Reduced-order Disturbance Observer Research Articles

Study on the Congestion Controller for Timedelay Networked Control Systems with External Disturbances

Abstract A successive approximation approach (SAA) is developed to obtain a new congestion controller for the singularly perturbed time-delay networked control systems affected by external disturbances. Based on the slow-fast decomposition theory of singular perturbations, the system is first decomposed into a fast non-delay subsystem and a slow time-delay subsystem with disturbances. Then, the perturbation approach is proposed to solve the slow-time scale time-delay optimal control problem, and the feedforward compensation technique is used to reject the external disturbances. We obtain the conditions of existence and uniqueness of the feedforward and feedback composite control (FFCC) law. The FFCC law consists of linear analytic functions and a time-delay compensation term which is a series sum of adjoint vectors. The linear analytic functions can be found by solving a Riccati matrix equation and a Sylvester equation respectively. The compensation term can be approximately obtained by an iterative formula of adjoint vector equations. A reduced-order disturbance observer is constructed to make the FFCC law physically realizable. Numerical examples are presented to illustrate the effectiveness and robustness of the proposed design approach.

Nonlinear Model-Predictive Control of an Electro-Pneumatic Clutch for Truck Applications

AbstractThis paper presents a nonlinear model predictive control design for an electropneumatic clutch for heavy trucks, which is required at start-up or during gear shifts to disconnect the combustion engine from the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque transmitted through the powertrain. The main idea of the used NMPC algorithm consists in a minimisation of the tracking error at the end of the prediction horizon. That way the computation load can be kept relatively small. A reduced-order disturbance observer estimates the internal pressure, which is usually not measured in truck applications. Thereby, high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the proposed control structure is emphasised by experimental results from a dedicated test rig.

Control of Pushing and Pulling Motion of a Wheeled Inverted Pendulum Based on a Reduced Order Observer

In this paper the control of the I-PENTAR, a wheeled inverted pendulum type robot being developed by the authors, for pushing and pulling a cart is examined. To control the movement of the object is being pushed or pulled, information regarding several external parameters, eg. Mass of the object and friction components, must be considered. In most cases these parameters are not known before hand or may change. One method of compensating for these unknown or changing external parameters is to represent them as an equivalent reaction force from the object. Our first subject of this research is to design a disturbance observer to estimate and compensate the equivalent force. Another situation is of pushing and pulling a cart with the inverted pendulum type robot traversing an inclined plane. As an initial step to solving this problem in this paper, a force application method using whole body motion of the inverted pendulum type robot is proposed. The whole body motion means changing the balance of the robot to attain a certain desired force. During application of this force the robot must remain in its stabilized or balanced state. For an inverted pendulum type robot, this instantly poses a major problem. To solve the problem, a reduced order disturbance observer is used in this paper to estimate the force applied by the robot. On the other hand, I-PENTAR is targeted for environments where it can interact with humans and so safety is a major concern. For example, in the event that an obstacle bumps the robot as it is pushing the cart, a large and sudden force estimator based on the disturbance observer is also built into the controller. Simulation and experiments using the reduced order disturbance observer and evaluation of the whole body motion force control are presented.

Saturating composite disturbance-observer-based control and H ∞ control for discrete time-delay systems with nonlinearity

This note is concerned with a saturating composite disturbance-observer-based control (DOBC) and H∞ control for a class of discrete time-delay systems with nonlinearity and disturbances. The disturbances are supposed to include two parts. One in the input channel is generated by an exogenous system with uncertainty, which can represent the harmonic signals with modeling perturbations. The other is supposed to have the bounded H2 norm, which can represent parametric uncertainties and external disturbance existing in the controlled object. The design approaches of reduced-order disturbance observer are presented for the estimation of the disturbance. By composite control law with saturation, the disturbances can be rejected and attenuated, simultaneously, the desired dynamic performances can be guaranteed for discrete time-delay systems with known and unknown nonlinear dynamics, respectively. Simulation for a flight control system is provided to show the effectiveness of the proposed scheme compared with the previous schemes.

IDA Passivity-Based Trajectory Control of an Overhead Travelling Crane

In this paper, a passivity-based control scheme is proposed for the two main translational axes of an overhead travelling crane to provide an active damping of crane load oscillations. The decentralised control structure consists of independent axis controllers, which are adapted to the varying rope length using gain-scheduling techniques. The tracking capabilities concerning desired trajectories for the crane load in the xyz-workspace can be improved by introducing feedforward control based on an inverse system model. Furthermore, a nonlinear reduced-order disturbance observer is utilised for the compensation of nonlinear friction forces. The achieved control performance is shown by selected experimental results obtained from an implementation on a test rig.

Passivity-Based Control of an Overhead Travelling Crane

In this paper, a passivity-based control scheme is proposed for the two main translational axes of an overhead crane to provide an active damping of crane load oscillations. The decentralised control structure consists of independent axis controllers, which are adapted to the varying rope length using gain-scheduling techniques. The tracking capabilities concerning desired trajectories for the crane load in the xy-plane can be improved by introducing feedforward control based on an inverse system model. Furthermore, a reduced-order disturbance observer is utilised for the compensation of nonlinear friction forces. The achieved control performance is shown by selected experimental results obtained from an implementation on a 5 t-overhead travelling crane.

Precision Tracking of a Rotating Shaft With Magnetic Bearings by Nonlinear Decoupled Disturbance Observers

Static offset and synchronous vibration are obstacles to precision tracking of a rotating shaft supported by active magnetic bearings (AMBs). A constant and harmonic disturbance observer is an effective approach to estimate and suppress these undesired effects. A disturbance observer is particularly well-suited for tracking applications since it can directly compensate for AMB force nonlinearity. In this paper, we propose a nonlinear reduced-order disturbance observer which is incorporated into a flatness-based tracking control. Since a reduced-order approach requires knowledge of velocity, we design an inner-loop velocity observer which can achieve convergence at a faster rate than the disturbance observer. This hierarchical observer simplifies the control because disturbance estimates are decoupled for each degree of freedom (DOF) and disturbance compensation is modularized. Experimental results on a commercially available 5-DOF system demonstrate accurate position tracking over the bearing air gap for a wide range of shaft velocities.