Output Feedback Control Algorithm Research Articles

Two-degree-of-freedom output feedback controllers for nonlinear processes

In this work, a nonlinear output feedback control algorithm is proposed, in the spirit of model-state feedback control. The structure provides state estimates using a process model, the measured output, and the residual between the model output and the measured output. These estimates will track the process states at a rate determined by a set of tunable parameters. An algebraic transformation of the state estimates is incorporated in the control structure to ensure that the input/output gain of the observer matches the model upon which the static state feedback control law is based. The transformed states are then used in the control law. This leads to a controller of minimal order possessing integral action. The control structure is shown to have the same properties as the standard model-state feedback structure. The resulting algorithm is a two-degree of freedom control law, in the sense that the control action is not a function of the error only, but the output and the set point are processed in different ways. Finally, a simulation example using an exothermic CSTR operating at an open-loop unstable steady state is used to demonstrate the closed-loop performance of the proposed method.

ADAPTIVE TUNING TO A BIFURCATION FOR NONLINEAR SYSTEMS WITH HIGH RELATIVE DEGREE

The problem of tuning of adjustable parameters of a nonlinear system to unknown values ensuring the desired bifurcation properties is introduced. An adaptive output feedback control algorithm providing solution of the problem for nonlinear systems with high relative degree from adjusted parameters to measured output is proposed. Several application examples are presented.

Adaptive tuning of bifurcation for time-varying nonlinear systems

An adaptive output feedback control algorithm providing exact tuning of adjustable parameters to unknown values, which ensure for the system desired bifurcation properties is proposed. Algorithm is based on passification based adaptive observer design. Several application examples are presented and illustrated by simulation results.

Seismic structural control using an electric servomotor active mass driver system

AbstractThis study investigates an electric‐type active mass driver (AMD) system for structural vibration control. Composed primarily of an electric servomotor and a ball screw, the electrical AMD system is free from noise problems, oil leakage, and labor‐intensive maintenance that commonly are associated with hydraulic AMD systems. The desired stroke amplification of the mass and the power demand of the servomotor can be adjusted via the ball screw pitch, which in turn affects the effectiveness and efficiency of the system. Meanwhile, an instantaneous optimal direct output feedback control algorithm is adopted. Numerical simulation is performed using a five‐story steel frame as the object structure under the conditions of the 1940 El Centro earthquake. The AMD system proves to be effective and efficient within a certain range of the ball screw pitch. The reductions of the peak responses can reach as high as 70% if properly designed. Requiring only the velocity measurement of the top floor for on‐line feedback control, the proposed control algorithm is recommended for practical implementation. Copyright © 2004 John Wiley & Sons, Ltd.

Power control of a doubly fed induction machine via output feedback

A new output feedback control algorithm for a doubly fed induction machine (DFIM) is presented. The asymptotic regulation of active and reactive power is achieved by means of direct closed-loop control of active and reactive components of the stator current vector, presented in a line-voltage-oriented reference frame. To get the maximum generality of the solution, the usual assumption of negligible stator resistance is not made. A full-order DFIM model is used for the control algorithm development. The proposed control system is robust with respect to bounded machine parameter variations and errors on rotor position measurement. In the paper, it is also shown how the proposed current control algorithm can be modified in order to achieve asymptotic active current tracking and zero reactive current stabilization during steady state. An extension for the speed control objective and output EMF control during the excitation–synchronization stage are also presented. Simulation and experimental tests demonstrate high dynamic performance and robustness of the control algorithm for typical operating conditions. The proposed controller is suitable for both energy generation and electrical drive application with restricted speed variation range.

Adaptive control of linear time-varying systems

Single-input single-output uncertain linear time-varying systems are considered, which are affected by unknown bounded additive disturbances; the uncertain time-varying parameters are required to be smooth and bounded but are neither required to be sufficiently slow nor to have known bounds. The output, which is the only measured variable, is required to track a given smooth bounded reference trajectory. The undisturbed system is assumed to be minimum-phase and to have known and constant relative degree, known sign of the ‘high frequency gain’, known upper bound on the system order. An adaptive output feedback control algorithm is designed which assures: (i) boundedness of all closed-loop signals; (ii) arbitrarily improved transient performance of the tracking error; (iii) asymptotically vanishing tracking error when parameter time derivatives are L 1 signals and disturbances are L 2 signals.

Experimental Investigation of Vibration Suppression Control for 2 Link Flexible Robot Arm by Sliding Mode Control.

A reduced order output feedback control algorithm based on a low order modeling methodology for suppressing the vibration and obtaining the high speed, high precision positioning of flexible robot arm is proposed and discussed. The proposed low order modeling methodology gives no modal truncation error and makes it possible to vary the mode shapes of the link according to the change of the boundary conditions due to the feedback gains and the payload at the tip of the arm. Furthermore, this methodology can take into account not only the flexibility of links but also the flexibility of joints. The reduced order output feedback control algorithm is designed by the combination of sliding mode controller and suboptimal output feedback controller so as to achieve both the damping of the system vibration and the stabilization at the same time. The results of numerical simulation and of experiment for a two-link robot arm model are compared. And they prove that the proposed modeling methodology is able to describe the dynamic behaviors of the arm, and the controller designed applying the suboptimal output feedback sliding mode control is able to control the arm quite well.

Seismic structural control using a novel high-performance active mass driver system

To resolve difficulties encountered by current technology in structural control against earthquakes, this study proposes a novel high-performance active mass driver (HP-AMD) system. Based on an active mass driver system, the device is integrated with a mechanical pulley system for stroke amplification to enhance simultaneously efficiency and save power. Meanwhile, an instantaneous optimal direct output feedback control algorithm is derived alongside the hardware development. Numerical simulation is performed using a five-storey steel frame as the object structure under the 1940 El Centro earthquake. To gain further insight into the HP-AMD system, the effects of stroke amplification as well as damper weight on system performance are explored. Analysis results demonstrate that the proposed HP-AMD system is a promising means to improving current active structural control techniques. Copyright © 2000 John Wiley & Sons, Ltd.

Vibration Suppression Control of 2 Link Flexible Robot Arm by Sliding Mode Control.

A low order modeling methodology and a reduced order output feedback control algorithm for suppressing the vibration and obtaining the high speed, high precision positioning of flexible robot are presented and discussed. The low order modeling methodology gives no modal truncation error and make it possible to vary the mode shapes of the link according to the change of the boundary conditions due to the feedback gains and the payload at the tip of the arm. The reduced order output feedback sliding mode control algorithm is designed by the combination of sliding mode controller and suboptimal output feedback controller so as to achieve both the damping of the system vigration and the stabilization at the same time. According to the presented method, the vibration suppression control of the two-link robot arm is realized by only 6 sensors, that is, this robot arm model is reduced to 6 output and 2 control input noncollocated system in spite of 34 state variables system.

Use of the active member concept in vibration mitigation of seismic structures

This paper aims to investigate the possible use of a control system that combines the concept of active members and a direct output feedback method to mitigate the seismic vibration of civil engineering structural systems. An active member, according to the definition used in this paper, is an added structural member in which an actuator, a sensor and a simple controller are highly integrated. By integrating these fundamental control devices together, the active members will be less vulnerable to environmental influence; moreover, each active member can be used as an independent control mechanism. In this study, an output feedback control algorithm called the Modal Truncated Output Feedback (MTOF), suitable for the active member control, is adopted. With this algorithm, the failure or malfunction of one active member will not impair the entire control system. A numerical example of the shear building type is used to demonstrate the proposed control system. It is shown that the concept of active members and the MTOF control algorithm together form a very stable, effective, and reliable control system for vibration control of seismic structures.

Exponentially Stable Output Feedback Control of Induction Motor

A new nonlinear output feedback control algorithm is designed for a full order model of an induction motor. The control algorithm is based on the concept of indirect field orientation and guarantees global exponential tracking of speed and flux reference trajectories in presence of unknown constant load torque. Besides, it provides new properties on system dynamic performance and has simple implementation.

Design of a permanent/electromagnetic magnetic bearing-controlled rotor system

This study proposes design procedures for the permanent-magnet-biased magnetic bearings (PEMBs) in rotor systems. Many aspects of designing magnetic bearings are discussed, e.g. the selection of a permanent magnet material, dimensions of electromagnets and permanent magnets, gap length, load capacity and maximum Ampere-turns. Linearization and DC current driver are the two constraints for determining feasible designs. According to an analytical model with a rigid body assumption for the rotor-bearing system, a decentralized output feedback control algorithm is employed to control this inherently unstable magnetic suspension rotor system. Experimental results indicate that the controlled rotor performs well at rotor speeds up to 12,000 rpm.

Optimal discrete-time structural control using direct output feedback

An optimal direct discrete-time output feedback control algorithm is developed. According to the proposed algorithm, optimal discrete-time output feedback gain is derived through a variational process such that a certain prescribed quadratic performance index is minimized. It is verified that the classical optimal discrete-time state feedback control algorithm is just a particular case of the proposed control algorithm. With the introduction of special matrix operations, optimal output feedback gain is obtained systematically by solving simultaneously linear algebraic equations iteratively. Control forces are then generated directly from output measurements multiplied by the pre-calculated shift-invariant output feedback gain. A small number of sensors and controllers, and simple on-line calculation make the proposed algorithm favorable to real-time control implementation. Numerical verification is illustrated by the control of a single degree-of-freedom (DOF) and a three degree-of-freedom structure subjected to real earthquake excitations. Differences between discrete-time and continuous-time output feedback control are discussed.

A position controller of a one‐link flexible robot arm

Abstract In this paper, a robust simplified adaptive controller is proposed to control the motion of a one‐link flexible robot arm. In the proposed controller, the natural frequency of the first vibration mode is identified, and the output feedback control algorithm with time‐varying gains is employed. The stability of the controlled system is proved through the use of the second Liapunov's theorem. Then, experiments are carried out to evaluate the perfromance of the proposed controller. It is found from the experimental results that the performance of the adaptive controller is satisfactory. Also, it is shown that the proposed controller is robust to parameter errors or variations.