Showing papers on "Open-loop controller published in 2010"

Trajectory tracking for non-holonomic cars: A linear approach to controlled leader-follower formation

Abstract: This article describes the design of a linear robust dynamic output feedback control scheme for output reference trajectory tracking tasks in a leader-follower non-holonomic car formation problem using the cars' kinematic models. A simplification is proposed on the follower's exact open loop position tracking error dynamics, obtained by flatness considerations, resulting in a system described by an additively disturbed set of two, second order, integrators with non-linear velocity dependent control input matrix gain. The unknown disturbances are modeled as absolutely bounded, additive, unknown time signals which may be locally approximated by arbitrary elements of, a, fixed, sufficiently high degree family of Taylor polynomials. Linear Luenberger observers may be readily designed, which include the, self updating, internal model of the unknown disturbance input vector components as generic time-polynomial models. The proposed Generalized Proportional Integral (GPI) observers, which are the dual counterpart of GPI controllers ([11]), achieve a, simultaneous, disturbance estimation and tracking error phase variables estimation. This, on-line, gathered information is used to advantage on the follower's linear output feedback controller thus allowing for a simple, yet efficient, disturbance and control input gain cancelation effort. The results are applied to control the fixed time delayed trajectory tracking of the leader path on the part of the follower. Simulations are presented which illustrate the robustness of the proposed approach.

Seamless Transfer of Single-Phase Grid-Interactive Inverters Between Grid-Connected and Stand-Alone Modes

Abstract: This paper presents a novel seamless transfer of single-phase grid-interactive inverters between grid-connected and stand-alone modes. The grid-connected inverter should operate in grid-tied and off-grid modes in order to provide power to the emergency load during system outages. However, the grid current controller and the output voltage controller are switched between the two modes, so the outputs of both controllers may not be equal during the transfer instant, which will cause the current or voltage spikes during the switching process. The transfer between the two controllers does not exist in the proposed method. In grid-tied mode, the voltage controller is used for compensating the filter capacitor current, and the current controller is used to control the grid current. In stand-alone mode, the voltage controller is used to regulate the output voltage, whereas the output of the current controller is zero. With the proposed control method, the seamless transfer can be achieved between both modes, even in polluted grid voltage. The principle and realization conditions of the control methods at both modes are analyzed. The detailed process of the seamless transfer between the two modes is illustrated. Finally, the simulation and experimental results verify the theoretical analysis.

Design of a Self-Tuning PI Controller for a STATCOM Using Particle Swarm Optimization

Abstract: A self-tuning proportional-integral (PI) controller in which the controller gains are adapted using the particle swarm optimization (PSO) technique is proposed for a static synchronous compensator (STATCOM). An efficient formula for the estimation of system load impedance using real-time measurements is derived. Based on the estimated system load, a PSO algorithm, which takes the best particle gains, the best global gains, and previous change of gains into account, is employed to reach the desired controller gains. To demonstrate the effectiveness of the proposed PSO self-tuning PI controller for a STATCOM, experimental results for a system under different loading conditions are presented. Results from the self-tuning PI controller are compared with those from the fixed-gain PI controllers.

Multivariable Servomechanism Controller for Autonomous Operation of a Distributed Generation Unit: Design and Performance Evaluation

Abstract: A linear time-invariant (LTI) robust servomechanism controller for islanded (autonomous) operation of a distributed generation (DG) unit and its local load is proposed. The DG unit utilizes a voltage-sourced converter (VSC) as the interface medium. The controller design is obtained by introducing a new optimal controller design procedure, in conjunction with a proposed non-conservative robustness constraint. The proposed controller utilizes 1) an internal oscillator for frequency control and 2) a robust servomechanism controller (RSC) to regulate the island voltage. Despite uncertainty of the load parameters, the proposed controller guarantees robust stability and pre-specified performance criteria, e.g., fast transient response and zero steady-state error. The theoretical aspects of the proposed robust servomechanism controller including the existence conditions, design of the controller, and robust stability analysis of the closed-loop system are studied. Moreover, the performance of the robust servomechanism controller based on 1) simulation studies in the MATLAB software environment, and 2) experiments in a laboratory-scale setup, is presented in this paper. In particular, reference signal tracking and robustness of the closed-loop system with respect to the load parameter uncertainty are investigated. Both computer simulation studies and experimental results confirm that the proposed robust controller provides the specified performance characteristics of the closed-loop system.

A New Method for Robust Damping and Tracking Control of Scanning Probe Microscope Positioning Stages

Abstract: This paper demonstrates a simple second-order controller that eliminates scan-induced oscillation and provides integral tracking action. The controller can be retrofitted to any scanning probe microscope with position sensors by implementing a simple digital controller or operational amplifier circuit. The controller is demonstrated to improve the tracking bandwidth of an NT-MDT scanning probe microscope from 15 Hz (with an integral controller) to 490 Hz while simultaneously improving gain-margin from 2 to 7 dB. The penalty on sensor induced positioning noise is minimal. A unique benefit of the proposed control scheme is the performance and stability robustness with respect to variations in resonance frequency. This is demonstrated experimentally by a change in resonance frequency from 934 to 140 Hz. This change does not compromise stability or significantly degrade performance. For the scanning probe microscope considered in this paper, the noise is marginally increased from 0.30 to 0.39 nm rms. Open and closed-loop experimental images of a calibration standard are reported at speeds of 1, 10, and 31 lines per second (with a scanner resonance frequency of 290 Hz). Compared with traditional integral controllers, the proposed controller provides a bandwidth improvement of greater than 10 times. This allows faster imaging and less tracking lag at low speeds.

Cascaded Nine-Level Inverter for Hybrid-Series Active Power Filter, Using Industrial Controller

Abstract: An industrial controller, specifically designed for two- and three-level converters, was adapted to work on an asymmetrical nine-level active power filter (APF) The controller is now able to make all required tasks for the correct operation of the APF, such as current-harmonic elimination and removal of high-frequency noise The low switching-frequency operation of the nine-level converter was an important advantage in the application of the industrial controller In addition, with the nine-level filter, switching losses were significantly reduced The filter was designed to work as voltage source and operates as harmonic isolator, improving the filtering characteristics of the passive filter The control strategy for detecting current harmonics is based on the “ p-q theory ” and the phase-tracking system in a synchronous reference frame phase-locked loop The dc-link voltage control is analyzed together with the effect of controller gain and delay time in the system's stability Simulations for this application are displayed and experiments in a 1-kVA prototype, using the aforementioned industrial controller, were tested, validating the effectiveness of this new application

Automated transitions power modes while continuously powering a power controller and powering down a media controller for at least one of the power modes

Abstract: A data storage device comprising a storage media, a media controller, a power system and a power controller is disclosed. The media controller is configured to read data from and write data to the storage media. The power system is configured to controllably power the media controller, and the power controller is configured to autonomously transition the data storage device between a plurality of power modes, wherein the power system continuously powers the power controller through the power modes and powers down the media controller for at least one of the power modes.

Robust Tracking and Vibration Suppression for a Two-Inertia System by Combining Backstepping Approach With Disturbance Observer

Abstract: In this paper, we consider the problem of designing a robust controller for a two-inertia system which contains arbitrarily large (but bounded) model uncertainties and disturbances. The research is motivated by the fact that a two-inertia system represents most of an industrial robot arm system that has a flexible joint, for which vibration suppression and robust control against model uncertainties and external disturbances are very important. The proposed controller consists of two parts: the outer-loop controller designed by the backstepping approach and the inner-loop controller by the new partial disturbance observer (DOB). The DOB is responsible for compensating the input-matched uncertainties and disturbances, while the backstepping controller is designed for dealing with the rest. The proposed controller makes tracking error and vibration of the system suppressed within an arbitrarily small bound during operation time when full states are measured. The results are verified by simulations and experiments with a Luenberger observer.

A Generalized Class of Stationary Frame-Current Controllers for Grid-Connected AC–DC Converters

Abstract: Within power systems, high-power pulsewidth-modulated ac-dc converters are used in flexible ac transmission systems controllers and for interfacing renewable energy sources to the grid. These converters traditionally employed PI controllers designed in the synchronous dq-frame with decoupling of d and q axes. Recently, stationary -frame proportional-resonant (PR) controllers have been proposed. Though both types of control are suitable for the regulation of three-phase converters, the PR controller displays steady-state and dynamic behavior that differs significantly from that of decoupled dq-frame controllers. This paper derives a stationary frame controller that is the exact equivalent of the commonly used synchronous frame controller with L decoupling. The new stationary frame “PRX2” controller consists of a proportional (P), a resonant (R), and two cross-coupling components. The PRX2 controller offers identical transient and steady-state performance and has the same frequency response as the decoupled synchronous frame PI controller. Unlike other stationary frame controllers containing resonant components, the PRX2 controller is unique because it contains a cross-coupling feedback component, which accounts for the behavior of the L decoupling branches present in synchronous frame controllers. It is shown that ignoring this decoupling component greatly increases the controller's sensitivity to frequency variation. Numerous stationary frame controllers, including the common PR controller, may be derived from the general PRX2 controller.

Open-Loop Controller Design and Dynamic Characteristics of a Spherical Wheel Motor

Abstract: This paper presents a control system design for a particular form of variable-reluctance spherical motors, referred to here as a spherical wheel motor (SWM). The method decoupling the spin from the inclination offers a means to control, in open loop (OL), the inclination of a continuously rotating shaft. Specifically, the OL controller presented in this paper combines a multispeed switching control law for controlling the spin motion and a dynamic model-based control law for regulating the rotor inclination of an SWM. The concept feasibility of the OL-controlled SWM (consisting of permanent magnets in a rotor and electromagnets in a stator) has been experimentally demonstrated. The experimental study not only demonstrates the design procedure but also provides intuitive insights into the effects of key operation parameters on the SWM dynamics. The results presented here will serve as a basis for developing feedback controllers for increasing accuracy and robustness for disturbance rejection.

Simulation and hybrid fuzzy-PID control for positioning of a hydraulic system

Abstract: Accuracy and precision of position control of hydraulic systems are key parameters for engineering applications in order to set more economical and quality systems. In this context, this paper presents modeling and position control of a hydraulic actuation system consisting of an asymmetric hydraulic cylinder driven by a four way, three position proportional valve. In this system model, the bulk modulus is considered as a variable. In addition, the Hybrid Fuzzy-PID Controller with Coupled Rules (HFPIDCR) is proposed for position control of the hydraulic system and its performance is tested by simulation studies. The novel aspect of this controller is to combine fuzzy logic and PID controllers in terms of a switching condition. Simulation results of the HFPIDCR based controller are compared with the results of classical PID, Fuzzy Logic Controller (FLC), and Hybrid Fuzzy-PID controller (HFPID). As a result, it is demonstrated that Hybrid Fuzzy PID Controller with Coupled Rules is more effective than other controllers.

Model predictive controller with tunable integral component to compensate for model mismatch

Abstract: An MPC controller technique integrates feedback control performance better than methods commonly used today in MPC type controllers, resulting in an MPC controller that performs better than traditional MPC techniques in the presence of process model mismatch. In particular, MPC controller performance is enhanced by adding a tunable integration block to the MPC controller that develops an integral component indicative of the prediction or other control error, and adds this component to the output of an MPC controller algorithm to provide for faster or better control in the presence of model mismatch, which is the ultimate reason for the prediction error in the first place. This technique enables the MPC controller to react more quickly and to provide better set point change and load disturbance performance in the presence of model mismatch, without decreasing the robustness of the MPC controller.

Output Power Control for Variable-Speed Variable-Pitch Wind Generation Systems

Abstract: A robust pitch control strategy for the output power control of wind generator systems in wide-wind-speed range is presented in this paper. The corresponding controller is designed, which consists of a nominal inverse-system controller and a robust compensator. The advantages of the proposed strategy include the simple implementation, tolerance of turbine parameter or some nonparametric uncertainties, and robust control of the generator output power with wind-speed variations. Theoretical analyses, simulation, and experimental results show that the proposed controller can work better in a wide-wind-speed range compared with the traditional proportional-integral-derivative controller. It has similar performance with the neural network controller, but less complexity. Additionally, it can be easily adapted to other wind generator systems.

A novel linear PID controller for an upper limb exoskeleton

Abstract: An upper limb exoskeleton is a wearable robotic system that is physically linked to the arm of the human operators and its seven actuated degrees of freedom (DOF) match the seven DOF of the human arm. The stability of such a system is critical given the proximity of its human operator. A new PID controller is developed which guarantee asymptotic stability for this class of robotic manipulators. A simulation was used to assess the system performance given the theoretical results of the controller's parameters with a unique exoskeleton system (EXO-UL7). The simulation also verify the semi-global asymptotic stability of the system. The proposed methodology eliminates the need of the system's dynamics model for the purpose of designing the controller. It provides an analytical tool for the controller design that is traditionally preformed experimentally (parameter tuning).

Quadrature-Corrected Feedforward Control Apparatus and Method for DC-AC Power Conversion

Abstract: An apparatus and method for controlling the delivery of a pre-determined amount of power from a DC source to an AC grid includes an inverter and an inverter controller The inverter includes an input converter, an energy storage capacitor, and an output converter The inverter controller includes an input converter controller and an output converter controller The input converter controller includes feedforward controller configured to perform a calculation to determine a value for the duty cycle for the input converter such that: (1) the input converter delivers the pre-determined amount of power and (2) the magnitude of a ripple signal reflected into the input source is attenuated toward zero The input converter controller may also include a quadrature corrector configured to determine the effectiveness of the calculation in attenuating the ripple and to adaptively alter the calculation to improve the effectiveness

Modeling and testing of a morphing wing in open-loop architecture

Abstract: This paper presents the modeling and experimental testing of the aerodynamic performance of a morphing wing in open-loop architecture. We show the method used to acquire the pressure data from the external surface of the flexible wing skin, using incorporated Kulite pressure sensors and the instrumentation of the morphing controller. The acquired pressure data are analyzed through fast Fourier transforms to detect the magnitude of the noise in the surface airflow. Subsequently, the data are filtered by means of high-pass filters and processed by calculating the root mean square of the signal to obtain a plot diagram of the noise in the airflow. This signal processing is necessary to remove the inherent noise electronically induced from the Tollmien-Schlichting waves, which are responsible for triggering the transition from laminar to turbulent flow. The flexible skin is required to morph the shape of the airfoil through two actuation points to achieve an optimized airfoil shape based on the theoretical flow conditions similar to those tested in the wind tunnel. Two shape memory alloy actuators with a nonlinear behavior drive the displacement of the two control points of the flexible skin toward the optimized airfoil shape. Each of the shape memory actuators is activated by a power supply unit and controlled using the Simulink/MATLAB® software through a self-tuning fuzzy controller. The methodology and the results obtained during the wind-tunnel test proved that the concept and validity of the system in real time are discussed in this paper. Real-time acquisition and signal processing of pressure data are needed for further development of the closed-loop controller to obtain a fully automatic morphing wing system.

An Intelligent Longitudinal Controller for Application in Semiautonomous Vehicles

Abstract: We present a neuro-fuzzy controller for intelligent cruise control of semiautonomous vehicles. This paper addresses the problem of longitudinal control that aims at regulating the speed of the controlled vehicle in order to maintain constant time headway with respect to the vehicle in front. A fuzzy radial basis function network (FRBFN) longitudinal controller is designed to incorporate the merits of fuzzy logics as well as neural networks. The FRBFN is prestructured, and its parameters are configured such that they are associated with their physical meaning. The parameters of the output layer are learned online via gradient algorithm. An attractive feature of the proposed method is that it does not require the training data and the vehicle longitudinal dynamic model. Simulation results on a vehicle theoretical model are provided to demonstrate the effectiveness of this controller. In order to investigate the proposed control algorithms in real-life situations, a small-scaled vehicle with computer and sensors onboard is developed. Experimental results of a conventional PID controller and the FRBFN controller are provided for comparison.

Apparatus and method for controlling dc-ac power conversion

Abstract: An apparatus and method for controlling the delivery of power from a DC source to an AC grid includes an inverter configured to deliver power from the unipolar input source to the AC grid and an inverter controller. The inverter includes an input converter, an active filter, and an output converter. The inverter controller includes an input converter controller, an active filter controller and an output converter controller. The input converter controller is configured to control a current delivered by the input converter to a galvanically isolated unipolar bus of the inverter. The output converter is configured to control the output converter to deliver power to the AC grid. Additionally, the active filter controller is configured to control the active filter to supply substantially all the power that is deliver by the output controller to the AC grid at a grid frequency.

Global and Semi-Global Stabilization of Linear Systems With Multiple Delays and Saturations in the Input

Abstract: This paper studies stabilization problems for linear systems with multiple delays in the input. Two types of delays are considered. The first type of delays is constant delays, which can be arbitrarily large, while the second type is time-varying with an arbitrarily large bound. With the first type of delays, under the condition that the open loop system is absolutely controllable with all its eigenvalues on the imaginary axis, (globally) stabilizing state and output feedback laws are constructed based on the solution to a family of parametric Riccati equations, which can be obtained explicitly through the solution of a parametric linear matrix equation. With the second type of delays, under the condition that the open-loop system is absolutely controllable with all its eigenvalues on the imaginary axis being zero, (global) state and output feedback laws are explicitly constructed based on the solution to a similar family of parametric Riccati equations. When the input is also subject to magnitude saturation, it is shown that semiglobal stabilization, instead of global stabilization, can still be achieved. Numerical examples illustrate the effectiveness of the proposed approach.

Multi-criteria analysis of wastewater treatment plant design and control scenarios under uncertainty

Abstract: Wastewater treatment plant control and monitoring can help to achieve good effluent quality, in a complex, highly non-linear process. The Benchmark Simulation Model no. 2 (BSM2) is a useful tool to competitively evaluate plant-wide control on a long-term basis. A method to conduct scenario analysis of process designs by means of Monte Carlo (MC) simulations and multi-criteria evaluation is presented. It is applied to the open loop version of BSM2 and to two closed loop versions, one with a simple oxygen controller and the other one with an ammonium controller regulating the set-point of the oxygen controller (cascade controller). The results show a much greater benefit of the cascade controller compared to the simple controller, both in environmental and economic terms. From an optimal process design point of view, the results show that the volume of the primary clarifier and the anoxic fraction of the reactor volume have an important impact on process performance. The uncertainty analysis of the optimal designs, also performed with MC simulations, highlights the improved and more stable effluent under closed loop control.

Universal apparatus and method for configurably controlling a heating or cooling system

Abstract: A system controller is disclosed that includes a communication means for transmitting and receiving information from an installed blower motor controller, and a removable memory device connected to the system controller. The removable memory device includes system parameter information stored thereon that relates to the particular heating or cooling system, where the system parameter information includes at least motor related parameters relating to the operation of one or more types of blower motors. The system controller further includes a processor configured to receive via the communication means the communication of identifying information from the blower motor controller that identifies the type of blower motor installed in the system. The processor is configured to retrieve motor related parameters corresponding to the specific identified blower motor controller from the memory device, and to send said corresponding motor related parameters to the blower motor controller.

Multi-loop PI controller design based on the direct synthesis for interacting multi-time delay processes.

Abstract: In this article, a new analytical method based on the direct synthesis approach is proposed for the design of a multi-loop proportional-integral (PI) controller. The proposed design method is aimed at achieving the desired closed-loop response for multiple-input, multiple-output (MIMO) processes with multiple time delays. The ideal multi-loop controller is firstly designed in terms of the relative gain and desired closed-loop transfer function. Then, the standard multi-loop PI controller is obtained by approximating the ideal multi-loop controller using the Maclaurin series expansion. The simulation study demonstrates the effectiveness of the proposed method for the design of multi-loop PI controllers. The multi-loop PI controller designed by the proposed method shows a fast, well-balanced, and robust response with the minimum integral absolute error (IAE).

Neural-Network-Based Low-Speed-Damping Controller for Stepper Motor With an FPGA

Abstract: We present a low-speed-damping controller for a stepper motor using artificial neural networks (ANNs). This controller is designed to remove nonlinear disturbance at low speeds. The proposed controller improves the stepper motor performance at less than the resonance speed of the stepper motor system. Due to its ability to learn, the proposed controller can adapt to different resonant speed ranges without any identification process for system parameters. Conversely, we also introduce the implementation of an ANN-based controller, online backpropagation learning, and a microstep driver on a single field-programmable gate array. An implementation and experimental results are conducted to verify the feasibility and the effectiveness of the proposed controller.

DC motor position control using fuzzy proportional-derivative controllers with different defuzzification methods

Abstract: This paper presents the design of a fuzzy control system to control the position of a DC motor. The motor was modelled and converted to a subsystem in Simulink. First, a crisp proportional-derivative (PD) controller was designed and tuned using a Simulink block instead of conventional tuning methods such as hand-tuning or Ziegler-Nichols frequency response method. Then a fuzzy proportional-derivative (FPD) controller was designed and system responses of FPDs with different defuzzification methods were investigated. A disturbance signal was also applied to the input of the control system. FPD controller succeeded to reject the disturbance signal without further tuning of the parameters whereby crisp PD controller failed.