Stability analysis of traffic flow with extended CACC control models

To further investigate car-following behaviors in the cooperative adaptive cruise control(CACC) strategy,a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models.In this control system,some vital comprehensive information,such as multiple preceding cars' speed differences and headway,variable safety distance(VSD) and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods.Local and string stability criterion for the velocity control(VC) model and gap control(GC) model are derived via linear stability theory.Numerical simulations are conducted to study the performance of the simulated traffic flow.The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion.     

DYNAMIC STABILITY OF TRAINS MOVING OVER BRIDGES SHAKEN BY EARTHQUAKES

The dynamic stability of trains moving over bridges shaken by earthquakes is studied. Unlike the seismic analysis of structures containing a single subsystem, the seismic analysis of a bridge sustaining a passing train requires not only information on acceleration, but also on velocity and displacement of the ground motion. Four typical earthquakes, including the 1999 Chi-Chi Earthquake, were adopted as the input excitations, each of which was normalized to have a moderate intensity. The results indicate that a train initially resting on the bridge can stay safely under the ground motions considered, if the bridge and track structures do not exhibit inelastic deformations during the earthquake. The type of the vertical component of ground motions can affect significantly the stability of the train-rail- bridge system. As a preliminary attempt, safety, possible instability and instability regions were established in a three-phase plot for the train running over the bridge for each of the earthquakes considered, from which the maximum allowable speed for the train to run safely under the specified ground acceleration can be obtained.     

Optimality and oscillations near the edge of stability in the dynamics of autonomous vehicle platoons

A model that includes the mechanical response of a vehicle to a demanded change in acceleration is analyzed to determine the string stability of a platoon of autonomous vehicles. The response is characterized by a first-order time constant τ$\tau$ and an explicit delay _td$t_d$. The minimum value of the acceleration feedback control gain is found from calculations of the velocity of vehicles following a lead vehicle that decelerates sharply from high speed to low speed. Larger values of ξ$\xi$ (in the stable range) give larger values of deceleration for vehicles in the platoon. Optimal operation is attained close to the minimum value of ξ$\xi$ for stability. Small oscillations are found after the main peak in deceleration for ξ$\xi$ in the stable region but near the transition to instability. A theory for predicting the frequency and amplitude of the oscillations is presented.     

Asymptotic stabilization of a nonlinear axially moving string by adaptive boundary control

In this paper, a robust adaptive boundary control for an axially moving string that shows nonlinear behavior resulting from spatially varying tension is investigated. A hydraulic actuator equipped with a damper is used as the control actuator at the right boundary of the string. The Lyapunov redesign method is employed to derive a robust control algorithm employing adaptation laws that estimate three unknown system parameters (mass per unit length of string, lumped mass of hydraulic actuator, and damping coefficient of damper) and an unknown boundary disturbance. The uniform asymptotic stability (when the three parameters are all unknown), the exponential stability (when they are known), and the uniform ultimate boundedness (with a bounded boundary disturbance) of the closed loop system are investigated. The convergence of the parameter estimates to the true values is shown. Numerical simulations are performed to demonstrate the effectiveness of the proposed robust adaptive boundary control.     

Boundary control of an axially moving string via fuzzy sliding-mode control and fuzzy neural network methods

The objective of this study is to develop intelligent control schemes for the transverse vibration reduction of an axially moving string. The proposed approaches are backboned by the methods of fuzzy sliding-mode control (FSMC) and fuzzy neural network control (FNNC). In practice, the control effort for the system is realized through a typical mass-damper-spring (MDS) system attached at the right-hand side boundary of the moving string. The dynamic coupling between the string and the MDS system provides an actuation force to suppress transverse vibration. In the first phase of this study, the framework of FSMC is designed, in which the techniques of region-wise linear fuzzy logic control design and generic algorithm technique are employed to facilitate FSMC to reduce a large number of fuzzy rule bases and to select optimal control gains, respectively. In the second phase, the FNNC is developed, which is, compared to the FSMC, easier to design the control rule, more robust against environment and capable of on-line learning. Numerical simulations are conducted and the comparison between various controllers is made based on simulations. The simulated results show that the transverse vibration can be well suppressed by both approaches. FSMC offers the capability to regulate the transient response, while FNNC holds advantage of on-line learning capability.     

Adaptive function project synchronization of Rössler hyperchaotic system with uncertain parameters

This Letter addresses the function project synchronization problem of two Rössler hyperchaotic in the presence of unknown system parameters. Based on Lyapunov stability theory an adaptive control law is proposed to make the states of two identical Rössler hyperchaotic systems asymptotically synchronized. Numerical simulations are presented to show the effectiveness of the proposed schemes.     

Adaptive synchronization of a critical chaotic system

This paper further investigates the synchronization problem of a new chaotic system with known or unknown system parameters. Based on the Lyapunov stability theory, a novel adaptive control law is derived for the synchronization of a new chaotic system with known or unknown system parameters. Theoretical analysis and numerical simulations show the effectiveness and feasibility of the proposed schemes.     

Chaos synchronization between Chen system and Genesio system

This Letter presents two synchronization schemes between two different chaotic systems. Active control synchronization and adaptive synchronization between Chen system and Genesio system are studied, different controllers are designed to synchronize the drive and response systems, active control synchronization is used when system parameters are known; adaptive synchronization is employed when system parameters are unknown or uncertain. Simulation results show the effectiveness of the proposed schemes.     

Lag Synchronization Between Two Coupled Networks via Open-Plus-Closed-Loop and Adaptive Controls

In this paper,we study lag synchronization between two coupled networks and apply two types of control schemes,including the open-plus-closed-loop(OPCL) and adaptive controls.We then design the corresponding control algorithms according to the OPCL and adaptive feedback schemes.With the designed controllers,we obtain two theorems on the lag synchronization based on Lyapunov stability theory and Barbalat's lemma.Finally we provide numerical examples to show the effectiveness of the obtained controllers and see that the adaptive control is stronger than the OPCL control when realizing the lag synchronization between two coupled networks with different coupling structures.     

Synchronization of hyperchaotic Chen systems: a class of the adaptive control approach

The synchronization of hyperchaotic Chen systems is considered. An adaptive synchronization approach and a cascade adaptive synchronization approach are presented to synchronize a drive system and a response system. By utilizing an adaptive controller based on the dynamic compensation mechanism, exact knowledge of the systems is not necessarily required, and the synchronous speed is controllable by tuning the controller parameters. Sufficient conditions for the asymptotic stability of the two synchronization schemes are derived. Numerical simulation results demonstrate that the adaptive synchronization scheme with four control inputs and the cascade adaptive synchronization scheme with only one control signal are effective and feasible in chaos synchronization of hyperchaotic systems.     

Synchronization of general complex networks via adaptive control schemes

In this paper, the synchronization problem of general complex networks is investigated by using adaptive control schemes. Time-delay coupling, derivative coupling, nonlinear coupling etc. exist universally in real-world complex networks. The adaptive synchronization scheme is designed for the complex network with multiple class of coupling terms. A criterion guaranteeing synchronization of such complex networks is established by employing the Lyapunov stability theorem and adaptive control schemes. Finally, an illustrative example with numerical simulation is given to show the feasibility and efficiency of theoretical results.     

统一超混沌系统的投影同步

利用两种方法研究了统一超混沌系统的同步问题.首先以全状态混合投影自适应同步方法,基于Lyapunov稳定性理论,设计了自适应控制器,理论证明了该控制器可以实现参数已知的统一超混沌系统的全状态混合映射同步.其次使用主动控制同步方法,设计了同步控制器,实现了统一超混沌系统的完全同步,最后数值仿真实验进一步验证了所提出方案的有效性. 关键词： 统一超混沌系统 自适应控制器 全状态混合投影同步 主动控制同步     

Stability of an axially accelerating string subjected to frictional guiding forces

The dynamic response of an axially translating continuum subjected to the combined effects of a pair of spring supported frictional guides and axial acceleration is investigated; such systems are both non-conservative and gyroscopic. The continuum is modeled as a tensioned string translating between two rigid supports with a time-dependent velocity profile. The equations of motion are derived with the extended Hamilton's principle and discretized in the space domain with the finite element method. The stability of the system is analyzed with the Floquet theory for cases where the transport velocity is a periodic function of time. Direct time integration using an adaptive step Runge-Kutta algorithm is used to verify the results of the Floquet theory. This approach can also be employed in the general case of arbitrary time-varying velocity. Results are given in the form of time history diagrams and instability point grids for different sets of parameters such as the location of the stationary load, the stiffness of the elastic support, and the values of initial tension. This work showed that presence of friction adversely affects stability, but using non-zero spring stiffness on the guiding force has a stabilizing effect. This work also showed that the use of the finite element method and Floquet theory is an effective combination to analyze stability in gyroscopic systems with stationary friction loads.     

基于PLC模糊自适应PID门座式起重机变频调速系统的设计与实现

为了进一步提高门座式起重机控制系统的平稳性和可靠性,在研究传统的起重机控制系统的基础上,设计了基于PLC模糊自适应PID的起重机变频调速系统,利用先进的模糊自适应PID算法与PLC控制技术相结合实现智能变频控制。系统直接由PLC实现函数运算取代常规的查表方式,改善调速性能,实现了变频调速系统的快速控制;同时,通过PLC对起重机变频器进行无触点控制,有效提高了的准确可靠性。仿真结果表明：加入模糊自适应PID控制的起重机变频调速系统比传统系统响应速度快,超调量低于3%,更加平稳可靠;同时降低了起重机功耗,节能近20%,并有效延长了电动机的使用寿命。     

Anti-synchronization of chaotic systems with uncertain parameters via adaptive control

In this Letter, an adaptive control scheme is developed to study the anti-synchronization behavior between two identical and different chaotic systems with unknown parameters. This adaptive anti-synchronization controller is designed based on Lyapunov stability theory and an analytic expression of the controller with its adaptive laws of parameters is shown. The adaptive anti-synchronization between two identical systems (Chen system) and different systems (Genesio and Lü systems) are taken as two illustrative examples to show the effectiveness of the proposed method. Theoretical analysis and numerical simulations are shown to verify the results.     

永磁同步电动机的自适应混沌控制

首先基于LaSalle不变集定理设计一种自适应控制器,实现了永磁同步电动机中的混沌控制. 然后在控制项中增加一个控制强度因子,给出了一种改进的自适应控制器. 与以往的控制方案相比,该控制方案具有最简形式,控制器可以施加在状态方程的任何一项上. 仿真结果表明了该方法的有效性和对外界随机干扰的鲁棒性. 关键词： 自适应控制 LaSalle不变集定理 永磁同步电动机 混沌控制     

Parametric control of an axially moving string via fuzzy sliding-mode and fuzzy neural network methods

This study is dedicated to design effective control schemes to suppress transverse vibration of an axially moving string system by adjusting the axial tension of the string. To this end, a continuous model in the form of partial differential equations is first established to describe the system dynamics. Using an energy-like system functional as a Lyapunov function, a sliding-mode controller (SMC) is designed to be applied when the level of vibration is not small. Due to non-analyticity of the SMC control effort generated as vibration level becoming small, two intelligent control schemes are proposed to complete the task — fuzzy sliding-mode control (FSMC) and fuzzy neural network control (FNNC). Both control approaches are based on a common structure of fuzzy control, taking switching function and its derivative as inputs and tension variation as output to reduce the transverse vibration of the string. In the framework of FSMC, genetic algorithm (GA) is utilized to search for the optimal scalings for the inputs; in addition, the technique of regionwise linear fuzzy logic control (RLFLC) is employed to simplify the computation procedure of the fuzzy reasoning. On the other hand, FNNC is proposed for conducting on-line tuning of control parameters to overcome model uncertainty. Numerical simulations are conducted to verify the effectiveness of controllers. Satisfactory stability and vibration suppression are attained for all controllers with the findings that the FSMC assisted by GA holds the advantage of fast convergence with a precise model while the FNNC is robust to model uncertainty and environmental disturbance although a relatively slower convergence could be present.     

Adaptive projective synchronization between different chaotic systems with parametric uncertainties and external disturbances

The article deals with adaptive projective synchronization between two different chaotic systems with parametric uncertainties and external disturbances. Based on Lyapunov stability theory, the projective synchronization between a pair of different chaotic systems with fully unknown parameters are derived. An adaptive control law and a parameter update rule for uncertain parameters are designed such that the chaotic response system controls the chaotic drive system. Numerical simulation results are performed to explain the effectiveness and feasibility of the techniques.     

近程巡飞弹姿态控制优化仿真研究

近程巡飞弹姿态控制系统是一个非线性、时变性及耦合性的复杂控制系统,是近程巡飞弹武器系统型号研制的关键技术之一;传统的PID控制在不同巡飞状态下调节稳定性较差、响应时间慢、影响姿态控制的稳定性和机动性;针对近程巡飞弹姿态控制系统中PID控制参数不可调,自适应、抗干扰性能较差等问题,引入了自适应模糊PID控制方法,使系统在不同巡飞姿态和干扰条件下能够实时整定PID的三个控制参数,提高系统的控制性能;在此基础上设计了近程巡飞弹的姿态角控制回路,并以俯仰角为例,在Matlab/Simulink平台下建立仿真模型,进行仿真实验;仿真结果显示,采用自适应模糊PID的控制方法,系统控制性能更好,抗干扰能力和自适应能力优于传统PID控制,减小了巡飞过程中姿态角的波动情况。     

混有协同自适应巡航控制车辆的异质交通流稳定性解析与基本图模型

针对传统车辆和协同自适应巡航控制(cooperative adaptive cruise control,CACC)车辆构成的异质交通流,研究其稳定性与基本图模型.应用实车测试验证的CACC模型和智能驾驶员模型(intelligent driver model)分别作为CACC车辆和传统车辆的跟驰模型,建立异质流稳定性解析框架,研究不同平衡态速度、不同CACC车辆比例时的异质流稳定性.推导异质流基本图模型,并进行数值仿真实验.研究结果表明,在传统车辆稳定的速度范围,异质流处于稳定状态.在传统车辆不稳定的速度范围,CACC车辆比例增加以及平衡态速度远离9.6—18.6 m/s速度范围,均能够改善异质流的不稳定性.通行能力随着CACC车辆比例的增加而提高.此外,CACC模型的期望车间时距越大,异质流稳定域越大,但通行能力降低.因此,恒定车间时距CACC控制策略下的期望车间时距取值应权衡异质流稳定域和通行能力两个方面的影响.