• Journal of Power Electronics
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• 제16권4호
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• pp.1526-1540
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• 2016

This work mainly discusses an accurate and fast islanding detection based on fractional wavelet packet transform (FRWPT)for multibus microgrid systems. The proposed protection scheme uses combined desirable features retrieved from discrete fractional Fourier transform (FRFT) and wavelet packet transform (WPT) techniques, which provides precise time-frequency information on minute perturbation signals introduced in the system. Moreover, this study focuses on the design of decoupling control with a distributed controller based on state feedback for the efficient operation of microgrid systems that are transitioning from the grid-connected mode to the islanded mode. An IEEE 9-bus test system with inverter based distributed generation (DG) units is considered for islanding assessment and smooth operation. Finally, tracking errors are greatly reduced with stability improvement based on the proposed controller. FRWPT based islanding detection is demonstrated via a time domain simulation of the system. Simulated results show an improvement in system stability with the application of the proposed controller and accurate islanding detection based on the FRWPT technique in comparison with the results obtained by applying the wavelet transform (WT) and WPT.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제11권4호
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• pp.275-279
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• 2011

In this paper, an observer-based sampled-data controller of linear system is proposed for the wave energy converter. Based on the sampled-data observer, the controller is design. In the closed-loop system with controller, it obtains the norm inequality between the continuous-time state variable and the discrete-time one. Using the norm inequality, sufficient condition is derived for the asymptotic stability of the closed-loop system and formulated in terms of linear matrix inequality. Finally, the wave energy converter simulation is provided to verify the effectiveness of the proposed technique.

• Journal of Biosystems Engineering
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• 제21권3호
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• pp.283-292
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• 1996

Automatic guidance of farm tractors would improve productivity by reducing operator fatigue and increasing machine performance. To control tractors within $\pm$5cm of the desired path, fuzzy and adaptive steering controllers were developed to evaluate their characteristics and performance. Two input variables were position and yaw errors, and a steering command was fed to tractor model as controller output. Trapezoidal membership functions were used in the fuzzy controller, and a minimum-variance adaptive controller was implemented into the 2-DOF discrete-time input-output model. For unit-step and composite paths, a dynamic tractor simulator was used to test the controllers developed. The results showed that both controllers could control the tractor within $\pm$5cm error from the defined path and the position error of tractor by fuzzy controller was the bigger of the two. Through simulations, the output of self-tuning adaptive controller was relatively smooth, but the fuzzy controller was very sensitive by the change of gain and the shape of membership functions. Contrarily, modeling procedure of the fuzzy controller was simple, but the adaptive controller had very complex procedure of design and showed that control performance was affected greatly by the order of its model.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.228-231
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• 2000

The active vibration control of laminated composite shell has been performed with the optimized sensor/actuator system. PVDF film is used fur the material of sensor/actuator. Finite element method is utilized to model the whole structure including the piezoelectric sensor/actuator system, The distributed selective modal sensor/actuator system is established to prevent the adverse effect of spillover. In the finite element discretization process, the nine-node shell element with five nodal degrees of freedoms is used. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator profiles are optimized for the first and the second modes suppression of singly curved cantilevered composite shell structure. Discrete LQG method is used as a control law. The real time vibration control with profile optimized sensor/actuator system has been performed. Experimental result shows successful performance of the integrated structure for the active vibration control.

• 전자공학회논문지C
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• 제36C권12호
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• pp.69-77
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• 1999

본 논문에서는 간편 간접추론방법을 이용한 퍼지 디지털 PID 제어기의 설계 방법을 제안하였다. 제안된 퍼지 제어기는 선형 디지털 PID 제어기에서 유도하였으며, 간편 간접추론을 이용한 퍼지화부, 제어규칙 베이스 및 퍼지화부의 설계방법을 설명하였다. 제안된 퍼지 제어기는 종래의 디지털 PID 제어기를 기초로 설계하였으므로 구조를 이해하기 쉽고, 퍼지입력에 의한 비선형 특성을 가지므로 선형 및 비선형 플랜트에 적응 능력을 가진다. 또한 각 입력변수 별로 간편 간접추론방법을 사용하여 추론하므로 고속 추론이 가능하고, 퍼지규칙의 수가 증가하여도 쉽게 적용 가능하다. 제안된 제어기의 성능을 D. Misir 등이 사용한 선형 및 비선형 플랜트에 모의 실험하여 효용성을 입증하였다.

• 한국정보통신학회논문지
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• 제4권3호
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• pp.619-625
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• 2000

많은 제어기법들이 이산시간영역제어계의 제어성능을 개선시키기 위해서 제안되고 있다. 위치제어계에서 일반적으로 제어기의 출력이 제어대상의 입력으로 사용된다. 그러나 불필요한 잡음이 제어기의 출력에 포함된다. 그러므로 이러한 잡음을 제거하기 위해서 전치보상기를 사용할 필요가 있다. 본 논문에서 전치보상기를 갖는 확대 I-PD 제어계를 구성하였고 이 전치보상기와 I-PD 제어기를 신경망으로 설계하였다. 그리고 전치보상기와 I-PD제어기의 계수들이 계의 응답특성들이 어떤 조건 하에서 변할 때 계의 희망하는 응답이 되도록 자동적으로 조정되도록 하였다.

• 한국지능시스템학회논문지
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• 제13권1호
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• pp.24-30
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• 2003

본 논문에서는 혼돈 시스템을 제어하기 위해 웨이블릿 신경 회로망을 예측기로 사용하여 일반형 예측 제어기를 설계하는 방법을 제안한다. 본 논문의 방법에서는 웨이블릿 신경 회로망의 각 파라미터에 대한 학습은 예측 오차를 이용한 경사 하강법에 의해 수행되며, 제어 신호는 웨이블릿 신경 회로망의 출력과 기준 신호 사이의 제어 오차를 최소화함으로써 생성된다. 한편, 모의 실험을 통해 본 논문에서 제안한 제어기를 각각 연속 시간 혼돈 시스템인 Doffing 시스템과 이산 시간 혼돈 시스템인 Henon 시스템에 적용하여 제어기의 효율성을 확인하고 아울러 신경 회로망을 이용한 예측 제어의 결과와 비교함으로써 제어기의 우수성을 검증한다

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1659-1663
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• 1991

A new control design methodology is presented here which is based on a nonlinear time-series reference model. It is indicated by highly nonlinear simulations that such designs successfully stabilize troublesome aircraft maneuvers undergoing large changes in angle of attack as well as large electric power transients due to line faults. In both applications, the nonlinear controller was significantly better than the corresponding linear adaptive controller. For the electric power network, a flexible a.c. transmission system (FACTS) with series capacitor power feedback control is studied. A bilinear auto-regressive moving average (BARMA) reference model is identified from system data and the feedback control manipulated according to a desired reference state. The control is optimized according to a predictive one-step quadratic performance index (J). A similar algorithm is derived for control of rapid changes in aircraft angle of attack over a normally unstable flight regime. In the latter case, however, a generalization of a bilinear time-series model reference includes quadratic and cubic terms in angle of attack. These applications are typical of the numerous plants for which nonlinear adaptive control has the potential to provide significant performance improvements. For aircraft control, significant maneuverability gains can provide safer transportation under large windshear disturbances as well as tactical advantages. For FACTS, there is the potential for significant increase in admissible electric power transmission over available transmission lines along with energy conservation. Electric power systems are inherently nonlinear for significant transient variations from synchronism such as may result for large fault disturbances. In such cases, traditional linear controllers may not stabilize the swing (in rotor angle) without inefficient energy wasting strategies to shed loads, etc. Fortunately, the advent of power electronics (e.g., high-speed thyristors) admits the possibility of adaptive control by means of FACTS. Line admittance manipulation seems to be an effective means to achieve stabilization and high efficiency for such FACTS. This results in parametric (or multiplicative) control of a highly nonlinear plant.

• Journal of Power Electronics
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• 제19권4호
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• pp.869-880
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• 2019

Due to the inherent feedforward of load current, capacitor current (CC) control shows a fast transient response that makes it suitable for the power supplies used in various portable electronic devices. However, considering the effect of the outer voltage loop, the stable range of the duty-cycle is significantly diminished in CC controlled buck converters. To investigate the stability effect of the outer voltage loop on buck converters, a CC controlled buck converter with a proportion-integral (PI) compensator is taken as an example, and its second-order discrete-time model is established. Based on this model, the instability caused by the duty-cycle is discussed with consideration of the outer voltage loop. Then the dynamical effects of the feedback gain of the PI compensator and the equivalent series resistance (ESR) of the output capacitor on the CC controlled buck converter with a PI compensator are studied. Furthermore, the design-oriented closed-loop stability criterion is derived. Finally, PSIM simulations and experimental results are supplied to verify the theoretical analyses.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1311-1318
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• 2012

본 논문에서는 차량 전복 방지를 위해 강인 제어기를 설계하고 적용하는 방법에 대해 제시한다. 운행 중인 차량은 속도나 무게중심과 같은 파라미터 변화가 쉽게 발생하는데, 차량 전복 방지 제어기가 파라미터 변화에 대해 강인하게 설계된다면 차량 전복 방지 성능을 더욱 향상시킬 수 있다. 이를 위해 본 논문에서는 이산시간영역에서 LMI 를 이용하여 $H_2$ 및 $H_{\infty}$ 강인제어기를 설계하고, 실험에 대한 신뢰도가 높은 차량 시뮬레이션 패키지인 CarSim 에서 차량 전복 방지를 위한 제어기의 성능을 검증한다.