挖掘机高压轴向柱塞泵的虚拟样机

为利用虚拟样机技术预测挖掘机高压轴向柱塞泵的各项性能,基于AMESim和Virtual.Lab开展液压系统建模、一维与三维刚柔耦合联合仿真建模、缸体的系统级疲劳分析以及柱塞泵的辐射噪声分析,得到流量和压力特性曲线、缸体疲劳损伤结果以及各场点的声压曲线,为开展优化设计提供参考.     

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。     

Performance analysis of a new energy-efficient variable supply pressure electro-hydraulic motion control method

Electro-hydraulic actuation is used in many motion control applications due to its high power density, excellent dynamic response and good durability. However fluid power actuation has been shown to be very energy inefficient, with an average efficiency for fluid power systems across all industries of 22% in the USA. This is a very significant problem, given that 3% of the energy used by mankind is transmitted in this way.The key challenge for researchers is to reduce energy losses in hydraulic actuation systems without increasing weight, size, and noise, and without reducing speed of response. Conventional high performance electro-hydraulic motion control systems use a fixed supply pressure with valve-controlled actuators (FPVC). This is inherently inefficient due to the need to use a valve to throttle the flow required by each actuator in the system down to match its load pressure. In this paper, a new load-prediction based method is proposed, in which the supply pressure is varied to track the pressure required by any actuator branch. By implementing this model-based approach using a high response servomotor-driven pump, it is shown that the dynamic response remains excellent. The load model not only allows feedforward control for servomotor speed based on the motion demand, but also feedforward for the control valves to supplement conventional proportional-integral feedback control.The new variable supply pressure valve-controlled (VPVC) method is investigated in simulation and experimentally using a two-axis hydraulic robot arm supplied by an axial piston pump. The performance has been rigorously compared with the same robot arm using a fixed supply pressure and proportional-integral joint position control. Experimental results showed that up to 70% hydraulic power saving was achieved, and that the dynamic tracking errors for VPVC were about half that for FPVC as a result of using feedforward control.     

双馈感应风力发电机组的非线性变结构空载并网控制策略

采用矢量控制结合PI控制来实现双馈感应发电机并网时,电机的各种磁链以及电压电流交叉耦合补偿部分都会降低电网电压跟踪的速度,使动态响应性能不够理想,令超调量增大.本文采用变结构控制与全状态反馈线性化解耦相结合的控制策略,来控制双馈感应发电机组的空载并网过程.在MATLAB仿真模型基础上,从空载并网时发电机定子电压对电网电压的跟踪、并网过渡过程中定转子电流变化情况,和并网后功率调节和最大风能捕获这3个阶段进行了仿真分析.最后将非线性变结构控制器与传统矢量控制外加PI调节控制的仿真结果进行了对比分析.结果表明,采用全状态反馈线性化变结构控制的双馈感应风力发电机组,可以实现发电机的平滑并网,并网效果较好,定子电流对电网冲击小,转子电流实现比较平稳的过渡.并网后,发电机能够有效地进行最大风能捕获,实现变速恒频发电和有功、无功功率的独立调节控制.通过与传统矢量控制的比较分析,可以看出,双馈感应风力发电机组采用状态反馈精确线性化变结构控制器比传统矢量PI控制器对电网电压跟踪速度更快,动态响应更快速、调节时间和超调量更小.     

Nonlinear model predictive control scheme for stabilizing annulus pressure during oil well drilling

This paper presents a nonlinear model predictive control scheme for stabilizing the well pressure during oil well drilling. While drilling, a fluid is pumped through the drill string and the drill bit, and is returning through the annulus between the drilled well and the drill string. Varying reservoir conditions and fluctuation in circulation flow rates cause sudden variations in the pressure conditions along the well. To compensate for these pressure fluctuations, the annulus choke valve opening can be adjusted. The proposed control scheme is based on a first-principles two-phase flow model using spatial discretization of the complete well. The optimal future choke settings are found using the Levenberg–Marquardt optimization algorithm. This control scheme is evaluated against two other control methods, a manual control scheme and a standard feed-back PI-control scheme of the choke valve with feed-forward control of the pump rates. The PI-control parameters are found using the Ziegler–Nichols closed-loop method based on simulations from a low-order model. The results show that both the PI-control scheme and the model predictive control scheme are superior to manual control. However, the PI-control scheme requires that the control parameters are re-designed when the operating conditions are deviating from the original design conditions. The model predictive control scheme will perform within the operating limits as long as the detailed model is able to describe the actual conditions of the well.     

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。     

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。     

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     

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。     

Model predictive control of axial dispersion chemical reactor

This paper discusses the development of model predictive control algorithm which accounts for the input and state constraints applied to the parabolic partial differential equations (PDEs) system describing the axial dispersion chemical reactor. Spatially varying terms arising from the nonlinear PDEs model are accounted for in model development. Finite-dimensional modal representation capturing the dominant dynamics of the PDEs system is derived for controller design through Galerkin's method and modal decomposition technique. Tustin's discretization and Cayley transform are used to obtain infinite-dimensional discrete-time dynamic modal representations which are used in subsequent constrained controller design. The proposed discrete-time constrained model predictive control synthesis is constructed in a way that the objective function is only based on the low-order modal representation of the PDEs system, while higher-order modes are utilized only in the constraints of the PDEs state. Finally, the MPC formulations are successfully applied, via simulation results, to the PDEs system with input and state constraints.