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1.
Recent investigations have shown that with systemic parameters falling into a certain area a power system undergoes subcritical and supercritical Hopf, saddle-node, and period-doubling bifurcations which severely threaten the secure and stable operation of power system, even to the point of inducing voltage collapse. To control these undesirable bifurcations, an adaptive control law is presented based on the LaSalle invariance principle, which can asymptotically stabilize an unstable power system to equilibrium points. The control technique does not require analytical knowledge of the system dynamics and operates without explicit knowledge of the desired steady-state position. Simulation results show that the proposed control law is very effective. The research of this paper may help to maintain the power system’s security operation. 相似文献
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In this paper, the global exponential stabilization for the chaotic brushless DC motor (BLDCM) is considered. Based on Lyapunov-like Theorem with differential and integral inequalities, a single and linear feedback control is proposed to realize the global stabilization of BLDCM with exponential convergence rate. The guaranteed exponential convergence rate can be also correctly estimated. Computer simulation results show that the proposed method is effective. 相似文献
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A novel nonlinear control scheme of induction motor (IM) is presented based on state error port-controlled Hamiltonian (PCH) systems and energy-shaping (ES) principle. The PCH model of IM system is established. Using interconnection assignment and damping injection method, the desired state error PCH structure is assigned to the closed-loop IM system by the ES principle. The controllers are designed when the load torque is known and unknown, respectively. A load torque estimator is developed in the presence of the load torque disturbance. Moreover, an observer is proposed to estimate the unknown load torque. The stability of the closed-loop system is also verified. Finally, speed regulation of the IM drive system is implemented based on space vector pulse-width modulation technology. The simulation results show that the system has good load disturbance attenuation and speed tracking performances. 相似文献
4.
该文主要讨论了永磁直流电机的动态特性理论和测量。动态特性研究的是电动机怎样响应运行指令。首先按普通直流电机的参数讨论了效电路的推导,并把摩擦负载和转动惯量等机械参数也转化成等效电路的电参数。然后按不同的条件求出来它的传递函数。最后提出了动态特性参数的测量方法。 相似文献
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Non-dimensional mathematical model of brushless DC motor (BLDCM) system is presented here. BLDCM is known to produce chaotic phenomenon under certain conditions. This paper fuses dynamic surface control, radial basis function neural network, and adaptive technology to control the BLDCM, which overcomes the repetitive differentiation of the nonlinear terms of backstepping and the boundedness hypothesis of control gain pre-determined. The tangent barrier Lyapunov function is also used for time-delay nonlinear system with parametric uncertainties. Simulation results under different conditions indicate that the proposed method works well to suppress chaos and effects of parameter variation. 相似文献
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T. Ruggeri 《Continuum Mechanics and Thermodynamics》1989,1(1):3-20
The Galilean invariance of a generic system of balance laws dictates a specific dependence of the densities and fluxes on velocity. Thus these quantities decompose in a unique manner into convective and non-convetive parts. Such a decomposition permits the elimination of velocity dependencies in the entropy principle, which becomes a constraint on the constitutive functions only. These results clarify the mathematical structure of extended thermodynamics. They also provide a connection between the equations of continuum thermodynamics and the Boltzmann equation. 相似文献
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J. R. Saraf 《Applied Scientific Research》1973,28(1):27-36
A variational principle has been utilized to study Couette flow, and Kramers' velocity slip problem with specular-diffuse
reflection. The method leads to extremely satisfactory analytic results for the velocity slip coefficient and also for the
variation of shear stress with inverse Knudsen number. This leads us to the conclusion that the present variational principle
even with extremely simple trial functions, essentially suggested by continuum flow theory, is a useful means of computing
macroscopic quantities of physical interest in rarefied gas dynamics. 相似文献
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In this paper, we perform an intensive study of the synchronization properties of interconnected network and the concepts of vital node, and the simplest and equivalent network is firstly introduced. We strictly derive the eigenvalues of Laplacian matrix and the synchronizability of interconnected network and its simplest and equivalent network through utilizing the master stability function approach. Firstly, we find the synchronizability of interconnected network is identical to its simplest and equivalent network. Secondly, we identify the general factors that determine the synchronizability of interconnected network and further analyze the impact of different factors on the synchronizability. Finally, theoretical analysis and numerical simulations are carried out to indicate the validity and effectiveness of current analysis. The current results are beneficial to understand the dynamical behaviors of complex networked systems. 相似文献
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针对较大幅度外部不确定扰动下的四旋翼姿态稳定问题,设计了一种基于浸入与不变原理(ⅠⅠ)的自适应反步滑模控制器(ABSMC)。首先建立了未知大扰动下四旋翼姿态系统动力学模型,然后以横滚角子系统搭建为例,设计并应用了反步法和基于趋进率的滑模控制策略。在扰动估计误差流型设计中,融合了ⅠⅠ原理,即自适应率的选取实现了误差流型的不变和吸引,确保估计误差收敛到0。最后,对系统进行了稳定性分析和数字仿真。结果表明,在较大未知扰动情况下,融合ⅠⅠ原理方法后,经10 s所测跟踪误差平方的累加和仅为传统ABSMC方法的11.2%,控制精度大幅提高。 相似文献
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This work constructs a theoretical framework for the stability analysis of nonlinear fractional-order systems. A new definition, the generalized Caputo fractional derivative, is proposed for the first time. Based on that, the comparison principles for scalar and vector fractional-order systems are constructed, respectively. Furthermore, a sufficient theorem for stability analysis is proved, and how to use this theorem in stabilization is also discussed. Three examples have been presented to illustrate how to use the developed theory to analyze the stability and to design stabilization controllers. With the proposed method, the problems of stabilization and synchronization of the fractional-order chaotic fractional-order systems can be easily solved with linear feedback control. 相似文献
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Nonlinear Dynamics - This paper presents a new fault-tolerant controller based on an immersion and invariance (I&I) observer to deal with the partial loss of actuator’s effectiveness... 相似文献
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Nonlinear Dynamics - This paper is devoted to the practical tracking control for a class of flexible-joint robotic manipulators driven by DC motors. Different from the related literature where... 相似文献
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G.C. Sih 《Theoretical and Applied Fracture Mechanics》2011,55(1):1-19
Multiscale reliability places priority on the shifting of space-time scale while dual-scale reliability concentrates on time limits. Both can be ranked by applying the principle of least variance, although the prevailing criteria for assessment may differ. The elements measuring reliability can be ideally assumed to be non-interactive or interactive as a rule. Different formulations of the latter can be adopted to yield weak, strong, and mixed reliability depending on the application. Variance can also be referred to the average based on the linear sum, the root mean square, or otherwise. Preference will again depend on the physical system under consideration. Different space-time scale ranges can be chosen for the appropriate time span to failure. Up to now, only partial validation can be made due to the lack of lower scale data that are generated theoretically.A set of R-integrals is defined to account for the evolution effects by way of the root functions from Ideomechanics. The approach calls for a “pulsating mass” model that can connect the physical laws for the small and large bodies, including energy dissipation at all scale level. Non-linearity is no longer an issue when characterization of matter is made by the multiscaling of space-time. Ordinary functions can also be treated with minor modifications.The key objective is not to derive new theories, but to explain the underlying physics of existing test data, and the reliability of diversified propositions for predicting the time span to failure. Present and past investigations have remained at the micro-macro or mi-ma scale range for several decades due to the inability to quantify lower scale data. To this end, the available mi-ma fatigue crack growth data are used to generate those at the na-mi and pi-na scale ranges. Reliability variances are computed for the three different scale ranges, covering effects from the atomic to the macroscopic scale. They include the initial crack or defect length and velocities. Specimen with large initial defects are found to be more reliable. This trend also holds for each of the na-mi and pi-na scale range. Also, large specimen data had smaller reliability variances than the smaller specimens making them more reliable. Variances for the nano- and pico-scale range had much more scatter and were diversified. Uncertainties and un-reliabilities at the atomic and sub-atomic scale are no doubt related, although their connections remain to be found.Reliability with high order precisions are also defined for multi-component systems that can involve trillions of elements at the different scale ranges. Such large scale computations are now within reach by the advent of super-speed computers, especially when reliability, risk, and among other factors may have to be considered simultaneously. 相似文献
15.
Giovanni P. Galdi 《Meccanica》1977,12(4):179-186
Summary The purpose of this paper is to study, with the aid of the invariance principle for dynamical systems stated by Dafermos, the asymptotic stability of the null solution of a mixed, non-linear, first order evolution problem. As a particular case, one obtains a theorem on unconditional, asymptotic stability of stationary flows of non-isothermal magnetohydrodynamics in the Boussinesq approximation.
Work performed under the auspices of CNR (Gruppo Nazionale per la Fisica Matematica). 相似文献
Sommario Tale lavoro è rivolto allo studio della stabilità asintotica della soluzione nulla di un problema di evoluzione del primo ordine, misto e non lineare. Il metodo adoperato è quello del principio di invarianza per i sistemi dinamici di Dafermos. Come conseguenza dei risultati ottenuti, poi, si determina un teorema di stabilità asintotica incondizionata per i moti stazionari della magnetoidrodinamica non isoterma nello schema di Boussinesq.
Work performed under the auspices of CNR (Gruppo Nazionale per la Fisica Matematica). 相似文献
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随着无线通信、互联网以及数据库技术的发展和成熟,陆地移动目标导航系统经历了点、面、球三个时期的发展过程,由于数据传输网络等因素引起的时间延迟已严重影响了陆地移动目标监控服务系统的性能,传统的技术方法已不能解决问题,必须探讨新的方法新的技术.为此,本文结合当前技术发展现状,提出了基于实时交通信息的陆地移动目标跟踪原理,充分利用陆地移动目标所处环境的实时交通信息,研究目标状态信息更新策略.通过监控服务系统的应用实验结果显示,在保持原有硬件设备和系统精度条件下,通过本方法可减少90%以上的数据传输量. 相似文献
18.
A procedure to identify the imperfection in thin plates is proposed in this paper. The modified potential energy principle, which serves as the theoretical basis of the identification procedure, is improved to allow for the experimental measurements in static tests. Several typical examples are studied to illustrate the effectiveness of the procedure. 相似文献
19.
双稳态结构可以在伸展和卷拢两种状态下均保持稳定,作为一种新型可展开空间结构,其在航空航天等领域具有广阔的应用前景。选取各向同性材料作为研究对象,并假定该材料为理想弹塑性材料。建立柱壳的力学计算模型,推导结构变形时应变能的解析表达式,基于能量原理导出柱壳在两个稳定状态下的卷曲半径。结果表明,基于全量理论和增量理论的模型均能反映结构的双稳态特性,但后者能更准确地预测两个稳态对应的卷曲半径的大小。对于文中给定的柱壳,全量理论导出的卷曲半径R3x相对于增量理论结果误差为5.2%~11.6%,R5y相对误差为29.8%~41.3%。另外,应用有限元软件ABAQUS对各向同性柱壳结构的双稳态过程进行数值模拟,数值结果与增量理论结果的相对误差为0.9%~13.2%,二者吻合较好。 相似文献
20.
In this study, a variational approach to the settlement analysis of an axially loaded pier embedded in a multi-layered soil profile is presented. In this method, the soil profile and the embedded pier are divided into a number of sub-layers according to the actual number of soil layers observed in the field. The displacement shape function of each soil layer is given as a product of an exponential equation along the pier depth and the Bessel's solution in the radial direction. The displacement relationship among the layers can be derived through the transformation matrices. One of the major features of this method is that the total number of pier elements is the same as that of soil sub-layers. All the field components, such as the displacement, stress, and strain in the soil, can be calculated by closed-form solutions except that the only unknown variable is the value β which can be determined by iteration techniques. Comparisons were made with the results of finite element analysis and the field observation in pile-loaded tests. 相似文献