PID Control of Planar Nonlinear Uncertain Systems in the Presence of Actuator Saturation

This paper investigates PID control design for a class of planar nonlinear uncertain systems in the presence of actuator saturation. Based on the bounds on the growth rates of the nonlinear uncertain function in the system model, the system is placed in a linear differential inclusion. Each vertex system of the linear differential inclusion is a linear system subject to actuator saturation. By placing the saturated PID control into a convex hull formed by the PID controller and an auxiliary linear feedback law, we establish conditions under which an ellipsoid is contractively invariant and hence is an estimate of the domain of attraction of the equilibrium point of the closed-loop system. The equilibrium point corresponds to the desired set point for the system output. Thus, the location of the equilibrium point and the size of the domain of attraction determine, respectively, the set point that the output can achieve and the range of initial conditions from which this set point can be reached. Based on these conditions, the feasible set points can be determined and the design of the PID control law that stabilizes the nonlinear uncertain system at a feasible set point with a large domain of attraction can then be formulated and solved as a constrained optimization problem with constraints in the form of linear matrix inequalities (LMIs). Application of the proposed design to a magnetic suspension system illustrates the design process and the performance of the resulting PID control law.      

Active disturbance rejection based trajectory linearization control for hypersonic reentry vehicle with bounded uncertainties

This paper investigates a novel compound control scheme combined with the advantages of trajectory linearization control (TLC) and alternative active disturbance rejection control (ADRC) for hypersonic reentry vehicle (HRV) attitude tracking system with bounded uncertainties. Firstly, in order to overcome actuator saturation problem, nonlinear tracking differentiator (TD) is applied in the attitude loop to achieve fewer control consumption. Then, linear extended state observers (LESO) are constructed to estimate the uncertainties acting on the LTV system in the attitude and angular rate loop. In addition, feedback linearization (FL) based controllers are designed using estimates of uncertainties generated by LESO in each loop, which enable the tracking error for closed-loop system in the presence of large uncertainties to converge to the residual set of the origin asymptotically. Finally, the compound controllers are derived by integrating with the nominal controller for open-loop nonlinear system and FL based controller. Also, comparisons and simulation results are presented to illustrate the effectiveness of the control strategy.     

Intriguing nonlinear dynamics of a controller with a sluggish actuator

We apply a bifurcation-theoretic approach to the standard Moore–Greitzer compressor model in effort to understand a curious phenomenon. When one forces the actuator to respond sluggishly to commanded inputs, performance of the controller improves dramatically. We show that the behavior can be explained via Hopf–Hopf interactions of surge and rotating stall. Also, we argue that there is a broad class of controllers which possess the general dynamic features responsible for the surprising effectiveness of sluggish actuators.     

Robust State Feedback Control Through Actuators With Generalized Sector Nonlinearities And Saturation

In control systems, actuators often have nonlinear characteristics that can not be neglected. For linear systems driven by actuators satisfying the generalized sector condition, a robust state feedback controller synthesis method is proposed to achieve the ultimate boundedness control. The method is based on the linear matrix inequality approach and is easy to apply. As an important special case of the generalized sector condition, the saturation characteristic of actuators is discussed separately, and non‐conservative results are obtained.     

An attempt to compare the performance of bioscrubbers and biotrickling filters for degradation of ethyl acetate in gas streams

This study presents a comparison of the efficiency of a bioscrubber and a biotrickling filter (BTF) for the removal of ethyl acetate (EA) vapour from a waste gas stream, under the same operating conditions. The maximum EA elimination capacity achieved in the bioscrubber was 550 g m^?3 h^?1 with removal efficiency higher than 96%. For higher EA loadings the bioscrubber was oxygen limited, which caused incomplete EA biodegradation. When pure oxygen was fed to the bioscrubber at a rate of 0.02 L min^?1, the bioscrubber recovered and could treat higher EA loadings without any oxygen limitation. The BTF achieved EA elimination capacity of 600 g m^?3 h^?1 with removal efficiency higher than 97% and the dissolved oxygen concentration remained substantially higher than in the bioscrubber. However, severe channelling and blockage of the spray nozzle occurred due to the excessive biomass growth. Overall, the bioscrubber system was easier to operate and control than the BTF, while an enhancement of the oxygen mass transfer in the bioscrubber could potentially increase its performance by up to three times. Copyright © 2005 Society of Chemical Industry     

Robustness issues in optimal control of unstable plants

This paper presents a robustness analysis of the optimal solution of the step tracking problem in a one-degree of freedom control architecture, for the discrete-time multivariable (MIMO) case. It is shown that the resulting closed loop becomes arbitrarily fragile, i.e. the sensitivity peak becomes arbitrarily large, for certain reference directions. The cause of this problem is that the optimal controller depends on the reference direction. The paper shows that this dependence can be eliminated with an alternative formulation of the optimal problem where the cost is averaged over all reference directions.     

BIMORPH PIEZOELECTRIC ACTUATOR FOR SMALL PIPE ROBOT

An experimental bimorph piezoelectric element (PZT) actuator for small pipe robot is developed. The robot can move in φ20 mm pipe, and can carry a CCD camera for detecting cracks or fine holes on inner surface of pipe. The velocity of the robot can reach 17～22 mm/s for vertical pipe up/down, respectively. Moving principle and its performance characteristics are presented.     

Constraints on benthic algal response to nutrient addition in oligotrophic mountain rivers

Nutrient availability has long been considered one of the most important factors regulating production of benthic algae in oligotrophic rivers; yet, empirical relationships do not have as wide an application as similar models derived for lentic systems. The aim of this research was to derive empirical relationships between nutrient concentrations and benthic algal abundance and to identify commonalities with other studies to improve our understanding of constraints on algae in oligotrophic rivers. Surveys of physical, chemical and biological attributes of oligotrophic mountain rivers in spring, summer and autumn for 2 years confirmed that small amounts of anthropogenic phosphorus (0.1–5.6 µg/L total phosphorus (TP)) resulted in 4‐ to 30‐fold increases in abundance of benthic algae and benthic macroinvertebrates (BMIs). Algal accrual along a gradient in nutrient availability was not masked by grazing pressure but was positively correlated with abundance of scrapers. Epilithic abundance was highest downstream of anthropogenic nutrient sources in autumn. We concluded that benthic algal abundance in these mountain rivers was weakly correlated with phosphorus availability if light was not limiting but ultimately controlled by temperature and river discharge. Therefore, we recommend more direct measures of nutrient limitation be used to predict changes in ecological integrity at the lower end of the resource gradient. Copyright © 2007 John Wiley & Sons, Ltd.     

A new anti‐windup strategy for PID controllers with derivative filters

This paper presents a new strategy for suppressing the windup effect caused by actuator saturation in proportional–integral–derivative (PID) controlled systems. In the proposed approach, the windup effect is modeled as an external disturbance imported to the PID controller and an observer‐based auxiliary controller is designed to minimize the difference between the controller output signal and the system input signal in accordance with an H‐infinite optimization criterion. It is shown that the proposed anti‐windup (AW) scheme renders the performance of the controlled system more robust toward the effects of windup than conventional PID AW schemes and provides a better noise rejection capability. In addition, the proposed PID AW scheme is system independent and is an explicit function of the parameters of the original PID controller. As a result, the controller is easily implemented using either digital or analog circuits and facilitates a rapid, on‐line tuning of the controller parameters as required in order to prevent the windup effect. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

基于数据挖掘的底水油藏开发预测新方法

底水油藏开发过程中受强底水、油柱高度低、地层原油黏度大、隔夹层分布复杂等因素影响,导致单井开发效果差异大。为解决目前常规方法所存在的多因素数据分析量大、应用局限性大等缺点,提出基于BP神经网络数据挖掘算法的底水油藏水平井可采储量预测新方法,通过数模机理模型分析了该方法的可靠性。针对底水油藏静动态资料,充分挖掘隐含其中的有效信息,在完成基础数据集建立的基础上,构建了基于数据驱动的底水油藏可采储量预测模型。实际应用结果表明,该方法实现了底水油藏水平井开发的影响因素和技术参数界限的定量分析,可采储量预测最大误差低于8%,拟合效果较好,可进一步应用于底水油藏水平井生产动态、开发界限、井位设计等方面。