Exogenous System Research Articles

Composite disturbance‐observer‐based output feedback control and passive control for Markovian jump systems with multiple disturbances

This study addresses the problems of the composite disturbance-observer-based (DOB) output feedback control and passive control for Markovian jump systems with non-linearity and multiple disturbances. The multiple disturbances include two kinds: one is supposed to be a norm-bounded vector; the other is described by an exogenous system with perturbations. The purpose of the problem addressed is to design a DOB output feedback controller such that (i) the resulting composite system is passive; and (ii) different types of the above disturbances can be attenuated and rejected, respectively. The characterisation of the gains of the desired disturbance observer and the matrices of the expected output feedback controller are derived based on the solution to a convex optimisation problem that can be easily solved by standard numerical software. Finally, a simulation example is employed to show the effectiveness of the composite control scheme proposed in this study.

Composite anti-disturbance control for a discrete-time time-varying delay system with actuator failures based on a switching method and a disturbance observer

The composite anti-disturbance control problem is developed for discrete-time systems with both time-varying delay and multiple disturbances under actuator failures in this paper. First, depending on the information of actuator failures, the system is transformed into a switched system. Then, considering the switched system, the composite controller is designed via a disturbance observer based control and an exponential l2−l∞ control method. A disturbance observer is constructed to estimate the disturbances generated by an exogenous system, and the estimated value is introduced into a memory exponential l2−l∞ state feedback control law, such that, the closed-loop system is asymptotically stable, and different types of disturbances are rejected and attenuated. Third, by resorting to the average dwell time approach and the free-weighting matrix technique, some sufficient criteria for the desired disturbance observer and the state feedback controller are established, and the corresponding solvability conditions using a cone complementarity linearization method are presented. A numerical example is provided to demonstrate the effectiveness of the proposed algorithms finally.

Composite hierarchical anti-disturbance control for robotic systems with multiple disturbances

Various sources of disturbances exist simultaneously in robotic systems, such as vibrations, frictions, measurement noises, and equivalent disturbances from unmodeled dynamics and nonlinearities. However, most results on anti-disturbance control focus on only one type of disturbances, which cannot reflect the real applications and may lead to design conservativeness due to partial use of the disturbance information. In this paper, we propose a composite hierarchical anti-disturbance control (CHADC) strategy for robotic systems in the presence of multiple disturbances as well as system uncertainties. Particularly, we assume the existence of two types of disturbances, where the first type represents disturbances from exogenous systems with model perturbations, while the second type includes other random disturbances satisfying the L2-norm bound condition. Accordingly, the CHADC control architecture is composed of a nonlinear disturbance observer (NDO) and an H∞ based PID controller, where the NDO is constructed to estimate the first type of disturbances and provide feed forward compensation, while the feedback PID loop is optimized using H∞ theory to minimize the second type of disturbances. Robustness against system uncertainties is also considered in this hierarchical control structure. The proposed control approach is applied to a two-link robotic manipulator and compared with the conventional DOBC (disturbance observer based control) strategies.

Cut Site Selection by the Two Nuclease Domains of the Cas9 RNA-guided Endonuclease

Cas9, the RNA-guided DNA endonuclease from the CRISPR-Cas (clustered regularly interspaced short palindromic repeat-CRISPR-associated) system, has been adapted for genome editing and gene regulation in multiple model organisms. Here we characterize a Cas9 ortholog from Streptococcus thermophilus LMG18311 (LMG18311 Cas9). In vitro reconstitution of this system confirms that LMG18311 Cas9 together with a trans-activating RNA (tracrRNA) and a CRISPR RNA (crRNA) cleaves double-stranded DNA with a specificity dictated by the sequence of the crRNA. Cleavage requires not only complementarity between crRNA and target but also the presence of a short motif called the PAM. Here we determine the sequence requirements of the PAM for LMG18311 Cas9. We also show that both the efficiency of DNA target cleavage and the location of the cleavage sites vary based on the position of the PAM sequence.

Optimal tracking control with feedforward compensation for offshore steel jacket platforms with active mass damper mechanisms

This paper presents the optimal tracking control methodology for an offshore steel jacket platform subject to external wave force. Based on a dynamic model of an offshore steel jacket platform with an active mass damper mechanism and a linear exogenous system model of the external wave force on the offshore platform, an optimal tracking control scheme with feedforward compensation is proposed to attenuate the wave-induced vibration of the offshore platform. A feedforward and feedback optimal tracking controller (FFOTC) can be obtained by solving an algebraic Riccati equation and a Sylvester equation, respectively. It is demonstrated that the wave-induced vibration amplitudes of the offshore platform under the FFOTC are much smaller than the ones under the feedback optimal tracking controller (FOTC) and the feedforward and feedback optimal controller (FFOC). Furthermore, the required control force under the FFOTC is smaller than the ones under the FOTC and the FFOC.

Sulfur concentration of martian basalts at sulfide saturation at high pressures and temperatures – Implications for deep sulfur cycle on Mars

To constrain sulfur concentration at sulfide saturation (SCSS) of martian magmas at mantle conditions, we simulated basalt-sulfide melt equilibria using two synthesized meteorite compositions, i.e., Yamato980459 and NWA2990 in both anhydrous and hydrous conditions at 1–5GPa and 1500–1700°C. Our experimental results show that SCSS decreases with increasing pressure and increases with increasing temperature. Based on our experimental SCSS and those from previous low-pressure experiments on high-FeO∗ martian basalts, we developed a parameterization to predict martian basalt SCSS as a function of depth, temperature, and melt composition. Our model suggests that sulfur contents as high as 3500–4300ppm can be transferred from the martian mantle to the martian exogenic system, and sulfur-rich gases might have caused the greenhouse conditions during the late Noachian. However, modeling of the behavior of sulfur along the liquid line of descent of a primitive martian basalt suggests that a fraction of the magmatic sulfur could precipitate as sulfides in the cumulates during cooling and fractional crystallization of basaltic magmas. Furthermore, the latter case is consistent with the S concentration of martian meteorites, which reflect variable amount of trapped liquid in cumulus mineral assemblage. Furthermore, our model predicts an average S storage capacity of 5700ppm for the martian magma ocean, whereas the same for Earth is only ∼860ppm. Lastly, high SCSS of martian magma ocean and its inverse correlation with depth along the mantle liquidus could have triggered a sulfur pump where the post-core-formation magma ocean of Mars would gain sulfur through interaction with SO2/H2S rich nascent atmosphere.

Controlled synchronization: a Huygens' inspired approach

This paper considers synchronization as a control problem. In particular, a (robust) controller for achieving synchronization in pairs of second order nonlinear systems is designed. The design is inspired by the classical experiment on synchronization of pendulum clocks, as described by Christiaan Huygens. In the proposed control scheme, the systems do not interact directly but through an exogenous system. Ultimately, it is demonstrated that Huygens' controller, can be used to perform in-phase and anti-phase synchronized tasks, with the advantage that 'small' control gains are required. The stability of the closed-loop system is analyzed using perturbation theory and the proposed controller is experimentally validated on a pair of Cartesian robots.

A semi-batch reactor modeling based on PWARX systems

In this paper, we address the problem of identifying a semi-batch olive oil esterification reactor. In fact, this reactor can be considered as a PieceWise AutoRegressive eXogenous (PWARX) system. The Chiu's clustering procedure for the identification of PWARX systems is then applied. It consists in estimating both the parameter vector of each submodel and the coefficients of each partition. The results of the experimental validation illustrate the effectiveness of the proposed method. A comparative study with three existing approaches is also considered in this paper which shows that the proposed approach gives the best results in terms of precision.

Robust Control for Uncertain Linear System Subject to Input Saturation

A robust control scheme using composite nonlinear feedback (CNF) technology is proposed to improve tracking control performance for the uncertain linear system with input saturation and unknown external disturbances. A disturbance observer is presented to estimate the unknown disturbance generated by a linear exogenous system. The designed gain matrix of the disturbance observer is determined by solving linear matrix inequalities (LMIs). Based on the output of the designed disturbance observer, a robust CNF controller including a linear feedback control item and a nonlinear item is developed to follow the desired tracking signals. The linear feedback controller is designed using LMIs and the stability of the closed-loop system is proved via rigorous Lyapunov analysis. Finally, the extensive simulation results are presented to illustrate the effectiveness of the proposed control scheme.

The nonlinear disturbance observer-based control for small rotary-wing unmanned aircraft

As a complex system, control performance of small rotary-wing unmanned aircraft is easily affected by measurement errors and environment disturbances. This paper proposes a nonlinear disturbance observer-based control to improve control performance. The constant and harmonic disturbance that is generated by the exogenous system with modeling perturbation can be estimated and rejected effectively. The random disturbance with certain bound can be reduced by the feedback control. By solving linear matrix inequality, the parameters for feedback control and nonlinear disturbance observer can be selected simultaneously. Therefore, the system stability can be guaranteed and the control performance can be improved effectively. The effectiveness of the nonlinear disturbance observer-based control is proved by a series of flight tests. Compared with feedback control, the disturbance observer-based control yields a better tracking performance in the presence of disturbances.

Active modes and switching instants identification for linear switched systems based on Discrete Particle Swarm Optimization

In this paper, a methodology for identifying switching sequences and switching instants of switched linear systems (SLS) is derived. The identification problem of a SLS is a challenging and non-trivial problem. In fact, it involves interaction between binary, discrete and real-valued variables. A SLS switches many times over a finite time horizon and thus estimating the sequence of activated modes and the switches locations is a crucial problem for both control and Fault Detection and Isolation (FDI). The proposed methodology is based on the Discrete Particle Swarm Optimization (DPSO) technique. The identification problem is formulated as an optimization problem involving noisy data (system inputs and outputs). Both a set of binary variables corresponding to each sub-model before and after each switch, and the corresponding switching instants are iteratively adjusted by the DPSO algorithm. Thus, the DPSO algorithm has to classify which sub-system has generated which data. The efficiency of the proposed approach is illustrated through a numerical example and a physical one. The numerical example is a Switched Auto-Regressive eXogenous (SARX) system and the physical one is a buck–boost DC/DC converter.

State-Space Approach to Modeling and Ripple Reduction in AC–DC Converters

This brief develops a systematic state-space approach to the modeling of boost type ac-dc converters and reduction of output ripples. The bridge rectifier voltage is modeled as a periodic disturbance whose harmonics have given frequencies but uncertain phases and magnitudes. These types of disturbances are described as the output of an external autonomous linear system, called an exogenous system, with uncertain initial conditions. The exogenous system is integrated with the boost converter as a whole system in state-space description. The whole system is a nonlinear system whose differential equation has a bilinear term, which is handled by an inclusion. Via a recently developed Lyapunov framework, the problem of ripple reduction is converted into a numerically efficient optimization problem, which involves linear matrix inequalities. The resulting feedback law is a simple linear state-feedback. Experimental results validate the effectiveness of the theoretical approach and design method.

Output Tracking in Causal Nonminimum Phase Systems Using Discrete-time Stable System Center

Output tracking is considered for discrete-time causal single input single output nth order linear time invariant system with nonminimum phase zeros via discrete-time variable structure control. The stable system center method was developed originally for controlling the output in continuous time nonminimum phase causal system using sliding mode control. The developed discrete-time stable system center technique transforms an output tracking problem to a corresponding state variable tracking problem. The causal disturbances and output tracking profiles are assumed to obey a linear exogenous system with known characteristic polynomial. The theoretical results are confirmed by discrete variable structure control synthesis for the tracking of const signal.

Composite anti-disturbance control for Markovian jump nonlinear systems via disturbance observer

This paper is concerned with the problems of composite disturbance-observer-based control (DOBC) and ℋ∞ control for Markovian jump systems with nonlinearity and multiple disturbances. Our aim is to design a disturbance observer to estimate the disturbance generated by an exogenous system, then construct the control scheme by integrating the output of the disturbance observer with state-feedback control law, such that, the closed-loop system can be guaranteed to be stochastically stable, and different types of disturbances can be attenuated and rejected. By constructing a proper stochastic Lyapunov–Krasovskii functional, sufficient conditions for the existence of the desired observer and the state-feedback controller are established in terms of linear matrix inequalities (LMIs), which can be readily solved by standard numerical software. Finally, a numerical example is provided to show the effectiveness of the proposed approaches.

Dynamic Mechanical System Analysis-Empirical Research of Wooden Window Enterprise

Competitive advantage is influenced by dual mechanical system: endogenous system and exogenous competitive system. Compared with uncontrollable exogenous competitive elements, endogenous competitive elements exerting structural competitive advantage is of vital importance for companies to battle against disadvantages and achieve competitive advantaged independently. Endogenous competitive elements comprise: firm culture, dynamic capabilities, and complementary assets. At the strategic level, firm culture influences firm decisions; at the organizational level, dynamic capabilities create core competence of a corporation; at the practice level, complementary assets erect barriers to competitors. This study empirically analyzed Firm Sayyas, a leading firm in wooden windows industry having encountered countless structural changes of competitive elements, to uncover how SMEs can achieve competitive advantage. The empirical analysis shows that, cultivating endogenous competitive elements based on “firm culture, dynamic capabilities, and complementary assets” in the dynamic competition is an effective way to maintain SMEs’ competitive advantages.

Composite Antidisturbance Control for a Class of Nonlinear Stochastic Systems via Disturbance Observer

The stabilization problem is investigated in this paper for a class of nonlinear systems with disturbances. The disturbances are supposed to be classified into two types. One type in the input channel is generated by an exogenous system, which can represent the constant or harmonic signals with unknown phase and magnitude. The other type is stochastic disturbance. Two kinds of nonlinear dynamics in the plants are considered, respectively, which correspond to the known and unknown functions. By integrating the disturbance observers with conventional control method, the first type of disturbances can be estimated and rejected. Simultaneously, the desired dynamic performances can be guaranteed. An example is given to show the effectiveness of the proposed scheme.

Distributed output regulation of switching multi‐agent systems subject to input saturation

In this study, we consider the distributed output regulation (DOR) problem of linear multi-agent systems subject to input saturation with switching topology. Owing to the input saturation elements, the considered systems is non-linear. It is natural to take the semiglobal frame for it which allows one to use distributed linear feedback controller. The basic problem is to design distributed feedback controller for the considered multi-agent systems in order to have all agents to track an active leader and/or distributed rejection with disturbance signals. Both the leader and the disturbance signal are modelled as the exogenous system with different dynamics and unmeasurable variables. A systematic distributed linear design approach based on the solvability condition is proposed for the considered DOR problem.

Composite Disturbance Observer-Based Control andH∞Output Tracking Control for Discrete-Time Switched Systems with Time-Varying Delay

This paper considers the problem ofH∞output tracking control for discrete-time switched systems with time-varying delay and external disturbances. The control scheme combining disturbance observer-based control (DOBC) andH∞control is proposed. The disturbances are assumed to include two parts. One part is generated by an exogenous system, which imposes on system with control inputs in the same channel. The other part is supposed to have the boundedH2norm. A new disturbance observer is developed to estimate and reject the first case disturbances for switched system with time-varying delay, and the second case disturbances are attenuated byH∞control scheme. The stability analysis of the closed-loop system is developed by switched Lyapunov function, and a solvable delay-dependent sufficient condition is presented in terms of linear matrix inequalities (LMIs) and cone complement linearization (CCL) methods. A numerical example is given to demonstrate the effectiveness of the proposed composite control scheme.

Thermodynamical Approach for Choosing the Carrier System for Tetraantraquinoporphyrazines

On the example of tetraantraquinoporphyrazines—potential photosensitizers for photodynamic therapy, thermodynamic approach to the choice of exogenous transport system was demonstrated. By means of isothermal titration calorimetry and electron absorption spectroscopy, the state of TAP in aqueous solutions was studied. The possibility of aggregation equilibrium displacement due to the pyridine adding was evaluated.

Modified function projective lag synchronization of chaotic systems with disturbance estimations

This paper addresses the modified function projective lag synchronization (MFPLS) for a class of chaotic systems with unknown external disturbances. The disturbances are supposed to be generated by the exogenous systems. By using the disturbance-observer-based control and the linear matrix inequality approach, the disturbance observers are developed to ensure the boundedness of the disturbance error dynamics. Then by employing the sliding mode control (SMC) technique, an active SMC law is established to guarantee the disturbance rejection and realize MFPLS between the master and slave systems. And the corresponding numerical simulation is provided to illustrate the effectiveness of the proposed method.