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Showing papers in "IEEE Transactions on Control Systems and Technology in 2005"


Journal ArticleDOI
TL;DR: It is seen that many PID variants have been developed in order to improve transient performance, but standardising and modularising PID control are desired, although challenging, and the inclusion of system identification and "intelligent" techniques in software based PID systems helps automate the entire design and tuning process to a useful degree.
Abstract: Designing and tuning a proportional-integral-derivative (PID) controller appears to be conceptually intuitive, but can be hard in practice, if multiple (and often conflicting) objectives such as short transient and high stability are to be achieved. Usually, initial designs obtained by all means need to be adjusted repeatedly through computer simulations until the closed-loop system performs or compromises as desired. This stimulates the development of "intelligent" tools that can assist engineers to achieve the best overall PID control for the entire operating envelope. This development has further led to the incorporation of some advanced tuning algorithms into PID hardware modules. Corresponding to these developments, this paper presents a modern overview of functionalities and tuning methods in patents, software packages and commercial hardware modules. It is seen that many PID variants have been developed in order to improve transient performance, but standardising and modularising PID control are desired, although challenging. The inclusion of system identification and "intelligent" techniques in software based PID systems helps automate the entire design and tuning process to a useful degree. This should also assist future development of "plug-and-play" PID controllers that are widely applicable and can be set up easily and operate optimally for enhanced productivity, improved quality and reduced maintenance requirements.

2,461 citations


Journal ArticleDOI
TL;DR: The primary emphasis of the paper is on the robustness of the closed-loop device as these flexure-stage-based, piezoactuated nano-positioners are nonlinear and operate in diverse conditions.
Abstract: In this paper, we present a systematic control design and analysis for a two-dimensional nano-positioner. The primary emphasis of the paper is on the robustness of the closed-loop device as these flexure-stage-based, piezoactuated nano-positioners are nonlinear and operate in diverse conditions. To this end, we have used many tools from modern control theory to model devices and to quantify device resolution, bandwidth, and robustness. The implementation of this procedure for the simultaneous achievement of the objectives of robustness, high precision and high bandwidth is presented. The merits of the paradigm are demonstrated through experimental results.

317 citations


Journal ArticleDOI
TL;DR: A new real-time fault estimation module that estimates the actuator effectiveness is developed and simulation results of a helicopter in vertical plane is presented to demonstrate the performance of the proposed fault-tolerant control scheme.
Abstract: In this brief, a methodology for detection and accommodation of actuator faults for a class of multi-input-multi-output (MIMO) stochastic systems is presented. First, a new real-time fault estimation module that estimates the actuator effectiveness is developed. The actuator fault diagnosis is based on the estimation of the state vector. Under some conditions, the stochastic system is transformed into two separate subsystems. One of them is not affected by actuator faults, so a reduced order Kalman filter can be used to estimate its states. The other, whose states are measurable, is affected by the faults. Then, the output of the nominal controller is reconfigured to compensate for the loss of actuator effectiveness in the system. Simulation results of a helicopter in vertical plane is presented to demonstrate the performance of the proposed fault-tolerant control scheme.

284 citations


Journal ArticleDOI
TL;DR: Analysis and simulation results for a two-degree-of-freedom (2-DOF) quarter-car model show possible improvements on ride comfort, while respecting time-domain hard constraints.
Abstract: This paper suggests a constrained H/sub /spl infin// control scheme for active suspensions with output and control constraints. The H/sub /spl infin// performance is used to measure ride comfort so that more general road disturbances can be considered. Time-domain constraints, representing requirements for: 1) good road holding which may have an impact on safety; 2) suspension stroke limitation; and 3) avoidance of actuator saturation, are captured using the concept of reachable sets and state-space ellipsoids. The proposed approach can potentially achieve the best possible ride comfort by allowing constrained variables free as long as they remain within given bounds. A state feedback solution to the constrained H/sub /spl infin// active suspension control problem is derived in the framework of linear matrix inequality (LMI) optimization and multiobjective control. Analysis and simulation results for a two-degree-of-freedom (2-DOF) quarter-car model show possible improvements on ride comfort, while respecting time-domain hard constraints.

276 citations


Journal ArticleDOI
TL;DR: Using an electric circuit model of the battery given in the literature, it is shown how the open-circuit voltage can be estimated based on the terminal voltage and current measurements provided there is sufficient variation in the battery current.
Abstract: This brief considers the state of charge (SOC) estimation problem for electrochemical batteries. Using an electric circuit model of the battery given in the literature, it is shown how the open-circuit voltage (which is directly related to the SOC) can be estimated based on the terminal voltage and current measurements provided there is sufficient variation in the battery current.

256 citations


Journal ArticleDOI
TL;DR: It is shown that the theory of symmetric polynomials can be exploited to reduce the degree of the polynomial equations that must be solved which in turn greatly reduces the computational burden.
Abstract: A method is presented to compute the switching angles in a multilevel converter so as to produce the required fundamental voltage while at the same time not generate higher order harmonics. Previous work has shown that the transcendental equations characterizing the harmonic content can be converted to polynomial equations which are then solved using the method of resultants from elimination theory. A difficulty with this approach is that when there are several dc sources, the degrees of the polynomials are quite large making the computational burden of their resultant polynomials (as required by elimination theory) quite high. Here, it is shown that the theory of symmetric polynomials can be exploited to reduce the degree of the polynomial equations that must be solved which in turn greatly reduces the computational burden. In contrast to results reported in the literature that use iterative numerical techniques to solve these equations, the approach here produces all possible solutions.

246 citations


Journal ArticleDOI
TL;DR: It is shown that dynamics-coupling from the scan axes (x and y axes) to the perpendicular z axis can generate significant positioning errors during high-speed AFM operation, i.e., when the sample is scanned at high speed.
Abstract: This paper addresses the compensation of the dynamics-coupling effect in piezoscanners used for positioning in atomic force microscopes (AFMs). Piezoscanners are used to position the AFM probe, relative to the sample, both parallel to the sample surface (x and y axes) and perpendicular to the sample surface (z axis). In this paper, we show that dynamics-coupling from the scan axes (x and y axes) to the perpendicular z axis can generate significant positioning errors during high-speed AFM operation, i.e., when the sample is scanned at high speed. We use an inversion-based iterative control approach to compensate for this dynamics-coupling effect. Convergence of the iterative approach is investigated and experimental results show that the dynamics-coupling-caused error can be reduced, close to the noise level, using the proposed approach. Thus, the main contribution of this paper is the development of an approach to substantially reduce the dynamics-coupling-caused error and thereby, to enable high-speed AFM operation.

242 citations


Journal ArticleDOI
P. Yih1, J.C. Gerdes1
TL;DR: Experimental results verify that with precise steering control and accurate state information, the handling modification is exactly equivalent to changing the front tire cornering stiffness.
Abstract: While changing the handling characteristics of a conventional vehicle normally requires physical modification, a vehicle equipped with steer-by-wire can accomplish the same effect through active steering intervention. This paper presents an intuitive method for altering a vehicle's handling characteristics by augmenting the driver's steering command with full vehicle state feedback. The vehicle can be made more or less responsive depending on the driver's preference and particular operating conditions. Achieving a smooth, continuous change in handling quality requires both accurate state estimation and well-controlled steering inputs from the steer-by-wire system. Accurate estimates of vehicle states are available from a combination of global positioning system (GPS) and inertial navigation system (INS) sensor measurements. By canceling the effects of steering system dynamics and tire disturbance forces, the steer-by-wire system is able to track commanded steer angle with minimal error. Experimental results verify that with precise steering control and accurate state information, the handling modification is exactly equivalent to changing the front tire cornering stiffness.

239 citations


Journal ArticleDOI
TL;DR: The H/sub /spl infin// approach is used to design the haptic interface and experimental results are presented to demonstrate its suitability for the intended application of minimally invasive surgical training.
Abstract: In this brief, we propose a "shared-control" architecture for design of a haptic interface for hands-on training in minimally invasive surgery. The interface is designed to allow experienced surgeons mentor trainee surgeons through shared control of a surgical robot. During shared control, the interface provides feedback forces to both surgeons, proportional to the difference of their actions and reversely proportional to the control authority shared between them. The control authority shared between the surgeons is chosen based on their relative level of surgical skills and experience and determines the extent to which the motion of the surgical robot depends on their individual commands. We use the H/sub /spl infin// approach to design the haptic interface and present experimental results to demonstrate its suitability for the intended application of minimally invasive surgical training.

182 citations


Journal ArticleDOI
TL;DR: This brief presents a real-time, feasible trajectory generation algorithm for unmanned air vehicles (UAVs) flying through a sequence of waypoints that produces extremal trajectories that transition between straight-line path segments in a time-optimal fashion.
Abstract: This brief presents a real-time, feasible trajectory generation algorithm for unmanned air vehicles (UAVs) flying through a sequence of waypoints. The algorithm produces extremal trajectories that transition between straight-line path segments in a time-optimal fashion. In addition, the algorithm can be configured so that the dynamically feasible trajectory has the same path length as the straight-line waypoint path. Implementation issues associated with the algorithm are described in detail. Simulation studies show the effectiveness of the proposed method.

178 citations


Journal ArticleDOI
TL;DR: The proposed new PO/PC approach is applied to PHANToM with high stiffness (K=5000N/m), and stable and smooth contact is guaranteed, and Resetting and active environment display problems can be solved with the reference energy following idea.
Abstract: A recently proposed method for stabilizing haptic interfaces and teleoperation systems was tested with a PHANToM commercial haptic device. The passivity observer (PO) and passivity controller (PC) stabilization method was applied to stabilize the system but also excited a high-frequency mode in the device. To solve this problem, we propose a method to use a time-varying desired energy threshold instead of fixed zero energy threshold for the PO, and make the actual energy input follow the time-varying energy threshold. With the time-varying energy threshold, we make the PC control action smooth without sudden impulsive behavior by distributing the dissipation. The proposed new PO/PC approach is applied to PHANToM with high stiffness (K=5000N/m), and stable and smooth contact is guaranteed. Resetting and active environment display problems also can be solved with the reference energy following idea.

Journal ArticleDOI
TL;DR: A spectral-approximation-based intelligent modeling approach is proposed for the distributed thermal processing of the snap curing oven that is used in semiconductor packaging industry and can be applied to a class of nonlinear DPSs in industrial thermal processing.
Abstract: A spectral-approximation-based intelligent modeling approach is proposed for the distributed thermal processing of the snap curing oven that is used in semiconductor packaging industry. The snap curing oven can be described by a nonlinear parabolic distributed parameter system (DPS) in the time-space domain. After finding a proper approximation of the complex boundary conditions of the system, the spectral methods can be applied to time-space separation and model reduction, and neural networks (NNs) can be used for state estimation and system identification. With the help of model reduction techniques, the dynamics of the curing process derived from physical laws can be described by a model of low-order nonlinear ordinary differential equations with a few uncertain parameters and unknown nonlinearities. A neural observer can then be designed to estimate the states of the ordinary differential equation model from measurements taken at specified locations in the field. Using the estimated states, a hybrid general regression NN is trained to be a nonlinear model of the curing process in state-space formulation, which is suitable for the further application of traditional control techniques. Real-time experiments on the snap curing oven show that the proposed modeling method is effective. This modeling methodology can be applied to a class of nonlinear DPSs in industrial thermal processing.

Journal ArticleDOI
TL;DR: The stochastic robust nonlinear control approach is applied to a highly nonlinear complex aircraft model, the high-incidence research model (HIRM), which addresses a high-angle-of-attack enhanced manual control problem.
Abstract: This paper considers probabilistic robust control of nonlinear uncertain systems. A combination of stochastic robustness and dynamic inversion is proposed for general systems that have a feedback-linearizable nominal system. In this paper, the stochastic robust nonlinear control approach is applied to a highly nonlinear complex aircraft model, the high-incidence research model (HIRM). The model addresses a high-angle-of-attack enhanced manual control problem. The aim of the flight control system is to give good handling qualities across the specified flight envelope without the use of gain scheduling and also to provide robustness to modeling uncertainties. The proposed stochastic robust nonlinear control explores the direct design of nonlinear flight control logic. Therefore, the final design accounts for all significant nonlinearities in the aircraft's high-fidelity simulation model. The controller parameters are designed to minimize the probability of violating design specifications, which provides the design with good robustness in stability and performance subject to modeling uncertainties. The present design compares favorably with earlier controllers that were generated for a benchmark design competition.

Journal ArticleDOI
TL;DR: A comparative analysis with a plenty of simulation results soundly confirmed that the performance of developed variable structure PID controller is better under than those of both classical PID controller and an existing variable structure controller with PID-sliding surface.
Abstract: In this brief, a new variable structure proportional-integral-derivative (PID) controller design approach is considered for the tracking stabilization of robot motion. The work corroborates the utility of a certain PID sliding mode controller with PID sliding surface for tracking control of a robotic manipulator. Different from the general approach, the conventional equivalent control term is not used in this controller because that needs to use the matching conditions and exact full robot dynamics knowledge, which involves unavailable parameter uncertainties. Though the sliding surface includes also the integral error term, which makes the robot tracking control problem complicated, the existence of a sliding mode and gain selection guideline are clearly investigated. Moreover, different from uniformly ultimately boundedness, the global asymptotic stability of the robot system with proposed controller is analyzed. The sliding and global stability conditions are formulated in terms of Lyapunov full quadratic form and upper and lower matrix norm inequalities. Reduced design is also discussed. The proposed control algorithm is applied to a two-link direct drive robot arm through simulations. The simulation results indicate that the control performance of the robot system is satisfactory. The chattering phenomenon is handled by the use of a saturation function replaced with a pure signum function in the control law. The saturation function results in a smooth transient performance. The proposed approach is compared with the existing alternative sliding mode controllers for robot manipulators in terms of advantages and control performances. A comparative analysis with a plenty of simulation results soundly confirmed that the performance of developed variable structure PID controller is better under than those of both classical PID controller and an existing variable structure controller with PID-sliding surface.

Journal ArticleDOI
TL;DR: An adaptive law is derived based on the Lyapunov function to tune the coupling factor of the hierarchical sliding-mode controller so as to achieve favorable decoupling performance with guaranteed stability.
Abstract: A design method using hierarchical fuzzy sliding-mode (HFSM) decoupling control is proposed to achieve system stability and favorable decoupling performance for a class of nonlinear systems. In this approach, the nonlinear system is decoupled into several subsystems and the state response of each subsystem can be designed to be governed by a corresponding sliding surface. Then the whole system is controlled by a hierarchical sliding-mode controller. In this design, an adaptive law is derived based on the Lyapunov function to tune the coupling factor of the hierarchical sliding-mode controller so as to achieve favorable decoupling performance with guaranteed stability. The proposed design method is applied to investigate the decoupling control of a double inverted pendulum system. Simulations are performed and a comparison between the proposed HFSM decoupling control and a conventional fuzzy sliding-mode (FSM) decoupling control is presented to demonstrate the effectiveness of the proposed design method.

Journal ArticleDOI
TL;DR: In this paper, a robust load governor is proposed to protect the fuel cells from oxygen starvation by regulating the current drawn from the fuel cell, and the pointwise-in-time constraints on the oxygen excess ratio and the oxygen mass inside the cathode are strictly enforced.
Abstract: The fuel cell oxygen starvation problem is addressed in this paper using a robust load governor. By regulating the current drawn from the fuel cell, the pointwise-in-time constraints on the oxygen excess ratio and on the oxygen mass inside the cathode are strictly enforced to protect the fuel cells from oxygen starvation. The load governor is designed using a nonlinear reference governor approach. Parameter uncertainties such as those due to imperfect controls of temperature and humidity are handled in the load governor design using a novel approach based on sensitivity functions. Simulation results are included to demonstrate the effectiveness of the proposed scheme. The results are compared with those of a linear filter which has been proposed in the prior literature to achieve similar goals.

Journal ArticleDOI
TL;DR: Sliding mode techniques are applied to pneumatic muscle actuators arranged in an agonist/antagonist, or opposing pair configuration, and a sliding mode controller is designed to give elbow angle tracking within a guaranteed accuracy despite modeling errors.
Abstract: Sliding mode techniques are applied to pneumatic muscle actuators arranged in an agonist/antagonist, or opposing pair configuration. The pneumatic muscle (PM) pair actuates a planar elbow manipulator, with PMs in place of bicep and tricep. The control objective is elbow angle tracking under load. A nonlinear mathematical model is derived for this system and a sliding mode controller is designed to give elbow angle tracking to within a guaranteed accuracy despite modeling errors. Static pressure requirements are also derived for stable arm behavior in the absence of a control signal. Stability results are derived, and the results of simulation studies are presented. The simulation studies also address the effects of PM heating.

Journal ArticleDOI
TL;DR: This paper examines the position control problem of piezoelectric stack actuators and presents a method for overcoming the hysteresis nonlinearity between the applied voltage and the actuator displacement.
Abstract: This paper examines the position control problem of piezoelectric stack actuators and presents a method for overcoming the hysteresis nonlinearity between the applied voltage and the actuator displacement. An inverting charge control circuit is implemented to linearize the stack actuator movement by taking advantage of the linear relationship between charge and displacement. The charge control feedback loop is analyzed in detail. It incorporates an operational amplifier to provide high loop gain, a high-voltage amplifier (HVA) to drive the stack actuator, and a lead compensator to ensure stability. Experiments were conducted to compare the responses of the stack actuator under voltage and charge control. The experimental data show that the charge control provides linear actuator operation from 1 Hz-10 Hz over approximately 35% of the actuator operating range, and from 1 Hz-20 Hz over approximately 19% of the operating range.

Journal ArticleDOI
TL;DR: A fairly comprehensive modeling and compensation of friction and nonlinearities of a typical voice-coil-motor actuator used in commercial HDDs, and the design of an HDD servo system using an enhanced nonlinear control technique that has outperformed the conventional proportional-integral-derivative control in settling time.
Abstract: Friction and nonlinearities result in large residual errors and deteriorate the performance of head positioning of hard disk drive (HDD) servo systems and other mechanical servo systems. Thus, it is highly desirable to characterize the behaviors of nonlinearities and friction in the servo systems. This paper presents a fairly comprehensive modeling and compensation of friction and nonlinearities of a typical voice-coil-motor (VCM) actuator used in commercial HDDs, and the design of an HDD servo system using an enhanced nonlinear control technique. Our contributions are two-fold: We will first obtain a complete model of the VCM actuator including friction and nonlinear characteristics through a careful examination of the configuration and structure of the actual system and through a thorough analysis of its physical effects together with its time-domain and frequency-domain responses. We will then proceed to design a servo system for the hard drive using an enhanced composite nonlinear feedback (CNF) control technique with a simple friction and nonlinearity compensation scheme. The enhanced CNF technique has a feature of removing the uncompensated portion of friction and nonlinearities without sacrificing the overall tracking performance. Simulation and experimental results for both the modeling and the servo design show that our approach is very effective and successful. In particular, our experimental results show that the enhanced CNF control has outperformed the conventional proportional-integral-derivative (PID) control in settling time by 76%. We believe that this approach can be adopted to solve other servomechanism problems.

Journal ArticleDOI
TL;DR: An energy management control system for a parallel hybrid electric vehicle incorporates an optimization scheme to assess the amount of engine torque for generating propulsive power as well as a charge sustaining scheme to ensure that battery's state of charge is maintained at sufficiently high level.
Abstract: An energy management control system for a parallel hybrid electric vehicle is presented. The proposed system incorporates an optimization scheme to assess the amount of engine torque for generating propulsive power (torque distribution task) as well as a charge sustaining scheme to ensure that battery's state of charge is maintained at sufficiently high level. In order to accomplish the torque distribution task, torque distribution control problem is formulated as a multi-objective nonlinear optimization problem, and recast and solved as a single objective linear optimization problem. Furthermore, a new vehicle-mode-based state-of-charge compensator is developed to accomplish the charge sustaining task. Computer simulation work is carried out to evaluate the proposed energy management system. Finally, through sensitivity analysis, robustness of the solution to changes in the parameters of the objective functions is investigated.

Journal ArticleDOI
TL;DR: Property of piezoelectric transducers driven by charge sources when used with resonant controllers for structural vibration control applications is investigated and it is found that it is now possible to effectively, and accurately control the charge deposited on the electrodes of a piezoeselectric transducer, and thereby avoid hysteresis altogether.
Abstract: Driving piezoelectric actuators by charge, or current rather than voltage is known to significantly reduce the hysteretic nature of these actuators. Although this feature of piezoelectric transducers has been known to the researchers for some time, still voltage amplifiers are being used as the main driving mechanism for piezoelectric devices. This is due to the perceived difficulty in building charge/current amplifiers capable of driving highly capacitive loads such as piezoelectric actuators. Recently, a new charge amplifier has been proposed which is ideal for driving piezoelectric loads used in applications such as active damping of vibration. Consequently, it is now possible to effectively, and accurately control the charge deposited on the electrodes of a piezoelectric transducer, and thereby avoid hysteresis altogether. This paper further investigates properties of piezoelectric transducers driven by charge sources when used with resonant controllers for structural vibration control applications. The paper reports experimental results of a multivariable resonant controller implemented on a piezoelectric laminate cantilever beam.

Journal ArticleDOI
TL;DR: A recently developed method for adaptive output feedback control permits adaptation to both parametric uncertainty and unmodeled dynamics, and incorporates a novel approach that permits adaptation under known actuator characteristics including actuator dynamics and saturation.
Abstract: Experimental results are presented that illustrate a recently developed method for adaptive output feedback control. The method permits adaptation to both parametric uncertainty and unmodeled dynamics, and incorporates a novel approach that permits adaptation under known actuator characteristics including actuator dynamics and saturation. Only knowledge of the relative degree of the controlled system within the bandwidth of the control design is required. The controller design was tested by controlling the pitch axis of a three degrees-of-freedom (DOF) helicopter model, using attitude feedback through a low-resolution optical sensor.

Journal ArticleDOI
TL;DR: In this brief, the investigational results for a robust adaptive vibration control of a translating tensioned beam with a varying traveling speed are presented and the Lyapunov method is employed to design robust adaptive boundary control laws for ensuring the vibration reduction of the nonlinear time-varying system.
Abstract: In this brief, the investigational results for a robust adaptive vibration control of a translating tensioned beam with a varying traveling speed are presented. The dynamics of beam and actuator is modeled via the extended Hamilton's principle, in which the tension applied to the beam is given as a nonlinear spatiotemporally varying function. The moving beam is divided into two parts, a controlled span and an uncontrolled span, by a hydraulic touch-roll actuator that is located in the middle section of the beam. The transverse vibration of the controlled span is suppressed by the touch-roll actuator, whereas the vibration of the uncontrolled span is treated as a disturbance, and the magnitude of unknown disturbance is estimated. In a proper mathematical manner, the Lyapunov method is employed to design robust adaptive boundary control laws for ensuring the vibration reduction of the nonlinear time-varying system, and also to ensure the stability of the closed-loop system. The effectiveness of the proposed controller is demonstrated via numerical simulations.

Journal ArticleDOI
TL;DR: A partial differential equation model for a flexible two-link manipulator is derived and transformed to a form appropriate for the development of stable control designs and a novel control design is developed using passivity and Lyapunov-based methods.
Abstract: A partial differential equation (PDE) model for a flexible two-link manipulator is derived and transformed to a form appropriate for the development of stable control designs. Stable control of this nonlinear infinite dimensional two-link system is then achieved by a novel control design developed using passivity and Lyapunov-based methods. A two-link hardware experimental setup is used to validate the analytical PDE model and the proposed stable control design scheme.

Journal ArticleDOI
TL;DR: This brief reports the experience with the identification of a nonlinear autoregressive with exogenous inputs (NARX) model for the PGT10B1 power plant gas turbine manufactured by General Electric-Nuovo Pignone.
Abstract: This brief reports the experience with the identification of a nonlinear autoregressive with exogenous inputs (NARX) model for the PGT10B1 power plant gas turbine manufactured by General Electric-Nuovo Pignone. Two operating conditions of the turbine are considered: isolated mode and nonisolated mode. The NARX model parameters are estimated iteratively with a Gram-Schmidt procedure, exploiting both forward and stepwise regression. Many indexes have been evaluated and compared in order to perform subset selection in the functional basis set and determine the structure of the nonlinear model. Various input signals (from narrow to broadband) for identification and validation have been considered.

Journal ArticleDOI
Yaoyu Li1, Mario A. Rotea1, George T.-C. Chiu1, Luc Mongeau1, Insu Paek1 
TL;DR: The performance of a prototype standing wave thermoacoustic cooler is optimized using an extremum seeking control (ESC) algorithm using a tunable Helmholtz resonator to change the boundary condition of the standing wave tube.
Abstract: In this paper, the performance of a prototype standing wave thermoacoustic cooler is optimized using an extremum seeking control (ESC) algorithm. A tunable Helmholtz resonator was developed for a thermoacoustic cooler to change the boundary condition of the standing wave tube. The volume of the resonator is changed by changing the location of a piston on a ball-screw assembly driven by a dc motor. Multiparameter ESC was applied to optimize the cooling power via tuning both the boundary condition (piston location) and the driving frequency. Experiments were conducted for the online optimization under both fixed and varying operating conditions. The experimental results demonstrated the effectiveness of using ESC for maintaining maximum achievable performance. The effect of changing parameters in the ESC algorithm on the transient behavior was also investigated.

Journal ArticleDOI
TL;DR: A method of analyzing data from routine operation to locate the root cause oscillation in a dynamic system of interacting control loops and to distinguish it from propagated secondary oscillations is described.
Abstract: A plant-wide oscillation in a chemical process often has an impact on product quality and running costs and there is, thus, a motivation for automated diagnosis of the source of such a disturbance. This brief describes a method of analyzing data from routine operation to locate the root cause oscillation in a dynamic system of interacting control loops and to distinguish it from propagated secondary oscillations. The novel concept is the application of a nonlinearity index that is strongest at the source. The index is large for the nonsinusoidal oscillating time trends that are typical of the output of a control loop with a limit cycle caused by nonlinearity. It is sensitive to limit cycles caused both by equipment and by process nonlinearity. The performance of the index is studied in detail and default settings for the parameters in the algorithm are derived so that it can be applied in a large scale setting such as a refinery or petrochemical plant. Issues arising from artifacts in the nonlinearity test when applied to strongly cyclic data have been addressed to provide a robust, reliable and practical method. The technique is demonstrated with three industrial case studies.

Journal ArticleDOI
TL;DR: The developed CCS has been implemented in a power plant in China, and satisfactory industrial operation results demonstrate that the proposed control strategy has enhanced the adaptability and robustness of the process and better control performance and economic benefit have been achieved.
Abstract: This paper presents the new development of the boiler-turbine coordinated control strategy using fuzzy reasoning and autotuning techniques. The boiler-turbine system is a very complex process that is a multivariable, nonlinear, slowly time-varying plant with large settling time and a lot of uncertainties. As there exist strong couplings between the main steam pressure control loop and the power output control loop in the boiler-turbine unit with large time-delay and uncertainties, automatic coordinated control of the two loops is a very challenging problem. This paper presents a new coordinated control strategy (CCS) which is organized into two levels: a basic control level and a high supervision level. Proportional-integral derivative (PID) type controllers are used in the basic level to perform basic control functions while the decoupling between two control loops can be realized in the high level. A special subclass of fuzzy inference systems, called the Gaussian partition with evenly (GPE) spaced midpoints systems, is used to self-tune the main steam pressure PID controller's parameters online based on the error signal and its first difference, aimed at overcoming the uncertainties due to changing fuel calorific value, machine wear, contamination of the boiler heating surfaces and plant modeling errors. For the large variation of operating condition, a supervisory control level has been developed by autotuning technique. The developed CCS has been implemented in a power plant in China, and satisfactory industrial operation results demonstrate that the proposed control strategy has enhanced the adaptability and robustness of the process. Indeed, better control performance and economic benefit have been achieved.

Journal ArticleDOI
TL;DR: A flight control design is presented that combines model inversion control with an online adaptive neural network (NN) that cancels the error due to approximate inversion and produces a consistency in response.
Abstract: A flight control design is presented that combines model inversion control with an online adaptive neural network (NN). The NN cancels the error due to approximate inversion. Both linear and nonlinear NNs are described. Lyapunov stability analysis leads to the online NN update laws that guarantee boundedness. The controller takes advantage of any available knowledge for system inversion, and compensates for the effects of the remaining approximations. The result is a consistency in response which is particularly relevant in human operation of some unconventional modern aircraft. A tiltrotor aircraft is capable of converting from stable and responsive fixed wing flight to sluggish and unstable hover in helicopter configuration. The control design is demonstrated to provide a tilt-rotor pilot with consistent handling qualities during conversion from fixed wing flight to hover.

Journal ArticleDOI
TL;DR: A unified Smith predictor (USP) approach is used to formulate the control design problem in the standard mixed sensitivity framework and the solution is sought numerically using linear matrix inequalities (LMIs) with additional pole-placement constraints.
Abstract: This brief illustrates a control design procedure for handling time delays encountered in transmitting the remote signals in power systems. A unified Smith predictor (USP) approach is used to formulate the control design problem in the standard mixed sensitivity framework. The solution to the problem is sought numerically using linear matrix inequalities (LMIs) with additional pole-placement constraints. The predictor based method is applied for designing a damping controller for a prototype power system. Simulation results show that the controller performs satisfactorily even though the feedback signals arrive at the control site after a finite time delay.