Composite Control Structure Research Articles

Decentralized control of ideal ternary reactive distillation column with inert

Decentralized control of an ideal hypothetical ternary reactive distillation column with an inert component is explored. Both composition measurement based and temperature inferential control structures are designed using simple heuristic approaches (two and three-point). The three-point composition control structure is proposed for the example RD column for the first time in this work. Although stable closed loop responses are seen for the throughput changes for all, the two-point structures have failed to achieve tight control of the product purity in the bottoms or purity of inert in the distillate for the inert composition changes due to fixed reflux ratio. The performances of the three-point control structures for the inert composition changes are quite satisfactory due to the indirect manipulation of the reflux ratio. The independent manipulation of the reflux rate and distillate (instead of fixed reflux ratio policy) is an important control decision for the successful regulation of the example RD column.

Experimental assessment of combined sliding mode & moment-based control (SM[formula omitted]C) for arrays of wave energy conversion systems

Motivated by the lack of comprehensive experimental implementation and assessment of the potential benefit that can be achieved with energy-maximising optimal control solutions for arrays of wave energy converters (WECs), we present, in this paper, the development, design, experimental implementation, and performance appraisal, of optimal moment-based control for arrays of WEC systems. Both centralised and decentralised controllers are evaluated. Four different WEC array layout configurations are considered, with up to three 1:20 scale prototypes of the Wavestar WEC system operating simultaneously within the basin, subject to a variety of sea state conditions. In particular, the proposed controller, termed sliding-mode-moment-based controller SM2C, is composed of a receding-horizon moment-based reference generation process, and a subsequent proportional–integral–derivative-like continuous sliding mode tracking controller. This composite control structure is implemented and assessed experimentally, providing a detailed analysis of key performance metrics. We show that the proposed SM2C strategy is able to maximise energy absorption for all the considered WEC array layouts, with up to 2.8 times energy improvement when compared to the benchmark controller case. The findings of this experimental study show tangible proof of the performance enhancement that can be achieved in real arrays of WEC systems with the use of appropriate control technology, demonstrating not only the feasibility of the proposed SM2C strategy in itself, but the key role that control systems have to play in the pathway towards effective exploitation of the yet largely untapped wave energy resource.

Multi-objective optimization and composition control of Sargent dividing-wall distillation columns

Sargent dividing-wall distillation columns (DWDCs) can significantly reduce the energy consumption required for separating quaternary mixtures. However, their effective design and strict product purity control can be challenging to achieve, which severely limits their development and application in the industry. To address this problem, a systematic study on their design and control was conducted in this article based on the case of separating a quaternary mixture of methanol, ethanol, 1-propanol, and n-butanol. Firstly, a multi-objective optimization framework was proposed, in which the total annual cost (TAC), CO2 emission, and condition number (CN) were taken as objective functions, and NSGA-III and TOPSIS algorithms were employed to search for the optimal design of the Sargent DWDC. To avoid the convergence difficulty issue of the rigorous model of the Sargent DWDC, a Random Forest surrogate model was used in the optimization process to predict its steady-state and dynamic performance accurately and rapidly. Secondly, a novel composition control structure, consisting of seven control loops, was proposed to achieve strict product purity control of the Sargent DWDC. Three composition difference control loops, located at the prefractionator and the middle column, are responsible for maintaining their composition profile shapes and thus mitigating the impact of feed disturbances on the main column. Additionally, four composition control loops, located at the main column, are responsible for strictly controlling the purities of the distillate, upper sidestream, lower sidestream, and bottom products. Dynamic simulation results showed that the Sargent DWDC can be operated stably under the proposed composition control structure for various feed composition and feed flow rate disturbances. These results not only confirmed the capability of the proposed composition control structure to strictly maintain product purities in the Sargent DWDC but also validated the effectiveness of the proposed multi-objective framework in achieving an energy-efficient and controllable Sargent DWDC.

Dynamic control of liquid-only transfer Kaibel dividing-wall column

The liquid-only transfer configuration widens the possibility of industrial application of DWCs, especially for the few industrial implementations of the Kaibel dividing-wall column (KDWC). This work focuses on the dynamic control of liquid-only transfer KDWC (LTS-KDWC) to separate a four-alcohol system. First, a composition control structure (CS1) is proposed and the numerical results show that CS1 could handle ±10% disturbances in the feed flow rate and composition except that a large purity deviation is discovered for the product of ethanol. Then temperature-control structure (CS2) is proposed, and the dynamic control performance illustrates that product purity is stabilized and returns to the designed value quickly. However, larger disturbances cannot be handled by CS2. Consequently, a temperature difference control scheme (CS3) is further proposed based on CS2. CS3 provides better control than CS2 and the integral absolute error in CS3 is smaller than that in CS2 as facing ±15% disturbances.

Distributed finite-time neural network observer-based consensus tracking control of heterogeneous underwater vehicles

This note scrutinizes the distributed finite-time tracking problem of heterogeneous multi-agent systems with uncertain dynamics and environmental disturbances. To estimate the exogenous disturbances, an adaptive neural network-based disturbance observer is developed in which the approximation error of the neural network is compensated using adaptation laws. Based on finite-time stability theory, a distributed finite-time observer is proposed for each follower in order to estimate the leader's position. Moreover, an adaptive dynamic sliding mode-based controller is also developed for each follower, which ensures finite-time convergence of the tracking error between the leader and the follower. Incorporating adaptive control into the developed composite control structure leads to reducing the chattering, as well as enhancing the robustness and accuracy. Stability analysis and finite-time convergence of the tracking error are performed using the Lyapunov theory and multiple time scale principle, respectively. Finally, simulations and comparisons are performed in order to verify the effectiveness of the developed control algorithm for a group of autonomous underwater vehicles (AUVs).

Composite disturbance observer-based backstepping stabilisation for 3-DOF ship-borne platform with unknown disturbances

ABSTRACT A composite anti-disturbance stabilisation control scheme is presented for the ship-borne platform system with completely unknown disturbances. The completely unknown disturbances consist of external time-varying disturbances and norm-bounded unmodelled dynamics. The composite anti-disturbance control scheme is built through integrating the nonlinear disturbance observer and the robustifying term with the vectorial backstepping technique. The nonlinear disturbance observer is designed to provide the on-line estimations of external time-varying disturbances such that the disturbance compensation term is introduced into the control design. The robustifying term with the adaptive law is employed to attenuate norm-bounded unmodelled dynamics. On the basis of the vectorial backstepping technique, the composite anti-disturbance control law is derived. The composite anti-disturbance control structure consists of the outer layer with the nonlinear disturbance observer for external time-varying disturbance cancellation as well as the inner layer with the vectorial backstepping control together with the robustifying term for unmodelled dynamic attenuation. By means of the Lyapunov stability theory, it is proven that the composite anti-disturbance stabilisation controller can achieve the disturbance rejection and attenuation simultaneously. It is verified by illustrative simulations that the composite anti-disturbance stabilisation control scheme can effectively stabilise the ship-borne stabilisation platform.

Dynamic controllability strategy of reactive-extractive dividing wall column for the separation of water-containing ternary azeotropic mixture

The reactive-extractive dividing wall column (REDWC), which combines conventional reactive distillation, extractive distillation, and dividing wall column, is a highly integrated process with a compact physical space and strong interrelations between variables. It is challenging to design robust control strategies for the REDWC process. However, there are no investigations reported on the control of REDWC. In this study, through analyzing open-loop controllability indicators of the steady-state process, the basic control structure (CS1) is constructed. Subsequently, four proportional-integral control schemes are further established on the CS1: the proportional control structure (CS2), the internal composition control structure (CS3), the feedforward control structure (CS4), and the three-point temperature control structure (CS5) with feedforward loops. The dynamic performance tests are conducted with ± 10 % feed flow rate and ± 10 % feed composition disturbances. The qualitative research demonstrates that the CS5 offers the best dynamic performance in terms of settling time, steady-state deviations, and overshoots without the use of expensive composition controllers. With the integral absolute error (IAE) as an evaluation criterion, it is quantitatively demonstrated that the CS5 has the best robustness and should be the preferred control scheme. Another key finding shows that the vapor split ratio and the stoichiometric ratio of the reactants are two crucial degrees of freedom to guarantee product quality in the REDWC. The major contributions of this work are to provide a meaningful reference for the control of the REDWC and even more complicated distillation.

Separating Mixture Glycols in DWC with Flow Rate-Composition Cascade Control Structure

Dividing wall column (DWC) is an advanced technology which could decrease energy consumption. As the vertical wall inserted in DWC increases the degree of freedom of systems, the control becomes more difficult than the conventional columns. In this study, the mixture glycols (1, 2-propanediol+ 1, 3-butanediol+ 1, 4-butanediol) were taken as feed, an optimized DWC structure was proposed, and three control structures for DWC were tested by ± 10% feed disturbances. The temperature control structure (CS1) was hard to control the system while composition control structure (CS2) and flow rate-composition cascade control structure (CS3) had good performance on controlling the DWC. It showed that CS3 was superior to CS2, as CS3 could stabilize the DWC within 4 hours, and the maximum deviations of the three products, namely 1, 2-propanediol, 1, 3-butanediol and 1, 4-butanediol, were 0.07%, 1.44%, and 0.46% respectively, while CS2 could realize the stability within 7 hours, and the corresponding numbers were 0.35%, 2.78%, and 0.41%, respectively.

Estimation and rejection of sinusoidal disturbance with unknown frequency using cascade disturbance observer

A disturbance rejection approach is presented for a class of uncertain systems subject to sinusoidal disturbance with unknown frequency. The proposed disturbance estimation method includes two types of observers that are connected in cascade form. The disturbance property is excited through an auxiliary filter, and then a frequency factor observer is constructed to generate the information required by full-order state observer. Thus, with the disturbance and system state estimation values, the composite control structure including a cascade disturbance observer (CDO) and a robust feedback controller is designed. As a result, the uncertain system with unknown-frequency sinusoidal component can be controlled within the disturbance observer-based control (DOBC) framework, where the asymptotic stability performance can be guaranteed.

Highly stable Co3O4 nanoparticles/carbon nanosheets array derived from flake-like ZIF-67 as an advanced electrode for supercapacacitor

Nanosized transition metal oxides (TMOs) are one class of the most potential candidates for supercapacitors due to their short electron transport channels and reversible redox reactions. However, their easy-aggregation characteristics and volume shrinkage/expansion during the charge/discharge process seriously limit the practical application. To address this issue, in this work, a two-step thermal conversion different from traditional approaches is reported to synthesize tightly aligned Co3O4/carbon materials. The architecture of cross-linked nanosheets and uniformly distributed Co3O4 nanoparticles (NPs) is obtained by in-situ reduction of cobalt cations in flake-like zeolitic imidazolate frameworks (ZIFs) within inert gas at 500 °C and subsequent mild oxidation of metallic cobalt NPs to Co3O4 NPs (Co3O4@C-500). As a result, this strategy effectively prevents structural collapse and defect formation, which are usually caused by direct oxidation of ZIF-67 nanosheets. In supercapacitor tests, Co3O4@C-500 shows an appreciable specific capacitance (703.3 F g−1 at 1 A g−1) and excellent cycling stability with the capacitance retention of 100% after 10,000 cycles at 10 A g−1. Moreover, the Co3O4@C-500//reduced graphene oxide (RGO) asymmetric supercapacitor (ASC) exhibits an energy density of 43.99 Wh kg−1 at a power density of 824.8 W kg−1, and excellent cycling performance with a capacity retention of 88% after 10,000 cycles. Such excellent performance might benefit from the rational composition control and unique structure of Co3O4 NPs embedded in the carbon skeleton, which results in short electrolyte diffusion channels as well as electron transport distance and effectively reduce negative effect of volume change of electrode materials during the charge/discharge process.

Composite anti-disturbance dynamic positioning of vessels with modelling uncertainties and disturbances

This paper presents a composite anti-disturbance control scheme for the dynamic positioning (DP) of the surface vessels with modelling uncertainties and ocean environmental disturbances. The composite control design builds on integrating the disturbance observer together with the H∞ optimal control. The composite control structure consists of the inner layer disturbance compensator and the outer layer attenuation controller. The inner layer disturbance compensator rejects slowly varying disturbances due to wave drifts, utilizing estimations from the disturbance observer. The outer layer attenuation controller attenuates norm-bounded disturbances due to residual filtered wave-induced disturbances as well as modelling uncertainties. The composite control scheme provides the computational efficiency. The DP motion closed-loop analysis proves that the composite anti-disturbance control maintains the vessel’s position and heading at the reference points and guarantees the closed-loop control stability. Simulations and comparisons on a supply vessel verify the availability and the superiority.

Dissipativity-Based Composite Antidisturbance Control for T–S Fuzzy Switched Stochastic Nonlinear Systems Subjected to Multisource Disturbances

In this article, a dissipativity-based composite antidisturbance control structure is constructed for Takagi–Sugeno (T–S) fuzzy switched stochastic nonlinear systems subjected to multisource disturbances. The inherent uncertain nonlinear and hybrid characteristics of the concerned system make it difficult to design a stable antidisturbance controller. To properly accommodate the characteristics of T–S fuzzy multisource disturbances and system models, a novel fuzzy switched disturbance observer is put forward to estimate the disturbances generated by a switched exogenous system. Then, a fuzzy composite antidisturbance control law is synthesized by fusing the estimation of the multisource disturbances and the state-feedback control scheme. By using the average dwell time technique and piecewise Lyapunov functions, it is proved that the resultant closed-loop system are stochastically stable and strictly $({{\mathscr Z},{\mathscr Y},{\mathscr X}})-\varepsilon -$ dissipative. The sufficient conditions for the existence of the fuzzy switched disturbance observer and state-feedback controller are established in terms of linear matrix inequalities, and the control and observation gains can be solved directly. Finally, a numerical example is presented to illustrate the effectiveness and favor performance of the proposed control algorithm.

OPERATIONAL DESIGN AND IMPROVEMENT OF CONVENTIONAL BATCH DISTILLATION AND MIDDLE-VESSEL BATCH DISTILLATION

Abstract Conventional batch distillation and middle-vessel batch distillation were studied for the separation of the ternary system of cyclohexane/n-heptane/toluene, which has low relative volatilities. The modified variable and constant reflux operations were applied in the conventional batch distillation. Two control structures were used: one of which was referred to as the composition control structure with a modified level-set point, and the other was referred to as the flowrate-limiting control structure. Thus, the middle-vessel batch distillation was able to simultaneously separate the components of the ternary mixture. Comparing the two control structures showed that the flowrate-limiting control structure was better than the composition control structure with a modified level-set point in terms of their applicability. Disturbances were introduced to assess the controllability of the flowrate-limiting control structure. The dynamic responses demonstrated that the control structure performed well. The results showed that the modified conventional batch distillation and middle-vessel batch distillation increased the purity of the separated components compared to previous studies.

Design and control of a middle-vessel batch distillation for separating DMC–EMC–DEC mixture

Abstract In this paper, the mixture of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate was separated by middle-vessel batch distillation with feeding in middle-vessel and process control characteristics were researched. The steady state simulation results in Aspen Plus were exported to Aspen Dynamics. Then control effect of liquid level control with HighSelector, composition control (structure1, structure2) and temperature control (proportional action, proportional integration action) were proposed. Composition control structure 2 and temperature control with PI action were investigated to achieve a good control effect.

Composite compensation control method for airborne opto-electronic platform mounted on multi-rotor UAV

In order to compensate disturbance and accomplish the stabilized tracking control for airborne platform mounted on multi-rotor unmanned aerial vehicle (MUAV), a self-adjusting tracking control method based on an improved disturbance observer (DOB) and radial basis function (RBF) neural network approximation is proposed. First, a compensated control is introduced into feedback loop in the structure of original disturbance observer, an improved disturbance observer is established based on velocity signals, and the ability of disturbance compensation and robustness are analyzed. Second, aiming at the compensation problem of nonlinear unknown disturbance, a method based on the RBF neural network (RBFNN) approximation properties is utilized. Finally, a composite compensation control structure is designed based on Lyapunov stability theory. The experimental results show that after applying the proposed method, the disturbance of airborne opto-electronic platform is compensated effectively. The proposed method has high precision and stable tracking control performance, and it can fully meet the requirement of airborne opto-electronic platform stability control.

Non-linear disturbance observer-based adaptive composite anti-disturbance control for non-linear systems with dynamic non-harmonic multisource disturbances

In this paper, an adaptive composite anti-disturbance control structure is constructed for a class of non-linear systems with dynamic non-harmonic multisource disturbances. The key point of this paper is that a kind of non-harmonic disturbance, which has non-linear internal dynamics and complex features, is involved. A non-linear exogenous system is employed to describe the dynamic non-harmonic disturbances and several useful assumptions are introduced. By introducing a non-linear damping term, a novel adaptive non-linear disturbance observer is constructed. Based on the disturbance/uncertainty estimation and attenuation (DUEA) schemes, a composite anti-disturbance control structure is synthesized. Meanwhile, a new sufficient condition is derived and the stability of the closed-loop system is proved. Several illustrative examples are employed to demonstrate the effectiveness of the proposed method.

Composite Path Tracking Control for Tractor–Trailer Vehicles Via Constrained Model Predictive Control and Direct Adaptive Fuzzy Techniques

Tractor–trailer vehicles will suffer from nonholonomic constraint, uncertain disturbance, and various physical limits, when they perform path tracking maneuver autonomously. This paper presents a composite path tracking control strategy to tackle the various problems arising from not only vehicle kinematic but also dynamic levels via two powerful control techniques. The proposed composite control structure consists of a model predictive control (MPC)-based posture controller and a direct adaptive fuzzy-based dynamic controller, respectively. The former posture controller can make the underactuated trailer midpoint follow an arbitrary reference trajectory given by the earth-fixed frame, as well as satisfying various physical limits. Meanwhile, the latter dynamic controller enables the vehicle velocities to track the desired velocities produced by the former one, and the global asymptotical convergence of dynamic controller is strictly guaranteed in the sense of Lyapunov stability theorem. The simulation results illustrate that the presented control strategy can achieve a coordinated control effect for the sophisticated tractor–trailer vehicles, thereby enhancing their movement performance in complex environments.

Data-Based Tuning of Reduced-Order Inverse Model in Both Disturbance Observer and Feedforward With Application to Tray Indexing

Performance of traditional model-based control relies upon accurate modeling. In motion control of flexible systems, it is desirable to use the reduced-order model for ease of trajectory planning and pole placement, but its performance is constrained by modeling inaccuracies due to the existence of friction and multiple flexible modes. To improve the tracking performance, we have developed a data-based method for iterative tuning of the parameters in the reduced-order inverse model within a three-degree-of-freedom composite control structure. The proposed method solely makes use of the input-output data obtained during closed-loop experiments to fine-tune the inverse system model, and accurate system modeling is not required. Unbiasedness of the cost function gradient estimation is proven under reasonable assumptions of stochastic properties of the perturbations. Simulation and experiments are conducted to further illustrate the proposed method and show its practical appeals in industrial applications.

A Novel and Simple Hybrid Fuzzy/PI Controller for Brushless DC Motor Drives

A novel speed controller for the trapezoidal three--phase Brushless DC (BLDC) Motor Drive is proposed using a hybrid fuzzy logic and proportional plus integral (PI) control. The fuzzy logic control structure is different from conventional fuzzy logic implementations such that it only uses three simple rules based on speed error being either in the positive, negative or zero regions. The controller outputs a reference current, that is enforced through the motor phases by pulsewidth modulation (PWM) control. The proposed fuzzy logic controller can be used individually in applications requiring lower computation load and accepting small steady state offset. For high performance applications requiring offset free tracking, a PI controller is augmented with the fuzzy logic controller and a simple switching scheme is devised based on error variance to switch the active controller based on operating conditions. The response of the drive system under the proposed composite control structure is compared with the conventional PI based and the sliding mode controllers to demonstrate its improved performance. Simulations studies using detailed models in MATLAB/Simulink's Simpowersystems toolbox are carried out to show the validity of proposed control.

Non-Obfuscated Unprovable Programs & Many Resultant Subtleties

The \emph{International Obfuscated C Code Contest} was a programming contest for the most creatively obfuscated yet succinct C code. By \emph{contrast}, an interest herein is in programs which are, \emph{in a sense}, \emph{easily} seen to be correct, but which can\emph{not} be proved correct in pre-assigned, computably axiomatized, powerful, true theories {\bf T}. A point made by our first theorem, then, is that, then, \emph{un}verifiable programs need \emph{not} be obfuscated! The first theorem and its proof is followed by a motivated, concrete example based on a remark of Hilary Putnam. The first theorem has some non-constructivity in its statement and proof, and the second theorem implies some of the non-constructivity is inherent. That result, then, brings up the question of whether there is an acceptable programming system (numbering) for which some non-constructivity of the first theorem disappears. The third theorem shows this is the case, but for a subtle reason explained in the text. This latter theorem has a number of corollaries, regarding its acceptable programming system, and providing some surprises and subtleties about proving its program properties (including universality, and the presence of the composition control structure). The next two theorems provide acceptable systems with contrasting surprises regarding proving universality in them. Finally the next and last theorem (the most difficult to prove in the paper) provides an acceptable system with some positive and negative surprises regarding verification of its true program properties: the existence of the control structure composition is provable for it, but anything about true I/O-program equivalence for syntactically unequal programs is not provable.