Stability analysis and stabilization of wireless networked control systems based on deadband control scheduling

The stability analysis and stabilization problems of the wireless networked control systems(WNCSs) with signal transmission deadbands were considered. The deadbands were respectively set up at the sensor to the controller and the controller to the actor sides in the WNCS, which were used to reduce data transmission, furthermore, to decrease the network collision and node energy consumption. Under the consideration of time-varying delays and signal transmission deadbands, the model for the WNCS was presented. A novel Lyapunov functional which took full advantages of the network factors was exploited. Meanwhile, new stability analysis and stabilization conditions for the WNCS were proposed, which described the relationship of the delay bounds, the transmission deadband bounds and the system stability. Two examples were used to demonstrate the effectiveness of the proposed methods. The results show that the proposed approach can guarantee asymptotical stability of the system and reduce the data transmission effectively.

Frequency Control of Power System with Solar and Wind Power Stations by Using Frequency Band Control and Deadband Control of HVDC Interconnection Line

In recent years, environmental problems are becoming serious and renewable energy has attracted attention as their solutions. However, the electricity generation using the renewable energy has a demerit that the output becomes unstable because of intermittent characteristics, such as variations of wind speed or solar radiation intensity. Frequency fluctuations due to the installation of large scale wind farm (WF) and photovoltaics (PV) into the power system is a major concern. In order to solve the problem, this paper proposes two control methods using High Voltage Direct Current (HVDC) interconnection line to suppress the frequency fluctuations due to large scale of WF and PV. Comparative analysis between these two control methods is presented in this paper. One proposed method is a frequency control using a notch filter, and the other is using a deadband. Validity of the proposed methods is verified through simulation analyses, which is performed on a multi-machine power system model.

Fault-Tolerant Control Research for Networked Control System under Communication Constraints

Implementing a control system over a communication network induces inevitable time delays that may degrade performance and even cause instability. One of the most effective ways to reduce the negative effect of delays on the performance of networked control system (NCS) is to reduce network traffic. In this paper, adjustable deadbands are explored as a solution to reduce network traffic in NCS. A method of fault-tolerant control of networked control system is presented, which takes into account system response as well as network traffic. The integrity design for a kind of NCS with sensor failures and actuator failures is analyzed based on robust fault-tolerant control theory and information scheduling. After detailed theoretical analysis, the paper also provides the simulation results, which further validate the proposed scheme.

Deadbands and the Dynamic Response and Performance of Large Water Transfer Canal System

An operating simulation mode for multireach canal system in series under gate regulating is established. The discharge feedforward plus water lever feedback PID controller was adopted. And the performance indicators are introduced to evaluate the control effects of canal operation. Influence on dynamic response process and dynamic performance as well as the control actions of canal system are studied according to the variation of the gate deadband and water level deadband. The results showed that the larger the gate deadband, the worse, the control effect of canal system over water level, and so done the stable process of gate discharge, yet the stable process of gate opening was getting better, while the upstream gate regulation of each canal pool was less at the time when canal stabilizes; the closer to downstream end of canal, the lager steady-state error of this canal pool was, and the lager influence of gate deadband on the steady-state error as well as response time of this canal pool was; the canal system can not acquire superiority in both the control performance and control actions when only the water level deadband was established.

Scheduling and control co-design for Networked Wind Energy Conversion Systems

Fieldbus, industrial Ethernet that is simple, reliable, economical, and practical, is widely used in Wind Energy Conversion Systems(WECSs). These techniques belong to the field of networked control systems. Network embedding to Wind Energy Conversion Systems brings many new challenges. Implementing a control system over a communication network causes inevitable time delays that may degrade performance and can even cause instability. This work addresses challenges related to the reliable control of wind energy conversion systems, based on the theoretical framework of networked control systems. A type of WECS with network-induced delay and packet dropout is modeled and adjustable deadbands are explored as a solution to reduce network traffic in WECSs. A method to study the reliable control of WECSs is presented, which takes into account system response as well as the network environment. After detailed theoretical analysis, simulation results are provided, which further demonstrate the feasibility of the proposed scheme.

一种双液压缸电液比例位置同步控制方法

双液压缸电液比例位置呈现静态与动态复杂变化,总扰动大,导致同步控制精度低。提出了一种针对双液压缸的电液比例位置同步控制方法。首先,构建双液压缸电液比例控制系统的数学模型;其次,根据系统数学模型推导动力学方程,在此基础上分析双液压缸电液比例控制系统的静态特性和动态特性;提出“同等+主从”控制策略,建立线性自抗扰同步控制器,估计并补偿双液压系统在运行过程中产生的总扰动,同时建立死区补偿器,以减小位置同步控制过程中的稳态误差,实现双液压缸电液比例位置的同步控制。实验结果表明,所提方法在x方向和y方向中,跟踪误差均控制在±1 mm以内,且超调量较小;最低可在0.51 s内达到阶跃期望位置,表现出了良好的效率和精度,具有一定应用价值。

计及调频死区的柔性风储联合频率控制策略

针对风电机组与储能系统频繁参与电力系统调频带来的机械疲劳及循环使用寿命的问题,提出一种计及调频死区的柔性风储联合频率控制策略。首先,构建含风储调频死区的系统频率响应模型,明晰调频死区变化对电网频率的动态影响;其次,通过人工设置调频死区,确定风储系统调频动作时机及限制其调频深度,将受扰系统的频率响应阶段分为无响应区、风机响应区、风储过渡区和储能响应区,同时风机在考虑有效旋转动能的基础上参与调频,平抑电网频率波动;然后,通过设置风储过渡区可有效缓解风机退出调频带来的机械疲劳问题,储能装置在荷电状态约束的条件下参与调频,遏制电网频率突变;最后,利用大扰动激励法,在连续变动风速场景下验证了所提策略的有效性。

网络控制系统动态死区反馈调度

为了在负载变化的网络环境中合理调度资源,提出了将死区控制与节点优先级分配相结合的调度器。死区控制可以在不严重影响控制质量,以及不改变系统采样率的情况下节省网络资源。结合优先级的合理分配,所设计的网络控制系统可以在网络负载较轻的时候充分利用带宽资源,在网络重负载的时候实现控制质量的逐渐降低。实验仿真结果表明:所设计的在线动态调度方法可以在变化的工作环境中改善网络控制系统的性能,提高应对工作负载变化的能力。

气动比例阀的死区补偿与仿真

针对气动比例阀的死区产生机理及对系统控制性能造成的不良影响,提出了1种新的对比例阀的死区进行补偿方法.首先分析了比例阀的摩擦力是造成其死区的主要原因,并利用神经网络控制对比例阀摩擦力进行软件补偿,消除了比例阀死区对系统稳定性的影响.并通过系统仿真研究,证明该控制方法用于气动比例阀死区补偿的正确性和有效性.该补偿方法具有较高的工程应用价值.

参数未知自相关过程的自适应边界调整策略

针对参数未知的自相关过程的质量控制问题,研究了每次调整成本固定下的自适应调整策略。建立了过程的状态空间方程模型以及未知参数的贝叶斯模糊先验分布,利用序贯蒙特卡洛法估计未知参数值进而得到了过程每个阶段的调整边界线,从而确定使过程总体损失最小的边界调整策略;给出了基于序贯蒙特卡洛法的边界调整策略的算法步骤,并通过算例验证了调整策略的有效性。结果表明,该调整策略具有较好的调整效果。

网络控制系统动态死区反馈调度的研究

针对动态环境下的网络化控制系统,基于反馈控制与网络调度协同设计的思想,提出了一种反馈调度策略,以优化系统整体控制性能为目标,根据可用带宽资源的动态变化,基于在线获取的网络运行状态,预测下一监测周期的网络利用率,然后基于网络利用率在不改变采样率的情况下对网络中各节点的死区进行在线调节,对可用带宽进行优化分配。实验仿真结果表明,所设计的动态调度方法可以在时变的网络环境中改善网络控制系统的性能。

长距离明渠调水工程蓄量动态调节控制算法研究

本文阐明了明渠渠池蓄量与节制闸闸前水位之间的单值对应关系,在此基础上提出一套通过动态调节渠池蓄量,实现闸前常水位运行的控制算法。该算法基于流量平衡和蓄量平衡关系推导,前馈控制与反馈控制相结合。前馈控制根据分水口计划主动调节各渠池蓄量,起粗调作用;反馈控制针对前馈控制过程出现的水位偏差,通过动态调节各渠池蓄量实时校正,起细调作用。该算法具有原理简单,参数率定简便,控制规则灵活,实用性强等特点。算法在南水北调东线工程胶东段渠道进行了仿真测试,模拟环境包含水位死区和闸门运动死区。结果表明,所提算法能够有效克服长距离明渠水力滞后的影响,及时有效消除各渠池闸前水位偏差,将水位波动限定在安全范围内。

基于双死区设计的空气悬架高度滑模控制方法

该文提出了一种双死区设计,运用滑模控制理论,对空气悬架的高度进行精确控制。创新点包括:区别于传统的气体多方变化假设模型,提出了基于热力学分析,利用温度-压强双控制方程建立的高精度非线性空气弹簧气室模型;提出空气悬架高度控制的双死区设置方法,通过大、小2个死区套合以提升控制精度,减少了单死区设置容易出现的振荡现象;运用滑模变结构控制理论,提出一种结合系统动力学特性、形式较简且受路面扰动和系统动力学参数变化影响较小的控制策略。通过MATLAB/Simulink仿真验证了高精度空气弹簧动力学模型和双死区设置的滑模控制策略的有效性。

带辅助控制的TCR型SVC控制策略研究

针对TCR型SVC稳态运行时为了维持电压稳定需要不断调整输出而造成损耗较多的问题,在基本电压控制策略中加入了电压死区辅助控制:在电压允许误差范围内锁定SVC,在范围外则释放SVC调节电压至范围内。在此基础上,为了能更有效地利用SVC有限的额定容量,对应设计了可根据电压大小而变化的电压参考值,确保SVC输出一直处于可调节范围内且可具有较多的无功储备。针对当系统中含有2次谐波电压分量时会导致TCR电流中产生大量的直流分量问题,加入了TCR平衡辅助控制:通过将快速傅里叶变换和PI调节相结合调制触发角使反并联的晶闸管达到在正方向和负方向的导通时间不相同,将直流电流分量减小到零,保证装置的安全运行。仿真结果表明上述辅助控制具有可行性和有效性。

一种网络资源受限情况下的NCS反馈调度方法

在网络控制系统中,网络负载的加重会使网络资源变得有限,从而使各个子系统的控制性能变差.为了改善这一情况下系统的控制品质(quality of control,QoC),本文提出了流动式死区反馈调度方法.通过对死区节点的动态选择和对死区范围的连续分配,整个系统在网络资源有限的情况下总的控制品质得到了提高.仿真结果表明,在网络资源紧缺时,该方法采用的流动式死区思想和死区范围连续化思想对系统QoC的提高是有效的.

网络控制系统中基于PID的死区反馈调度方法

在网络控制系统中,网络负载的加重会使网络资源稀缺,并导致各个子系统控制性能变差.为了改善整个系统的控制品质(QoC),提出了基于PID死区反馈调度方法,在该方法中,各节点优先级和死区节点是根据每个节点的当前控制品质动态分配和选择的,死区节点上死区范围大小采用PID调节,使得时限错过率稳定在优化的范围之内。仿真结果表明,在网络资源紧缺时,该方法能提高整个系统的控制品质。此外,该算法耗时较少,能满足实际应用中实时性和简便性的要求。

网络控制系统中的改进型死区反馈调度方法

在网络控制系统(NCS)中,死区反馈调度方法可以在网络资源紧缺时提高服务质量(QoS),但同时以牺牲控制系统的控制品质为代价。本文提出了改进型的死区反馈调度方法,在控制器中加入了预测环节,近似地恢复了失去的采样值,并计算出相应的控制信号对目标进行控制。仿真实验表明:该方法能够提高整个系统的控制性能,在一定程度上弥补死区调度方法的缺点,同时又能保证网络资源的有效利用。

阳西电厂超临界600MW机组一次调频控制功能优化

针对阳西电厂超临界600MW机组一次调频控制功能存在的发电机出口频率与电网辅助系统考核频率的差异、频率变送器精度偏差、机组负荷小幅波动时一次调频动作准确率低等问题进行了减小一次调频的动作死区等优化,优化后一次调频动作正确率达到99.92%以上,合格率考核电量为0。

基于混合死区调度策略的网络控制系统控制器设计

该文针对带宽受限的网络控制系统,在传感器端和控制器端同时设计了采用不同死区调度策略的传输死区,在传感器端采用基于信号差值的死区调度策略,在控制器端采用基于系统误差的死区调度策略,建立了考虑死区调度、时延、丢包的网络控制系统数学模型,给出了保证系统指数稳定的控制器设计方法。进行了基于真实网络和模拟被控对象的半实物仿真。实验结果表明,所提方法在保证系统稳定的基础上,明显降低了传感器和控制器的网络流量。

泵控马达调速系统中转速反馈信号的数字滤波

通过理论计算数字滤波器的等效噪声带宽,为泵控马达调速系统的电液伺服控制系统选取数字滤波器.试验表明:在采用常规PID控制算法,实施调速系统马达输出转速控制过程中,运用设置控制死区的数字滤波器,能显著提高调速系统马达输出转速的响应品质.