Showing papers on "Open-loop controller published in 2004"

Interconnection and damping assignment passivity-based control of mechanical systems with underactuation degree one

Abstract: We consider the problem of (asymptotic) stabilization of mechanical systems with underactuation degree one. A state-feedback design is derived applying the interconnection and damping assignment passivity-based control methodology. Its application relies on the possibility of solving a set of partial differential equations that identify the energy functions that can be assigned to the closed-loop. The following results are established: 1) identification - in terms of some algebraic inequalities - of a subclass of these systems for which the partial differential equations are trivially solved; 2) characterization of all systems which are feedback-equivalent to this subclass; and 3) introduction of a suitable parametrization of the assignable energy functions that provides the designer with a handle to address transient performance and robustness issues. An additional feature of our developments is that the open-loop system need not be described by a port-controlled Hamiltonian (or Lagrangian) model, a situation that arises often in applications due to model reductions or preliminary feedbacks that destroy the structure. The new result is applied to obtain an (almost) globally stabilizing controller for the inertia wheel pendulum, a controller for the chariot with pendulum system that can swing-up the pendulum from any position in the upper half plane and stop the chariot at any desired location, and an (almost) globally stabilizing scheme for the vertical takeoff and landing aircraft with strong input coupling. In all cases we obtain very simple and intuitive solutions that do not rely on, rather unnatural and technique-driven, linearization or decoupling procedures but instead endows the closed-loop system with a Hamiltonian structure with desired potential and kinetic energy functions.

On Fractional PIλ Controllers: Some Tuning Rules for Robustness to Plant Uncertainties

Abstract: The objective of this work is to find out optimum settings for a fractional PIλ controller in order to fulfill three different robustness specifications of design for the compensated system, taking advantage of the fractional order, λ. Since this fractional controller has one parameter more than the conventional PI controller, one more specification can be fulfilled, improving the performance of the system and making it more robust to plant uncertainties, such as gain and time constant changes. For the tuning of the controller an iterative optimization method has been used, based on a nonlinear function minimization. Two real examples of application are presented and simulation results are shown to illustrate the effectiveness of this kind of unconventional controllers.

Odd-harmonic digital repetitive control of a single-phase current active filter

Abstract: Shunt active power filters have been proved as useful elements to correct distorted currents caused by nonlinear loads in power distribution systems. This work presents an all-digital approach, based on the repetitive control technique, for their control. In particular, a special digital repetitive plug-in controller for odd-harmonic discrete-time periodic references and disturbances is used. This approach does not introduce high gain at those frequencies for which it is not needed, and thus it improves robustness. Additionally, the necessary data memory capacity is lower than in traditional repetitive controllers. The design is performed for the particular case of single-phase shunt active filter with a full-bridge boost topology. Several experimental results are also presented to show the good behavior of the closed-loop system.

Dynamic feedback controller of Euler angles and wind parameters estimation for a quadrotor unmanned aerial vehicle

Abstract: A nonlinear dynamic model for a quadrotor unmanned aerial vehicle is presented with a new vision of state parameter control which is based on Euler angles and open loop positions state observer. This method emphasizes on the control of roll, pitch and yaw angle rather than the translational motions of the UAV. For this reason the system has been presented into two cascade partial parts, the first one relates the rotational motion whose the control law is applied in a closed loop form and the other one reflects the translational motion. A dynamic feedback controller is developed to transform the closed loop part of the system into linear, controllable and decoupled subsystem. The wind parameters estimation of the quadrotor is used to avoid more sensors. Hence an estimator of resulting aerodynamic moments via Lyapunov function is developed. Performance and robustness of the proposed controller are tested in simulation.

Information-theoretic approach to the study of control systems

Abstract: We propose an information-theoretic framework for analyzing control systems based on the close relationship of controllers to communication channels. A communication channel takes an input state and transforms it into an output state. A controller, similarly, takes the initial state of a system to be controlled and transforms it into a target state. In this sense, a controller can be thought of as an actuation channel that acts on inputs to produce desired outputs. In this transformation process, two different control strategies can be adopted: (i) the controller applies an actuation dynamics that is independent of the state of the system to be controlled (open-loop control); or (ii) the controller enacts an actuation dynamics that is based on some information about the state of the controlled system (closed-loop control). Using this communication channel model of control, we provide necessary and sufficient conditions for a system to be perfectly controllable and perfectly observable in terms of information and entropy. In addition, we derive a quantitative trade-off between the amount of information gathered by a closed-loop controller and its relative performance advantage over an open-loop controller in stabilizing a system. This work supplements earlier results (Phys. Rev. Lett. 84 (2000) 1156) by providing new derivations of the advantage afforded by closed-loop control and by proposing an information-based optimality criterion for control systems. New applications of this approach pertaining to proportional controllers, and the control of chaotic maps are also presented.

A global output-feedback controller for simultaneous tracking and stabilization of unicycle-type mobile robots

Abstract: We present a time-varying global output-feedback controller that solves both tracking and stabilization for unicycle-type mobile robots simultaneously at the torque level. The controller synthesis is based on a coordinate transformation, Lyapunov's direct method, and backstepping technique. Simulations demonstrate the result.

Adaptive fuzzy sliding-mode control for induction servomotor systems

Abstract: An adaptive fuzzy sliding-mode control design method is proposed for induction servomotor system control. The proposed adaptive fuzzy sliding-mode control system is comprised of a fuzzy controller and a compensation controller. The fuzzy controller is the main tracking controller, which is used to approximate an ideal computational controller. The compensation controller is designed to compensate for the difference between the ideal computational controller and the fuzzy controller. A tuning methodology is derived to tune the premise and consequence parts of the fuzzy rules. The online tuning algorithm is derived in the Lyapunov sense; thus, the stability of the control system can be guaranteed. Moreover, to relax the requirement for the uncertain bound in the compensation controller, an estimation mechanism is investigated to observe the uncertain bound, so that the chattering phenomena of the control efforts can be relaxed. To illustrate the effectiveness of the proposed design method, a comparison between a conventional fuzzy control and the proposed adaptive fuzzy sliding-mode control is made. Simulation and experimental results verify that the proposed adaptive fuzzy sliding-mode control design method can achieve favorable control performance with regard to parameter variations and external disturbances.

Performance recovery under output feedback sampled-data stabilization of a class of nonlinear systems

Abstract: This paper studies sampled-data output feedback control of a class of nonlinear systems. It is shown that the performance of a stabilizing continuous-time state feedback controller can be recovered by a sampled-data output feedback controller when the sampling period is sufficiently small. The output feedback controller uses a deadbeat discrete-time observer to estimate the unmeasured states. Two schemes are proposed to overcome large initial transients when the controller is switched on.

Stabilization of a mini-rotorcraft having four rotors

Abstract: In this paper we present a controller design and implementation on a mini-rotorcraft having four rotors A Lagrangian model of the helicopter was used for the controller synthesis The proposed controller is based on Lyapunov analysis Experimental results show that the controller is able to perform autonomously the tasks of taking-off, hovering and landing

Data-driven control design for neuroprotheses: a virtual reference feedback tuning (VRFT) approach

Abstract: This paper deals with design of feedback controllers for knee joint movement of paraplegics using functional electrical stimulation (FES) of the paralyzed quadriceps muscle group. The controller design approach, virtual reference feedback tuning (VRFT), is directly based on open loop measured data and fits the controller in such a way that the closed-loop meets a model reference objective. The use of this strategy, avoiding the modeling step, significantly reduces the time required for controller design and considerably simplifies the rehabilitation protocols. Linear and nonlinear controllers have been designed and experimentally tested, preliminarily on a healthy subject and finally on a paraplegic patient. Linear controller is effective when applied on small range of knee joint angle. The design of a nonlinear controller allows better performances. It is also shown that the control design is effective in tracking assigned knee angle trajectories and rejecting disturbances.

Adaptive tracking and regulation of a wheeled mobile robot with controller/update law modularity

Abstract: A new adaptive controller is developed for wheeled mobile robots with parametric uncertainty in the dynamic model. The main theoretical contribution is the modular manner in which the control law and parameter update law are designed. This feature allows for design flexibility in the selection of the update law, and can be exploited to improve the transient response of the adaptive controller. The proposed controller also has the important feature of being applicable to both the tracking and regulation problems. The modularity of the adaptive controller is experimentally demonstrated on a K2A Cybermotion mobile robot that has been modified to allow for the implementation of torque-level control inputs. In particular, the adaptive controller with a gradient update law is evaluated vis-a/spl grave/-vis a least-squares update law.

Vehicle control method and apparatus

Abstract: A vehicle mode controller, a driving mode collecting means, and a plurality of subsystem controllers including an engine management system, a transmission controller, a steering controller, a brakes controller and a suspension controller, provide an improved system and method of operating a vehicle control system in a host vehicle in a manner suitable for a respective driving surface in a plurality of different off-road surfaces and terrains such as might be encountered when driving off-road. An improved method is provided for controlling a vehicle control system by avoiding unplanned combinations of subsystem configuration modes and minimizing the transition time when changing between subsystem configuration modes.

Hybrid fuzzy control of robotics systems

Abstract: This paper presents a new approach towards optimal design of a hybrid fuzzy controller for robotics systems. The salient feature of the proposed approach is that it combines the fuzzy gain scheduling method and a fuzzy proportional-integral-derivative (PID) controller to solve the nonlinear control problem. The resultant fuzzy rule base of the proposed controller can be decomposed into two layers. In the upper layer, the gain scheduling method is incorporated with a Takagi-Sugeno (TS) fuzzy logic controller to linearize the robotics system for a given reference trajectory. In the lower layer, a fuzzy PID controller is derived for all the locally linearized systems by replacing the conventional PI controller by a linear fuzzy logic controller, which has different gains for different linearization conditions. Within the guaranteed stability region, the controller gains can be optimally tuned by genetic algorithms. Simulation studies on a pole balancing robot and a multilink robot manipulator demonstrate the effectiveness and robustness of the proposed approach.

Iterative learning-based high-performance current controller for switched reluctance motors

Abstract: Switched reluctance motors (SRMs) are being considered for variable speed drive applications due to their simple construction and fault-tolerant power-electronic converter configuration. However, inherent torque ripple and the consequent vibration and acoustic noise act against their cause. Most researchers have proposed a cascaded torque control structure for its well-known advantages. In a cascaded control structure, accurate torque control requires accurate current tracking by the inner current controller. As SRM operates in magnetic saturation, the system is highly nonlinear from the control point of view. Developing an accurate current tracking controller for such a nonlinear system is a big challenge. Additionally, the controller should be robust to model inaccuracy, as SRM modeling is very tedious and prone to error. In this paper, we have reviewed various current controllers reported in the literature and discussed their merits and demerits. Subsequently, we have proposed and implemented a novel high-performance current controller based on iterative learning, which shows improved current tracking without the need for an accurate model. Experimental results provided for a 1-hp, 8/6-pole SRM, demonstrate the effectiveness of our proposed scheme.

PWM controller for synchronous rectifier of flyback power converter

Abstract: A synchronous rectifier PWM (SR-PWM) controller controls a MOSFET in response to the value of a secondary current and the status of a synchronous signal for both discontinuous and continuous operation mode. The secondary current is generated in a secondary circuit and is detected by two threshold-detection terminals of the SR-PWM controller. The SR-PWM controller produces the synchronous signal by detecting a switching signal of the transformer via a detection terminal of the SR-PWM controller. Furthermore, a delay-time is inserted after the MOSFET is turned off and before the next switching cycle starts to ensure a proper operation of the MOSFET. In one embodiment, an equivalent series resistance (ESR) of an output capacitor can be used as a sensor to detect the secondary current. Therefore, no additional current sensor is required and the efficiency can be improved.

Walking control of the humanoid platform KHR-1 based on torque feedback control

Abstract: This work presents three online controllers for maintaining dynamic stability of a humanoid robot using force/torque sensor. Those are damping controller, landing orientation controller and landing position controller. The legs of a humanoid robot are relatively long and serially connected with compliant force/torque sensor at the ankle. This architecture has the inherent characteristics of a lightly damped system. Most research on balance control overlook the deterministic vibration caused by structural compliance. In addition, the vibration was not positively considered to improve the characteristics of the system. Therefore, a simple inverted pendulum model with compliant joint is proposed. For this model, the damping controller that increases system damping is proposed as a balance controller. Furthermore, the performance of maintaining balance against external forces is experimentally shown. A landing orientation controller at the ankle joints is presented to manage fast and stable ground contact. A landing position controller is implemented in order to modify the prescribed trajectory of the swing foot and to reduce the landing impact during unexpected landing. The effectiveness of the proposed controllers is confirmed by walking experiments that has been applied on the KAIST humanoid robot platform KHR-1.

A robust hybrid current control for permanent-magnet synchronous motor drive

Abstract: Recently, the permanent-magnet synchronous motor (PMSM) has found widespread utilization in modern adjustable AC drives. This is achieved by using current-controlled voltage source inverter (VSI) systems. Because of its ease of implementation, fast current control response and inherent peak current-limiting capability, hysteresis current control is considered as the simplest technique used to control the motor currents for an AC machine. On the other hand, the ramp comparator controller has some advantages, such as limiting maximum inverter switching frequency to the carrier triangular waveform frequency and producing well-defined harmonics. In order to take advantage of the position features of both these two controllers, this paper presents the design and software implementation of a hybrid current controller. The proposed intelligent controller is a simultaneous combination and contribution of the hysteresis current controller and the ramp comparator. Comparisons using simulations on a 0.9-kW PMSM confirm that the proposed hybrid current controller gives better performance and has the advantage of conceptual simplicity. In particular, harmonic spectra of the stator current, obtained using a fast Fourier transform (FFT), are used for comparison purposes.

Controller and observer design for Lipschitz nonlinear systems

Abstract: We consider three related problems for stabilization of a class of Lipschitz nonlinear systems: (1) full-state feedback controller design, (2) observer design, and (3) output feedback controller design. Sufficient conditions are developed for the design of an exponentially stable linear full-state feedback controller and an exponentially stable nonlinear observer. Given that the sufficient conditions of the controller and observer problem are satisfied, we show that the proposed controller with estimated state feedback from the proposed observer will achieve exponential stabilization. Simulation results on an example are given to numerically verify the proposed designs.

Adaptive controller design for a linear motor control system

Abstract: Three different adaptive controllers for a permanent magnet linear synchronous motor (PMLSM) position-control system are proposed. The proposed controllers include: a backstepping adaptive controller, a self-tuning adaptive controller, and a model reference adaptive controller. The detailed systematic controller design procedures are discussed. A PC-based position control system is implemented. Several experimental results including transient responses, load disturbance responses, and tracking responses of square-wave, sinusoidal-wave, and triangular-wave commands are discussed and compared. The proposed system has a good robustness performance even though the inertia of the system is increased to 10 times. The experimental results validate the theoretical analysis.

DC motor velocity control through a DC-to-DC power converter

Abstract: This paper considers the development of a smooth "starter" for a DC motor based on a switch controlled DC-to-DC power converter of the "buck" type. The dynamic feedback controller is based on a suitable combination of passivity based control, flatness and a /spl Sigma/ - /spl Delta/ modulator implementation of the average designed controller. The scheme proposes an indirect regulation of the motor shaft speed by means of input current regulation on the "buck" converter circuit. As a consequence, the proposed feedback controller does not require the use of an electromechanical velocity sensor for measuring the angular velocity. The effectiveness of the proposed controller was verified by computer simulations using the P-Spice circuit simulation program.

Design of sliding mode controller for Lorenz chaotic system with nonlinear input

Abstract: In this paper, a sliding mode controller is presented to control Lorenz chaos subject to sector nonlinear input. The proposed control law is robust against both the uncertainty in system parameters and external disturbance. Simulation results show that the system state can be regulated to a specified point in the state space. It is also seen that the system still possesses the advantage of fast response and good transient performance even though the control input is nonlinear.

Linear Feedback Control

Abstract: The principle of feedback is introduced together with the popular proportional-integral-derivative controller in a general way and under different forms. Its influence on dynamics of simple linear processes is emphasized.

Primary-side-control power converter having a switching controller using frequency hopping and voltage and current control loops

Abstract: A power converter includes a switch and a controller. The switch switches electrical power in the power converter. The controller generates a switching signal to control the switch in response to a first feedback signal associated with a voltage control loop and a second feedback signal associated with a current control loop. The controller can also allow the switching frequency to hop from frequency to frequency according to a digital pattern.

Energy optimization of induction motor drives

Abstract: This paper deals with energy optimization of induction motor drives. In many applications, efficiency optimization of induction motors represents an important factor of control especially for autonomous electrical traction. In this paper different approaches to improve efficiency in vector controlled induction motor drives at steady state condition are compared. Three methods are possible to control the excitation: Methods based on induction motor losses, methods based on the use of look-up table and methods based on search controllers of minimum. We expose in this paper some methods, which use the search controller techniques. These techniques consist in changing flux level in small steps to keep the output power of the motor constant and find the minimum of input power. These controllers are efficient at steady state condition and do not require knowledge of motor and converter parameters. However, the search controller using the stator current instead of power give similar results to their using power. This technique is less complex and doesn't need measurement of PWM quantities. The proposed search controller is based on fuzzy algorithm. The advantages of this controller are compared with others known as Rosenbrock method and Golden section. Fuzzy search controller presents a good trade off between convergence time and oscillations of stator current ripple.