Adaptive minimum energy cognitive lighting control: Integer order vs fractional order strategies in sliding mode based extremum seeking

To achieve comfortable illumination while minimizing the energy consumption in hybrid lighting, a minimum energy point tracking algorithm is developed to achieve the minimized energy usage despite of environmental variations in this paper. A hardware-in-the-loop prototype of an adaptive minimum energy cognitive lighting control is proposed, designed and built. A sliding mode based extremum seeking controller (SM–ESC) including integer order (IO) and fractional-order (FO) strategies is firstly employed to minimize energy usage in the lights, while a PID controller is applied to maintain a light level. The performance of the designed controller is compared with both fractional order and integer order controllers which are designed based the proposed lighting system. The hardware-in-the-loop experimental results are presented to demonstrate the practicality and effectiveness of the proposed cognitive lighting control scheme.     

Passivity-based fractional-order integral sliding-mode control design for uncertain fractional-order nonlinear systems

This paper concerns with the problem of designing a passivity-based fractional-order (FO) integral sliding mode controller for uncertain FO nonlinear systems. Utilizing the FO calculus, it is showed that the state trajectories of the closed-loop system reach the FO switching manifold in finite time. The control law ensures the asymptotical stability on the sliding surface. A parameter adjustment scheme for FO integral sliding surface is proposed by using the linear matrix inequality (LMI) approach. The proposed controller can be applied to different systems such as chaotic systems. Finally, simulation results are provided to show the effectiveness of the proposed method controlling chaos in FO Chua circuit and FO Van-der-Pol oscillator.     

Preisach-model-based position control of a shape-memory alloy linear actuator in the presence of time-varying stress

Tensioned shape-memory alloy (SMA) wires can repeatedly contract and extend, according to hysteretic loops defined by the shape-memory effect (SME), when subject to cyclic heating and cooling. Empirical evidence shows that these periodic hysteretic deformations are also a function of the loading stress applied to the tested wire. Therefore, to achieve accurate position control of an SMA wire-actuator, the SME hysteretic phenomenon in the presence of time-varying loading stress must be explicitly modeled in order to be compensated. To this end, we use a Preisach-model-based forward mapping that relates the time-varying exciting temperature and stress signals as inputs with the produced strain signal as the output, and whose parameters are experimentally estimated a priori through a series of steps in a nonlinear system identification process. Then, the identified parameters are employed by a Preisach-model-based inversion algorithm that is integrated into a feedforward inverse control scheme designed to mitigate the effects of hysteresis affecting the tested SMA wire. In the proposed scheme, the inverse controller reads two time-varying inputs, a strain reference and the known stress signal exciting the controlled SMA wire-actuator, and then it computes the corresponding temperature reference that, once enforced on the SMA material of the wire, generates the desired strain output. This approach to position tracking control can be realized using lightweight sensors and, as demonstrated in this paper through experimental results, is computationally efficient, which are the two most essential features required for the implementation of controllers on centimeter-scale autonomous robots. Using data obtained through real-time experiments, we demonstrate that the introduced position control scheme is highly effective and suitable to be used in future microrobotic applications. Furthermore, we show that the proposed methods for the system identification of the nonlinear hysteretic dynamics of SMA wires and for the synthesis of inverse controllers can be easily modified to be applied to the tracking control of SMA actuators thermally excited by means other than Joule heating.     

新型终端滑模在光电稳定平台中的应用

为了提高光电伺服稳定平台的跟踪精度,针对系统中干扰的影响提出一种新型终端滑模控制算法。首先,提出一种新型终端滑模干扰观测器的设计方法,实现对系统中干扰的快速估计和实时补偿。其次,设计新型终端滑模控制器来提高系统的跟踪精度,结合有限时间收敛和自适应控制的思想,对切换增益进行在线调整,有效地抑制了滑模控制中的抖振问题,使系统状态能够在有限时间内快速地收敛到所设计的滑模面上,并对未估计干扰进行精细化补偿。最后利用Lyapunov理论证明控制系统的稳定性。实验结果表明:该控制策略保证了光电跟踪系统视轴对运动目标的跟踪精度,在0.05 Hz时误差小于0.002,在2 Hz时误差小于0.034,增强了系统的鲁棒性。     

High-gain observer-based integral sliding mode tracking control for heavy vehicle electro-hydraulic servo steering systems

The electro-hydraulic servo steering system (EHSSS) is the key element to determine the handling and stability of heavy vehicles. Accurate steering control is challenged due to its complicated structure and a wide range of steering loads. In this paper, an output feedback integral sliding mode control (ISMC) method based on high-gain observer is proposed to solve this issue. First, a new Hurwitz matrix design method is presented for EHSSS with non-chain integrator, in order to prove the convergence of the observer error dynamics. Then, the Lyapunov stability of the observer-based controller is verified. Finally, a test bench is established to experimentally validate the proposed method's effectiveness through multiple test scenarios. The results show the tracking error of the proposed method is significantly smaller than PI and similar to full-state feedback integral sliding mode controller. This paper provides a valuable reference for high-gain observer-based nonlinear control applied to a typical electro-hydraulic servo steering system.     

A simple fractional-order chaotic system without equilibrium and its synchronization

There has been an increasing interest in discovering no-equilibrium chaotic systems recently. In this paper, a novel three dimensional fractional-order chaotic system, which has no equilibrium, is introduced. Dynamics of the system has been studied. It is interesting that the system can exhibit coexisting chaotic attractors for the order as low as 2.7. The adjustable feature of a variable is studied by introducing a single controlled constant. Circuit implementation of the system is proposed to show its feasibility. In addition, we have designed the controllers to investigate coexisting synchronization types of such a new fractional-order system. Numerical examples have verified the proposed synchronization schemes.     

A new controller for boost dc–dc converters based on a novel sliding surface

ABSTRACT

In this paper, two control schemes for boost converters affected by uncertainties in input voltage and load are proposed. The boost converter dynamics is redefined in terms of new state variables to facilitate the use of a disturbance observer that can estimate matched and unmatched disturbances. A sliding surface, which is new in the context of boost converters, is proposed to enable tracking and regulation of output voltage without requiring measurement of input voltage and load current. The stability of the overall system including the disturbance observer, the sliding variable and the output is proved. The performance of the schemes is assessed for regulation of output voltage and tracking of reference voltage by simulation as well as experimentation in which various types of uncertainties and various types of reference voltages are considered.     

Robust adaptive stick-slip friction compensation

In this paper, a robust adaptive tracking control scheme is proposed for compensation of the stick-slip friction in a mechanical servo system. The control scheme has a sliding control input to compensate friction forces. The gain of the sliding control input is adjusted adaptively to estimate the linear bound of the stick-slip friction. By introducing the sliding control input, the global stability and the tracking error asymptotic convergence to the predetermined boundary are established via Lyapunov's stability theorem. The proposed scheme is shown to be robust to variations of the system and/or friction characteristics, and a bounded external disturbance. Computer simulations and experiments on an X-Y table verify the effectiveness of the proposed scheme     

不确定分数阶多驱动一响应混沌系统同步

针对一类新的多驱动一响应混沌系统同步方式,基于分数阶系统稳定性理论和Lyapunov稳定性理论,运用追踪控制和滑模自适应控制方法设计了同步控制律和参数自适应律.对象模型考虑了不确定因素的影响,首先选取一类稳定的分数阶滑模曲面,然后提出了一种鲁棒同步方案.最后数值仿真验证了方案的正确性和有效性.     

New fractional-order LADRC scheme based on a novel filtered-Bode’s ideal transfer function for integer-order systems

In this paper, a new Fractional-Order Linear Active Disturbance Rejection Control scheme (FO-LADRC) is proposed to enhance the robustness against loop gain variations of the standard Active Disturbance Rejection Control (ADRC) in the case of uncertain integer-order systems. A new filtered Bode’s ideal transfer function (F-BITF) is proposed to be used as a reference model in the design approach of the proposed control scheme to ensure the dynamic behavior of the closed-loop BITF to the controlled system. A Fractional-order Extended State Observer (F-ESO) is used in the proposed FO-LADRC structure to approximate the system to be controlled by a filtered fractional-order integrator. The fractional order of the F-ESO is a design parameter to tune to achieve the desired overshoot of the closed-loop step response. For the tuning of FO-LADRC structure, an analytical method is proposed. The performance of the proposed FO-LADRC and the Chen’s et al. FO-ADRC structures are evaluated thorough numerical simulation, and then validated in practice in the case of a Cart-Pendulum. Both the simulation and the experimental results show that the proposed FO-LADRC is able to achieve the desired dynamics of the F-BITF and guarantee the robustness with respect to the controller gain variation and the system parameter uncertainties. The comparative study conducted also reveals that the proposed control scheme is more robust than that of Chen.     

高超声速飞行器递阶滑模控制研究

针对高超声速飞行器轨迹高度和速度跟踪控制问题,基于纵向动力学的输入/输出线性化模型,设计了递阶滑模控制器和非线性扰动观测器,用于解决系统存在不确定性问题和执行机构带有死区非线性问题,对于所设计的控制器和观测器进行了稳定性分析,并且通过仿真验证了本文提出的方法能够提高系统的收敛速度和收敛精度并能克服执行机构死区的影响。     

Finite-time control of DC–DC buck converters via integral terminal sliding modes

This article presents novel terminal sliding modes for finite-time output tracking control of DC–DC buck converters. Instead of using traditional singular terminal sliding mode, two integral terminal sliding modes are introduced for robust output voltage tracking of uncertain buck converters. Different from traditional sliding mode control (SMC), the proposed controller assures finite convergence time for the tracking error and integral tracking error. Furthermore, the singular problem in traditional terminal SMC is removed from this article. When considering worse modelling, adaptive integral terminal SMC is derived to guarantee finite-time convergence under more relaxed stability conditions. In addition, several experiments show better start-up performance and robustness.     

基于投影法的不确定分数阶混沌系统自适应同步

针对一类具有未知参数、未知非线性函数及外部扰动的分数阶混沌系统,基于分数阶系统稳定性理论和Lyapunov稳定性理论,该文提出一种基于滑模自适应和投影法的同步控制策略。首先选取一类稳定的分数阶积分滑模面,运用自适应技术对不确定项进行估计,设计了同步控制器。然后对自适应设计中容易出现的增长型自适应律运用投影法进行修正,以保证参数有界,从而也保证控制输入有界。最后数值仿真证明了所设计控制器的正确性和有效性。     

Discrete-Time Output Integral Sliding-Mode Control for a Piezomotor-Driven Linear Motion Stage

In this paper, a discrete-time output integral sliding-mode control (DOISMC) is developed for the precision control of a piezomotor-driven linear motion stage. A new integral-type sliding surface is first designed for arbitrary output reference tracking control. To estimate the unknown state and disturbance, two observers based on the integral-type sliding surface are designed. It is shown in this paper, through both theoretical analysis and experiments, that the discrete-time output integral sliding mode controller, together with the state and disturbance estimation, achieves an $O(T^{2})$ tracking precision w.r.t. the sampling period $T$. The superior performance of DOISMC achieved in the control of piezomotor-driven linear stage indicates that it is a suitable control method for precision control or servo applications.      

Hierarchical autonomous switching control of a multi-modes omnidirectional mobile robot

Adequate control flexibility and tracking precision of the omnidirectional mobile robot (OMR) are difficult to be guaranteed with a fixed control mode. To address this challenge, this paper presents a modified hierarchical autonomous switching control scheme for an OMR with multiple maneuver-modes, which is capable of switching the alternative modes to adapt to the operational conditions and performing a satisfactory trajectory tracking control. Utilizing a hierarchical switching signal, the design begins by formulating a hybrid discrete OMR system with multiple subsystems cascading to its alternative kinematic states. Under the integrated system constraints, a new hierarchical switched fractional-order receding horizon control is presented to offer more adjusting flexibilities, which constructs a novel fractional-order cost function and then derives a numerical solvable solution. Meanwhile, with a Lyapunov-principle-based supervisory variable, an autonomous switching law is proposed so that the preferred subsystem can be selected to enhance the moving maneuverability. Under certain average dwell time conditions, the asymptotic stability of the resultant system is guaranteed. Finally, comparative experiments implemented on the real-world scenarios are provided to demonstrate the superior tracking performance and enhanced robustness of the proposed hierarchical autonomous switching control method as compared to traditional control schemes.     

Chaos generation in fractional-order switched systems and its digital implementation

A double-scroll chaotic attractor generated by a fractional-order switched system is presented. Based on unstable dissipative systems (UDS) and a switching law, a fractional-order UDS is proposed. Chaos behavior is found with a fractional order as low as 2.568 by satisfying the stability criterion for fractional order chaotic systems. The fractional-order switched system is transformed to an equivalent switched system with augmented states. Then, the equivalent system is straightforward implemented on an ARM system-on-chip board by using Python high level programming language. Numerical simulations are in good agreement with experimental results, which demonstrates the usefulness of proposed method. Additionally, the test 0–1 and a chaos definition for finite state sets are given to demonstrate chaotic behavior. Finally, a random number generator is also proposed as a possible application.     

自适应的分数阶达尔文粒子群优化算法

针对分数阶达尔文粒子群算法收敛性能依赖于分数阶次α,易陷入局部最优的特点,提出了一种自适应的分数阶达尔文粒子群优化（AFO-DPSO）算法,利用粒子的位置和速度信息来动态调整分数阶次α,并引入自适应的加速系数控制策略和变异处理机制,以获取更优的收敛性能。对几种典型函数的测试结果表明,相比于现有的粒子群算法,所提的AFO-DPSO算法的搜索精度、收敛速度和稳定性都有了显著提高,全局寻优能力得到了进一步提高。     

Passivity-based non-fragile control of a class of uncertain fractional-order nonlinear systems

This article investigates the issues of passivity and feedback passification of a class of fractional-order (FO) nonlinear systems with time-varying norm-bounded parameter uncertainties in both the state and output matrices. Firstly, new passivity conditions presented by linear matrix inequalities (LMIs) are established based on new notions of passivity of FO systems. Secondly, considering inaccuracies or uncertainties may occur during controller implementation, non-fragile state feedback passification controller is proposed when the states are available. The obtained results extend and improve some recent results. Finally, the applicability and effectiveness of the developed results are examined via numerical examples with simulation results.     

Robust power control of CDMA cellular radio systems with time-varying delays

Power control is an important factor to increase communication link quality and system capacity in the direct-sequence code-division multiple access (DS-CDMA) cellular radio systems. The Smith prediction filter can achieve the unbiased asymptotic tracking about a desired target signal to interference noise ratio (SINR) under the fixed round-trip delay. However, it is sensitive to the variation of round-trip delay. In order to track the desired SINR with the time-varying round-trip delay, a multiple-mode Smith prediction filter, which combines the multiple Smith predictors with a likelihood function, is proposed for the power control of CDMA systems. The proposed scheme can compensate for the unknown time-varying round-trip delay. Simulation results show that the performance of the proposed multiple-mode power control method is robust to time-varying round-trip delay in the CDMA cellular radio systems.     

Exponential H ∞ Output Tracking Control for Switched Neutral System with Time-Varying Delay and Nonlinear Perturbations

In this paper, the problem of exponential H _∞ output tracking control is addressed for a class of switched neutral system with time-varying delay and nonlinear perturbations. The considered system consists of different neutral and discrete delays. By resorting to the average dwell time approach, a new Lyapunov–Krasovskii functional is proposed to establish sufficient conditions for the exponential stability and H _∞ performance of switched neutral systems. Then, the problem of exponential H _∞ output tracking control is investigated, an explicit expression for the desired exponential tracking controller is also given. Finally, a numerical example is provided to demonstrate the potential effectiveness of the proposed method.