Fixed time integral sliding mode controller and its application to the suppression of chaotic oscillation in power system

Chattering phenomenon and singularity are still the main problems that hinder the practical application of sliding mode control. In this paper, a fixed time integral sliding mode controller is designed based on fixed time stability theory, which ensures precise convergence of the state variables of controlled system, and overcomes the drawback of convergence time growing unboundedly as the initial value increases in finite time controller. It makes the controlled system converge to the control objective within a fixed time bounded by a constant as the initial value grows, and convergence time can be changed by adjusting parameters of controllers properly. Compared with other fixed time controllers, the fixed time integral sliding mode controller proposed in this paper achieves chattering-free control, and integral expression is used to avoid singularity generated by derivation. Finally, the controller is used to stabilize four-order chaotic power system. The results demonstrate that the controller realizes the non-singular chattering-free control of chaotic oscillation in the power system and guarantees the fixed time convergence of state variables, which shows its higher superiority than other finite time controllers.

Robust controller design for compound control missile with fixed bounded convergence time

A robust controller for bank to turn(BTT) missiles with aerodynamic fins and reaction jet control system(RCS) is developed based on nonlinear control dynamic models comprising couplings and aerodynamic uncertainties. The fixed time convergence theory is incorporated with the sliding mode control technique to ensure that the system tracks the desired command within uniform bounded time under different initial conditions. Unlike previous terminal sliding mode approaches, the bound of settling time is independent of the initial state, which means performance metrics like convergence rate can be predicted beforehand. To reduce the burden of control design in terms of robustness, extended state observer(ESO) is introduced for uncertainty estimation with the output substituted into the controller as feedforward compensation. Cascade control structure is employed with the proposed control law and therein the compound control signal is obtained.Afterwards, control inputs for two kinds of actuators are allocated on the basis of their inherent characteristics. Finally, a number of simulations are carried out and demonstrate the effectiveness of the designed controller.

FIXED-DESIGN REGRESSION FOR LINEARTIME SERIES

This paper obtains asymptotic normality for double array sum of linear time series zeta(t), and gives its application in the regression model. This generalizes the main results in [1].

Fixed-time Consensus for Leader-follower Second-order Multi-agent Systems

We analyse the fixed-time consensus problem for multi-agent systems with leaderfollower mode. Based on a follower’s observation structure for the leader’s information, it is proved that the estimation errors can be converged to zero at a fixed time. From this stability and a sliding mode structure, we derive a control input of followers, which provides a critical support for fixed-time consensus. The simulation results demonstrate that this control approach does conduce to the implementation of the fixed-time synchronization.

FIXED-DESIGN SEMIPARAMETRIC REGRESSION FOR LINEAR TIME SERIES

This article studies parametric component and nonparametric component estimators in a semiparametric regression model with linear time series errors; their r-th mean consistency and complete consistency are obtained under suitable conditions. Finally, the author shows that the usual weight functions based on nearest neighbor methods satisfy the designed assumptions imposed.

A novel robust fixed time synchronization of complex network subject to input nonlinearity in the presence of uncertainties and external disturbances

This paper studies the global fixed time synchronization of complex dynamical network,including non-identical nodes with disturbances and uncertainties as well as input nonlinearity.First,a novel fixed time sliding manifold is constructed to achieve the fixed time synchronization of complex dynamical network with disturbances and uncertainties.Second,a novel sliding mode controller is proposed to realize the global fixed time reachability of sliding surfaces.The outstanding feature of the designed control is that the fixed convergence time of both reaching and sliding modes can be adjusted to the desired values in advance by choosing the explicit parameters in the controller,which does not rest upon the initial conditions and the topology of the network.Finally,the effectiveness and validity of the obtained results are demonstrated by corresponding numerical simulations.

Fixed-Time and Finite-Time Synchronization for a Class of Output-Coupling Complex Networks via Continuous Control

This paper mainly investigates the finite-time and fixed-time synchronization problem for a class of general output-coupling complex networks with output feedback nodes. The fixed-time and finite-time synchronization protocols are presented based on continuous controller strategies which can efficaciously eliminate chattering phenomenon existing in some previous results. Several sufficient conditions ensuring fixed-time and finite-time synchronization are derived by employing Lyapunov stability theory, linear matrix inequality (LMI) and adaptive technique. Furthermore, aimed at the model of this article, we study the problem of adaptive coupling strength in fixed-time synchronization which is rarely involved in previous results. Finally, several numerical examples are given to illustrate the effectiveness of our results.

Fixed Time Control of Dynamic Positioning Ship with Unknown Interference

This paper proposes a fixed-time control scheme to ensure that the dynamic positioning can accurately reach the specified position under external interference. A fixed-time state observer was developed to accurately estimate the total external unknown interference. Based on the dynamic positioning ship motion model, the inversion design method is used to ensure the stability of the system and eliminate various uncertain effects. A fixed-time backstepping sliding mode controller is designed. Finally, the simulation results show that the method has good performance and advantages.

Some Further Results on Fixed-Time Synchronization of Neural Networks with Stochastic Perturbations

In this paper, fixed-time (FXT) synchronization issue of a type of neural networks (NNs) with stochastic perturbations is considered. First, we obtained some novel sufficient criteria to guarantee the FXT synchronization of considered networks via introducing two types of controllers and employing some inequality techniques. Lastly, our theoretical results are verified via giving two numerical examples with their Matlab simulations.

ANN-Time Varying GARCH Model for Processes with Fixed and Random Periodicity

Financial Time Series Forecasting is an important tool to support both individual and organizational decisions. Periodic phenomena are very popular in econometrics. Many models have been built aiding capture of these periodic trends as a way of enhancing forecasting of future events as well as guiding business and social activities. The nature of real-world systems is characterized by many uncertain fluctuations which makes prediction difficult. In situations when randomness is mixed with periodicity, prediction is even much harder. We therefore constructed an ANN Time Varying Garch model with both linear and non-linear attributes and specific for processes with fixed and random periodicity. To eliminate the need for time series linear component filtering, we incorporated the use of Artificial Neural Networks (ANN) and constructed Time Varying GARCH model on its disturbances. We developed the estimation procedure of the ANN time varying GARCH model parameters using non parametric techniques.

Time-and Frequency-Domain Analysis of Ice-Induced Displacement Responses Offshore Fixed Platforms

On the basis of ice- induced forced vibration model, ice- induced displacement responses of offshore fixed platforms are investigated in both time domain and frequency domain. The relationships of ice-induced displacement responses with ice breaking modes, ice acting directions and platform structures are analyzed and determined. The results lead to an important conclusion obtained for the first time that ice breaking frequency and the natural frequency of the first mode of the platform are the two main factors that dominate the degree of vibration. The present work provides a firm basis for both design and operation of fixed platforms against ice loading.

针对机动目标的三维领从协同制导律

针对多飞行器协同拦截机动目标的实际需求,提出一种三维领从时空协同制导律。在视线方向上,基于齐次度理论和固定时间稳定理论设计一种领从协同制导律,确保从飞行器与领飞行器的相对距离和相对速度在固定时间内趋于一致,并且给出一致性误差收敛时间的上界,实现多飞行器的同时刻拦截。在视线法向上为实现以特定的碰撞角度拦截目标,设计一种固定时间收敛的非奇异终端滑模制导律,实现攻击角度的固定时间收敛,并避免了制导指令奇异引起的控制饱和问题。考虑到目标的机动对制导系统产生的不利影响,引入固定时间扰动观测器对目标加速度进行前馈补偿。运用李雅普诺夫稳定性理论来证明系统的固定时间稳定特性。通过仿真实验验证所设计制导律可以有效控制多飞行器在领从框架下同时打击机动目标,并以期望的终端角度攻击目标。

旋翼飞行机械臂固定时间滑模控制

针对旋翼飞行机械臂轨迹跟踪控制中的不确定性和扰动问题,提出了一种基于固定时间滑模观测器的滑模控制算法。首先,在广义坐标系下建立了旋翼飞行机械臂运动学与动力学模型,并设计出固定时间观测器对模型参数不确定性与外部扰动进行估计,通过在滑模中引入分段函数和饱和函数抑制固定时间观测器的抖振,加快其收敛速度。随后,将旋翼飞行机械臂划分为位置、姿态以及机械臂3个子系统,基于固定时间理论,分别对3个子系统设计了新型固定时间滑模控制器,并设计自适应趋近律以抑制滑模控制器的抖振。与传统滑模控制器相比,该控制器具有更快的收敛速度与更好的跟踪性能。利用Lyapunov稳定性理论证明了系统的稳定性。最后通过仿真实验验证了所提算法的有效性,该算法对旋翼飞行机械臂轨迹跟踪控制具有较好效果。

用于有界噪声时变矩阵计算的终端零化神经网络

为提升零化神经网络(ZNN)求解时变矩阵计算问题时的收敛性能,提出一种具有抗噪能力的终端零化神经网络(TZNN)及其对数加速形式(LA-TZNN)。对误差动态的终态吸引性展开分析,结果表明所提网络在受到有界噪声干扰时仍能在固定时间内使误差归零,其中LA-TZNN可实现对数调节时间稳定,收敛速度相较于TZNN更快。考虑到实际情况中初始误差有界,给出半全局意义上的调节时间上界,并通过设置可调参数,使网络实现预定义时间稳定。将2种模型应用于时变矩阵求逆和PUMA560机械臂重复运动规划问题,仿真结果验证了所提方法相较于传统ZNN设计,调节时间更短,收敛精度更高,并能够有效抑制有界噪声干扰。

基于事件触发的多智能体固定时间滑模一致性控制

针对具有未知扰动的非线性领导跟随多智能体系统一致性问题,提出一种基于自适应事件触发机制的分布式积分滑模固定时间一致性控制方法。考虑到未知外部扰动会使系统出现抖振,设计基于连续积分滑模面的分布式控制协议;为降低系统中各智能体的事件触发次数及能源损耗,保证向邻居智能体更新并传递采样信息,设计基于状态误差的自适应事件触发机制;采用固定时间稳定性理论证明设计的控制协议和事件触发机制可确保系统能迅速稳定;与有限时间相比,固定时间理论可使系统的稳定时间摆脱初值限制。仿真结果表明,相同条件下所提方法分别和引入连续积分滑模面的静态事件触发控制方法以及引入不连续积分滑模面的自适应事件触发控制方法相比可将触发次数分别平均降低32.01%和20.24%,在系统存在未知扰动的情况下5.2 s内即可达到状态一致,减少收敛时间的同时保证各跟随者的跟踪误差始终保持在±0.05以内。

状态受限机械臂的固定时间收敛双环自适应控制方法

针对机械臂轨迹跟踪控制中存在状态有界、参数摄动和跟踪时间不能预知的实际工程问题,提出一种固定时间收敛的双环自适应跟踪控制算法。该算法可根据控制参数预估机械臂轨迹跟踪时间,保证轨迹跟踪误差在预设有界范围内变化,且对系统内部参数摄动和外部干扰具有较强鲁棒性。数值仿真结果表明,该算法结构简单,具有较好的控制效果和工程应用前景。

多智能体系统固定时间一致性的多永磁同步电机转速协同控制

为了提高多电机转速协同控制精度,该文提出一种多智能体系统固定时间一致性的多永磁同步电机转速协同控制新思想。首先,将多永磁同步电机调速系统视为一个多智能体系统,设计了基于无向通信拓扑图的固定时间一致性协议;同时,设计了固定时间滑模观测器估计扰动并在一致性协议中引入前馈补偿,从而得到期望的q轴电流。然后,在矢量控制调速系统的框架下设计了固定时间互补滑模电流控制器,用于跟踪q轴参考电流。利用李雅普诺夫函数分别证明了控制器和观测器可以在与系统初始状态无关的情况下实现固定时间内收敛。最后,在三台永磁同步电机调速系统实验平台上与传统偏差耦合控制算法进行了对比实验验证,证明了所提控制算法的可行性和鲁棒性。

高质量的内部控制会提高企业回函效率吗?——基于证券交易所年报问询函的经验证据

年报问询函监管制度作为证券交易所监管市场的重要手段日益获得认可。为探索企业内部控制质量对年报问询函的影响,本文基于企业回函视角,运用stata15软件,采用固定效应模型进行检验及异质性分析。研究发现,高质量的企业内部控制能够提升回函效率。同时,由于产权性质和问询问题性质的不同,其回函效率亦有所差异。实证显示:非国有企业回函态度更积极,而如果问询问题性质越严重,则内部控制质量越高的企业回函效率越高。本文研究结论对于促进企业加强内部控制,提升会计信息披露质量,促进问询监管制度更好发挥效用具有积极意义。

色纺纱用黏胶纤维的连续染色工艺与染色性能

采用散纤维连续染色技术对黏胶散纤维进行连续浸渍染色后再冷堆固色,然后进行连续式水洗。分析了固色时间对黏胶纤维外观形貌、色泽指标及力学性能的影响,并对染色黏胶纤维成品的色牢度、pH和甲醛含量进行测试。结果表明:连续浸渍染色后的黏胶纤维,经冷堆24 h固色后,可获得较好的匀染性;染色黏胶纤维的力学性能略有下降,其中强度下降约15%,断裂伸长率下降约16%;染色黏胶纤维的各项色牢度、pH和甲醛含量均符合要求。

基于自适应扰动观测器的旋转弹神经网络过载驾驶仪设计

旋转弹在飞行过程中受多种干扰的影响,包括跨域飞行气动参数剧烈变化引起的模型不确定性以及飞行过程中受到的外部扰动。为了解决高动态飞行环境中双通道旋转弹的鲁棒控制问题,基于轨迹线性化控制方法,设计伪逆反馈控制器。采用径向基函数神经网络,设计自适应前馈补偿控制器,有效实现对模型不确定性的精确逼近。将神经网络逼近误差和外部扰动处理为总扰动,并基于固定时间稳定理论设计一种自适应扰动观测器,实现对总扰动的精确估计及补偿。通过Lyapunov理论,严格证明了闭环系统的最终一致有界性。通过数值仿真验证了所设计方法的有效性。