Transient Performance Improvement Research Articles

Distributed extremum-seeking control over networks of dynamically coupled unstable dynamic agents

In this paper, a distributed extremum seeking control technique is proposed to solve a class of real-time optimization problems over a network of dynamic agents with unknown unstable dynamics. Each dynamic agent measures a cost that is shared over a network. A dynamic average consensus approach is used to provide each agent with an estimate of the total network cost. The extremum seeking controller operates at each agent to allow each agent to contribute to the optimization of the total cost, in a cooperative fashion. The extremum seeking control technique is based on a proportional–integral approach that provides improvements in transient performance over standard techniques. The contribution of the proposed technique is to solve the simultaneous stabilization and real-time optimization. A dynamic network simulation example is presented to demonstrate the effectiveness of the technique.

A novel surface-cluster approach towards transient modeling of hydro-turbine governing systems in the start-up process

Transient process, an essential condition for the operation of the hydro-turbine governing system, is critical for the safety and stability of a hydropower station. This research focuses on the transient modeling and dynamic analysis of the hydro-turbine governing system in the start-up process. A novel approach is developed to establish the dynamic model of the hydro-turbine governing system in transient process. The flow equation and torque equation were improved to reflect the dramatic changes of system parameters during the start-up process. As a pioneering work, the effect of guide vane opening law on the dynamic characteristics of the hydro-turbine governing system in the start-up process was investigated by numerical simulations. The results of this research can promote the development of transient modeling and performance improvement of hydro-turbine governing systems in transient process.

Design of novel adaptive sliding mode controller for perturbed Chameleon hidden chaotic flow

This article proposes a novel adaptive sliding mode control technique for the finite-time stabilization and transient performance improvement in perturbed Chameleon hidden chaotic flow. The Chameleon hidden chaotic flow is a unique and interesting simple chaotic flow which introduces three well-known families of hidden attractors plus self-excited attractors. In Chameleon chaotic system, based on the changes of constant parameters, the self-excited attractor and three types of hidden attractors (line of equilibria, no equilibrium, or one stable equilibrium point) can be existed. The global sliding surface provides the robust performance by the removal of the reaching phase, causes reduction in the control effort, and forms sliding around the surface right from the initial moment. The designed adaptation laws eliminate the requirement of knowledge for the bounds of disturbances and the nonlinear function $$\psi $$ is employed in the sliding surface to improve the damping ratio of the system. Illustrative simulation results on perturbed Chameleon hidden chaotic flow with different values of the constant parameters, initial states and external disturbances are addressed to prove the efficiency of the proposed approach. Finally, inspired by the interest in the study of hyper-chaos, a novel Chameleon hyper-chaotic flow realized by the addition of a feedback law in the Chameleon chaotic system is presented.

Composite nonlinear feedback control for strict-feedback nonlinear systems with input saturation

ABSTRACTThis paper focuses on composite nonlinear feedback (CNF) controller design for tracking control problem of strict-feedback nonlinear systems with input saturation to address the improvement of transient performance. First, without considering the input saturation, a stabilisation control law is designed by using standard backstepping technique for the nonlinear system, then a feedforward control law is added to the backstepping-based stabilisation control law to construct a tracking control law. The tracking control law is tuned to drive the output of the closed-loop system to track a command input with quick response. Then, an additional nonlinear feedback law is constructed and combined with the tracking control law to obtain a CNF control law. The role of this additional nonlinear feedback law is to smoothly change the damping ratio of the closed-loop system while the system output approaches the command input, and to reduce overshoot caused by the tracking control law. It is shown that the extra-adding nonlinear feedback part does not cause the loss of stability of the closed-loop system in its attractive basin.

Transient Performance Improvement in Tracking Control for a Class of Nonlinear Systems with Input Saturation

This paper addresses the composite nonlinear feedback (CNF) control for a class of singleinput single-output nonlinear systems with input saturation to track a time varying reference target with good transient performance. The CNF control law consists of a tracking control law and a performance compensator. The tracking control law is designed to drive the output of the system to track the time varying reference target rapidly, while the performance compensator is used to reduce the overshoot caused by the tracking control law. The stability of the closed-loop system is established. The design procedure and the improvement of transient performance of the closed-loop system are illustrated with a numerical example and the controlled Van del Pol oscillator.

Transient performance improvement of model reference adaptive control: LMI‐based resetting

SummaryIn this paper, a resetting mechanism is proposed to enhance the transient performance of model reference adaptive control. While the suggested method has a simple structure, it is capable of taking into account both the desired steady‐state behavior and the transient response, simultaneously. Whenever the transient specification is not satisfying, there is a jump in the controller parameters. This jump is determined by designing an optimal reset law. At the reset times, the after‐reset values of parameters are calculated based on a minimization problem. The considered cost function is a mixed H2/H∞ criterion, which minimizes the tracking error. The optimization problem is converted to an LMI formulation, and the reset law is designed by solving this LMI at certain reset times. To verify the effectiveness of the proposed approach, simulation results are presented.

Robust path-following control for a fully actuated marine surface vessel with composite nonlinear feedback

This paper presents a fast and accurate robust path-following control approach for a fully actuated marine surface vessel in the presence of external disturbances. The path following is realized by simultaneously converging the yaw rate and sway velocity to their respective desired values, which are generated according to the path-following demand. An improved combined control strategy using an integral terminal sliding mode (ITSM) based composite nonlinear feedback (CNF) technique considering the external disturbances, time-varying tracking reference, input saturations and transient performance improvement is proposed in this study. The proposed ITSM-CNF combines the advantages of the CNF control in improving the transient performance and of the ITSM control in guaranteeing good robustness and finite-time convergence. A continuous and smooth sliding mode controller, based on an integral nonsingular terminal sliding surface, is added to the CNF controller to eliminate chattering. The overall stability of the closed-loop system is strictly proved based on the Lyapunov method. Simulations verify the effectiveness of the ITSM-CNF controller in improving the transient path-following performance, inhibiting overshoots, eliminating steady-state errors, rejecting external disturbances and removing chattering effects, considering input saturations, varying path curvature and finite-time convergence.

Consensus tracking control with transient performance improvement for a group of unmanned aerial vehicles subject to faults and parameter uncertainty

ABSTRACTThis paper considers the consensus tracking synthesised with transient performance improvement problem for a network of unmanned aerial vehicles with faults. In practical situations, the parameter variations, modelling errors and disturbances are of particular interest. Thus, it is assumed that the dynamics of vehicles are subject to parameter uncertainty. As the main contribution of this paper, a set of fault-estimator-based protocols is proposed to drive the overall network performance below the given H∞ synthesised with transient performance index. Sufficient conditions for designing the protocols which utilise the relative output information among neighbouring vehicles are given by applying the robust control theory. Simulations are performed to validate the proposed results.

Optimal adaptive reset control with guaranteed transient and steady state tracking error bounds

In this paper, a solution for improvement of transient performance in adaptive control of nonlinear systems is proposed. An optimal adaptive controller based on a reset mechanism and a prescribed performance bound is devised. The suggested controller has the structure of adaptive backstepping controller in which the estimated parameters are reset to an optimal value. The designed controller ensures both the transient bound and the asymptotical convergence of the states. It is shown that the tracking error satisfies the prescribed performance bound all the time, besides the speed of the convergence rate is increased by resetting the estimated parameters. The results have been proved through both the analytical and simulation studies. The proposed method is applied to an Augmented Quarter Car Model as a case study. Simulation results verify the established theoretical consequences that the prescribed performance bound based optimal adaptive reset controller can enhance the transient performance of the adaptive controller.

Interleaved cuk converter with improved transient performance and reduced current ripple

Boost DC–DC converters are widely used in non-conventional power conversions namely in solar and wind power generation systems. It is also used in switched mode power supplies. Since there is no filter inductor on output side, output current of boost converter is pulsed and it is not desirable. The quality of power required is very high when DC–DC converters are employed for transferring the requisite amount of power. In this study, the conventional cuk converter (CCC) having a continuous current at both input and output sides is taken as the candidate for performance analysis. Accordingly an interleaved cuk converter (ICC) is proposed and designed to reduce the input current ripple and also to improve transient performances. Both the CCC and the proposed ICC are simulated and validated experimentally. The proposed converter is having better efficiency attributable to cancellation of source current ripple, reduction of ripple content in both output voltage and current, and improvement of transient performance.

Transient tracking performance improvement for nonlinear nonminimum phase systems: an additive-state-decomposition-based control method

ABSTRACTTo study the problem of improving transient tracking performance for nonlinear systems, this paper proposes an additive-state-decomposition-based control method for a class of nonlinear nonminimum phase (NMP) systems. This method ‘additively’ decomposes the original problem into two more tractable problems, namely a tracking problem for a linear time-invariant NMP ‘primary’ system and a state stabilisation problem for a certain nonlinear ‘secondary’ system. Then, controller for each system is designed respectively by employing existing methods, i.e. the linear quadratic regulator (LQR) method for the primary system and the backstepping method for the secondary system. Next, these two controllers are combined together to achieve the original tracking goal. Furthermore, the adjustment of weighting matrix Q in the LQR regulates the transient response of the closed-loop nonlinear system. Finally, two illustrative examples are provided to demonstrate the effectiveness of the proposed method.

Transient performance improvement in indirect model reference adaptive control using perturbation‐based extremum seeking identifier

AbstractOne of the main drawbacks of model reference adaptive control (MRAC) is the weakness of its transient performance. The key reason of this imperfection is parameter's estimation error convergence. For many cases in the closed‐loop control, the plant input signal cannot satisfy the persistence of excitation (PE) condition which yields poor parameters estimation error convergence. In this paper, we use a fast perturbation‐based extremum seeking (PES) scheme without steady‐state oscillation as the parameter identifier in indirect MRAC. The estimated parameters through the PES identifier contain the additive sinusoidal signals with distinct frequencies in the transient, which satisfy the PE condition of the plant input. Therefore, convergence of the parameters estimation error to zero will be guaranteed that results in improvement of transient performance for indirect MRAC. Also, the contrary effects on the steady‐state behaviour is eliminated since the sinusoidal excitation signals amplitude exponentially converge to zero and reinitiate with every change in the unknown parameters. Simulation results for a second order example have been presented to illustrate the effectiveness of the proposed scheme.

Two Time-Scale Tracking Control of Nonholonomic Wheeled Mobile Robots

In this paper, a practical control law is proposed for wheeled mobile robots in order to both improve the transient performance and repress the tracking errors. In particular, a two time-scale filtering technique, which can derive a fast variable to compensate for the disturbance, is applied during the carbot’s moving process. The nominal system is governed using a controller derived under the back-stepping framework. Such a design can effectively realize the system’s tracking objective and enhance robustness via properly configured parameters. In the meantime, a two time-scale filter is applied to the system function to estimate the disturbances, essentially improving the system’s precision. By virtue of this innovative technique, the final performance of the system is satisfactory in terms of both transient response and tracking error rejection. A previous sliding mode based control law is compared with the propounded one with respect to transient behavior and steady-state errors, and two types of disturbances, respectively the constant and sinusoid are simulated to verify the filter’s effectiveness. Since, from the results, there is significant improvement in both transient and steady-state performance, the proposed method is confirmed to be practical for tracking control of the wheeled mobile robots.

Robust Composite Nonlinear Feedback Path-Following Control for Underactuated Surface Vessels With Desired-Heading Amendment

This paper addresses the transient performance improvement for path-following control of underactuated surface vessels (USVs) in the presence of oceanic disturbances. The traditional practice that chooses the tangent direction of the desired path as the desired heading may deteriorate the tracking performance in the curve following due to the nonzero sideslip angle therein. Also, the disturbances in wave filed greatly affect the transient path-following control. To this end, three contributions are made in this paper: 1) an amendment to the definition of the desired heading using the sideslip-angle compensation is presented to achieve a more accurate path-following maneuver; 2) a novel disturbances observer-based composite nonlinear feedback (DO-CNF) controller is proposed to restrain system overshoots and eliminate steady-state errors while dealing with multiple oceanic disturbances with unknown bounds; and 3) the variation of the yaw-rate reference for path-following objective is handled in the controller design, which can enhance the vessel's robustness to the changing of the path curvature. Comparative simulations verify the reasonability of the desired-heading amendment and the effectiveness of the DO-CNF approach in improving the transient path-following performance of USVs while satisfying actuator saturation considering the unknown disturbances and changing reference.

Improving transient performance of adaptive control via a modified reference model and novel adaptation

SummaryThis paper presents a new model reference adaptive control (MRAC) framework for a class of nonlinear systems to address the improvement of transient performance. The main idea is to introduce a nonlinear compensator to reshape the closed‐loop system transient, and to suggest a new adaptive law with guaranteed convergence. The compensator captures the unknown system dynamics and modifies the given nominal reference model and the control action. This modified controlled system can approach the response of the ideal reference model. The transient is easily tuned by a new design parameter of this compensator. The nominal adaptive law is augmented by new leakage terms containing the parameter estimation errors. This allows for fast, smooth and exponential convergence of both the tracking error and parameter estimation, which again improves overall reference model following. We also show that the required excitation condition for the estimation convergence is equivalent to the classical persistent excitation (PE) condition. In this respect, this paper provides an intuitive and numerically feasible approach to online validate the PE condition. The salient feature of the suggested methodology is that the rapid suppression of uncertainties in the controlled system can be achieved without using a large, high‐gain induced, learning rate in the adaptive laws. Extensive simulations are given to show the effectiveness and the improved response of the proposed schemes. Copyright © 2016 John Wiley & Sons, Ltd.

Transient Performance Improvement in the Boundary Control of Boost Converters using Synthetic Optimized Trajectory

This paper focuses on an improvement in the transient performance of Boost converters when the load changes abruptly. This is achieved on the basis of the nature trajectory in Boost converters. Three key aspects of the transient performance are analyzed including the storage energy change law in the inductors and capacitors of converters during the transient process, the ideal minimum voltage deviation in the transient process, and the minimum voltage deviation control trajectory. The changing relationship curve between the voltage deviation and the recovery time is depicted through analysis and simulations when the load suddenly increases. In addition, the relationship curve between the current fluctuation and the recovery time is obtained when the load suddenly decreases. Considering the aspects of an increasing and decreasing load, this paper proposes the transient performance synthetic optimized trajectory and control laws. Through simulation and experimental results, the transient performances are compared with the other typical three control methods, and the ability of proposed synthetic trajectory and control law to achieve optimal transient performance is verified.

Split-path nonlinear integral control for transient performance improvement

In this paper, we introduce the split-path nonlinear integrator (SPANI) as a novel nonlinear filter designed to improve the transient performance of linear systems in terms of overshoot, while preserving good rise-time and settling behavior. In particular, this nonlinear controller targets the well-known trade-off induced by integral action, which removes steady-state errors due to constant external disturbances, but deteriorates transient performance in terms of increased overshoot. The rationale behind the proposed SPANI filter is to ensure that the integral action has, at all times, the same sign as the closed-loop error signal, which, as we will show, enables a reduction in overshoot thereby leading to an overall improved transient performance. The resulting closed-loop dynamics is modeled by a hybrid dynamical system, for which we provide sufficient Lyapunov-based conditions for stability. Furthermore, we illustrate the effectiveness, the design and the tuning of the proposed controller in a benchmark simulation study of an industrial pick-and-place machine.

Control of twin-rotor MIMO system using multiple models with second level adaptation

Abstract In this paper an adaptive control method for nonlinear MIMO coupled systems is proposed in general and applied to twin rotor MIMO system (TRMS) in particular. A feedback linearization technique for MIMO coupled system is used to design a static state feedback control which linearizes as well as decouples the system. An adaptive control method using multiple models with second level adaptation is proposed for nonlinear MIMO systems. The unknown parameters of the system are assumed to be bounded within a well defined region. The estimation model of the system is used to tune the parameters. The estimation error is shown to converge to zero asymptotically and the adaptive law for tuning of unknown parameters is derived using Lyapunov stability criterion. A TRMS model is simulated to validate the theoretical establishments. An Extended Kalman Filter (EKF) has been used to observe the unavailable states of the TRMS. The improvement in transient and steady state performance using the proposed scheme is validated by simulation results.

Coordinated Control of SFCL and SMES for Transient Performance Improvement of Microgrid With Multiple DG Units

Aiming at a microgrid system with multiple distributed generation (DG) units, this paper proposes the coordinated control of a flux-coupling-type superconducting fault current limiter (SFCL) and superconducting magnetic energy storage (SMES), so as to improve its transient performance under fault conditions. On the one hand, using the SFCL and the SMES enhances the microgrid’s fault ride-through capability. And for some specific faults, the microgrid should disconnect from the main network, and the coordinated control of the SFCL and the SMES makes the microgrid carry out a smooth transition between its grid-connected and islanded modes. Relevant theory analysis of structure principle, control strategy, and capacity design is conducted, and simulations under different fault conditions are performed in MATLAB. From the results, the coordinated control of the SFCL and the SMES can contribute to limit the fault current, improve the voltage at the point of common coupling (PCC), and alleviate the frequency/reactive power fluctuations. Thus, the microgrid’s robustness against short-circuit faults can be well increased.

Volumetric solar heating of nanofluids for direct vapor generation

Traditional solar–thermal receivers suffer from high surface temperatures, which increase heat losses to the surroundings. To improve performance, volumetric receivers based on nanoparticles suspended in liquid (nanofluids) have been studied as an approach to reduce surface losses by localizing high temperatures to the interior of the receiver. Here, we report measured vapor generation efficiencies of 69% at solar concentrations of 10sun using graphitized carbon black, carbon black, and graphene suspended in water, representing a significant improvement in both transient and steady-state performance over previously reported results. To elucidate the vapor generation mechanism and validate our experimental results, we develop numerical and analytical heat transfer models that suggest that nanofluid heating and vapor generation occur due to classical global heating of the suspension fluid. This work demonstrates high nanofluid-assisted vapor generation efficiencies with potential applications in power generation, distillation, and sterilization.