Nonlinear PI control for variable pitch wind turbine

Wind turbine uses a pitch angle controller to reduce the power captured above the rated wind speed and release the mechanical stress of the drive train. This paper investigates a nonlinear PI (N-PI) based pitch angle controller, by designing an extended-order state and perturbation observer to estimate and compensate unknown time-varying nonlinearities and disturbances. The proposed N-PI does not require the accurate model and uses only one set of PI parameters to provide a global optimal performance under wind speed changes. Simulation verification is based on a simplified two-mass wind turbine model and a detailed aero-elastic wind turbine simulator (FAST), respectively. Simulation results show that the N-PI controller can provide better dynamic performances of power regulation, load stress reduction and actuator usage, comparing with the conventional PI and gain-scheduled PI controller, and better robustness against of model uncertainties than feedback linearization control.     

针对液压检测差动变压器位移传感器的设计

介绍了采用差动变压器作为传感器,通过检测其铁芯在液压和大气压2个相反方向的压力作用下产生的位移来达到检测液压的目的。详细介绍了采用平衡调制解调器芯片实现差动变压器信号检测与处理的原理和方法。由于对差动变压器副边线圈输出的差动信号进行了检相、滤波、积分等处理,经验证明:与其它检测方法相比,该传感器具有更高的灵敏度、更高的准确度、更大的灵活性。     

Nonlinear trajectory control of high pressure thawing

This paper deals with the control of the thawing front propagation in a foodstuff. Recently, many results were obtained about the large influence of the pressure on the thawing time. However, such a technology is used without any control of the thawing kinetics, which seems to affect the quality of the foodstuff. With a view to improving it and to choosing the thawing time, the melting front propagation rate has to be mastered. To achieve this objective, we propose here to use a nonlinear control methodology. This methodology is carried out on water thawing.     

Nonlinear control of mechanical systems with an unactuated cyclic variable

Numerous robotic tasks associated with underactuation have been studied in the literature. For a large number of these in the plane, the mechanical models have a cyclic variable, the cyclic variable is unactuated, and all shape variables are independently actuated. This paper formulates and solves two control problems for this class of models. If the generalized momentum conjugate to the cyclic variable is not conserved, conditions are found for the existence of a set of outputs that yields a system with a one-dimensional exponentially stable zero dynamics-i.e., an exponentially minimum-phase system-along with a dynamic extension that renders the system locally input-output decouplable. If the generalized momentum conjugate to the cyclic variable is conserved, a reduced system is constructed and conditions are found for the existence of a set of outputs that yields an empty zero dynamics, along with a dynamic extension that renders the system feedback linearizable. A common element in these two feedback problems is the construction of a scalar function of the configuration variables that has relative degree three with respect to one of the input components. The function arises by partially integrating the conjugate momentum. The results are illustrated on two balancing tasks and on a ballistic flip motion.     

Precise piston trajectory control for a free piston engine

A free piston engine removes the mechanical constraint on the piston motion by eliminating the crankshaft. The extra degree of freedom offers many advantages for reducing fuel consumption and emissions. Nevertheless, stability and robustness of the engine operation has been affected in the meantime. To ensure smooth engine operation, an active motion controller, which utilizes robust repetitive control, was developed previously to regulate the piston motion of a hydraulic free piston engine to track pre-defined trajectories. However, the long piston stroke length, high operating frequency and system nonlinearity impose challenges to precise piston motion control. Therefore, feedforward controllers are investigated in this paper to complement the repetitive control to further improve the tracking performance. The first feedforward design involves the inversion of a linear plant model that describes the dynamics of the engine operation, and the second design is based on the flatness approach, which involves the inversion of a nonlinear model of the system. The two feedforward controllers are designed and implemented on the free piston engine. The experimental and simulation results demonstrate the effectiveness of the proposed control under various operating conditions and reference piston trajectories.     

电容式位移传感器的非线性拟合比较

针对控制棒落棒时棒位指示传感器的电容和位移关系,在水平位置下,在4种不同的工况下将控制棒数据进行标定,对标定得到的电容值取最大值和最小值的二分之一作为拟合值,分别采用三次样条插值、最小二乘法、BP神经网络的方法对数据进行拟合,然后使用4种工况下得到的原始数据进行插值观察误差并做残差分析。MATLAB拟合结果表明,三次样条插值具有良好的效果。     

Fuzzy variable structure control

A new methodology is presented to improve the design and tuning of a fuzzy logic controller (FLC) using variable structure control (VSC) theory. A VSC-type rule base is constructed and the fundamentals of FLC explored quantitatively by VSC theory. A very concise mathematical expression for the FLC is presented, in which the Lyapunov stability criterion can be applied to guide the design and tuning. This results in a simpler and more systematic procedure. Application of the method to higher order systems is made straight forward by applying a hierarchical technique. The validity of the design methodology is demonstrated by simulation.     

基于Laguerre多项式的LVDT位移传感器非线性校正

针对线性可变差动变压器(LVDT)位移传感器输出电压值与位移量之间存在非线性的问题,建立了基于Laguerre多项式的位移特性曲线模型.采用递推最小二乘法对标定样本数据进行拟合,以确定位移特性曲线的模型参数.该方法根据LVDT位移传感器输出电压的测量值即可高精度计算出相应的位移量.仿真结果表明:绝对测量误差不超过0.1mm,具有明显的非线性校正效果,在位移检测领域具有重要的理论和应用价值.     

轴流压缩系统失稳现象的主动控制

为了开展对压缩系统旋转失速和喘振两类失稳现象的主动控制研究,进一步改善压缩系统防喘振控制的效果,选取了轴流压缩系统的四阶失稳模型,将容腔出口节流阀作为主动控制的作动机构,用非线性控制理论中的backstepping方法,设计抑制压缩系统失稳现象的主动控制律,应用于失稳模型,通过仿真,验证了在变转速条件下,旋转失速、喘振以及旋转失速和喘振先后发生时的控制效果.肯定了失稳主动控制比传统的防喘振控制和单纯的喘振主动控制的优越性,并通过仿真,考察了控制律对于系统特性参数和结构参数变化的鲁棒性.结论:研究压缩系统失稳的主动控制,无论在理论和实用都有重要意义.     

一种气缸位移控制系统的设计

针对传统可控位置气缸成本高的问题,设计了一种低成本气缸位移控制系统。首先,利用红外测距传感器测量活塞实际位移量;其次,通过期望位移量与实际位移量得到误差量;最后,基于BP神经网络建立气缸位移控制系统误差模型,完成误差补偿工作。实验表明:系统通过BP神经网络误差补偿后,可得最大位移误差量控制在±2 mm。     

Continuous approximation of variable structure control

A straightforward modification of the theory of ‘sliding’ variable structure control systems is used to design a control law that is a continuous arbitrarily close approximation, within a predefined subspace, to the discontinuous variable structure control law. Linear combinations of eigenvectors, and certain null spaces, are used to analyse the state trajectory under the influence of the continuous control law. Comparisons are drawn and the inherent robustness properties of variable structure control systems are retained, while the undesirable chatter motion of the sliding mode is eliminated. The accuracy of the approximation to the idealized case can easily be calculated. The general results are illustrated by the simulation of a time-invariant fourth-order multivariable system with two controls     

变频恒压供水系统模糊PID混合控制策略研究

针对城市二次供水系统的非线性、随机性、大惯性和纯滞后特性,提出一种模糊PID混合控制策略实现变频恒压供水。该策略在偏差很小时,控制量主要由PID控制算法给出:在偏差较大时,控制量主要由模糊控制算法给出,充分利用了PID控制的高调节精度和模糊控制良好动态响应性能的优点。仿真实验结果表明:该控制策略能较好地解决城市二次供水的水压不稳问题,同时对供水系统模型参数变化具有很好的适应性,在城市二次供水系统中具有广阔应用前景。     

Intelligent control for large-scale variable speed variable pitch wind turbines

Large-scale wind turbine generator systems have strong nonlinear multivariable characteristics with many uncertain factors and disturbances. Automatic control is crucial for the efficiency and reliability of wind turbines. On the basis of simplified and proper model of variable speed variable pitch wind turbines, the effective wind speed is estimated using extended Kalman filter. Intelligent control schemes proposed in the paper mchde two loops which operate in synchronism with each other. At below-rated wind speed, the inner loop adopts adaptive fuzzy control based on variable universe for generator torque regulation to realize maximum wind energy capture. At above-rated wind speed, a controller based on least square support vector machine is proposed to adjust pitch angle and keep rated output power. The simulation shows the effectiveness of the intelligent control.     

Nonlinear control of magnetically-geared drive-trains

The paper considers certain impedimental issues related to the use of magnetic gearbox and magnetic coupling technologies in high performance servo control systems. A prototype magnetic coupling is used as a basis for demonstrating that the underlying torque transfer characteristic is significantly nonlinear when transmitted torque approaches the maximum designed pull-out torque of the device. It is shown that linear controllers for speed control proportional plus integral （PI） and position control proportional plus derivative （PD） result in acceptable performance provided the magnetic coupling operates below 80 % of designed pull-out torque. To fully compensate for the inherent nonlinearity of the torque transfer characteristic, feedback linearizing control laws and state transformations are derived resulting in exactly linear input-output characteristic for position and speed control of magnetically-geared drive-trains. With the addition of state feedback, the closed-loop dynamics for both position and speed control of a magnetically-geared drive-train can be designed to satisfy the integral of time multiplied by absolute error （ITAE） optimized linear response for a step input. Outstanding results are demonstrated through simulation and experimental real-time implementation on a demonstrator magnetically-geared drive-train.     

FBG可变灵敏度压力传感器设计

为了实现对压力的多灵敏度状态下监测,设计了一种利用光纤Bragg光栅（ FBG）的可变灵敏度压力传感探头。将裸光栅固定在薄膜片中心与下部外壳之间,传感器探头表面的压力通过薄膜片传递给裸光栅,并可通过灵敏度变换阀改变膜片大小从而改变传感器的灵敏度。对薄膜片进行有限元仿真优化计算,得到其变形特性。薄膜片厚1 mm,工作半径分别调节为10,9,8 cm状态下,最大变形出现在膜片中心区域,在0.1 MPa的表面压力作用下,膜片中心处变形分别为3.875,2.561,1.579 mm,裸光栅固定后,对应的灵敏度分别为：38.44,25.62,15.79 mm/ MPa,实现灵敏度变换。     

NOFC-VRTT:一种基于变RTT的非线性AQM算法

针对网络拥塞设计一种基于变往返时间的主动队列管理算法.给出了一种新的TCP窗口观测器,证明当丢包率取值范围在0～1之间时,TCP窗口观测值渐近收敛到TCP窗口真实值.通过反步设计法设计了一种非线性输出反馈控制算法,并给出了控制参数的取值范围.NS仿真表明,NOFC-VRTT算法具有较好的鲁棒性,较高的链路利用率和较低的丢包率,并且维持了各TCP源之间的公平性.     

变截面压杆对应变式压杆压力传感器测量影响研究

用数值模拟的方法对应变式压杆压力传感器系统进行仿真,研究压杆的变截面对应变式压杆压力传感器测试结果的影响;数值模拟了不同上升前沿的梯形脉冲和三角形脉冲条件下变截面压杆的响应误差.与非变截面压杆相比,变截面压杆的应力波幅值和波形均发生了很大变化,无论梯形脉冲还是三角形脉冲,变截面压杆的应力波幅值都要降低.模拟结果对实验测试结果的分析有一定参考价值.     

基于压力和位移传感器的汽车节胎系统

针对大吨位的运输车辆(特别是半挂车)轮胎磨损严重,空载时造成轮胎无谓磨损及耗油等问题,介绍了基于压力和位移双传感器汽车智能节胎系统,通过机电一体化智能节胎的新方法,可以自适应调节汽车在重载时挂车三桥12轮工作,而当空载时挂车均为单桥4轮工作。从而减少了约30%的轮胎磨损,实现节胎、节能、延长车辆的使用寿命和保证安全行车目的。     

Structurally variable control of time-varying Lurie systems

This poses and solves the problem of structurally variable control synthesis for time-varying Lurie systems, which has both theoretical and engineering significance. A theorem on absolute stability of a set related to Lurie systems solves the problem. The theorem is basic for proving control algorithms that ensure absolute stability of a sliding subspace or its stability with finite reachability time. Moreover, they ensure the attraction in the whole of the zero equilibrium state of the whole control system of the plant on N(L). The selection of the sliding subspace can be such that the system nonlinearity does not influence the sliding motion.