Vibration Control of A Flexible Marine Riser System Subject to Input Dead Zone and Extraneous Disturbances

An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances.The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision.Specifically,based on the adaptive backstepping framework,virtual control laws and Lyapunov functions are designed for each subsystem.Three direction interference observers are designed to track the timevarying boundary disturbance.On this basis,the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone.In addition,the stability of the closed-loop system is proven by Lyapunov stability theory.All the system states are bounded,and the vibration offset of the riser converges to a small area of the initial position.Finally,four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller.

Adaptive Fuzzy Control for a Class of MIMO Nonlinear Systems with Unknown Dead-zones

A design scheme of adaptive fuzzy controller for a class of uncertain MIMO nonlinear systems with unknown dead-zones and a triangular control structure is proposed in this pa-per. The design is based on the principle of sliding mode control and the property of Nussbaum function. The approach does not require a priori knowledge of the signs of the control gains and the upper bounds and lower bounds of dead-zone parameters to be known a priori. By introducing the integral-type Lyapunov function and adopting the adaptive compensation term of the upper bound of the optimal approximation error and the dead-zone disturbance, the closed-loop control system is proved to be semi-globally stable in the sense that all signals involved are bounded, with tracking errors converging to zero.

ADAPTIVE CONTROL OF FLEXIBLE BEAM WITH UNKNOWN DEAD-ZONE IN THE DRIVING MOTOR

Adaptive control of a flexible beam system preceded by an unknown dead-zonein the driving motor is investigated in state space form. By introducing an important lemma forsimplifying error equation between the flexible beam model and the matching reference model, arobust adaptive control scheme is developed by involving the dead-zone inverse terms. The newadaptive control law ensures global stability of the entire system and achieves desired trackingprecision even when the slopes of the dead-zone are not equal. Simulations performed on a typicalflexible beam system illustrate and clarify the validity of this approach.

Adaptive Variable Structure Control of MIMO Nonlinear Systems with Time-varying Delays and Unknown Dead-zones

In this paper, adaptive variable structure neural control is presented for a class of uncertain multi-input multi-output （MIMO） nonlinear systems with state time-varying delays and unknown nonlinear dead-zones. The unknown time-varying delay uncer- tainties are compensated for using appropriate Lyapunov-Krasovskii functionals in the design. The approach removes the assumption of linear function outside the deadband without necessarily constructing a dead-zone inverse as an added contribution. By utilizing the integral-type Lyapunov function and introducing an adaptive compensation term for the upper bound of the residual and optimal approximation error as well as the dead-zone disturbance, the closed-loop control system is proved to be semi-globally uniformly ultimately bounded. In addition, a modified adaptive control algorithm is given in order to avoid the high-frequency chattering phenomenon. Simulation results demonstrate the effectiveness of the approach.

A Flux DC Bias Suppression Scheme of Single-stage Full-bridge PFC Converters Based on Dead Zone Adjustment

由于单级桥式功率因数校正（power factor correction,PFC）AC/DC变换技术电路的特点,导致高频变压器存在偏磁现象,影响了系统正常工作。传统方式通过增加变压器气隙或使用隔直电容来防止变压器出现偏磁,但是该类方案影响了系统性能,并增加了电路的复杂程度。结合有源钳位单级PFC变换器工作特点,提出一种基于死区调节的偏磁抑制策略,通过改变系统的开关时序,能够有效抑制偏磁,具有不增加主电路复杂程度、不影响系统性能、数字控制和模拟控制都能够实现等优点。在提出抑制策略的基础上,设计实现电路,给出死区设计方法及影响规律,最后进行实验研究。理论分析及实验结果表明,该策略能够在不影响系统性能的基础上,有效抑制单级桥式PFC变换器的高频变压器偏磁。

Design of Observer-based Adaptive Controller for Nonlinear Systems with Unmodeled Dynamics and Actuator Dead-zone

This paper presents an up-to-date study on the observer-based control problem for nonlinear systems in the presence of unmodeled dynamics and actuator dead-zone.By introducing a dynamic signal to dominate the unmodeled dynamics and using an adaptive nonlinear damping to counter the effects of the nonlinearities and dead-zone input,the proposed observer and controller can ensure that the closed-loop system is asymptotically stable in the sense of uniform ultimate boundedness.Only one adaptive parameter is needed no matter how many unknown parameters there are.The system investigated is more general and there is no need to solve Linear matrix inequality （LMI）.Moreover,with our method,some assumptions imposed on nonlinear terms and dead-zone input are relaxed.Finally,simulations illustrate the effectiveness of the proposed adaptive control scheme.

Adaptive variable structure control for large-scale time-delayed systems with unknown nonlinear dead-zone

The problem of adaptive fuzzy control for a class of large-scale, time-delayed systems with unknown nonlinear dead-zone is discussed here. Based on the principle of variable structure control, a design scheme of adaptive, decentralized, variable structure control is proposed. The approach removes the conditions that the dead-zone slopes and boundaries are equal and symmetric, respectively. In addition, it does not require that the assumptions that all parameters of the nonlinear dead-zone model and the lumped uncertainty are known constants. The adaptive compensation terms of the approximation errors axe adopted to minimize the influence of modeling errors and parameter estimation errors. By theoretical analysis, the closed-loop control system is proved to be semiglobally uniformly ultimately bounded, with tracking errors converging to zero. Simulation results demonstrate the effectiveness of the approach.

Parameter estimation for dual-rate sampled Hammerstein systems with dead-zone nonlinearity

The identification of nonlinear systems with multiple sampled rates is a difficult task.The motivation of our paper is to study the parameter estimation problem of Hammerstein systems with dead-zone characteristics by using the dual-rate sampled data.Firstly,the auxiliary model identification principle is used to estimate the unmeasurable variables,and the recursive estimation algorithm is proposed to identify the parameters of the static nonlinear model with the dead-zone function and the parameters of the dynamic linear system model.Then,the convergence of the proposed identification algorithm is analyzed by using the martingale convergence theorem.It is proved theoretically that the estimated parameters can converge to the real values under the condition of continuous excitation.Finally,the validity of the proposed algorithm is proved by the identification of the dual-rate sampled nonlinear systems.

New Dead⁃zone Compensation Approach for Proportional Flow Valve

To solve the dead⁃zone in the output flow curve of the proportional flow valve without displacement sensor,a dead⁃zone compensation approach is proposed in this paper.Instead of detection and feedback of the valve spool position,the proposed approach adopted the pressure drop across the valve metering orifice to accomplish the dead⁃zone compensation.The first step was to test and get the_(max)imum output flow,Q_(max),at a preset reference pressure drop,such asΔP_(0).The next step was to construct the target compensation flow curve,which is a line through(0,0)and(ΔP_(0),Q_(max)).Then a compensation law was designed to approach the target curve.However,the research results show that the above strategy caused over⁃compensation once the actual pressure drop deviated fromΔP_(0).Thus a correction coefficient,β,was presented to correct the initial compensation law as the pressure drop deviated fromΔP_(0).For example,the test results indicate that the corrected compensation approach could reduce the dead⁃zone from 53.9%to 3.5%at a pressure drop of 1 MPa;as the pressure drop was increased to 5 MPa,the dead⁃zone was reduced from 51.7%to 3.5%.Therefore,the following conclusions can be drawn:the proposed compensation approach is feasible,which can effectively reduce the dead⁃zone and improve the output flow static performance of the proportional flow valve without spool displacement feedback.

基于改进快速行进平方法的无人帆船动态避碰方法

[目的]为解决无人帆船在开阔水域的多船避碰问题,对基于改进快速行进平方(IFMS)法的局部动态避碰算法进行研究。[方法]考虑到帆船的速度不可控,将其避碰行为转化为航向控制问题,并以总势场梯度下降方向为期望避碰航向。当帆船没有碰撞危险或顺风航行时,仅通过构造时间势场来避开所有静止不规则障碍并到达目标点;而当帆船存在航行约束时,根据《国际海上避碰规则》(COLREGS)为特定会遇场景设计高斯似然函数用以动态地构建障碍势场。同时,考虑到帆船的航行死区,引入局部风势场,实现帆船动态避碰与“之”字形航行策略相结合的应用需求。[结果]结果显示,所提算法可以使无人帆船在遵守避碰规则和避免航行死区的同时,成功地在各种会遇场景下实现与其他帆船、受限机动船的避碰操作,相比原始快速行进平方(FMS)算法,逆风航行时间大大缩短,避碰航迹也更加合理、安全。[结论]所提方法符合帆船运动特性及避碰规则,在复杂环境下具有较高的安全性和鲁棒性,对无人帆船自主避障技术发展具有一定的科学价值。

不同进水方式对污泥床膨胀的影响

为了探究不同进水方式对污泥膨胀床性能的影响,设计一种侧向进水物理模型和四种不同进水夹角的底部进水口的数值模型,对比分析计算流体力学的三维模拟与实物模型的运行状态。结果表明:侧向进水方式污泥床在进水时膨胀速率比底部进水方式快19%;进水流量对两种进水方式的污泥膨胀高度及死区面积的减少有显著影响,在模拟中倾角为15°时,流量提升2.7倍,死区面积减少87%;底部圆锥倾角的变化,对死区产生显著的影响;侧向进水时,流场分为左右两部分,未有明显的优先流,底部进水则存在沿中轴线前进的主流,两侧的速度场分布梯度较小。

含高比例新能源的异步互联送端系统直流FLC的阶跃死区控制策略及优化

针对含高比例新能源的异步送端系统直流频率限制控制器(FLC)死区控制及参数优化问题,提出了一种直流FLC阶跃死区控制策略。基于考虑含高比例新能源的多机系统频率响应模型,分析了直流FLC死区参数以及高比例新能源装机容量对送端系统频率响应的影响。加入阶跃决策系统,构建改进型直流FLC阶跃死区控制策略。搭建兼顾直流FLC动作特性以及对送端系统频率偏差抑制效果的改进型直流FLC阶跃死区控制策略参数优化模型。使用群智能算法求解出改进型直流FLC阶跃死区控制器最优参数。仿真结果表明优化后的直流FLC死区控制方法可以显著改善送端系统的频率稳定支撑能力。

基于自适应平滑死区逆的航天气化炉氧气流量控制

航天气化炉氧气流量对象具有大噪声、非线性和强干扰特性,氧气流量控制系统自动化程度低。由于氧气阀门具有死区非线性,人工操作和常规控制策略常常无法获得理想的控制效果,因此提出了一种自适应平滑死区逆算法,补偿氧气阀门的死区非线性,再引入氧气主管压力的变化速度作为前馈量,补偿氧气压力波动带来的干扰。自适应平滑死区逆与前馈控制成功应用于航天气化炉氧气流量控制系统,控制效果明显改善。

瓦斯隧道多工作面施工通风死区控制方法研究

针对瓦斯隧道多工作面作业时,易形成施工通风死区这一安全问题,以阳宗公路瓦斯隧道为依托工程,对压入式通风方案中风管最优布设方式进行研究,并在此基础上确定射流风机的最佳布设距离,进而探究多作业面通风系统中的射流风机最佳布设方案。研究结果显示:在满足最低需风量的压入式通风方案中,不同的风管布设方案会使隧道内通风死区体积变化较大,为控制并消除通风死区,风管出口应尽可能靠近掌子面且风管直径不宜过大;随着隧道掘进距离的增加,在掌子面前方会形成固定范围的非通风死区,此时为布设射流风机的最佳距离;射流风机的布设能有效地消除通风死区,但其作用范围有限,当隧道距离过长时,应有序间隔布设射流风机。

机械搅拌驱动下固液混沌混合特性数值模拟

混沌搅拌对于理解复杂系统行为、改善混合过程的效率和质量以及推动科学和技术的发展具有重要意义。通过数值模拟计算,从搅拌迹线和流场揭示了混沌搅拌的搅拌效果优于普通匀速搅拌。通过流场迹线分析,得出混沌搅拌强化搅拌效果的根本原因是混沌搅拌打破了搅拌的隔离死区。同时混沌搅拌所产生的整个流场的紊乱程度要远远大于普通匀速搅拌。

地层动态测试器流量死区补偿方法

地层动态测试器在石油资源勘探领域中承担重要角色,其核心功能为通过预测试室测量地层渗透率。随着勘探任务逐渐走向超深井化,受井下高温影响,地层动态测试器预测试室模块的电液系统存在明显流量死区现象。因此,通过数值仿真定量分析其性能缺陷具有重要意义。首先介绍地层动态测试器预测试室模块的电液系统组成及特性;其次建立Simulink-AMESim联合仿真模型,结合数学模型对流量死区进行分析;接着结合实际工况确定动态性能补偿方案,并进行仿真验证。结果表明,提出的方案可以有效减轻高温导致的性能缺陷,有利于提升地层动态测试器作业的稳定性。

一种添加振荡抑制的移动机器人避障算法

针对室内移动机器人动态避障算法易出现局部死区问题,提出一种改进VFH动态避障算法。首先,针对传统VFH类算法,在候选波谷评价函数中引入波谷宽度和路径长度评价指标以降低移动机器人陷入局部死区的概率,提高路径平滑性;其次,针对局部避障算法受限于局部环境易在障碍物附近发生来回振荡的问题,引入振荡评价函数,通过计算移动机器人位姿到起始点和终点的加权欧氏距离绘制振荡评价曲线,利用自动峰值检测和一阶前向差分曲线获取振荡位置,并添加振荡抑制,使移动机器人逃离局部死区。仿真验证表明,在100组仿真场景中,改进算法陷入局部死区的场景减少约70组,平均规划迭代次数降低约32.3次,平均路径长度降低约26.2%,平均累计转折角度降低约79.6%。该算法有效降低了局部避障的代价,提高路径平滑度的同时降低在局部特殊环境下陷入死区的概率。

具有死区非线性输入的柔性臂自适应边界控制

研究了具有死区非线性和输入信号量化的柔性机械臂系统的边界控制问题。考虑柔性臂系统分布参数的特点,采用偏微分方程和边界条件描述柔性机械臂系统的动力学模型,并采用随机量化器对输入信号进行量化。对于输入受限的柔性机械臂系统,设计了一种自适应边界控制器,使柔性机械臂系统到达期望角度的同时抑制柔性机械臂系统的振动。该控制方案既能保证系统的稳定性,又能在输入信号量化和死区非线性的前提下满足控制要求。同时,利用Lyapunov方法证明了柔性机械臂系统的最终一致有界性。最后,通过数值仿真验证了所提出方法的有效性。

高比例新能源电网中储能调频死区优化设定控制策略

高比例新能源的接入使新型电力系统的净功率波动以及低惯量特性不断增强,给系统频率调节与稳定带来更大挑战。针对日益提升的调频需求,提出一种电网储能死区优化调频控制策略。首先,构建了含储能调频死区的电网频率响应模型,分析了随着新能源渗透率的提升系统频率的变化特性,并阐述了传统死区的不足之处。其次,提出一种基于调频阶段分区的死区优化设置方法,根据频率当前变化状态,设定不同的死区响应模式。基于描述函数法定量分析了死区非线性环节对系统稳定性的影响,给出了考虑死区影响的储能调频下垂系数的稳定边界。此外,提出了储能参与调频的容量配置方法。最后,搭建含新能源场站的区域电力系统模型,对比了不同死区设定下的系统调频动态特性。结果表明,所提新型死区设定方法可以有效改善电网的频率质量,减轻系统的调频负担,且所提死区设定方法不会增加储能的容量配置需求,具有一定的经济实用价值。