Showing papers on "Open-loop controller published in 1998"

Comparison of current control techniques for active filter applications

Abstract: This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations.

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.

Two-loop controller for maximizing performance of a grid-connected photovoltaic-fuel cell hybrid power plant

Abstract: Maximizing performance of a grid-connected photovoltaic (PV)-fuel cell hybrid system by use of a two-loop controller is discussed. One loop is a neural network controller for maximum power point tracking, which extracts maximum available solar power from PV arrays under varying conditions of insolation, temperature, and system load. A real/reactive power controller (RRPC) is the other loop. The RRPC achieves the system's requirements for real and reactive powers by controlling incoming fuel to fuel cell stacks as well as switching control signals to a power conditioning subsystem. Results of time-domain simulations prove not only the effectiveness of the proposed computer models of the two-loop controller but also its applicability for use in stability analysis of the hybrid power plant.

Non-fragile controller design: an overview

Abstract: In this paper we give an overview of nonfragile controller design for linear systems. The controller fragility problem is basically the problem of performance deterioration of a feedback control system due to inaccuracies in controller implementation. The literature on the fragility problem is reviewed and methods for designing nonfragile controllers are summarized.

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.

Plant control system

Abstract: A plant control system using response specifying control that makes it possible to independently set a follow-up behavior for an output value of a plant when a target output value of the plant changes and a convergent behavior for a difference between a target output value and an output value when the output value of the plant changes. The control system has a controller for determining a clutch stroke on the basis of a model equation of a clutch device such that a target rotational speed and an actual rotational speed of the clutch device coincide with each other. The controller includes a target value filter for carrying out filtering computation on a target rotational speed to calculate a filtering target value that converges to the target rotational speed with a response delay, and a response specifying control unit that determines the clutch stroke by response specifying control such that the filtering target value and the clutch rotational speed coincide with each other.

Control design and simulation of unified power flow controller

Abstract: The unified power flow controller (UPFC) is a solid-state controller which can be used to control active and reactive power flows in a power transmission line. In this paper, the authors propose a control strategy for UPFC in which they control real power flow through the line, while regulating magnitudes of the voltages at its two ports. They design a controller for this purpose which uses only local measurements. The control strategy is evaluated using digital simulation for a case study.

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

Parameter identification of induction motor model using genetic algorithms

Abstract: The paper deals with methods of identification of the parameters of an induction motor model using genetic algorithms. It is supposed that the inverter supplying the motor is directly accessible for control of the conduction sequences of its power switches. This makes it possible to carry out a test consisting of a transient from standstill to steady-state operation at a given frequency and successive free motion to standstill. During this test, data are acquired referring to stator voltages, and currents and speed. Then, a genetic algorithm is employed with the aim of determining the mechanical and electrical parameters of the model, so as to reproduce the input-output behaviour of a real open-loop system.

Thermal management in a system

Abstract: A system including a component (e.g., a processor) with a clock and a thermal management controller that monitors a temperature in the system. The thermal management controller varies the component between different performance states (e.g., cycles the processor between a high and a low performance state) when an over-temperature condition is detected. The thermal management controller further throttles the clock of the component while in the low performance state until the over-temperature condition is removed.

Self-commissioning controller for a field-oriented elevator motor/drive system

Abstract: A self-commissioning controller 7 for a field-oriented elevator motor controller 14 includes calculating an integral gain K I , a proportional gain Kp, and an overall gain (Gc) for the motor controller; obtaining initial values of a rotor time constant τ R , magnetizing current Id, and motor torque constant K T for the motor controller 14, and obtaining a value of a motor transient inductance Lσ; calculating final values for said rotor time constant τ R and magnetizing current Id, using said transient inductance Lσ; and calculating a system inertia J* parameter for speed loop compensation 16 within the motor controller 14. The controller 7 may also include calculating the initial values for τ R , Id, and K T *, and performing self-commissioning automatically upon receiving a command from a service tool 80.

A PM synchronous servo motor drive with an on-line trained fuzzy neural network controller

Abstract: A permanent magnet (PM) synchronous servo motor drive with integral-proportional (IP) position controller and a proposed on-line trained fuzzy neural network (FNN) controller is introduced in this paper. First, an IP position controller is designed according to the estimated plant model to match the time-domain command tracking specifications. Then the resulting closed-loop tracking transfer function is used as the reference model, and an adaptive signal generated from the proposed FNN controller, whose membership functions and connective weights are trained on-line according to the model-following error of the states, is added to the control system to preserve a favorable model-following characteristics under various operating conditions.

A new control method for 400 Hz ground power units for airplanes

Abstract: This paper presents a new control strategy for a ground power unit, which is used for airplanes on the ground. In such a system, the ratio between the switching frequency and the fundamental frequency is low and in order to obtain high output performance, the controller has to be digital. The control is performed by a pulsewidth modulator and a voltage controller in the synchronously rotating reference frame (d-q). Design roles are given and a simulation tool is used for investigation of the controller. A 90 kVA prototype is used for validation of the principle. It is concluded by the experiments that the new controller gives a high output performance both stationary and dynamically at linear and nonlinear loads. Synchronization with the airplane is also shown to work successfully.

Controller for pulse width modulation circuit using AC sine wave from DC input signal

Abstract: A pulse width modulation (PWM) controller suitable for use with a variety of open loop topology power supply circuits including ring generator circuits. The controller and the circuit realized therefrom utilizes an open loop topology to achieve the desired output voltage waveform. The PWM controller is suitable for realizing a plurality of different open loop converter topologies such as such as buck, boost, forward and push-pull topologies. The PWM controller is adapted to provide the required signals to control the various possible open loop converter topologies. The controller functions to generate a PWM signal that is used to generate a half wave sine wave signal. The controller includes the necessary functionality to control the duty cycle of the generated PWM signal so as to produce a full wave sine wave at the output of the output bridge circuit.

An adaptive run-to-run optimizing controller for linear and nonlinear semiconductor processes

Abstract: This paper presents a new run-to-run (R2R) multiple-input-multiple-output controller for semiconductor manufacturing processes. The controller, termed optimizing adaptive quality controller (OAQC), can act both as an optimizer-in case equipment models are not available-or as a controller for given models. The main components of the OAQC are shown and a study of its performance is presented. The controller allows one to specify input and output constraints and weights, and input resolutions. A multivariate control chart can be applied either as a deadband on the controller or simply to provide out of control alarms. Experimental designs can be utilized for on-line (recursive) model identification in the optimization phase. For testing purposes, two chemical mechanical planarization processes were simulated based on real equipment models. It is shown that the OAQC allows one to keep adequate control even if the input-output transfer function is severely nonlinear. Software implementation including the integration of the OAQC with the University of Michigan's Generic Cell Controller (GCC) is briefly discussed.

Sequential design of hysteresis current controller for three-phase inverter

Abstract: In this paper, a novel multivariable hysteresis current controller for three-phase inverters is presented. Hysteresis controllers are intrinsically robust to system parameters, exhibit very high dynamics, and are suitable for simple implementation. The main drawback of the hysteresis controller is a limited control on transistors' switching frequency. Very high switching frequency may result if three independent controllers are used. Multivariable solutions were proposed in the literature to solve the problem. In this paper, it is shown how the use of a sequential design for the multivariable controller can further contribute to transistors' switching frequency reduction, with no significant increase in the hardware implementation complexity. The proposed controller is illustrated and compared with other hysteresis controllers presented in the literature. It ensures a significant reduction of transistors' switching frequency with respect to the other tested controllers, under the same operating conditions. A prototype controller is also presented. The effects of noise captured by current sensors (especially Hall-effect type) on the performance of industrial hysteresis controllers are discussed. It is shown how the sequential design of the controller can also help in solving this critical problem. Experimental results are reported to confirm the quality of the proposed controller. The system stability condition is derived in an appendix.

Fuzzy logic based unified power flow controllers for transient stability improvement

Abstract: A fuzzy logic approach is applied to coordinate three control inputs: in-phase voltage control; quadrature voltage control; and shunt compensation, of a unified power flow controller to improve the transient stability of a power system. The fuzzy rules for the controller are created based on a bang-bang control strategy whose objectives are minimising the first swing, damping the oscillations at an optimum rate and maximising the transient stability margin. The proposed controller also incorporates a technique of reducing the chattering of generator output which naturally results from the application of bang-bang control. Simulation results show that the fuzzy logic based controller provides satisfactory performance, meeting the design objectives. The results also show the robustness of the controller.

Design of a genetic fuzzy controller for the nuclear steam generator water level control

Abstract: The nuclear steam generator is a nonminimum-phase system, which is caused by the swell and shrink effects. Since its inverse system has unstable dynamics, it is difficult to train the fuzzy controller via the conventional backpropagation of the system output errors. In this paper, a genetic algorithm is applied for the simultaneous design of membership functions and rule sets for a fuzzy control method for a steam generator water level. The genetic fuzzy controller for the steam generator is a fuzzy logic controller which is tuned offline by the genetic algorithm using the water level, feedwater flowrate, and steam flowrate signals of the steam generator. The symmetric Gaussian membership functions based on the flowrate and water level errors are applied. The proposed genetic fuzzy controller has a generalized and simplified rule base. The same genetic algorithm that is used to optimize the genetic fuzzy controller tunes a conventional proportional-integral (P-I) controller, and the performance of two controllers is compared. The genetic fuzzy controller shows good response that its swell and shrink phenomena are smaller and its response is faster than those of a well-tuned P-I controller are.

A new Smith predictor and controller for unstable and integrating processes with time delay

Abstract: A new Smith predictor for control of an unstable process with time delay and a process with an integrator and long dead-time is proposed. The controller decouples the setpoint response from the load response. The design approach is based on standard forms of the closed loop system response and on the Nyquist stability analysis. Simulation results show high performance for the setpoint response and load disturbance rejection.

Controller Design of Two-Mass Resonant System by Coefficient Diagram Method

Abstract: In the controller design of position or velocity control, the flexibility of the mechanical system is always the limiting factor to the higher performance. In this paper, the speed control of a two-mass resonant system, where the speed sensor is located only on the drive motor side, is investigated. Such a system is typically found in steel mill drives. The controller design is made successfully in practical sense using various design techniques, such as classical control, resonance ratio control with disturbance observer, and H∞ control. However, a unified theoretical approach is needed to understand the real nature of the problem. For this purpose, a new controller design approach, called “Coefficient Diagram Method”, is introduced. The result shows that the optimum controller, in normalized form, is the sole function of the ratio of motor inertia to the total inertia. As the ratio increases, the controller type needed varies from PI control to PI control with lag, and finally to PID control with lag where D control is week positive feedback. The typical controller designed in the past have been compared with this design.

PWN controller use with open loop flyback type DC to AC converter

Abstract: A controller and ring generator circuit realized therefrom utilizing an open loop flyback topology to achieve a desired output voltage waveform. A characteristic feature of the controller is that it provides the required signals to control a ring generator circuit having an open loop fly back topology. The controller functions to generate a PWM signal that is used to switch the primary of a transformer on and off. The controller includes the necessary functionality to control the duty cycle of the generated PWM signal so as to produce a sine wave output on the secondary of the transformer. The controller also includes overcurrent protection circuitry that tracks the load current by sensing the current through the primary winding. In addition, the circuit permits negative current in the secondary by use of a synchronous rectifier circuit coupled to an additional secondary transformer winding. An output bridge circuit creates a full sine wave from the generated half wave output.

Adaptive fuzzy control of satellite attitude by reinforcement learning

Abstract: The attitude control of a satellite is often characterized by a limit cycle, caused by measurement inaccuracies and noise in the sensor output. In order to reduce the limit cycle, a nonlinear fuzzy controller was applied. The controller was tuned by means of reinforcement learning without using any model of the sensors or the satellite. The reinforcement signal is computed as a fuzzy performance measure using a noncompensatory aggregation of two control subgoals. Convergence of the reinforcement learning scheme is improved by computing the temporal difference error over several time steps and adapting the critic and the controller at a lower sampling rate. The results show that an adaptive fuzzy controller can better cope with the sensor noise and nonlinearities than a standard linear controller.

Multi-rate controller for hard disk drive with redesign of state estimator

Abstract: This paper describes a new multi-rate controller for hard disk drives, which has a modified state estimator to correct estimated states not only at measurement instances of the position error signal but also at every control instance of updating the control input. This modification makes the control input smoother compared to the conventional multi-rate scheme. The effectiveness of the modified scheme is demonstrated by experiments.

Neural network system for online controller adaptation and its application to underwater robot

Abstract: Describes a neural network system which executes identification of robot dynamics and controller adaptation in parallel with robot control. The system consists of two parts: real-world part and imaginary-world part. The real-world part is a feedback control system for the actual robot. In the imaginary-world part, the model of robot and the controller are adjusted continuously in order to deal with the change of dynamic property caused by disturbance and so on. The system is designed to be suitable for a computer system with parallel processing ability. In the paper, adaptability of the controller system is investigated by heading keeping and path following experiments on the condition that unknown disturbances are given to the robot.

Auto-tuned, adaptive process controlled, injection molding machine

Abstract: An injection molding machine uses a summed, multi-term control law to control ram velocity during the injection stroke of a molding cycle to emulate a user set velocity profile. An automatic calibration method sets no load ram speeds to duplicate user set ram speeds. Finite impulse response filters produce open loop, no load control signals at advanced positions on the velocity profile to account for lag in system response. An adaptive, error term indicative of load disturbance, observed from a preceding cycle is added at the advanced travel position predicted by the finite impulse response filter to produce a predictive open loop, load compensated control signal. Finally, an auto tuned PID controller develops a real time, feedback load disturbance signal summed with the open loop control signal to produce a drive signal for the machine's proportioning valve.

Flux and torque control of switched reluctance machines

Abstract: The theory and implementation of a flux-linkage controller applied to a switched reluctance machine drive are described. Analysis of the simplified discrete time load model shows that a simple flux-linkage controller can produce a ‘dead-beat’ system response. Comparison of the response from a discrete time PID current controller, hysteresis current controller and the new flux-linkage controller, show that the flux controller has a much improved response. The experimental controller is used to control an IGBT converter, driving a commercial 7.5 kW switched reluctance motor. A method of constant torque operation is introduced. This takes account of limitations imposed by the finite DC-link voltage and rotor speed when calculating the reference values. The method is based on ‘flux ramps’, where the ramps are chosen to give constant shaft torque, and remain within the capabilities of the power converter. Correct selection of the flux ramps allows constant torque operation to be achieved over a wide speed and torque range. Measured results for the experimental drive demonstrate the low torque ripple achieved for motoring and generating operation over a range of speed and torque values.

Iterative feedback tuning of linear time-invariant MIMO systems

Abstract: Iterative feedback tuning (IFT) is a direct method to tune controller parameters based on closed loop data. In recent years a wide range of applications have been reported as well as extensions of the method. In this contribution we show how to use IFT to tune controllers for linear time-invariant (LTI) multivariable systems. The method is applied to a laboratory model of a helicopter.

Method of implementing a linear discrete-time state-space servo control system on a fixed-point digital signal processor in a disc drive

Abstract: A method of implementing a model based servo controller in a digital signal processor in a disc drive includes obtaining matrices for a discrete-time state-space realization of the servo controller. Controller states of the controller are scaled to reduce a worst case bound on the controller states. The controller states are transformed to a desired format which reduces a number of required mathematical operations. Further, the matrices are converted to fixed point format.