Switching Manner Research Articles

Stabilization of a class of nonlinear parametrized systems by a flexible switching adaptive backstepping

In this paper, we consider global adaptive feedback control of nonlinear systems with unknown parameters entering nonlinearly. Such unknown parameters are also not required to lie in a known compact set. Unlike previous results, our proposed adaptive controller is a new double dynamical switching-type controller in which the controller parameter is tuned in a flexible switching manner via a monotonically decreasing switching logic and the controller combines the traditional adaptive theorem with the switching scheme perfectly. Global stability results of the closed-loop system have been proved.

Output feedback adaptive sensor failure compensation for a class of parametric strict feedback systems

Abstract In this paper, an adaptive output feedback compensation control scheme is proposed for a class of nonlinear systems with unknown sensor failures. For estimating the unmeasured states, a novel switching-type adaptive observer is constructed, in which the observer gains are tuned in a switching manner. To compensate for the failure effects on transient performance, a new error signal which contains an adaptive compensation coefficient is introduced into backstepping procedure. It is shown that the proposed controller can guarantee the closed-loop system is globally uniformly ultimately bounded, and system output converges to an adjustable neighborhood of the origin. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

A note on chaotic and predictable representations for Itô–Markov additive processes

ABSTRACTIn this article, we provide predictable and chaotic representations for Itô–Markov additive processes X. Such a process is governed by a finite-state continuous time Markov chain J which allows one to modify the parameters of the Itô-jump process (in so-called regime switching manner). In addition, the transition of J triggers the jump of X distributed depending on the states of J just prior to the transition. This family of processes includes Markov modulated Itô–Lévy processes and Markov additive processes. The derived chaotic representation of a square-integrable random variable is given as a sum of stochastic integrals with respect to some explicitly constructed orthogonal martingales. We identify the predictable representation of a square-integrable martingale as a sum of stochastic integrals of predictable processes with respect to Brownian motion and power-jumps martingales related to all the jumps appearing in the model. This result generalizes the seminal result of Jacod–Yor and is of importance in financial mathematics. The derived representation then allows one to enlarge the incomplete market by a series of power-jump assets and to price all market-derivatives.

Tuning function design for nonlinear adaptive control systems with multiple unknown control directions

To overcome the drawback of overparametrization in existing nonlinear adaptive control design with multiple unknown control directions, we propose a new algorithm which combines nonlinear integrator backstepping, tuning function design and a logic-based switching mechanism that tunes the control directions online in a switching manner. Global asymptotic tracking control is achieved for parametric-strict-feedback systems without overparametrization. The logic-based switching criterion is based on monitoring incremental errors caused during two consecutive switching moments, and thus can identify the true control direction quickly.

Zero-current-switching pulse charger for high capacity batteries in renewable energy applications

Fast charging of high capacity batteries is of great concern, especially in renewable energy and electric vehicle (EV) applications. Pulse charging has become the preferred method for fast charging with heavy currents. However, it presents drawbacks due to switching losses involved in hardswitching of semiconductor devices. This paper presents a soft switched pulse charging mechanism for high capacity Pb-acid and Li-ion batteries, which minimises switching losses that makes the methodology very suitable for implementing the National Electric Code (NEC) level-1, level-2 chargers or specially the level-3 charger more conveniently for EVs. The fully clamped quasi-resonant DC link (FCQDL) converter generates current pulses to charge the battery in a zero-current switching (ZCS) manner to minimise switching losses. The simulated and experimental results show that the proposed charger can implement constant current (CC) and constant voltage (CV) modes of charging. The experimental results show that the proposed charging methodology reduces the charging time of Pb-acid batteries by 14.01 % in contrast to the conventional CC-CV charging method. Furthermore, discharging curves for the conventional and pulse charging methods are compared to evaluate the effective useful charge that is put into the battery. The results reveal that the effective charge capacity of a battery is significantly improved due to the use of pulse charging.

Simplex Guided Extremum Seeking Control With Convergence Detection to Improve Global Performance

This paper presents a novel approach to improve the global performance of extremum seeking control (ESC). This algorithm employs perturbation-based ESC to find local extrema and a simplex-based algorithm to search for the global extremum. The two methods are employed in an iterative switching manner. We propose a novel frequency-domain criterion to detect when the state of a system under ESC has converged to a local optimum. Switching from ESC to the simplex method is triggered when this criterion is satisfied. We prove that this criterion will be met within finite time, under conditions on the ESC law. Simulations and experiments demonstrate and statistically prove that this algorithm outperforms ESC or simplex-based algorithms for optimizing objective functions with multiple extrema.

Global finite-time adaptive stabilization for nonlinear systems with multiple unknown control directions

In this paper, the problem of global finite-time stabilization is addressed for a class of nonlinear systems with multiple unknown control directions. Unlike all the existing works on finite-time stabilization, our work allows the control directions of the considered systems to be unknown. This paper is the first to focus on the global finite-time control of such uncertain systems. To overcome the main obstacle arising from unknown control directions, we develop a novel Lyapunov-based logic switching rule, and then the desired adaptive switching controllers are designed, where the controller parameters are to be tuned online in a switching manner according to the proposed switching logic. It is shown that the obtained controllers guarantee the closed-loop systems being globally finite-time stable. A simulation example is provided to illustrate the effectiveness of the proposed control algorithms.

Multi-model predictive control for wind turbine operation under meandering wake of upstream turbines

In wind farm operation, the performance and loads of downstream turbines are heavily influenced by the wake of the upstream turbines. Furthermore, the actual wake is more challenging due to the dynamic phenomenon of wake meandering, i.e. the turbine wake often demonstrates dynamic shift over time. To deal with the time-varying characteristics of wake meandering, a multiple model predictive control (MMPC) scheme is applied to the individual pitch control (IPC) based load reduction. The coherence function in the spectral method is used to generate the stochastic wind profile including wake meandering at upstream turbine, and a simplified wake meandering model is developed to emulate the trajectory of the wake center at downstream turbine. The Larsen wake model and Gaussian distribution of wake deficit are applied for composing wind profiles across the rotor of downstream turbines. A set of MMPC controllers are designed based on different linearized state-space models, and are applied in a smooth switching manner. Simulation results show significant reduction in the variation of both rotor speed and blade-root flapwise bending moment using the MMPC based IPC by including the wake meandering, as compared to a benchmark PI controller designed by NREL.

Nonlinear adaptive control for power integrator triangular systems by switching linear controllers

Summary In this paper, a nonlinear adaptive stabilizer is designed for a class of power integrator triangular systems with the following four features: (i) the chained integrators have the powers of positive odd numbers, which makes the linearization of the studied system uncontrollable; (ii) the nonlinear function contains the virtual control variables; (iii) the bound of the nonlinear parameters entering the function nonlinearity is not required to be known a priori; and (iv) there exists an unknown control coefficient with the unknown bound in the control channel. Our proposed adaptive controller is a switching type controller, in which the designed adaptive stabilizer takes a two-step procedure: a linear stabilizing controller containing the tuning gains is first designed by the adding a power integrator technique. Switching logic is then proposed to tune online the gains in a switching manner. The proposed adaptive controller globally asymptotically stabilizes the considered system in the sense that, for any initial conditions, the state converges to the origin while all the signals of the closed-loop system are bounded. Simulation studies clarify and verify the approach. Copyright © 2014 John Wiley & Sons, Ltd.

A retrospective study of antipsychotic drug switching in a pediatric population

BackgroundAntipsychotic drugs can be used to help treat a wide variety of psychiatric disorders. However, specific antipsychotic drugs for any particular patient may need to be changed for a number of different reasons, including a lack of therapeutic efficacy and / or intolerance to medication side-effects. Drug switching may occur through a limited number of established patterns. The nature of these changes is not well characterized in youth, despite their frequent occurrence.MethodsA retrospective analysis of antipsychotic drug switches was conducted on patients who had been admitted as inpatients to a tertiary care child and adolescent psychiatric institute. PharmaNet (a large, central administrative database) records of all medications prescribed in the 52 weeks prior to admission, and then between admission and discharge, were analyzed for switching patterns. Additional data regarding diagnoses were obtained from medical chart review.ResultsPatients represented a diagnostically heterogeneous population, and almost all antipsychotic drugs were administered off-label. In the one year prior to and during admission to the hospital, a total of 31 out of 139 patients switched antipsychotic drugs. The frequency of switching increased closer to the time of admission, and the proportional rate of switching was even higher during hospital stay. The most common switch was from risperidone to quetiapine. Our analysis identified three main patterns of drug switching, all occurring with similar frequency: titrated drug switches, abrupt drug switches and concurrent drug administration.ConclusionsThe present study indicates that antipsychotic drug switching in youth may be relatively common, particularly in the year prior to hospitalization. No specific manner of drug switching predominates. This study also demonstrates the feasibility of using large administrative databases to characterise switching patterns in youth.

OPTICAL BISTABILITY IN ONE-DIMENSIONAL COUPLED RESONATOR NONLINEAR OPTICAL WAVEGUIDE

In this paper, the optical bistability in finite size one-dimensional coupled resonator nonlinear optical waveguide has been investigated. To calculate the bistable switching manner in five proposed structures, we use the linear and nonlinear transfer matrices with fixed point iteration method. Our results show that the threshold and domain of bistable switching answer depend on the defect region in one-dimensional coupled resonator nonlinear optical waveguides. Also, the best answer of switch takes place at the left and right edges of the photonic band gap of the structures depending on the defect regions. In fact, due to the presence of the photonic band gap in the slow wave system, the density of states of the electromagnetic fields is large at the photonic band edge and photonic defect modes and thus the group velocity is small, and the local field is enhanced. All these factors contribute to a significant decrease in the threshold of optical bistable switching devices.

Informative Property of the Data Set in a Single-input Single-output (SISO) Closed-loop System with a Switching Controller

Closed-loop identification is important and necessary to various model-based advanced process control strategies, whose performance depends greatly on the informative property of the data set. Switching control is an important method in process control. Therefore, this paper studies the informative property of a data set in a single-input single-output (SISO) closed-loop system with a switching controller. It is proved that this data set is informative if the controller switches among at least two modes (i.e., feedback laws). Our result does not require any assumption on the way of switch and removes the constraints on the switching manner required in some classical literature. Finally, simulation case studies based on a continuous stirred-tank reactor (CSTR) process are given to validate the results.

Nonlinear Adaptive Learning Control With Disturbance of Unknown Periods

In this technical note, we consider adaptive learning control problem for a class of nonlinear systems with periodic bounded disturbances. The bounds of the disturbance are unknown, and the minimum period T* of the disturbance can be written as T* = l* τ , with τ being a known constant and l* being an unknown integer. Our proposed adaptive controller consists of a learning law and two kinds of parameter tuning mechanisms: one is the conventional parameter update law, and the other is a logic-based switching mechanism which tunes in a switching manner the saturation level and the period in the learning law. It has been proved that under our proposed control all closed-loop states are bounded and asymptotic regulation is achieved.

Nonlinear adaptive control by switching linear controllers

We consider a global adaptive stabilization problem for feedback nonlinear systems with nonlinear parametrization. In our previous work [15], we showed that for such systems global adaptive stabilization can be achieved by switching nonlinear controllers. In this paper, we further show that global adaptive stabilization can still be achieved by switching linear controllers. From the consideration of implementation, the linear controller has obvious advantages. The design of our adaptive stabilizer takes a two-step procedure. We first design a linear stabilizer with “undetermined” gains and then design a set of switching logics to tune online the gains in a switching manner. It is shown that under our proposed control, for any initial conditions, all closed-loop states are bounded and asymptotic regulation is achieved.

Dynamic alternation of primate response properties during trial-and-error knowledge updating

Humans and animals seek appropriate solutions to novel problems through trial-and-error (TE) actions and observation of their outcomes. Once an individual has obtained the knowledge (rule) to solve a problem, knowledge-based (KB) actions may be applied in a stereotypical manner. Solutions can thus be based on TE or KB actions. To characterize this learning process at the behavioral level, we developed a new cognitive task for a laboratory monkey (Macaca fuscata) to perform. In this task, a search array consisting of six elements of different colors was presented, one of which was the behaviorally relevant target. The target color was changed unpredictably with no instruction or signal, requiring the monkey to use a TE search strategy to find the target color. We found that once the monkey identified the relevant color by chance after a color change, correct performance increased in a step-like manner and at the same time, other response properties (reaction time and color-choice tendency) also changed discontinuously. These step-like alternations in behavioral performance may be attributed to the subject’s switching between TE and KB search strategies in the two phases. The present study has therefore provided behavioral evidence for the timing and manner of switching between search strategies during the process of updating knowledge.

Droplet bistability and its application to droplet control

Novel methods for controlling droplets precisely in the microchannels are presented, which employ microfluidic bifurcation channels with outlet restrictions based on droplet bistability, utilizing the Laplace pressure caused by interfacial tension that arises when a droplet encounters a narrow restriction. The bistable geometry possesses two symmetric branches and restrictions that operate as capillary valves allowing a droplet to be trapped in front of a restriction and released through it when the next droplet arrives at the other restriction. This trap-and-release occurs repeatedly and regularly by the succeeding droplets. Furthermore, a critical flow rate is found to exist, which is necessary for achieving droplet bistability. This occurs only when the apparent Laplace pressure surpasses the pressure drop across the droplet. By adopting a simplified hydrodynamic resistance model, the droplet bistable mechanism is clearly explained, and droplet bistability is shown to enable the simple and precise control of droplets at a bifurcation channel. Thus, precise droplet traffic control is achieved at a bifurcation channel connected with a single inlet channel and two outlet channels using an appropriate channel design that induces droplet bistability. In particular, droplets are distributed at a junction in a manner of perfect alternation or perfect switching between the two outlet channels. This article proposes that bistable components can be used as elaborately embedded droplet traffic signals for red light (trap), green light (release), and turn light (switching) in complex microfluidic devices, where droplets provide both the chemical or biological materials and the processing signal.

Adaptive stabilization of time-delay feedforward nonlinear systems

In this paper, we consider the adaptive stabilization problem for feedforward nonlinear systems with time delays. An adaptive stabilizer is proposed. Our stabilizer takes a nested saturation feedback, and a set of switching logics is designed to tune online the saturation levels in a piecewise constant or switching manner. It has been shown that under our proposed control, all closed-loop states are bounded and asymptotic regulation is achieved.

The design of smooth switching control with application to V/STOL aircraft dynamics under input and output constraints

This paper presents a smooth switching gain-scheduled control approach for linear parameter varying (LPV) system dynamics, indexed by a scalar varying parameter. The proposed approach is demonstrated by application to the planar vertical/short takeoff and landing (V/STOL) aircraft dynamics subject to input and output constraints. In the design of switching control, the switch logic determines the switching process between control laws. The usual switching logics use the instantaneous switching manner, which can cause discontinuous chattering control signal. By performing convex weightings between two individual control laws for neighboring subsystems, the proposed smooth switching gain-scheduled control approach can provide improved performance but does not arouse control signal chattering. For the studied application, the nonlinear aircraft dynamics are represented in the form of LPV systems with parameter dependence on attitude angle. The resulting design is verified by the obtained relative stability and time response simulations. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Innovative Active Magnetic Bearing Design to Reduce Cost and Energy Consumption

An innovative switching-type self-sensing magnetic bearing is presented in this article. The so-called switch-type refers to the operation of each pair of magnetic poles in which, at any time epoch, a sole single pole is energized by feeding electric current while the other is not activated at all. Each pair of poles in the magnetic bearing shares a set of power amplifiers in a switching manner so that the required number of amplifiers can certainly be reduced. In addition, a self-sensing technique is employed by extracting the induced current in the coil wrapped on the pole convex to replace gap sensors that are conventionally used to provide the position deviation measure of the spindle. That is, the cost to equip any position sensor or device can be waived. The proposed magnetic bearing not only reduces the bearing size, but also drastically prevents unnecessary power loss. A self-tuning proportion-derivative controller is synthesized to account for the effects of non linearities of the rotor/bearing system. The proposed switching-type self-sensing control system is verified by intensive experiments to illustrate the validity of the proposed electromagnet design and superiority of the self-tuning proportion-derivative strategy to efficiently stabilize the inherently unstable magnetic suspension system.

Pseudo-decentralized adaptive stabilization of large-scale feedforward nonlinear systems

In this paper, we propose a pseudo-decentralized adaptive control scheme for a class of large-scale feedforward nonlinear systems with unknown nonlinear effects within subsystems and unknown nonlinear interactions among subsystems. The local controller of each subsystem takes a nested saturation feedback, using the state of its own subsystem, and the saturation levels are tuned online in a switching manner via a set of switching logics, which requires some binary flag communication among subsystems. Global asymptotic regulation of the closed-loop states is achieved.