinity, provided a regularizing term through a fourth order dispersive operator is added. Introducing damping mechanisms, the authors also show that the energy of solutions for this modified Mindlin-Timoshenko system decays exponentially, uniformly with respect to the parameter k. As κ→∞, the authors obtain the damped von Karman model with associated energy exponentially decaying to zero as well.
基金supported by the National Natural Science Foundation of China (20873017)the Program for Changjiang Scholars and Innovative Research Teams in University (IRT0714)
文摘The polarizabilities and hyperpolarizabilities of the tetrahydropyrrole diradical in different electronic states have been investigated using ab initio and density functional theory （DFT） methods combined with the finite field （FF） approach. The polarizability average value as is a maximum for the singlet state, while that for the closed-shell is a minimum. The trend in second hyperpolarizability average value yis in good agreement with that for as The yvalues of the singlet and triplet states are, respectively, about 3 and 2 times larger than that of the closed-shell. The order of the first hyperpolarizability total effective value βtot is βot （closed shell） βtot （singlet） 〉 βtot （triplet）. The as, βtot, and 7 values of different electronic states obtained using the B3LYP and MP4SDQ methods are close to those obtained using the reliable CCSD method. The nonlinear optical （NLO） properties of two systems isoelectronic with the tetrahydropyrrole diradical-cyclopentane and tetrahydrofuran diradicalsshow that the polarizabilities and hyperpolarizabilities of these systems are all smaller than those of the tetrahydropyrrole diradical in the three electronic states.
