• Smart Structures and Systems
• /
• 제31권5호
• /
• pp.437-454
• /
• 2023

Real-time hybrid simulation (RTHS), which has the advantages of a substructure pseudo-dynamic test, is widely used to investigate the rate-dependent mechanical response of structures under earthquake excitation. However, time delay in RTHS can cause inaccurate results and experimental instabilities. Thus, this study proposes a model-based adaptive control strategy using a Kalman filter (KF) to minimize the time delay and improve RTHS stability and accuracy. In this method, the adaptive control strategy consists of three parts-a feedforward controller based on the discrete inverse model of a servohydraulic actuator and physical specimen, a parameter estimator using the KF, and a feedback controller. The KF with the feedforward controller can significantly reduce the variable time delay due to its fast convergence and high sensitivity to the error between the desired displacement and the measured one. The feedback control can remedy the residual time delay and minimize the method's dependence on the inverse model, thereby improving the robustness of the proposed control method. The tracking performance and parametric studies are conducted using the benchmark problem in RTHS. The results reveal that better tracking performance can be obtained, and the KF's initial settings have limited influence on the proposed strategy. Virtual RTHSs are conducted with linear and nonlinear physical substructures, respectively, and the results indicate brilliant tracking performance and superb robustness of the proposed method.

• 한국항행학회논문지
• /
• 제24권6호
• /
• pp.607-612
• /
• 2020

본 논문에서는 시변 지연 시간이 있는 선형 이산 시스템에 비구조화된 불확실성이 존재하는 경우에 대하여 안정조건을 다룬다. 안정조건은 리아프노프 안정 조건을 기반으로 유도되며, 이 새로운 조건에는 불확실성에 의한 영향이 포함되어 반영된다. 논문에서 고려된 불확실성은 그의 특성을 정확하게 파악할 수 없고, 단지 그 크기만을 알 수 있는 비구조화 형태로 반영된다. 이와 관련된 기존의 결과 대비하면, 안정성 기준을 적용할 수 있는 시스템을 확장할 수 있으며, 기 제안된 안정 조건보다 유연한 것으로 안정성 판정에 있어 더욱 효과적인 결과이다. 제안된 안정 조건들은 간단한 부등식의 형태로 표현되며, 시변 지연에 대한 영향과 불확실성에 대한 영향이 모두 수식에 포함되어 있다. 제안된 안정조건을 기존의 조건들과 비교한 결과를 수치 예제를 통하여 제시하며, 제안된 조건의 효용성과 우수성을 검증한다.

• 전기전자학회논문지
• /
• 제23권4호
• /
• pp.1265-1272
• /
• 2019

본 논문에서는 상수 입력지연을 갖는 이산시간 선형시스템을 위한 기존의 예측기 피드백 제어기의 구조적 모델 불확실성에 대한 강인성을 해석한다. 상수 입력지연을 1차 PdE (Partial difference Equation)로 모델링하여 입력지연을 PdE 상태변수로 대체하고 백스테핑 변환을 적용하여 목표 시스템을 구축한다. 목표 시스템을 기반으로 전체 상태변수를 포함하는 명시적 리아푸노프 함수를 구성하여 안정성이 유지되는 구조적 모델 불확실성의 최대 크기의 존재를 증명하고 예측기 피드백 제어기의 강인성을 확립한다. 모의실험을 통하여 모델 불확실성이 존재하는 경우에도 닫힌 루프 시스템의 안정성이 유지되는 것을 예증하고 예측기 피드백 제어기의 강인성을 검증한다.

• 한국지진공학회논문집
• /
• 제19권3호
• /
• pp.103-108
• /
• 2015

This work introduces a modal testing and analysis results of the mock-up for a layered stone pagoda. The pagoda has been horizontally excited by an impact hammer. As to the measured acceleration time responses, the first five lower mode shapes and natural frequency are extracted by the TDD technique. It is observed that the time delay of a shear wave occurs through friction surfaces. Such phenomena cannot be described by using the traditional analytical models such as a continuum cantilever beam model or a discrete shear building model. However, the time delay typically affects only the phases of the pagoda system. The frequencies of the pagoda system are not affected by such time delay. It is found in the first time that the layered stone pagoda system has a set of closely placed modes in near of natural frequency. It is believed that such modes are due to the friction characteristics in friction surfaces. Based on the stick-slip friction model, it seems that the one of the closely placed mode can be a self-excited one.

• Journal of Mechanical Science and Technology
• /
• 제19권11호
• /
• pp.1975-1987
• /
• 2005

An input time delay always exists in practical systems. Analysis of the delay phenomenon in a continuous-time domain is sophisticated. It is appropriate to obtain its corresponding discrete-time model for implementation via digital computers. In this paper a new scheme for the discretization of nonlinear systems using Taylor series expansion and the zero-order hold assumption is proposed. The mathematical structure of the new discretization method is analyzed. On the basis of this structure the sampled-data representation of nonlinear systems with time-delayed multi-input is presented. The delayed multi-input general equation has been derived. In particular, the effect of the time-discretization method on key properties of nonlinear control systems, such as equilibrium properties and asymptotic stability, is examined. Additionally, hybrid discretization schemes that result from a combination of the scaling and squaring technique (SST) with the Taylor series expansion are also proposed, especially under conditions of very low sampling rates. Practical issues associated with the selection of the method's parameters to meet CPU time and accuracy requirements, are examined as well. A performance of the proposed method is evaluated using a nonlinear system with time delay maneuvering an automobile.

• 전자공학회논문지SC
• /
• 제39권2호
• /
• pp.95-103
• /
• 2002

본 논문에서는 상태에 시변 시간지연을 가지는 이산 선형 시스템에 대한 H/sub ∞/ 제어기 설계문제를 다룬다. H/sub ∞/ 제어기가 존재할 충분조건과 설계방법에 대해 논의한다. 본 논문에서 다루는 H/sub ∞/ 제어기법은 상태궤환 제어기로서 시변 시간지연의 상한값과 S-procedure를 이용한다. 또한, 변수 치환, Schur 여수정리 등을 이용하여 충분조건을 모든 변수에 대한 선행 행렬 부등식(linear matrix inequality)으로 표현한다.

• Journal of Power Electronics
• /
• 제19권4호
• /
• pp.1000-1010
• /
• 2019

The use of internal-model-based linear controller, such as resonant controller, is a well-established technique for the current control of grid-connected systems. Attractive properties for resonant controllers include their two-sequence tracking ability, the simple control structure, and the reduced computational burden. However, in the case of continuous-designed resonant controller, the transient performance is inevitably degraded at a low switching frequency. Moreover, available design methods for resonant controller is not able to realize the direct design of transient performances, and the anticipated transient performance is mainly achieved through trial and error. To address these problems, the zero-order-hold (ZOH) characteristic and inherent time delay in digital control systems are considered comprehensively in the design, and a corresponding hold-equivalent discrete model of the grid-connected converter is then established. The relationship between the placement of closed-loop poles and the corresponding transient performance is comprehensively investigated to realize the direct mapping relationship between the control gain and the transient response time. For the benefit of automatic tuning and real-time adaption, analytical expressions for controller gains are derived in detail using the required transient response time and system parameters. Simulation and experimental results demonstrate the validity of the proposed method.

• 한국지능시스템학회:학술대회논문집
• /
• 한국퍼지및지능시스템학회 2005년도 추계학술대회 학술발표 논문집 제15권 제2호
• /
• pp.125-128
• /
• 2005

This paper presents a simple methodolosy that makes a continuous-time nonlinear system chaotic using fuzzy control. The nonlinear system is represented by the T-S fuzzy model. Then, a fuzzy controller makes the T-S fuzzy model, which could be stable or unstable, bounded and chaotic. The verification of chaos in the closed-loop system is done by the following procedures. We establish an asymptotically approximate relationship between a continuous-time T-S fuzzy system with time-delay and a discrete-time T-S fuzzy system. Then, we verify the chaos in the closed-loop system by applying the Marotto theorem to its associated discrete-time T-S fuzzy system.

• 한국지능시스템학회:학술대회논문집
• /
• 한국퍼지및지능시스템학회 2004년도 춘계학술대회 학술발표 논문집 제14권 제1호
• /
• pp.115-118
• /
• 2004

In this paper, a systematic design approach based on parallel distributed compensation techniques is proposed for anticontrol of chaos in a general continuous-time Takagi-Sugeno (TS) fuzzy system. The verification of chaos in the controlled continuous-time TS fuzzy system is done by the following procedure. First, we establish an asymptotically approximate relationship between a continuous-time TS fuzzy system with time-delay and a discrete-time TS fuzzy system. Then Marotto theorem is applied. The boundedness in the controlled continuous-time TS fuzzy system is also proven via its associated discrete-time TS fuzzy system.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1989년도 하계종합학술대회 논문집
• /
• pp.134-137
• /
• 1989

A digital controller for a discrete-data control system can take many forms. For example, they can be passive RC networks, general purpose digital computers, special purpose of mini-computer, and delay lines. With the recent advent of the microprocessor, its use as a digital controller is evident. This work discusses the hardware and software development of a microprocessor-based digital controller for a discrete-data control system. A second-order, Type 1 system is implemented on an analog computer; a Intel 80-286 microprocessor is used to implemented the controller; and, output response are obtained for step, ramp, and parabolic inputs. The results demonstrate that the microprocessor has potential as a digital controller. Finally, a brief discussion on the results indicate possible areas of improvement of the controller and future investigation.