• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2289-2297
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• 2017

Applying a periodic load torque to an AC motor generates a ripple, which is synchronized to the frequency of the periodic load torque, at the speed of the motor. Consequently, numerous studies have focused on reducing the speed ripple caused by the load torque. However, it is difficult to reduce the speed ripple when there is a time delay in acquiring speed information, such as that from a sensorless control. Therefore, we propose a speed control method for reducing speed ripples caused by a periodic load torque when there is a time delay in acquiring the speed information. The proposed method is verified by conducting simulations using the Simulink program from MATLAB, and by applying the method to an actual motor in which speed ripples occur due to a periodic load torque that is synchronized with the speed of the motor.

• 한국공간구조학회논문집
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• 제20권4호
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• pp.149-158
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• 2020

The governing equation for a dome-type shallow spatial truss subjected to a transverse load is expressed in the form of the Duffing equation, and it can be derived by considering geometrical non-linearity. When this model under constant load exceeds the critical level, unstable behavior is appeared. This phenomenon changes sensitively as the number of free-nodes increases or depends on the imperfection of the system. When the load is a periodic function, more complex behavior and low critical levels can be expected. Thus, the dynamic unstable behavior and the change in the critical point of the 3-free-nodes space truss system were analyzed in this work. The 4-th order Runge-Kutta method was used in the system analysis, while the change in the frequency domain was analyzed through FFT. The sinusoidal wave and the beating wave were utilized as the periodic load function. This unstable situation was observed by the case when all nodes had same load vector as well as by the case that the load vector had slight difference. The results showed the critical buckling level of the periodic load was lower than that of the constant load. The value is greatly influenced by the period of the load, while a lower critical point was observed when it was closer to the natural frequency in the case of a linear system. The beating wave, which is attributed to the interference of the two frequencies, exhibits slightly more behavior than the sinusoidal wave. And the changing of critical level could be observed even with slight changes in the load vector.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2012년도 전력전자학술대회 논문집
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• pp.409-410
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• 2012

Speed output has ripple such as periodic torque ripple if load torque with periodic ripple was injected in AC motor. In this paper, it is proposed method to reduce speed ripple through novel speed control method. It replaces algorithm to compensate torque ripple. Proposed method demonstrated through simulation using MATLAB SIMULINK.

• 전기학회논문지
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• 제68권3호
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• pp.430-438
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• 2019

For a pump or a compressor motor, a high periodic load torque variation is induced by the mechanical works, and it causes system vibration and noise. To minimize these problems, load torque compensation method, injecting periodic torque current, could be utilized. However, with the sensorless control method, which is usually utilized in the pump and compressor for low cost, the periodic torque current degrades the accuracy of the rotor position estimation owing to the inductance variation. This paper analyzes the rotor position and speed estimation error of sensorless control method with constant motor parameters under period loading. Assuming the constant speed by the accurate load torque compensation, the speed error equation is derived in frequency domain with inductance depending on the stator current. Further, it is also shown that the rotor position error could be minimized by compensating the inductance variation. The simulation and experimental results verify that the derived speed error model and the validity of the inductance compensation method.

• 정보처리학회논문지A
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• 제14A권1호
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• pp.63-72
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• 2007

본 논문에서 웹 서버 클러스터 환경에서 웹 요청들의 분산을 위한 부하 분산 기법을 제안한다. 전통적인 주기적 부하 정보 갱신 기반의 부하 분산 기법에서는 동기화된 부하 정보와 동적 페이지에 포함된 스크립트들의 갱신 정보 때문에 Cyber Foraging 서비스 같은 동적 웹 응용프로그램에서는 적합하지 않다. 이를 해결하기 위해 Update-on-Finish 부하 분산 알고리즘은 비주기적인 부하 갱신 방법을 사용하고 있다. 웹 스위치는 비주기적인 부하 리포팅 후, 서버들의 실제 부하 정보를 알 수 있다. 그런후 실제 정보에 따라 부하 분산 스케줄을 재배열한다. 하지만 Update-on-Finish 알고리즘의 경우 부하 정보를 유지하기 위한 통신 부하가 크다는 문제점을 가진다. 본 논문에서는 각 서버가 K%의 작업을 마친 후 비주기적 부하 정보 보고를 통하여 부하 감소시킨 방법을 제안한다. 또한 서버의 처리능력이 다른 환경을 고려하여 서로 다른 threshold Ti값을 적용함으로써, 다양한 처리 능력을 가진 서버들을 위한 로드 밸런싱 알고리즘으로 확장하여 제안하고 있다. 시뮬레이션 결과에서 제안된 K-Percent-Finish Reporting 방법은 Update-on-Finish 방법보다 최소 50% 이상의 통신 부하를 감소시키면서, 기존 주기적 부하정보 갱신 기반의 관련 연구들보다 향상된 시스템 처리 능력을 보여주고 있다.

• 전기학회논문지
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• 제67권11호
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• pp.1434-1446
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• 2018

This paper presents new speed control strategy for periodic load torque injected in AC motor. If motor drive system has a periodic load torque, it causes a periodic motor speed ripple bringing about vibrations and noises. This paper proposed new control method consisting of PIR(proportional-integral-resonant) controller and repetitive controller. PIR controller controls DC, low frequency and fundamental components and repetitive controller controls other harmonics. The performance has been verified through computer simulations using MATLAB Simulink and experiments.

• Journal of applied mathematics & informatics
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• 제27권3_4호
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• pp.501-515
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• 2009

A second order nonlinear ordinary differential equation is obtained by solving the initial-boundary value problem of a class of elas-todynamics equations, which models the radially symmetric motion of a incompressible hyper-elastic solid sphere under a suddenly applied surface tensile load. Some new conclusions are presented. All existence conditions of nonzero solutions of the ordinary differential equation, which describes cavity formation and motion in the interior of the sphere, are presented. It is proved that the differential equation has singular periodic solutions only when the surface tensile load exceeds a critical value, in this case, a cavity would form in the interior of the sphere and the motion of the cavity with time would present a class of singular periodic oscillations, otherwise, the sphere remains a solid one. To better understand the results obtained in this paper, the modified Varga material is considered simultaneously as an example, and numerical simulations are given.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.352-364
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• 2007

It is essential to reduce track maintenance costs and to extend the periodic replacements of continuous welded rails based on accumulated passing tonnage. As recently train load decrease and rail joints wear down less, the periodic replacements of continuous welded rails can be extended. There are many kinds of rail damage like squat, head-check and corrugation. These can be taken nondestructive or naked eye test. So the periodic replacements of continuous welded rails based on accumulated passing tonnage were examine with focusing on a crack of rail bottom of continuous welded rail. Therefore, this study measure dynamic response of track by metro train load, it compute impact coefficient and track spring coefficient for estimating a condition of actual track system. Also, it is converted the measured stress waveform into stress frequency histogram by the rain-flow counting methods, and then the equivalence of stress is calculated. As apply s-n curve of a new welded rail, accumulated fatigue damage ratio of laid rail and remaining service lives is estimated. This study suggest a plan of the periodic replacements of continuous welded rails based on accumulated passing tonnage classified by the types of track system.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1058-1070
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• 2007

Internal and external railway management corporations are using the periodic replacement criteria of rail by accumulated passing tonnage and wear to maintain rails for servicing. However, internal the periodic replacement criteria of continuous welded rail(CWR) by accumulated passing tonnage is the one(50kg/m-5 million gross tonnage, 60kg/m-6 million gross tonnage) presented in Japan before. It was estimated with the fatigue life about 50kg N rail joints applied diesel train load but it wasn't applied to current conditions of track; elimination of rail joint, using the concrete slab track and operation of light train load and effect of welding, manufacturing technique, grinding of rail. Therefore, in this study, it was investigated the types of damage and cause in welded rails and examined standards and information resources. Also, this study presents preliminary data to revise the periodic replacement criteria of CWR by current accumulated passing tonnage in bending test of laid welded rail and a survey of track maintenance history of Seoul metro.

• Structural Engineering and Mechanics
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• 제48권1호
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• pp.103-124
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• 2013

This paper studies the static and dynamic characteristics of composite plates subjected to an arbitrary periodic load in hygrothermal environments. The material properties of composite plates are depended on the temperature and moisture. The governing equations of motion of Mathieu-type are established by using the Galerkin method with reduced eigenfunction transforms. A periodic load is taken to be a combination of axial pulsating load and bending stress in the example problem. The regions of dynamic instability of laminated composite plates are determined by solving the eigenvalue problems based on Bolotin's method. The effects of temperature rise and moisture concentration on the dynamic instability of laminated composite plates are investigated and discussed. The influences of various parameters on the instability region and dynamic instability index are also investigated. The numerical results reveal that the influences of hygrothermal effect on the dynamic instability of laminated plates are significant.