Min-Sung Koo

Output Feedback Regulation of a Chain of Integrators With an Unbounded Time-Varying Delay in the Input

We consider a problem of global regulation of a chain of integrators that has an unknown time-varying delay in the input. In contrast to the previous works in the literature, the upper bound of delay is not known. Moreover, there is no given information on the time-varying rate of delay, either. Using the dynamic gain approach inspired by the method in and the control structure of together, we construct an adaptive output feedback controller to solve the considered control problem. The only requirement is that the time-varying delay is bounded.

Global regulation of a class of feedforward and non-feedforward nonlinear systems with a delay in the input

In this paper, we propose a new state feedback controller using dynamic gain for input-delayed systems with high-order nonlinearity terms in both feedforward and non-feedforward forms. The controller design is based on a reduction method to remove the input delay and a gain scaling technique involving appropriate powers of high-order nonlinearity. As a result, more generalized systems containing feedforward and nonfeedforward terms with an input delay are regulated when the proposed power order condition of the nonlinear function is satisfied. An example is given to show the generality of our result over existing results.

Global Regulation of a Class of Uncertain Nonlinear Systems by Switching Adaptive Controller

There are several results on the stabilization or regulation of nonlinear systems with either triangular or feedforward nonlinearity. However, the existing results are applicable to their considered systems when the nonlinearity structure is known a priori. In this technical note, we propose a switching adaptive controller which tunes the dynamic gain depending on the nonlinearity structure. Thus, as a benefit over the existing results, the structural information on the nonlinearity is not needed. Although the linear growth condition is assumed, the rate of growth is unknown and arbitrary large with our control scheme.

Universal control of nonlinear systems with unknown nonlinearity and growth rate by adaptive output feedback

Over the past several years, triangular or feedforward nonlinear systems have received considerable attention and there are many independent results for stabilization or regulation problems. These results are often specifically targeted for only one of these systems and they are applicable when the system nonlinearity is known a priori. In this paper, we propose an adaptive output feedback controller coupled with switching logic to universally regulate both triangular and feedforward systems without recognizing the system nonlinearity. Moreover, with our control scheme, the linear growth rate is not required to be known.

Global asymptotic stabilization of a chain of integrators with a time-varying delay in the input by output feedback

In this paper, we consider a stabilization problem of a chain of integrators which allows a time-varying delay in the input. Among the plethora of papers on the stabilization of input-delayed chain of integrators, the existing results are only with constant delays. We show that with the proposed output feedback controller, the considered system can be globally asymptotically stabilized as long as the time-varying delay is bounded by a finite constant. That is, the time-varying rate is irrelevant in the stability result.

Measurement Feedback Control of a Class of Nonlinear Systems via Matrix Inequality Approach

We propose a measurement state feedback controller for a class of nonlinear systems that have uncertain nonlinearity and sensor noise. The new design method based on the matrix inequality approach solves the measurement feedback control problem of a class of nonlinear systems. As a result, the proposed methods using a matrix inequality approach has the flexibility to apply the controller. In addition, the sensor noise can be attenuated for more generalized systems containing uncertain nonlinearities.

Nonlinear Control of an Electromagnetic Levitation System Using High-gain Observers for Mmagnetic Bearing Wheels

In this paper, we develop a functional test model for magnetic bearing wheels. The functional test model is an electromagnetic levitation system that has three degree of freedom, which consists of one axial suspension from gravity and two axes gimbaling capability to small angels. A nonlinear controller with high-gain observers is proposed and the real-time experiment results show that the rotor is accurately levitated at the desired position and well-balanced, which is a suitable result for the potential use an magnetic bearing wheels. Also, the proposed scheme exhibits better performance when it is compared with the conventional PID control method.

Global Regulation of a Class of Nonlinear Systems with Time-varying Delays in the Input and States with Matrix Inequality and Non-predictor Methods

We deal with the regulation problem of nonlinear systems with time-varying delays in both the states and input. A new state feedback controller with dynamic gains is developed based on matrix inequality and non-predictor methods. The proposed control scheme is analyzed using the Razumikhin theorem, and its effectiveness is demonstrated with simulation results.

A Global Regulation Method of Nonlinear Systems with Unbounded Parameters Under State Feedback Frame

In this paper, we consider a regulation problem of nonlinear systems under two triangular conditions where there possibly exist unbounded parameters in the systems. We propose a state feedback controller with dynamic gains in order to deal with unbounded parameters based on the condition of the time-varying rate of the growing parameter. The analysis of our control scheme is carried out by Lyapunov stability method. Our control method is verified by simulation results.

Output Feedback Control of a Class of Nonlinear Systems with Sensor Noise Via Matrix Inequality Approach

We present an output feedback controller for a class of nonlinear systems with uncertain nonlinearity and sensor noise. The sensor noise has both a finite constant component and a time-varying component such that its integral function is finite. The new design and analysis method is based on the matrix inequality approach. With our proposed controller, the states and output can be ultimately bounded even though the structure of nonlinearity is more general than that in the existing results.