Showing papers on "Control theory published in 2006"

Proportional-resonant controllers and filters for grid-connected voltage-source converters

Abstract: The recently introduced proportional-resonant (PR) controllers and filters, and their suitability for current/voltage control of grid-connected converters, are described. Using the PR controllers, the converter reference tracking performance can be enhanced and previously known shortcomings associated with conventional PI controllers can be alleviated. These shortcomings include steady-state errors in single-phase systems and the need for synchronous d-q transformation in three-phase systems. Based on similar control theory, PR filters can also be used for generating the harmonic command reference precisely in an active power filter, especially for single-phase systems, where d-q transformation theory is not directly applicable. Another advantage associated with the PR controllers and filters is the possibility of implementing selective harmonic compensation without requiring excessive computational resources. Given these advantages and the belief that PR control will find wide-ranging applications in grid-interfaced converters, PR control theory is revised in detail with a number of practical cases that have been implemented previously, described clearly to give a comprehensive reference on PR control and filtering.

Attitude stabilization of a VTOL quadrotor aircraft

Abstract: In this paper, we propose a new quaternion-based feedback control scheme for exponential attitude stabilization of a four-rotor vertical takeoff and landing aerial robot known as a quadrotor aircraft. The proposed controller is based upon the compensation of the Coriolis and gyroscopic torques and the use of a PD/sup 2/ feedback structure, where the proportional action is in terms of the vector quaternion and the two derivative actions are in terms of the airframe angular velocity and the vector quaternion velocity. We also show that the model-independent PD controller, where the proportional action is in terms of the vector-quaternion and the derivative action is in terms of the airframe angular velocity, without compensation of the Coriolis and gyroscopic torques, provides asymptotic stability for our problem. The proposed controller as well as some other controllers have been tested experimentally on a small-scale quadrotor aircraft.

Method, system, and computer program product for managing controlled residential or non-residential environments

Abstract: A control server, or similar central processor, manages the distribution of data (including audio and video), voice, and control signals among a plurality of devices connected via a wired and/or wireless communications network. The devices include audio/visual devices (such as, televisions, monitors, PDAs, notepads, notebooks, MP3, portable stereo, etc.) as well as household appliances (such as, lighting, ovens, alarm clocks, etc.). The control server supports video/audio serving, telephony, messaging, file sharing, internetworking, and security. A portable controller allows a user to access and control the network devices from any location within a controlled residential and/or non-residential environment, including its surrounding areas. The controllers are enhanced to support location-awareness and user-awareness functionality.

Active disturbance rejection control: a paradigm shift in feedback control system design

Abstract: The question addressed in this paper is: just what do we need to know about a process in order to control it? With active disturbance rejection, perhaps we don't need to know as much as we were told. In fact, it is shown that the unknown dynamics and disturbance can be actively estimated and compensated in real time and this makes the feedback control more robust and less dependent on the detailed mathematical model of the physical process. In this paper we first examine the basic premises in the existing paradigms, from which it is argued that a paradigm shift is necessary. Using a motion control metaphor, the basis of such a shift, the active disturbance rejection control, is introduced. Stability analysis and applications are presented. Finally, the characteristics and significance of the new paradigm are discussed.

Multiple harmonics control for three-phase grid converter systems with the use of PI-RES current controller in a rotating frame

Abstract: Voltage source inverters connected to the grid in applications such as active rectifiers, active filters, uninterruptible power supplies, and distributed generation systems need an optimal ac current control. To obtain zero steady-state error at the fundamental frequency (i.e., unity power factor), the use of a standard integrator in a rotating frame is as effective as the use of a resonant controller in a stationary frame. However, the grid voltage harmonics influence the current controller and generate current harmonics unless several integrators in multiple rotating frames or resonant compensators in a stationary frame are adopted. In this letter, a hybrid system consisting of a proportional integral (PI) controller plus a generic hth harmonic resonant controller implemented in a frame rotating at the n th harmonic frequency is discussed in detail. The hth harmonic controller is able to decrease both the (h - n)th and (h + n)th harmonics, while the PI controller is able to decrease other harmonics if the synchronization phase signal adopted for the frame transformation is unfiltered. It is demonstrated that the use of a PI and sixth harmonic resonant compensator is effective for both positive and negative sequence fifth and seventh harmonics; hence, four harmonics are compensated with the proportional integral-resonant (PI-RES) controller implemented in a synchronous frame. Simulation and experimental tests validate the proposed analysis

H/sub /spl infin// control for networked systems with random communication delays

Abstract: This note is concerned with a new controller design problem for networked systems with random communication delays. Two kinds of random delays are simultaneously considered: i) from the controller to the plant, and ii) from the sensor to the controller, via a limited bandwidth communication channel. The random delays are modeled as a linear function of the stochastic variable satisfying Bernoulli random binary distribution. The observer-based controller is designed to exponentially stabilize the networked system in the sense of mean square, and also achieve the prescribed H/sub /spl infin// disturbance attenuation level. The addressed controller design problem is transformed to an auxiliary convex optimization problem, which can be solved by a linear matrix inequality (LMI) approach. An illustrative example is provided to show the applicability of the proposed method.

Autonomous Inverted Helicopter Flight via Reinforcement Learning

Abstract: Helicopters have highly stochastic, nonlinear, dynamics, and autonomous helicopter flight is widely regarded to be a challenging control problem. As helicopters are highly unstable at low speeds, it is particularly difficult to design controllers for low speed aerobatic maneuvers. In this paper, we describe a successful application of reinforcement learning to designing a controller for sustained inverted flight on an autonomous helicopter. Using data collected from the helicopter in flight, we began by learning a stochastic, nonlinear model of the helicopter’s dynamics. Then, a reinforcement learning algorithm was applied to automatically learn a controller for autonomous inverted hovering. Finally, the resulting controller was successfully tested on our autonomous helicopter platform.

Backstepping Control for a Quadrotor Helicopter

Abstract: This paper presents a nonlinear dynamic model for a quadrotor helicopter in a form suited for backstepping control design. Due to the under-actuated property of quadrotor helicopter, the controller can set the helicopter track three Cartesian positions (x, y, z) and the yaw angle to their desired values and stabilize the pitch and roll angles. The system has been presented into three interconnected subsystems. The first one representing the under-actuated subsystem, gives the dynamic relation of the horizontal positions (x, y) with the pitch and roll angles. The second fully-actuated subsystem gives the dynamics of the vertical position z and the yaw angle. The last subsystem gives the dynamics of the propeller forces. A backstepping control is presented to stabilize the whole system. The design methodology is based on the Lyapunov stability theory. Various simulations of the model show that the control law stabilizes a quadrotor with good tracking.

Passive Bilateral Teleoperation With Constant Time Delay

Abstract: We propose a novel control framework for bilateral teleoperation of a pair of multi-degree-of-freedom nonlinear robotic systems under constant communication delays. The proposed framework uses the simple proportional-derivative control, i.e., the master and slave robots are directly connected via spring and damper over the delayed communication channels. Using the controller passivity concept, the Lyapunov-Krasovskii technique, and Parseval's identity, we can passify the combination of the delayed communication and control blocks altogether robustly, as long as the delays are finite constants and an upper bound for the round-trip delay is known. Having explicit position feedback through the delayed P-action, the proposed framework enforces master-slave position coordination, which is often compromised in the conventional scattering-based teleoperation. The proposed control framework provides humans with extended physiological proprioception, so that s/he can affect and sense the remote slave environments mainly relying on her/his musculoskeletal systems. Simulation and experiments are performed to validate and highlight properties of the proposed control framework

Family of multiport bidirectional DC¿DC converters

Abstract: Multiport DC-DC converters are of potential interest in applications such as generation systems utilising multiple sustainable energy sources. A family of multiport bidirectional DC-DC converters derived from a general topology is presented. The topology shows a combination of DC-link and magnetic coupling. This structure makes use of both methods to interconnect multiple sources without the penalty of extra conversion or additional switches. The resulting converters have the advantage of being simple in topology and have a minimum number of power devices. The proposed general topology and basic cells show several possibilities to construct a multiport converter for particular applications and provide a solution to integrate diverse sources owing to their flexibility in structure. The system features a minimal number of conversion steps, low cost and compact packaging. In addition, the control and power management of the converter by a single digital processor is possible. The centralised control eliminates complicated communication structures that would be necessary in the conventional structure based on separate conversion stages. A control strategy based on classical control theory is proposed, showing a multiple PID-loop structure. The general topology and a set of three-port embodiments are detailed.

Standard and adaptive techniques for maximizing energy capture

Abstract: 1066-033X/06/$20.00©2006IEEE W ind energy is the fastest-growing energy source in the world, with worldwide wind-generation capacity tripling in the five years leading up to 2004 [1]. Because wind turbines are large, flexible structures operating in noisy environments, they present a myriad of control problems that, if solved, could reduce the cost of wind energy. In contrast to constantspeed turbines (see “Wind Turbine Development and Types of Turbines”), variable-speed wind turbines are designed to follow wind-speed variations in low winds to maximize aerodynamic efficiency. Standard control laws [2] require that complex aerodynamic properties be well known so that the variable-speed turbine can maximize energy capture; in practice, uncertainties limit the efficient energy capture of a variable-speed turbine. The turbine used as a model for this article’s research is the Controls Advanced Research Turbine (CART) pictured in Figure 1. CART is located in Golden, Colorado, at the U.S. National Renewable Energy Laboratory’s National Wind Technology Center (see “The National Renewable Energy Laboratory and National Wind Technology Center”). A modern utility-scale wind turbine, as shown in Figure 2, has several levels of control systems. On the uppermost level, a supervisory controller monitors the turbine and wind resource to determine when the wind speed is sufficient to start up the turbine and when, due to high winds, the turbine must be shut down for safety. This type of control is the discrete if-then variety. On the middle level is turbine control, which includes generator torque control, blade pitch control, and yaw control. Generator torque control, performed using the power electronics, determines how much torque is extracted from the turbine, specifically, the high-speed shaft. The extracted torque opposes the aerodynamic torque provided by the wind and, thus, indirectly regulates the turbine speed. Depending on the pitch actuators and type of generator and power electronics, blade pitch control and generator torque control can operate quickly relative to the rotor-speed time constant. STANDARD AND ADAPTIVE TECHNIQUES FOR MAXIMIZING ENERGY CAPTURE

Sliding Mode Control of a Quadrotor Helicopter

Abstract: In this paper, we present a new design method for the flight control of an autonomous quadrotor helicopter based on sliding mode control. Due to the under-actuated property of a quadrotor helicopter, the controller can make the helicopter move three positions (x, y, z) and the yaw angle to their desired values and stabilize the pitch and roll angles. A sliding mode control is proposed to stabilize a class of cascaded under-actuated systems. The global stability analysis of the closed-loop system is presented. The advantage of sliding mode control is its insensitivity to the model errors, parametric uncertainties and other disturbances. Simulations show that the control law robustly stabilizes a quadrotor.

Interfacing Renewable Energy Sources to the Utility Grid Using a Three-Level Inverter

Abstract: This paper presents a novel approach for the connection of renewable energy sources to the utility grid. Due to the increasing power capability of the available generation systems, a three-level three-phase neutral-point-clamped voltage-source inverter is selected as the heart of the interfacing system. A multivariable control law is used for the regulator because of the intrinsic multivariable structure of the system. A current source (playing the role of a generic renewable energy source) is connected to the grid using a three-level inverter in order to verify the good performance of the proposed approach. Large- and small-signal d-q state-space averaged models of the system are obtained and used to calculate the multivariable controller based on the linear quadratic regulator technique. This controller simultaneously regulates the dc-link voltage (to operate at the maximum power point of the renewable energy source), the mains power factor (the power is delivered to the grid at unity power factor), and the dc-link neutral-point voltage balance. With the model and regulator presented, a specific switching strategy to control the dc-link neutral-point voltage is not required. The proposed controller can be used for any application, since its nature makes possible the control of any system variable. The good performance of the presented interfacing solution in both steady-state and transient operation is verified through simulation and experimentation using a 1-kW neutral-point-clamped voltage-source-inverter prototype, where a PC-embedded digital signal processor board is used for the controller implementation

Brief paper An ISS-modular approach for adaptive neural control of pure-feedback systems

Abstract: Controlling non-affine non-linear systems is a challenging problem in control theory. In this paper, we consider adaptive neural control of a completely non-affine pure-feedback system using radial basis function (RBF) neural networks (NN). An ISS-modular approach is presented by combining adaptive neural design with the backstepping method, input-to-state stability (ISS) analysis and the small-gain theorem. The difficulty in controlling the non-affine pure-feedback system is overcome by achieving the so-called “ISS-modularity” of the controller-estimator. Specifically, a neural controller is designed to achieve ISS for the state error subsystem with respect to the neural weight estimation errors, and a neural weight estimator is designed to achieve ISS for the weight estimation subsystem with respect to the system state errors. The stability of the entire closed-loop system is guaranteed by the small-gain theorem. The ISS-modular approach provides an effective way for controlling non-affine non-linear systems. Simulation studies are included to demonstrate the effectiveness of the proposed approach. 2006 Elsevier Ltd. All rights reserved.

Adaptive output control of nonlinear systems with uncertain dead-zone nonlinearity

Abstract: In this note, we present a new scheme to design adaptive controllers for uncertain systems preceded by unknown dead-zone nonlinearity. The control design is achieved by introducing a smooth inverse function of the dead-zone and using it in the controller design with backstepping technique. For the design and implementation of the controller, no knowledge is assumed on the unknown system parameters. It is shown that the proposed controller not only can guarantee stability, but also transient performance.

Linear Time Logic Control of Discrete-Time Linear Systems

Abstract: The control of complex systems poses new challenges that fall beyond the traditional methods of control theory. One of these challenges is given by the need to control, coordinate and synchronize the operation of several interacting submodules within a system. The desired objectives are no longer captured by usual control specifications such as stabilization or output regulation. Instead, we consider specifications given by linear temporal logic (LTL) formulas. We show that existence of controllers for discrete-time controllable linear systems and LTL specifications can be decided and that such controllers can be effectively computed. The closed-loop system is of hybrid nature, combining the original continuous dynamics with the automatically synthesized switching logic required to enforce the specification

Pile driving control apparatus and pile driving system

Abstract: A pile driving control apparatus for a pile driving system includes a hydraulic control system that controls a throttle of a pile driving hammer, and thereby controls an impact velocity of the hammer with a pile. A controller provides a control signal to the hydraulic control system. Based on the control signal, the hydraulic control system controls an impact velocity of the hammer during a subsequent hammer stroke. The controller may determine one or more control parameters such as sound pressure at a sound control location during a hammer stroke, vibration at a vibration control location during a hammer stroke, an impact force imparted to the pile during a hammer stroke, and/or actual pile capacity of the pile, and provide to the hydraulic control system a control signal based on the determined control parameter(s).

Apparatus and method for current control in H-Bridge load drivers

Abstract: An electronic current control circuit is provided. This electronic circuit comprises a power-supply, an H-Bridge module connected to a load, and a current sensor connected between the H-Bridge module and the power-supply and adapted to sense load current characteristics. A computerized controller is connected to the current sensor and the H-Bridge module, includes at least a module for operating load current analysis algorithm for analyzing the load current characteristics to determine current control parameters that provide over-current protection and load current control. A load current control module controls the H-Bridge module based upon the current control parameters.

Neural Networks for Real-Time Traffic Signal Control

Abstract: Real-time traffic signal control is an integral part of the urban traffic control system, and providing effective real-time traffic signal control for a large complex traffic network is an extremely challenging distributed control problem. This paper adopts the multiagent system approach to develop distributed unsupervised traffic responsive signal control models, where each agent in the system is a local traffic signal controller for one intersection in the traffic network. The first multiagent system is developed using hybrid computational intelligent techniques. Each agent employs a multistage online learning process to update and adapt its knowledge base and decision-making mechanism. The second multiagent system is developed by integrating the simultaneous perturbation stochastic approximation theorem in fuzzy neural networks (NN). The problem of real-time traffic signal control is especially challenging if the agents are used for an infinite horizon problem, where online learning has to take place continuously once the agent-based traffic signal controllers are implemented into the traffic network. A comprehensive simulation model of a section of the Central Business District of Singapore has been developed using PARAMICS microscopic simulation program. Simulation results show that the hybrid multiagent system provides significant improvement in traffic conditions when evaluated against an existing traffic signal control algorithm as well as the SPSA-NN-based multiagent system as the complexity of the simulation scenario increases. Using the hybrid NN-based multiagent system, the mean delay of each vehicle was reduced by 78% and the mean stoppage time, by 85% compared to the existing traffic signal control algorithm. The promising results demonstrate the efficacy of the hybrid NN-based multiagent system in solving large-scale traffic signal control problems in a distributed manner

Design and implementation of an adaptive fuzzy logic-based controller for wheeled mobile robots

Abstract: In this paper, a control structure that makes possible the integration of a kinematic controller and an adaptive fuzzy controller for trajectory tracking is developed for nonholonomic mobile robots. The system uncertainty, which includes mobile robot parameter variation and unknown nonlinearities, is estimated by a fuzzy logic system (FLS). The proposed adaptive controller structure represents an amalgamation of nonlinear processing elements and the theory of function approximation using FLS. The real-time control of mobile robots is achieved through the online tuning of FLS parameters. The system stability and the convergence of tracking errors are proved using the Lyapunov stability theory. Computer simulations are presented which confirm the effectiveness of the proposed tracking control law. The efficacy of the proposed control law is tested experimentally by a differentially driven mobile robot. Both simulation and results are described in detail.

Sliding-Mode Control for Integrated Missile Autopilot Guidance

Abstract: A sliding-mode controller is derived for an integrated missile autopilot and guidance loop. Motivated by a differential game formulation of the guidance problem, a single sliding surface, defined using the zero-effort miss distance, is used. The performance of the integrated controller is compared with that of two different two-loop designs. The latter use a sliding-mode controller for the inner autopilot loop and different guidance laws in the outer loop: one uses a standard differential game guidance law, and the other employs guidance logic based on the sliding-mode approach. To evaluate the performance of the various guidance and control solutions, a two-dimensional nonlinear simulation of the missile lateral dynamics and relative kinematics is used, while assuming first-order dynamics for the target evasive maneuvers. The benefits of the integrated design are studied in several endgame interception engagements. Its superiority is demonstrated especially in severe scenarios where spectral separation between guidance and flight control, implicitly assumed in any two-loop design, is less justified. The results validate the design approach of using the zero-effort miss distance to define the sliding surface.

Control of fully actuated ocean surface vessels using a class of feedforward approximators

Abstract: In this brief, we consider the problem of tracking a desired trajectory for fully actuated ocean vessels, in the presence of uncertainties and unknown disturbances. The combination of approximation-based and domination design techniques allows us to handle time-varying disturbances, without the need for explicit knowledge of the bounds. Using backstepping and Lyapunov synthesis, the stable tracking controller is first designed for the full-state feedback case. Subsequently, the output feedback problem is tackled by employing a high-gain observer to estimate the unmeasurable states required by the stable tracking controller. Under the proposed control, semiglobal uniform boundedness of the closed-loop signals is guaranteed for both full-state and output feedback cases.

New maximum power point tracker for PV arrays using fuzzy controller in close cooperation with fuzzy cognitive networks

Abstract: The studies on the photovoltaic (PV) generation are extensively increasing, since it is considered as an essentially inexhaustible and broadly available energy resource. However, the output power induced in the photovoltaic modules depends on solar radiation and temperature of the solar cells. Therefore, to maximize the efficiency of the renewable energy system, it is necessary to track the maximum power point of the PV array. In this paper, a maximum power point tracker using fuzzy set theory is presented to improve energy conversion efficiency. A new method is proposed, by using a fuzzy cognitive network, which is in close cooperation with the presented fuzzy controller. The new method gives a very good maximum power operation of any PV array under different conditions such as changing insolation and temperature. The simulation studies show the effectiveness of the proposed algorithm

Video game system with wireless modular handheld controller

Abstract: A home entertainment system for video games and other applications includes a main unit and handheld controllers. The handheld controllers sense their own motion by detecting illumination emitted by emitters positioned at either side of a display. The controllers can be plugged into expansion units that customize the overall control interface for particular applications including but not limited to legacy video games.

Hybrid Control of the Berkeley Lower Extremity Exoskeleton (BLEEX)

Abstract: The Berkeley Lower Extremity Exoskeleton is the first functional energetically autonomous load carrying human exoskeleton and was demonstrated at U.C. Berkeley, walking at the average speed of 0.9 m/s (2 mph) while carrying a 34 kg (75 lb) payload. The original published controller, called the BLEEX Sensitivity Amplification Controller, was based on positive feedback and was designed to increase the closed loop system sensitivity to its wearer's forces and torques without any direct measurement from the wearer. This controller was successful at allowing natural and unobstructed load support for the pilot. This article presents an improved control scheme we call "hybrid" BLEEX control that adds robustness to changing BLEEX backpack payload. The walking gait cycle is divided into stance control and swing control phases. Position control is used for the BLEEX stance leg (including the torso and backpack) and a sensitivity amplification controller is used for the swing leg. The controller is also designed to smoothly transition between these two schemes as the pilot walks. With hybrid control, the controller does not require a good model of the BLEEX torso and payload, which is difficult to obtain and subject to change as payload is added and removed. As a tradeoff, the position control used in this method requires the human to wear seven inclinometers to measure human limb and torso angles. These additional sensors require careful design to securely fasten them to the human and increase the time to don and doff BLEEX.

Digital Current Control of a Voltage Source Converter With Active Damping of LCL Resonance

Abstract: Inductance-capacitor-inductance (LCL)-filters installed at converter outputs offer higher harmonic attenuation than L-filters, but careful design is required to damp LCL resonance, which can cause poorly damped oscillations and even instability. A new topology is presented for a discrete-time current controller which damps this resonance, combining deadbeat current control with optimal state-feedback pole assignment. By separating the state feedback gains into deadbeat and damping feedback loops, transient overcurrent protection is realizable while preserving the desired pole locations. Moreover, the controller is shown to be robust to parameter uncertainty in the grid inductance. Experimental tests verify that fast well-damped transient response and overcurrent protection is possible at low switching frequencies relative to the resonant frequency