Showing papers on "PID controller published in 1998"

Iterative feedback tuning: theory and applications

Abstract: We have examined an optimization approach to iterative control design. The important ingredient is that the gradient of the design criterion is computed from measured closed loop data. The approach is thus not model-based. The scheme converges to a stationary point of the design criterion under the assumption of boundedness of the signals in the loop. From a practical viewpoint, the scheme offers several advantages. It is straightforward to apply. It is possible to control the rate of change of the controller in each iteration. The objective can be manipulated between iterations in order to tighten or loosen performance requirements. Certain frequency regions can be emphasized if desired. This direct optimal tuning algorithm is particularly well suited for the tuning of the basic control loops in the process industry, which are typically PID loops. These primary loops are often very badly tuned, making the application of more advanced (for example, multivariable) techniques rather useless. A first requirement in the successful application of advanced control techniques is that the primary loops be tuned properly. This new technique appears to be a very practical way of doing this, with an almost automatic procedure.

Variable speed wind turbine generator

Abstract: A variable speed system for use in systems, such as, for example, wind turbines, is described. The system comprises a wound rotor induction generator, a torque controller and a proportional, integral derivative (PID) pitch controller. The torque controller controls generator torque using field oriented control, and the PID controller performs pitch regulation based on generator rotor speed.

PID controller tuning for desired closed‐loop responses for SI/SO systems

Abstract: Proportional integral, and derivative (PID) parameters are obtained for general process models by approximating the feedback form of an IMC controller with a Maclaurin series in the Laplace variable. These PID parameters yield closed-loop responses that are closer to the desired responses than those obtained by PID controllers tuned by other methods. The improvement in closed-loop control performance becomes more prominent as the dead time of the process model increases. A new design method for two degree of freedom controllers is also proposed. Such controllers are essential for unstable processes and provide significantly improved dynamic performance over single degree of freedom controllers for stable processes when the disturbances enter through the process.

Design of a hybrid fuzzy logic proportional plus conventional integral-derivative controller

Abstract: Presents approaches to the design of a hybrid fuzzy logic proportional plus conventional integral-derivative (fuzzy P+ID) controller in an incremental form. This controller is constructed by using an incremental fuzzy logic controller in place of the proportional term in a conventional PID controller, By using the bounded-input/bounded-output "small gain theorem", the sufficient condition for stability of this controller is derived. Based on the condition, we modify the Ziegler and Nichols' approach to design the fuzzy P+ID controller. In this case, the stability of a system remains unchanged after the PID controller is replaced by the fuzzy P+ID controller without modifying the original controller parameters. When a plant can be described by any modeling method, the fuzzy P+ID controller can be determined by an optimization technique. Finally, this controller is used to control a nonlinear system. Numerical simulation results demonstrate the effectiveness of the fuzzy P+ID controller in comparison with the conventional PID controller, especially when the controlled object operates under uncertainty or in the presence of a disturbance.

Fault diagnostics and fault tolerant control

Abstract: A novel simultaneous fault detection and diagnostics (FDD) and fault tolerant control (FTC) strategy for nonlinear stochastic systems in closed loops based on a continuous stirred tank reactor (CSTR) is presented. The purpose of control is to track the reactant concentration setpoint. Instead of output feedback we propose here to use proportional-integral-derivative (PID) state feedback, which is shown essential to achieve FTC against sensor faults. A new concept of "equivalent bias" is proposed to model the sensor faults. Both the states and the equivalent bias are on-line estimated by a pseudo separate-bias estimation algorithm. The estimated equivalent bias is then evaluated via a modified Bayes' classification based algorithm to detect and diagnose the sensor faults. Many kinds of sensor faults are tested by Monte Carlo simulations, which demonstrate that the proposed strategy has definite fault tolerant ability against sensor faults, moreover the sensor faults can be on-line detected, isolated, and estimated simultaneously.

Tracking control of an electrohydraulic manipulator in the presence of friction

Abstract: Analysis and estimation of friction and compensation for its effects in the control of an electrohydraulic manipulator is addressed. The specific hydraulic manipulator is an integral part of an automated fish processing machine which has been developed in our laboratory. The analysis reveals that considerable static and dynamic friction exists in the system. An available nonlinear observer for Coulomb friction, is modified to simultaneously estimate friction, velocity, and acceleration. A novel observer-based friction compensating control strategy is developed for improved tracking performance of the manipulator. The approach is based on acceleration feedback control. Experimental investigations show that this controller significantly outperforms the conventional PD controller. The general approach presented in this paper, may be applied to compensate for friction in any servomechanism, particularly when the actuator dynamics is not negligible.

Intelligent pressure regulator

Abstract: An intelligent pressure regulator for maintaining a fluid in a process at a predetermined pressure includes an electronic controller which enhances regulator performance and provides self-diagnostics and communications capabilities. The electronic controller includes a pressure sensor which provides a signal indicating the pressure of the fluid being controlled, an adjusting pressure for adjusting the position of a throttling element; and a PID controller which receives the signal indicating the pressure of the fluid being controlled and applies the adjusting pressure to the actuator in response to the signal.

PID controller tuning to obtain desired closed loop responses for cascade control systems

Abstract: A new method for PID controller tuning based on process models for cascaded control systems is proposed in this paper The method consists of first finding the ideal controller that gives the desired closed loop response and then finding the PID approximation of the ideal controller by Maclaurin series This method can be applied to any open loop stable processes Furthermore, it enables us to tune the PID controllers both for the inner loop and the outer loop simultaneously while existing tuning methods tune the inner loop first and the outer loop next Closed loop responses of cascade control loops tuned by the proposed method are compared with those of existing methods such as the frequency response method and the ITAE method The results show that the proposed tuning method is superior to the existing methods

Modeling and L/sub 2/-stability of a shape memory alloy position control system

Abstract: Shape memory alloys (SMAs) are inherently nonlinear devices exhibiting significant hysteresis in their stress-strain-temperature characteristic. As a consequence most SMA actuator systems presented in the literature employ some form of proportional-integral-derivative (PID) or pulse-width modulated (PWM) control. However, due to the hysteresis of the SMA, the theoretical stability of these systems has been largely ignored. This paper extends the work of Ikuta et al. (1991) to arrive at a new model of an SMA actuator. The key feature of the model is its ability to model minor hysteresis loops. The model is suitable for computer simulation, even of closed-loop control systems, as well as control system analysis. Indeed, the model is used to prove the L/sub 2/-stability of a position control system.

New antiwindup PI controller for variable-speed motor drives

Abstract: The windup phenomenon appears and results in performance degradation when the proportional-integral (PI) controller output is saturated. A new antiwindup PI controller is proposed to improve the control performance of variable-speed motor drives, and it is experimentally applied to the speed control of a vector-controlled induction motor driven by a pulsewidth modulated (PWM) voltage-source inverter (VSI). The integral state is separately controlled, corresponding to whether the PI controller output is saturated or not. The experimental results show that the speed response has much improved performance, such as small overshoot and fast settling time, over the conventional antiwindup technique. Although the operating speed command is changed, similar control performance can be obtained by using the PI gains selected in the linear region.

PID tuning for unstable processes based on gain and phase-margin specifications

Abstract: PID control is widely used to control stable processes, however, PID control for unstable processes is less common. In the paper, simple formulas are derived to tune the PID controller for unstable processes to meet gain and phase margin specifications. The stability of the closed-loop system is ensured by the Nyquist stability criterion. These formulas are derived for first- and second-order processes with time delay. Simulation results are given to show the accuracy of the formulas and the performance that can be achieved.

A new class of nonlinear PID controllers with robotic applications

Abstract: This paper introduces a new class of simple nonlinear PID controllers and provides a formal treatment of their stability analysis. These controllers are comprised of a sector-bounded nonlinear gain in cascade with a linear fixed-gain P, PD, PI, or PID controller. Three simple nonlinear gains are proposed: the sigmoidal function, the hyperbolic function, and the piecewise]linear function. The systems to be controlled are assumed to be modeled or approximated by second-order transfer functions, which can represent many robotic applications. The stability of the closed-loop systems incorporating nonlinear P, PD, PI, and PID controllers are investigated using the Popov stability criterion. It is shown that for P and PD controllers, the nonlinear gain is unbounded for closed-loop stability. For PI and PID controllers, simple expressions are derived that relate the controller gains and system parameters to the maximum allowable nonlinear gain for stability. A numerical example is given for illustration. The stability of partially-nonlinear PID controllers is also discussed. Finally, the nonlinear PI controller is implemented as a force controller on a robotic arm and experimental results are presented. These results demonstrate the superior performance of the nonlinear PI controller relative to a fixed-gain PI controller. Q 1998

Rule-based autotuning based on frequency domain identification

Abstract: A frequency domain procedure is proposed for the automatic tuning of proportional integral derivative (PID) controllers. The nonparametric open-loop frequency response function is estimated online (in closed loop), and simple discriminatory parameters are obtained, which enable appropriate tuning of the controller. For processes with some prior knowledge of the dynamics, the method removes the need for relay tuning or open-loop step response testing. If there is little or no prior knowledge of the process dynamics, relay or step response testing can be used initially, with the method then being used for the subsequent tuning. As part of the paper, a comprehensive comparison of existing rule-based tuning formulas is given using realistic plant examples.

Asynchronous distributed-object building automation system with support for synchronous object execution

Abstract: A computer-implemented building automation system is provided with an asynchronous object-oriented operating environment that is able to provide support for synchronous object execution with respect to real time, including those used to maintain closed-loop control over a system. The operating environment for supporting standard objects includes a clock mechanism for maintaining time and a scheduling mechanism for initiating the methods associated with the standard objects. A control method (i.e. PID control method) of a first standard object is scheduled for execution at a predefined schedule time with the schedule mechanism, and at some later time is initiated by the schedule mechanism. Upon execution, the control method determines an actual time of initiation by reading the clock mechanism and adjusts its control method using this actual time when the actual time exceeds the schedule time. More specifically, the actual time is determined by reading an elapsed time from the clock mechanism and computing a difference between this elapsed time and a start time that was determined by reading the clock mechanism at the time the control method was scheduled.

Vehicle Steering Intervention Through Differential Braking

Abstract: This paper examines the usefulness of a brake steer system (BSS) which uses differential brake forces for steering intervention in the context of Intelligent Transportation Systems. The resulting moment on the vehicle affects yaw rate and lateral position, thereby providing a limited steering function. The steering function achieved through BSS can then be used to control lateral position in an unintended road departure system. Control design models for the vehicle and the brake system are presented. A state feedback regulator and PID controller are developed to explore BSS feasibility and capability. Computer simulation results, using a nonlinear seven degree-of-freedom vehicle model are included, and show the feasibility and limitations of BSS.

Automatic Landing System Design Using Fuzzy Logic

Abstract: A fuzzy logic system is developed for automatic landing control of a transport aircraft. A linear longitudinal aircraft model, with landing gear and flaps deployed at the sea level, is employed for fuzzy logic controller design of automatic landing system including the two landing phases - the glide-path capture and the flare maneuver. In addition, the fuzzy control system is tested using different values of fuzzy controller scaling factors on a six degree of. freedom nonlinear aircraft model. It is shown that the simple tuning fuzzy controller with altered scaling factors is well suited for controlling the trajectory of the aircraft in the landing phase which requires simultaneous control of engine thrust for the velocity and elevator for the pitch attitude in order to change altitude with a constant airspeed.

Implementation of a neural network tracking controller for a single flexible link: comparison with PD and PID controllers

Abstract: The objective of this paper is to show the results of the practical implementation of a neural network (NN) tracking controller on a single flexible link and compare its performance to that of proportional derivative (PD) and proportional integral derivative (PID) standard controllers. The NN controller is composed of an outer PD tracking loop, a singular perturbation inner loop for stabilization of the fast flexible-mode dynamics, and an NN inner loop used to feedback linearize the slow pointing dynamics. No off-line training or learning is needed for the NN. It is shown that the tracking performance of the NN controller is far better than that of the PD or PID standard controllers. An extra friction term was added in the tests to demonstrate the ability of the NN to learn unmodeled nonlinear dynamics.

Control of an omnidirectional mobile robot

Abstract: Holonomic or nonholonomic omnidirectional mobile robots are known to be constructed by applying a specialized wheel or mobile mechanism In particular, some representative control approaches are described for a holonomic and omnidirectional mobile robot with three lateral orthogonal-wheel assemblies The uses of resolved acceleration control method, PID method, fuzzy model method, and stochastic fuzzy servo method are highlighted

Application of an Immune Feedback Mechanism to Control Systems

Abstract: As a control engineering application of a biological immune system, an immune feedback law featuring rapid response to foreign materials and quick stabilization of the immune system and a design method for an immune-mechanism-inspired feedback controller is described. Focusing on the T-cell regulated immune circuit, we propose an immune feedback law that includes both an active term to control the response speed and an inhibitive term to control the stabilization effect. We have also designed a PID-type immune-mechanism-inspired feedback controller based on both the immune feedback law and conventional PID control. Simulation results obtained for a discrete-time single-input single-output system show the feasibility of using the immune-mechanism-inspired feedback controller to control a nonlinear system and reveal the controller characteristics. Experimental results for velocity tracking control of a DC servo motor demonstrate the effectiveness of the immune-mechanism-inspired feedback controller for controlling a practical mechanical system even with existing nonlinear disturbances.

High-bandwidth high-accuracy rotary microactuators for magnetic hard disk drive tracking servos

Abstract: Reports on the design, fabrication, and testing of an electrostatic microactuator for a magnetic hard disk drive (HDD) tracking servo The design requirements for a microactuator are investigated These include high Z-directional stiffness, low in-plane stiffness, high structural aspect ratio, large output force, high area efficiency, low cost, and mass batch production An area-efficient rotary microactuator design was devised, and microactuators were successfully fabricated using innovative processing technologies The microactuator has a structural thickness of 40 /spl mu/m with a minimum gap/structure width of approximately 2 /spl mu/m Its frequency response was measured and it was determined that it can be modeled as a second-order linear system, up to the 26-kHz frequency range Moreover, the microactuator will enable the design of a servo system that exceeds a 5-kHz servo bandwidth, which is adequate to achieve a track density of more than 25 kilotrack per inch (kTPI) The microactuator/slider assembly was also tested on a spinning disk, with its position controlled by a PID controller using the magnetic position error signal written on the disk An accuracy of about 005 /spl mu/m was observed when the servo controller was turned on Continuous-time dual-stage servos were designed and simulated using the /spl mu/-synthesis technique A sequentially designed SISO and a MIMO control design method have been shown to be capable of meeting prescribed uncertainty and performance specifications

Variable structure control of robotic manipulator with PID sliding surfaces

Abstract: SUMMARY Dynamic behaviour of a system in sliding mode is entirely defined by the sliding surface. Customarily, the surface is selected as a hyperplane in the system’s state-space resulting in a PD-type sliding surface. This is not the only possible structure, and other designs with more complex or time-varying surfaces may provide definite advantages. Slotine and Spong1 included an integral term in the sliding surface expression that resulted in a type of PID sliding surface. However, the advantages of such a design were not elaborated in following publications of these or other researchers. In this paper we present a new design procedure and stability analysis for robotic variable structure controllers with PID-like sliding surfaces. Two versions of the controller are presented: regular and adaptive. The former is very simple and can operate with an unknown dynamic model; the only information required is a bound on one parameter. The latter provides an on-line estimation for this bound. Both controllers are robust with respect to bounded external disturbances and some unmodelled dynamic e⁄ects. The simulation results have demonstrated stability, with minimum transient responses that may be significantly faster than responses of traditional PD-manifold controllers under the same conditions. ( 1998 John Wiley & Sons, Ltd.

Sequential design method for multivariable decoupling and multiloop PID controllers

Abstract: Underlying algorithms for designing multivariable decoupling and multiloop PI/PID controllers in a sequential fashion are addressed. A single-loop technique, composed of biased relay identification schemes and tuning formulae leading to the minimum weighted integral of square error, is developed to tune each loop in the predetermined sequence of loop closing. The proposed tuning technique is appropriate for a wide range of process dynamics in a multivariable environment. A method is then proposed to design decouplers to compensate for the effect of interactions and tune the resultant weakly interacting, single-loop PI/PID controllers sequentially. The decouplers, together with the single-loop controllers, constitute the multivariable decoupling controller. If the interactions are not significant, multiloop PI/PID controllers, which do not incorporate decouplers, could be employed. Simulation and comparative results are shown for one 2 × 2 and one 3 × 3 multivariable system from the literature. Despite its...

Method of predicting overshoot in a control system response

Abstract: A process control system including a method of suppressing overshoot of a process variable beyond the process value setpoint by predicting the overshoot by observing a waveform associated with the process variable, observing the waveform associated with the process variable, without regard to time scaled or to amplitude scale, taking corrective action to reduce or eliminate said overshoot by utilizing a fuzzy logic module with a proportional integral derivative control to take corrective action of the process variable.

Experimental dynamometer emulation of non-linear mechanical loads

Abstract: Industrial processes often contain nonlinear mechanical loads driven by electrical drives. PI and PID controllers, widely used in industrial drives, may not give satisfactory results for some nonlinear loads since they are linear controllers. Adaptive, robust and intelligent nonlinear control methods are attracting considerable attention to design a good controller for these nonlinear mechanical loads. As far as research is concerned, it is not practical to have different kinds of linear or nonlinear mechanical loads in the laboratory. The solution is to have a programmable load emulator (dynamometer) to provide realistic nonlinear loads for the experimental validation of advanced control techniques in the laboratory. This paper describes a dynamometer control strategy in which the emulation preserves the dynamic structure of a desired load model so that the emulation can be used in closed loop control. Experimental results of the closed loop control of some nonlinear loads are presented. Computer simulation results are also provided for comparison purposes to show the performance of the proposed load emulation method.