Coordinated formation control of multiple nonlinear systems

A general method of controller design is developed for the purpose offormation keeping and reconfiguration of nonlinear systems with multiple subsystems, such as theformation of multiple aircraft, ground vehicles, or robot arms. The model consists of multiplenonlinear systems. Controllers are designed to keep the subsystems in a required formation and tocoordinate the subsystems in the presence of environmental changes. A step-by-step algorithm ofcontroller design is developed. Sufficient conditions for the stability of formation tracking areproved. Simulations and experiments are conducted to demonstrate some useful coordination strategiessuch as movement with a leader, simultaneous movement, series connection of formations, andhuman-machine interaction.

Multi-objective nonlinear model predictive control through switching cost functions and its applications to chemical processes

This paper proposes a switching multi-objective model predictive control(MOMPC) algorithm for constrained nonlinear continuous-time process systems.Different cost functions to be minimized in MPC are switched to satisfy different performance criteria imposed at different sampling times.In order to ensure recursive feasibility of the switching MOMPC and stability of the resulted closed-loop system,the dual-mode control method is used to design the switching MOMPC controller.In this method,a local control law with some free-parameters is constructed using the control Lyapunov function technique to enlarge the terminal state set of MOMPC.The correction term is computed if the states are out of the terminal set and the free-parameters of the local control law are computed if the states are in the terminal set.The recursive feasibility of the MOMPC and stability of the resulted closed-loop system are established in the presence of constraints and arbitrary switches between cost functions.Finally,implementation of the switching MOMPC controller is demonstrated with a chemical process example for the continuous stirred tank reactor.

Coordinated nonlinear robust control of TCSC and excitation for multi-machine systems

An advanced nonlinear robust control scheme is proposed for multi-machine power systems equipped with thyristor-controlled series compensation (TCSC). First, a decentralized nonlinear robust control approach based on the feedback linearization and H∞ theory is introduced to eliminate the nonlinearities and interconnections of the studied system, and to attenuate the exogenous disturbances that enter die system. Then, a system model is built up, which has considered all the generators’ and TCSC’s dynamics, and the effects of uncertainties such as disturbances. Next, a decentralized nonlinear robust coordinated control law is developed based on this model. Simulation results on a six-machine power system show that the transient stability of the power system is obviously improved and die power transfer capacity of long distance transmission lines is enhanced regardless of fault locations and system operation points. In addition, the control law has engineering practicality since all the variables in the expression of he control strategy can be measured locally.

Wind Farm Coordinated Control for Power Optimization

以降低风电场尾流损失、优化风场出力为目标,设计基于Laguerre函数非线性预测控制（nonlinear modelpredictive control,NLMPC）方案的风场集群控制器。该控制器应用风场动态尾流模型,通过NLMPC统一调整风场内各机组转速以提升风场功率。在控制器设计中,使用有效风速预测误差校正对预测模型失配及超短期风速预测误差进行补偿,引入Laguerre函数降低滚动时域优化计算负担并分析了控制器对风速预测误差的鲁棒性能。仿真研究表明,集群控制器能够在不同风速条件下提升风场功率、降低优化计算负担,且对风速预测模型失配与风场自然风速预测误差具有鲁棒性。

The multi-objective optimal control with X-Q adaptive controller

This paper proposes a new type of nonlinear controllers and a large phase angle allowance design method based on the multi-objective optimal control system. With the proposed method, the performance of the system becomes better than that of the original system. Then, an example of the radar servo system is designed with a large phase angle allowance multi-objective optimal design method. Finally, the performance based on computer simulation demonstrates that the multi-objective optimal system is superior to linear optimal systems.

Dynamic optimization oriented modeling and nonlinear model predictive control of the wet limestone FGD system

Nonlinear model predictive control(NMPC)scheme is an effective method of multi-objective optimization control in complex industrial systems.In this paper,a NMPC scheme for the wet limestone flue gas desulphurization(WFGD)system is proposed which provides a more flexible framework of optimal control and decision-making compared with PID scheme.At first,a mathematical model of the FGD process is deduced which is suitable for NMPC structure.To equipoise the model’s accuracy and conciseness,the wet limestone FGD system is separated into several modules.Based on the conservation laws,a model with reasonable simplification is developed to describe dynamics of different modules for the purpose of controller design.Then,by addressing economic objectives directly into the NMPC scheme,the NMPC controller can minimize economic cost and track the set-point simultaneously.The accuracy of model is validated by the field data of a 1000 MW thermal power plant in Henan Province,China.The simulation results show that the NMPC strategy improves the economic performance and ensures the emission requirement at the same time.In the meantime,the control scheme satisfies the multiobjective control requirements under complex operation conditions(e.g.,boiler load fluctuation and set point variation).The mathematical model and NMPC structure provides the basic work for the future development of advanced optimized control algorithms in the wet limestone FGD systems.

Open multilevel hierarchic intelligent control system for eco-industrial system

In allusion to the characteristics of the open complex giant system, an open multilevel hierarchic intelligent control system is established for the eco-industrial system. With the idea of the open engineering system, using the hall for workshop of metasynthetic engineering （HWME）, intelligent control techniques, the expert system and the design of experiments are integrated within the framework of the nonlinear multiobjective decision support system to develop a robust, top-level design specification so as to make the system have the quality of adaptive control, self-organizing, self-learning and robustness. Finally, an illustrative example is given to clarify the effectiveness of the method.

Multi-objective Coordination Control of Distributed Power Flow Controller

In this paper,distributed power flow controller(DPFC)constraints are analyzed.The energy balance relationship between fundamental wave and third harmonic in series and shunt-side converter is deduced.A proportional integral(PI)controller of the DPFC is constructed.The PI controller uses the voltage amplitude and phase angle injected into the system in the series side,along with the modulation ratio of the three-phase converter on the shunt side as the control variables.A multiobjective coordinated control equation is proposed,which factors the constraints of the energy balance between series and shunt side,device capacity limit,safe operation limit,fundamental component,as well as third harmonic component of the injection voltage at the series side.The equation minimizes the variance between the actual value of the control target and its given value to ensure that the DC capacitor voltage,both in the series and shunt side,is stable at target value.Simulations are conducted to verify correctness and effectiveness of the proposed control method.

Path-Following Based on Nonlinear Model Predictive Control with Adaptive Path Preview

This paper presents a Nonlinear Model Predictive Controller(NMPC)for the path following of autonomous vehicles and an algorithm to adaptively adjust the preview distance.The prediction model includes vehicle dynamics,path following dynamics,and system input dynamics.The single-track vehicle model considers the vehicle’s coupled lateral and longitudinal dynamics,as well as nonlinear tire forces.The tracking error dynamics are derived based on the curvilinear coordinates.The cost function is designed to minimize path tracking errors and control effort while considering constraints such as actuator bounds and tire grip limits.An algorithm that utilizes the optimal preview distance vector to query the corresponding reference curvature and reference speed.The length of the preview path is adaptively adjusted based on the vehicle speed,heading error,and path curvature.We validate the controller performance in a simulation environment with the autonomous racing scenario.The simulation results show that the vehicle accurately follows the highly dynamic path with small tracking errors.The maximum preview distance can be prior estimated and guidance the selection of the prediction horizon for NMPC.

A URI 4-NODE QUADRILATERAL ELEMENT BY ASSUMED STRAIN METHOD FOR NONLINEAR PROBLEMS

In this paper one-point quadrature'assumed strain'mixed element formulation based on the Hu-Washizu variational principle is presented.Special care is taken to avoid hourglass modes and volumetric locking as well as shear locking.The assumed strain fields are constructed so that those portions of the fields which lead to volumetric and shear locking phenomena are eliminated by projection,while the implementation of the proposed URI scheme is straightforward to suppress hour- glass modes.In order to treat geometric nonlinearities simply and efficiently,a corotational coordinate system is used.Several numerical examples are given to demonstrate the performance of the suggested formulation,including nonlinear static/dynamic mechanical problems.

Neural Network Based Adaptive Tracking of Nonlinear Multi-Agent System

In this paper,the problems of robust consensus tracking control for the second-order multi-agent system with uncertain model parameters and nonlinear disturbances are considered.An adaptive control strategy is proposed to smooth the agent’s trajectory,and the neural network is constructed to estimate the system’s unknown components.The consensus conditions are demonstrated for tracking a leader with nonlinear dynamics under an adaptive control algorithm in the absence of model uncertainties.Then,the results are extended to the system with unknown time-varying disturbances by applying the neural network estimation to compensating for the uncertain parts of the agents’models.Update laws are designed based on the Lyapunov function terms to ensure the effectiveness of robust control.Finally,the theoretical results are verified by numerical simulations,and a comparative experiment is conducted,showing that the trajectories generated by the proposed method exhibit less oscillation and converge faster.

五轴联动数控刀具切削加工误差非线性插补方法研究

在五轴联动数控刀具切削加工过程中,机床摆心运动轨迹和刀具运动轨迹之间的误差导致加工精度难以保持较高水平,为此提出五轴联动数控刀具切削加工误差非线性插补方法。分析刀具切削加工误差产生的原因,获得理想刀轴矢量,通过插值处理两旋转轴的运动角度,获得实际刀轴矢量误差。通过计算刀轴控制点的距离偏移值,调整刀位和刀闸位置,并使用线性补偿位移调整刀具的位移。同时,根据角度变化计算误差插补量,进一步优化刀具运行轨迹,以确保刀具轨迹始终与理想轨迹保持一致,从而实现五轴联动数控刀具运行轨迹的位移补偿。经实验验证,采用所提方法开展误差插补后,五轴联动数控刀具运行误差小,且运行轨迹贴近理想轨迹。

基于能量分析的自供能式电磁混合悬架分层协调控制

为了在保证减振性能的同时提高主动悬架的能量回收性能,提出一种基于电磁混合作动器的自供能式主动悬架系统,采用分层协调切换控制策略,包括上层控制器和下层控制器。在考虑电机损耗的情况下分析作动器的能量流动状态,得出自供能判据,设计下层非线性双闭环控制器通过馈能/供能电路实现对作动器的控制;根据对下层系统的分析,设计拥有主动、半主动、馈能3种模式的上层协调切换控制器。在MATLAB/Simulink环境中对控制策略有效性进行仿真验证,并分析电磁混合主动悬架性能,结果表明,所提出的悬架系统动态性能与无能量回收功能的主动悬架基本一致,且储能模块的平均功率小于0,符合自供能判据,在该控制策略下悬架系统可实现自供能。

面向越野车辆通过性安全的转矩协调分配研究

为了实现在通过越野地形和通过平整路面上大功率驱动时飞转车轮滑转率的快速平滑收敛,以及在执行器外特性与稳定性约束下实时优化各轮毂电机驱动功率利用率,采用前馈-反馈的闭环架构设计了纵向运动控制策略,其中前馈环节是基于垂向轮荷的实时估计与力矩矢量的预分配,优化驱动响应性并使各轮滑转率的方差最小。引入自适应滑模控制器动态跟踪四轮滑转率控制误差,构建基于鲁棒性、稳定性优化的反馈回路。仿真结果表明:该转矩协调控制系统可以有效地改善车辆的越野通过性,同时将轮胎滑移率控制在稳定范围内,提高车辆安全性。

多体柔性机械臂的非线性能量阱被动控制研究

柔性机械臂具有质量轻、能耗低、灵敏性高等优点,近年来在航空航天、机器人、军事等高科技领域被广泛应用。针对两端铰接中间亦铰接的双柔性机械臂,将其简化为多柔体梁系统。基于绝对节点坐标法推导其质量矩阵和非线性刚度矩阵,进而建立动力学模型,并采用能量原理验证模型的正确性。之后对集中荷载作用下两端铰接多柔体梁的振动响应进行分析,使用非线性能量阱对其振动进行抑制。结果表明,非线性能量阱能对多柔体梁系统由外载荷激起的振动进行有效地抑制。此外,随着非线性能量阱质量参数的增加,系统振动幅值衰减得更快,系统的振动能量损耗更迅速。

Adaptive fuzzy sliding mode control for coordinated longitudinal and lateral motions of multiple autonomous vehicles in a platoon

In this paper, the platoon control problem of autonomous vehicles in highway is studied. Since the autonomous vehicles have the characteristics of nonlinearities, external disturbances and strong coupling, a novel adaptive fuzzy sliding coordinated control system is constructed to supervise the longitudinal and lateral motions of autonomous vehicles, in which the fuzzy system is employed to approximate the unknown nonlinear functions. Due to the low sensitivity to disturbances and plant parameter variations, the proposed control approach is an efficient way to handle with the complex dynamic plants operating under un-certainty conditions. The asymptotic stability of adaptive coordinated platoon close-loop control system is verified based on the Lyapunov stability theory. The results indicate that the presented adaptive coordinated platoon control approach can accurately achieve the tracking performance and ensures the stability and riding comfort of autonomous vehicles in a platoon. Finally,simulation test is exploited to demonstrate the effectiveness of the proposed control approach.

多馈入直流系统协调控制综述

基于多馈入直流系统的强非线性、强耦合特征,分析了多馈入直流系统对协调控制技术应用于工程实际的迫切需求,从线性和非线性控制、集中和分散控制等角度综述了多馈入直流系统协调控制技术发展过程及研究现状。首先,讨论了经典线性控制、非线性控制、最优控制、鲁棒控制、自适应控制等控制方法在多馈入直流系统协调控制中的应用。然后,针对多馈入直流系统集中协调控制方法需要反馈大量远方和不可测量信号存在的工程应用问题,阐述了近年来基于分散建模理论与关联测量、分布式闭环反馈、广域测量信号反馈等方法相结合的多直流分散协调控制研究成果。最后,探讨了协调控制应用于多馈入交直流系统所面临的重要问题和未来研究方向。

基于扩张状态观测器的电力系统非线性鲁棒协调控制

该文提出了一种基于扩张状态观测器的非线性鲁棒协调控制方法(Extended-State-Observer based Nonlinear RobusCoordinated Control, ENRCC):将电力系统对象归纳为一类内环为非线性系统、外环为伪线性系统的多输入多输出对象。在此基础上,完整地阐述了 ENRCC 的控制原理:利用一簇低阶扩张状态观测器对内环非线性系统进行动态反馈线性化和解耦设计,利用线性鲁棒控制方法对已线性化的内环系统和外环伪线性系统进行预期动力学设计,最终可实现观测器+线性化+鲁棒协调控制三者的有机结合。实例仿真结果表明:该控制规律严谨简单,方法原理直观清晰,便于工程应用,具有很强的适应性和鲁棒性,能有效地解决一类 不确定+非线性+分散性的电力系统多输入多输出(MIMO)对象的控制问题。

660MW机组负荷-压力非线性特性的分析

通过实验和对运行数据的统计分析,确定1台660MW机组在50%～100%负荷范围内负荷/压力对象的简化非线性动态模型和模型中主要参数的变化规律.在此基础上对非线性模型进行线性化,获得不同负荷/压力工作点时的线性化模型,并发现其增益、惯性、非最小相位特性随工作点变化.分析表明,机组负荷/压力模型的相对非线性度随工作点均匀变化;模型非线性对系统影响主要体现在燃料指令对机前压力增益和锅炉蓄热惯性的变化上.对模型非线性特性分析的结论,可以为协调控制系统设计提供依据.现有协调控制系统中增益调度、发热量校正可以在一定程度上克服非线性的影响.

机炉协调系统的非线性输出跟踪控制

为了克服非线性环节以及能量供需之间关联耦合作用对协调系统控制品质的影响,提高单元制发电机组的快速负荷响应能力,本文基于非线性稳定逆原理,采用非线性输出跟踪控制结构,针对一个通用的非线性协调系统模型,设计出非线性输出跟踪控制器。该控制器由稳定逆系统及反馈控制器两部分组成,稳定逆系统相当于前馈部分,用于提高系统的响应速度;反馈控制器保证了系统的稳定。在不同负荷下的仿真试验表明,依据非线性输出跟踪控制策略设计出的控制系统具有良好的解耦效果和设定点跟踪能力。