Showing papers on "Proportional control published in 1997"

Design and experience with a fuzzy logic controller for automatic generation control (AGC)

Abstract: This paper describes the design, implementation and operational performance of a fuzzy controller as part of the automatic generation control (AGC) system in Eskom's National Control Centre. The fuzzy controller was implemented in the control ACE (area control error) calculation, which determines the shortfall or surplus generation that has to be corrected. This paper sets out the problems associated with secondary frequency control and AGC. The difficulties associated with optimising the original standard AGC controller, the design, implementation and optimisation of the fuzzy controller and the operational performance of the new controller over two years, are discussed. The fuzzy controller was integrated into the existing off-the-shelf-AGC system with only a few modifications. The operational performance over two years showed an overall improvement of over 50% in the reduction of control compared to the original AGC controller, and an initial improvement of 20% in the quality of control of the optimised original controller.

Control-system synthesis for open-loop unstable process with time delay

Abstract: To avoid performance limitations caused by an open-loop unstable pole, a three-element structure, which is equivalent to a two-degrees-of-freedom control design, is proposed to synthesise a control system for an open-loop unstable process with time delay. Through this proposed approach, control problems such as stabilising an unstable pole, servo-tracking and disturbance rejection can be treated independently. The resulting three-element structure can then be used to derive conventional two-degrees-of-freedom elements or conventional PID systems. Tuning rules for a PID controller are also provided. Examples are presented to illustrate the proposed method.

A control theoretic approach to the design of closed loop rate based flow control for high speed ATM networks

Abstract: We present a control theoretic approach to the design of closed loop rate based flow control in high speed networks. The proposed control uses a dual proportional derivative controller, where the control parameters can be designed to ensure the stability of the control loop in a control theoretic sense, over a wide range of traffic patterns and propagation delays. We show how the control mechanism can be used to design a controller to support available bit rate (ABR) service based on feedback of explicit rates. We demonstrate the excellent transient and steady state performance of the controller through a number of examples.

On-Line Process Identification Using the Laguerre Series for Automatic Tuning of the Proportional-Integral-Derivative Controller

Abstract: A new on-line identification method based on the approximation of closed-loop response is proposed to tackle the shortcomings of previous autotuning methods using a proportional controller as a tes...

Throttle valve controller

Abstract: A throttle valve controller achieves high output response to the smaller deviation of the actual opening from the demand opening of the throttle valve and achieves high control stability against the larger deviation. It has a preset data table containing proportional gain values and integral gain values of PID control in correspondence to deviation values in inversely proportional arrangement. During the transitional state of control system, a pair of provisional gain values are read out of the table in response to the deviation value: (step S3), these gain values are compared with those of the previous operation cycle and the smaller gain value pair are selected: (steps S4-S7), and the valve drive signal is calculated from the selected gain values:(steps S8, S11). Consequently, the controller achieves high output response to the smaller deviation due to the larger gain value and high control stability without the overshooting of valve movement against the larger deviation due to the smaller gain value.

Incremental fuzzy PI control of a solar power plant

Abstract: Between 1987 and 1997, considerable research effort has been devoted to improving the efficiency of solar thermal power plants with distributed collectors, not only in the field of optical technology but also from the control and optimisation viewpoint. The article deals with this second aspect, and presents results obtained in the control of the distributed solar collector field of the solar power plant of Almeria (Spain) using a fuzzy logic control approach. A distributed collector field consists of a series of parabolic mirrors which reflect solar radiation onto a pipe where oil gets heated while circulating. The object of the control system is to maintain the outlet oil temperature of the field (collector field) at a desired level in spite of disturbances such as changes in the solar radiation level, mirror reflectivity or inlet oil temperature. Since solar radiation cannot be adjusted this can only be achieved by adjusting the flow of oil. An incremental fuzzy PI controller (IFPIC) has been developed to cope with this control problem in which all parameters of a PI controller are updated online as a function of the operating conditions of the controlled plant, thus improving the behaviour of the classical fixed PI controllers which are usually employed. The strategy has been implemented in series with a simple feedforward controller which compensates for the disturbances acting on the system. Simulation results using a nonlinear computer model of the field and real tests are provided.

Control of chaos in excitable physiological systems: A geometric analysis

Abstract: Model-independent chaos control techniques are inherently well-suited for the control of physiological systems for which quantitative system models are unavailable. The proportional perturbation feedback (PPF) control paradigm, which uses electrical stimulation to perturb directly the controlled system variable (e.g., the interbeat or interspike interval), was developed for excitable physiological systems that do not have an easily accessible system parameter. We develop the stable manifold placement (SMP) technique, a PPF-type technique which is simpler and more robust than the original PPF control algorithm. We use the SMP technique to control a simple geometric model of a chaotic system in the neighborhood of an unstable periodic orbit (UPO). We show that while the SMP technique can control a chaotic system that has UPO dynamics which are characterized by one stable manifold and one unstable manifold, the success of the SMP technique is sensitive to UPO parameter estimation errors. (c) 1997 American Institute of Physics.

Self-tuning control of an industrial pilot-scale reheating furnace: Design principles and application of a bilinear approach

Abstract: The design of a bilinear self-tuning control strategy and its application to a pilot-scale reheating furnace are described. A comparison with standard PID control shows that the new approach offers significant potential benefits.

Discrete time stability analysis of an explicit rate algorithm for the ABR service

Abstract: The study pursues a discrete stability analysis of a control algorithm for the available bit rate (ABR) service, denoted proportional rate and queue control algorithm (PRQCA), applied on an ATM system using FCFS scheduled switch buffers for the ABR traffic. The analysis establishes a stability condition for the control parameters of the PRQCA by using a control theoretic approach to the feedback control. The discrete model enables an implicit relation between the control parameters and the sample rate of the system, which is not possible in a continuous time model. Furthermore, for cases with different feedback delays, a mean value approximation, denoted effective delay, is introduced to replace the individual feedback delays in the analysis. A relation is derived to set the additive increase rate parameter (AIR) to avoid initial oscillations during low rates of backward resource management (RM) cells without affecting the dynamics during sufficient RM cell rates. An enhancement of the algorithm used to estimate the fair share rate (CCR averaging), is introduced to enable a mix of connections with and without rate constraints in the system while the reference values for both the rate and the queue length are still met.

Device for diagnosing oxygen sensor deterioration

Abstract: The air/fuel ratio of an engine is feedback controlled based upon the output of an oxygen sensor. The control includes proportional control and also correction of a control variable for this proportional control according to the actual air/fuel ratio. The period of the output signal of the oxygen sensor during feedback control is measured, a decision value is set corresponding to change in the control variable, and deterioration of the oxygen sensor is determined by comparing the period of the output signal with the decision value. By doing this, change in the control variable is prevented from exerting any influence upon the period of the output signal of the oxygen sensor, and the accuracy of deterioration diagnosis for the oxygen sensor is enhanced.

Stability analysis and design guidelines for a speed-sensorless induction motor drive

Abstract: In this paper, the authors propose a novel stability analysis for induction motor drive speed sensorless vector control systems based on the parametric approach which results in the analytical necessary conditions for stability. It is pointed out that the system can be unstable in the low-speed region with regenerative load. Assigning an appropriate feedback gain of the flux observer, however, can render stability and reduce the unstable region. As a guideline for designing the adaptive PI gain, it is shown that the integral gain determines the tracking speed of the estimates during acceleration/deceleration while the sensitivity to current measurement noises depends on the proportional gain. In addition, to avoid an oscillation in the speed estimator, a suitable corner frequency of the adaptive PI gain is required as a design trade-off.

Theoretic and genetic design of a three-rule fuzzy PI controller

Abstract: This paper describes the optimal design of a fuzzy PI controller based on theoretical fuzzy analysis and genetic-based optimizations. The most important feature of the proposed controller is its simple structure, consisting of a single input variable, three rules, and four design parameters. The four parameters are a fuzzy integral gain, a scalar factor for crisp output, and two parameters for the allocation of the membership functions of the fuzzy sets. A closed-form solution for the proportional control action is defined in terms of the design parameters. The nonlinear proportional gain is explicitly presented in the error domain. Through genetic algorithms, the optimal design of the system is achieved. This new method has been applied for two problems, a first-order process with/without a time delay, and an overdamped second-order process. A practical limitation on actuator saturation is considered in the simulation. Good simulation results were obtained using the present method, which produced superior control performance in handling nonlinearities due to time delay and saturation.

Hydraulic actuator operation controller

Abstract: A hydraulic actuator operation controller is shown to make it possible to easily change the operation speeds of a hydraulic actuator for a control input of an operating instrument. A signal input from a control input detection device for detecting the control input of an operating lever is converted according to a logical function by a signal conversion unit. The signal conversion unit increases or decreases the signal in magnitude and outputs the converted signal to a pump control device. The pump control device outputs an instruction to a capacity change device such as an electromagnetic proportional control valve connected to a hydraulic pump. The converted signal is also provided to a valve control device for outputting an instruction to a valve opening-degree control device such as electromagnetic proportional control valves connected to a control valve.

Tactile force control feedback in a parallel jaw gripper

Abstract: Carrying out an autonomous object prehension task needs some active interaction with the environment, which can only be done with sensory integration of the robot tools. A study of contact force control performed with tactile feedback in a low cost servo-controlled parallel jaw gripper is presented in this article. This gripper integrates matricial tactile sensors and proximity sensors. Considering the nonlinear nature of the control system, hybrid control strategies were used, inter-relating classical digital control strategies with heuristic rules and logic. Two control algorithms were studied and experimentally validated in a force-compliant mechanical system: a hybrid proportional controller; and a hybrid proportional integral and derivative controller.

PI control of periodic oscillations of relay systems

Abstract: In automatic control applications, the relay nonlinearity is used to describe a sensor or actuator behavior. Such nonlinearity combined with stabilizing feedback loops often leads to limit cycles for the closed loop system. We study the control of such limit cycles by use of a proportional+integral control law with the delayed output of a relay sensor.

Distributed parameter control of a large space structure with lumped and distributed flexibility

Abstract: In this paper, a simple distributed parameter controller for a large space structure with lumped and distributed flexibility is discussed. We consider two flexible beams connected by a spring as a simple example of the large space structures. The flexible beams and the spring can be regarded as an element of the structure with the distributed flexibility and a connective part with lumped flexibility, respectively. We derive dynamic equations by means of Hamilton's principle. We introduce Lyapunov function related to the total energy of the distributed parameter system and derive a simple sensor output feedback control law. Using LaSalle's theorem and the characteristic of the differential operator, we can prove the asymptotic stability of the closed-loop system and the convergence property to the desired stationary state. The proposed controller is the proportional, derivative and strain feedback control law named PDS controller. As the PDS controller is a static feedback controller using the joint angle, the angular velocity and the strain data, it is easy to implement. As we don't need an approximated finite-dimensional model at the controller design phase, the controller based on the original distributed parameter system is robust and simple. In order to demonstrate the validity of the derived model and the proposed controller, experiments have been carried out.

Cascade PI-controllers with fuzzy tuning

Abstract: This paper presents some simple fuzzy logic schemes for online tuning proportional-integral controller parameters to improve system robustness. It is shown that, with fuzzy tuning, the reference response is well-damped and the maximum deviation of the disturbance response is reduced even in the case of changing plant parameters. The fuzzy-tuned controllers can then be applied to multiloop control systems using the conventional cascade control principles. Simulation results for a two-mass servo system indicate that good performance can be achieved in the presence of parameter and load variations, and backlash nonlinearity. Explicit expressions for the controller parameters facilitate the training process at a low computational cost. The proposed method can be applied for a variety of controlled objects suffering from uncertainties.

Wheel torque proportioning, rear steering, and normal force control: a structural investigation

Abstract: This paper is concerned with various analysis and design issues for a possible set of control channels which may be used to improve the maneuverability and handling of automobiles. Of the possible set of controls, the current paper is limited to variable wheel torque proportioning, rear steering, and normal force control. The analysis and design issues are studied using an extensive linear model representing the lateral, longitudinal, and vertical dynamics, including their interactions. For the investigation of the finite-time behavior of system dynamics, we first introduce the notion of a reachable set where the attainability of a particular state vector at a particular time instant is considered. Next, we examine the attainability of a particular output trajectory within a finite-time interval using the notion of output function controllability. Several structural properties of these concepts have been studied. Various degenerate operating points are identified, where the effectiveness of the control channels deteriorates. In the steady-state analysis, the reference tracking and regulation problems are considered. It is shown that for some input/output subsystems those problems are generically solvable due to the minimum phase structure of the subsystems. For some others, those problems are solvable provided that the equilibrium point is not a degenerate equilibrium point. Finally, we show that for some input/output subsystems those problems are generically unsolvable.

Application of H/sub /spl infin// control with eigenvalue perturbations to stabilize a transonic compressor

Abstract: Robust linear control is used to stabilize the flow field perturbations which lead to rotating stall and surge in a transonic single-stage axial compressor. As in previous low-speed compressor control experiments with uniform inlet flow, a separate control is implemented for each of the decoupled spatial harmonics of the pre-stall perturbations. However, due to compressibility effects in a high-speed compressor, there are multiple lightly damped modes for each of the pre-stall harmonics which are not present in the low-speed case. Therefore, constant gain proportional control, which is effective in low-speed applications, cannot extend the operating range of this highspeed compressor at design speed. Instead, H/sub /spl infin// control laws are implemented to stabilize the flow field perturbations. Standard transfer function weightings are incorporated into the design to address actuator saturation and bandwidth limitations. Additionally, an eigenvalue perturbation technique, developed by Smith (1995) and Smith et al. (1994) is included to allow for a range of dominant eigenvalue locations and thus addresses model uncertainty and changing eigenvalue locations with varying compressor mass flow. Results are presented which demonstrate control effectiveness along the design-speed compressor characteristic as well as the ability to reject large amplitude transient disturbances.

Optimal control of a magnetic bearing without bias flux

Abstract: Conventional active magnetic bearings are operated using a bias current (or flux) to achieve greater linearity and dynamic capability. Bias results in undesirable rotating losses and consequent rotor heating. In this paper, optimal control of a magnetic bearing without bias is investigated. A single degree-of-freedom system consisting of a mass and two opposing electromagnets is considered. The optimal control problem is examined for a cost function that penalizes both poor regulation and rotational energy lost. Although a standard optimization procedure does not directly yield an analytical solution, it does show that the optimal control is always bang-bang with possibly a singular arc. First, the minimum time problem is solved for a simple switching law in three dimensional state space. A non-standard, physics-based approach is then employed to obtain an optimal solution for the general problem. The final result is an optimal variable structure feedback controller.

Comment on “The equivalence of second-order impedence control and proportional gain explicit force control.”

Abstract: In a series of papers, Volpe and Khosla (1993a, 1993b, 1995) demonstrate that one form of an impedance controller is equivalent to proportional gain explicit force control in certain interaction situations. They then use this equivalence to compare the performance of impedance control with other forms of explicit force control. In the following, we show that the equivalence applies only to a limited set of situations and to a particular impedance controller. We also comment on the comparison between impedance control and force feedback control, since we feel that the two strategies are fundamentally different,

Modeling, actuation, and control of an active fluid vibration isolator

Abstract: An integrated mathematical model for the dynamics, actuation, and control of an active fluid/elastomeric tuned vibration isolator in a two mass system is presented. The derivation is based on the application of physical principles for mechanics, fluid continuity, and electromagnetic circuits. Improvement of the passive isolator performance is obtained with a feedback scheme consisting of frequency shaped notch compensator in series with integral control ofoutput acceleration and combined with proportional control of the fluid pressure in the isolator. The control is applied via an electromagnetic actuator for excitation of the fluid in the track connecting the two pressure chambers of the isolator. Closed loop system equations are transformed to a nondimensional state space representation and a key dimensionless parameter for isolator-actuator interaction is defined. A numerical example is presented to show the effect of actuator parameter selection on system damping, the performance improvement of the active over the passive isolator, the robustness of the control scheme to parameter variation, and the electrical power requirements for the actuator.

Controllable combined power system using an active power source rotation speed as the proportional control reference

Abstract: A controllable combined power system including an active power source and an auxiliary power source uses the active power source as a basis for controlling the speed or torque of the auxiliary power source, either in the same direction as the active power source or in a reverse direction to provide damping.

Improving diffusion furnace capability using model-based temperature control in a production environment

Abstract: This paper describes the design, development, and implementation of model-based temperature control (MBTC) to improve diffusion furnace capability in a production environment. An integrated manufacturable approach for modeling and robust H/sub /spl infin// multivariable controller design is developed to replace standard proportional integral derivative (PID) furnace control. The design was originally evaluated on an oxidation furnace and is presently being propagated throughout the entire diffusion area. Production results demonstrate excellent temperature control, tighter process results, and increased utilization. Manually induced disturbances during ironman testing, as well as normal production disturbances, have shown the system requires no adjustment or reconfiguration for improved control of oxidation growth and LPCVD film deposition.

Analysis and electronic implementation of a fuzzy system for the control of a liquid tank

Abstract: This paper presents a comparative study between a fuzzy system and a PI conventional controller for the real control of a liquid tank. The final fuzzy system is electronically implemented in a low-cost multifunction microcontroller, the PIC16C71. For nonlinear problems, fuzzy systems are useful tools: as shown in this paper, the performance of the fuzzy controller is superior to that of conventional methods. There are various means of implementing the transfer characteristic of a controller. As is discussed in this paper, the division of the output surface into different planes is the optimum solution, as this requires the least amount of memory (420 lines in PIC assembler language). The final structure of the autonomous system is very compact.

To design optimized fuzzy and digital PID controllers for a single phase power factor preregulator-genetic algorithm approach

Abstract: The optimized fuzzy logic and digital PID controllers for a single-phase power factor correction (PFC) converter used in an online uninterruptible power supply (UPS) are proposed in this paper. Parameters such as input membership functions, output membership functions, inference rules of fuzzy logic controller and proportional gain, integral gain and derivative gain of digital PID controller are selected and optimized by genetic algorithms; hence the tedious and time consuming parameters tuning process normally associated with fuzzy logic and digital PID controllers design is eliminated. The selection and optimization criteria are based on time domain specifications such as response time, percent of overshoot etc. for a step reference. The simulation shows excellent results in terms of response time and output overshoot for a step reference. This design approach provides an attractive alternative method to select and optimize the parameters of fuzzy logic and digital PID controllers when they are used to control a single-phase PFC converter. It can also be easily extended to applications for switching regulator control loop design.

An intelligent PID controller with a neural supervisor

Abstract: It is difficult to control nonlinear systems using a PID controller with fixed gains. Many types of PID controllers with variable gains have been proposed based on advanced control techniques. In this paper, an advanced PID controller for nonlinear systems is proposed. Since the nonlinear input/output characteristics can be explained using a set of linear input/output characteristics, we consider that a set of linear system self-tuning PID controllers are used through switching based on signals from the control system. The switching is carried by a neural network based supervisor. This supervisor selects the linearized model which is most accurate for the next step. The effectiveness of this method is investigated through two numerical simulations.