• International Journal of Control, Automation, and Systems
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• v.3 no.4
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• pp.640-645
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• 2005

Closed-loop model-free optimization of positive feedback time delay controllers for dominant time delay systems is presented. Iterative feedback tuning (IFT) is applied to the tuning of positive feedback time delay controller. Three experiments are carried out to perform the model-free gradient descent optimization. The initial controller parameters and duration in specifying the cost function are suggested. The effects of step size, filter function and time weighting function on the performance of the optimized controlled are given. Simulation and experimental studies are included to demonstrate the effectiveness of the tuning scheme.

• Proceedings of the KIEE Conference
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• 2008.04a
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• pp.213-214
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• 2008

This paper considers design of a robust controller that alleviates disturbance effects and compensates performance degradation of plants with time-delay. Disturbance observer(DOB) approach as a tool of robust control has been widely employed in industry. However, since the time-delay makes the plant non-minimum phase, classical DOB cannot be applied directly to the time-delay system. By using a new DOB structure for non-minimum phase systems together with the Smith Predictor, we propose a new control algorithm for reducing the effects of disturbance and time-delay of the system.

• Journal of Power Electronics
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• v.12 no.1
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• pp.98-103
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• 2012

This paper presents a digital pulse width modulator (DPWM) with a reduced digital modulation delay (a transport delay of the modulator) during the transient response of power converters. During the transient response operation of a power converter, as a result of dynamic variations such as load step-up or step-down, the closed loop controller will continuously adjust the duty cycle in order to regulate the output voltage. The larger the modulation delays, the larger the undesired output voltage deviation from the reference point. The three conventional DPWM techniques exhibit significant leading-edge and/or trailing-edge modulation delays. The DPWM technique proposed in this paper, which results in modulation delay reductions, is discussed, experimentally tested and compared with conventional modulation techniques.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.108.1-108
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• 2001

A time-delay feedback control approach is proposed for making a given stable continuous-time Takagi-Sugeno (TS) fuzzy system chaotic, which is based on the fuzzy feedback linearization and a suitable approximate relationship between a time-delay differential equation and a discrete map. The time-delay feedback controller, chosen among several candidates, is a simple sinusoidal function of the delay states of the system, which has small amplitude. This approach is mathematically proven for rigorous generation of chaos from stable continuous-time TS fuzzy systems, where the generated chaos is in the sense of Li and Yorke. Numerical examples are included to visualize the theoretical analysis and the controller design.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.10
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• pp.895-901
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• 2012

The stability robustness problem of linear discrete systems with time-varying unstructured uncertainty of delayed states with time-varying delay time is considered. The proposed conditions for stability can be used for finding allowable bounds of timevarying uncertainty and delay time, which are solved by using LMI (Linear Matrix Inequality) and GEVP (Generalized Eigenvalue Problem) known as powerful computational methods. Furthermore, the conditions can imply the several previous results on the uncertainty bounds of time-invariant delayed states. Numerical examples are given to show the effectiveness of the proposed algorithms.

• International Journal of Control, Automation, and Systems
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• v.6 no.2
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• pp.263-268
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• 2008

An improved linear matrix inequality (LMI) representation of delay-independent $H_2$ performance analysis is introduced for linear delay systems with delays of any size. Based on this representation we propose a new $H_2$ memoryless state feedback design. By introducing a new matrix variable, the new LMI formulation enables us to parameterize memoryles s controllers without involving the Lyapunov variables in the formulations. By using a parameter-dependent Lyapunov function, this new representation proposed here provides us the results with less conservatism.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.49-57
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• 2016

A modular multilevel converter is widely adapted for a high-voltage direct current power transmission system. This study proposes a design methodology for a novel digital control that mitigates the negative effects caused by time delay, including communication transport delay for a modular multilevel converter. The modeling and negative effect of time delay are analyzed theoretically in a frequency domain, and its compensation methodology based on an inverse model is described fully with practical considerations. The proposed methodology is verified through several simulation results using a modular 21-level converter system.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.7
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• pp.1158-1168
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• 1994

A variable structure control scheme(VSCS) with sliding mode that can be applied to the process with input/output(I/O) delay is proposed and its control performances is evaluated. The proposed VSCS with and output feedback scheme comprises a variable structure controller, a servo dynamic for tracking the set-poing, and a Smith predictor for compensating the effects of time delay. The robustness against the parameter variations and external disturbances can be achieved by the proposed VSCS even when the controlled process includes I/O delay. And the desired transient response is obtained by simple adjustment of the coefficients of the switching surface equation.

• International Journal of Control, Automation, and Systems
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• v.4 no.6
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• pp.682-688
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• 2006

This paper deals with the delay-dependent and rate-independent stabilization of systems with multiple unknown time-varying delays and time-varying structured uncertainties. All the linear matrix inequalities based conditions are derived by employing free-weighting matrices to express the relationships between the terms in the Leibniz-Newton formula. The criteria do not require any tuning parameters. Numerical examples demonstrate the validity of the method.

• International Journal of Control, Automation, and Systems
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• v.1 no.1
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• pp.127-133
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• 2003

This paper proposes a new numerical method to check the stability of a general class of time delay systems. The proposed method checks whether there are characteristic roots whose real values are nonnegative through two steps. Firstly, rectangular bounds of characteristic roots whose real values are nonnegative are computed. Secondly, the existence of roots inside the bounds are checked using the numerical computation of argument principles. An adaptive discretization is proposed for the numerical computation of argument principles.