• 대한기계학회논문집A
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• 제33권5호
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• pp.463-468
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• 2009

Torsional oscillations of the drivetrain in electric vehicles are generated under rapid driving conditions. These lead to an uncomfortable jerking of the vehicle and an increased stress of the mechanical components. To suppress torsional oscillations, the low pass and notch filters between the torque command from the acceleration pedal and electric motor input torque are suggested. The filter parameters are optimized based on Taguchi method with $L_{18}(3^5)$ orthogonal array. The signal to noise (S/N) ratio mainly depends on slew rate of motor input torque, damping ratio and natural frequency of notch filter. With the proposed suppression control scheme, the S/N ratio is shown to be increased by 4.7dB and the torque overshoot of the drive shaft is reduced to 30%.

• International Journal of Fluid Machinery and Systems
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• 제8권2호
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• pp.102-112
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• 2015

In the Nordic grid, a trend observed the recent years is the increase in grid frequency variations, which means the frequency is outside the normal range (49.9-50.1 Hz) more often. Variations in the grid frequency leads to changes in the speed of rotation of all the turbines connected to the grid, since the speed of rotation is closely related to the grid frequency for synchronous generators. When the speed of rotation changes, this implies that the net torque acting on the rotating masses are changed, and the material of the turbine runners must withstand these changes in torque. Frequency variations thus leads to torque oscillations in the turbine, which become dynamical loads that the runner must be able to withstand. Several new Francis runners have recently experienced cracks in the runner blades due to fatigue, obviously due to the runner design not taking into account the actual loads on the runner. In this paper, the torque oscillations and dynamic loads due to the variations in grid frequency are simulated in a 1D MATLAB program, and measured grid frequency is used as input to the simulation program. The maximum increase and decrease in the grid frequency over a 440 seconds interval have been investigated, in addition to an extreme event where the frequency decreased far below the normal range within a few seconds. The dynamic loading originating from grid frequency variations is qualitatively found by a constructed variable $T_{stress}$, and for the simulations presented here the variations in $T_{stress}$ are found to be around 3 % of the mean value, which is a relatively small dynamic load. The important thing to remember is that these dynamic loads come in addition to all other dynamic loads, like rotor-stator interaction and draft tube surges, and should be included in the design process, if not found to be negligible.

• 제어로봇시스템학회논문지
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• 제20권6호
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• pp.635-640
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• 2014

Detection and diagnosis of incipient bearing fault in an induction motor is important for the prevention of serious motor failure. This paper presents an analysis of the effect of a faulty bearing on the stator current of an induction motor. A bearing fault leads to torque oscillations which result in phase modulation of the stator current. Since the torque oscillations cause specific frequency components at the stator current spectrum to rise sharply, the bearing fault can be detected by checking out the faultrelated frequency. In this paper, a mathematical model of the load torque oscillation caused by a bearing fault is presented. The proposed model can be used to analyze the physical phenomenon of a bearing fault in an induction motor. In order to represent the bearing fault effect, the proposed model is combined with an existing model of vector-controlled induction motors. A set of simulation results demonstrate the effectiveness of the proposed model and represent that bearing fault detection using a stator current is useful for vector-controlled induction motors.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 하계학술대회 논문집
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• pp.409-411
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• 2007

This paper deals with an automatic tuning method of the notch filter to suppress oscillations in a permanent magnet linear synchronous motor(PMLSM) drive. First, it saves automatically the reference torque-component current when oscillations are detected. Then the oscillation frequency of the saved data is calculated by using the fast Fourier transform(FFT) algorithm. And also the Hanning function is used to reduce the leakage components due to the aperiodic measurement data. Finally, the proposed method tunes the notch filter to suppress oscillations. Experimental results on the test rig show the validity of the proposed method.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.825-829
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• 2005

This paper presents an approach for designing a fuzzy logic-based adaptive SVC damping In controller for damping low frequency power oscillations. Power systems are often subject to low Frequency electro-mechanical oscillations resulting from electrical disturbances. Generally, power system stabilizers are designed to provide damping against this kind of oscillations. Another means to achieve damping is to design supplementary damping controllers that are equipped with SVC. Various approaches are available for designing such controllers, many of which are based on the concepts of damping torque and others which treat the damping controller design as a generic control problem and apply various control theories on it. In our proposed approach, linear optimal controllers are designed and then a fuzzy logic tuning mechanism is constructed to generate a single control signal. The controller uses the system operating condition and a fuzzy logic signal tuner to blend the control signals generated by two linear controllers, which are designed using an optimal control method. First, we design damping controllers for the two extreme conditions; the control action for intermediate conditions is determined by the fuzzy logic tuner. The more the operating condition belongs to one of the two fuzzy sets, the stronger the contribution of the control signal from that set in the output signal. Simulation studies done on a one-machine infinite-bus and a four-machine two-area test system, show that the proposed fuzzy adaptive damping SVC controller effectively enhances the damping of low frequency oscillations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.420-425
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• 1996

In this paper a robust speed controller for an induction motor is proposed. The speed controller consists or a fuzzy sliding adaptive controller(FSAC) and a sliding mode torque observer(SMTO). FSAC removes the problem or oscillations caused by discontinuous inputs of the sliding mode controller. The controller also provides robust characteristics against parameter and sampling time variations. Although, however, the performance of FSAC is better than PI controller and fuzzy controller in robustness, it generates the problem of slow response time. To alleviate this problem, a compensator, which performs feedforward control using torque signals produced by SMTO, is added. The simulation and hardware implementation results show that the proposed system is robust to the load disturbance, parameter variations, and measurement noises.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권3호
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• pp.105-109
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• 2001

In this paper, the windmill type ultrasonic motors with 11.35 mm diameter, 2.87 mm thickness of metal endcap and 1.47 g weight were fabricated. Effects of slots and thickness on torque characteristic in the windmill type ultrasonic motor were investigated, when stator's slots were changed from 4, 6, 8 and thickness 0.15 mm, respectively. Specially designed metal endcaps with windmill shaped cutting can provide longitudinal and torsional displacements simultaneously as the ceramic disk vibrates radically. The windmill type ultrasonic motor has only three components: a stator element with windmill shape slotted metal endcap, a rotor and bearing. Ultrasonic motor stimulated to ultrasonic oscillations by piezoelectrics to drive a rotor via friction contact. The ultrasonic motor fabricated here was the windmill type ultrasonic motor operated by single-phase AC source. Bidirectional revolution using single-phase high frequency for driving the ultrasonic motor was presented.

• Journal of Electrical Engineering and Technology
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• 제9권4호
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• pp.1145-1153
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• 2014

It is well known that line switching operations like reclosing are able to cause transient power oscillations which can stress or damage turbine generators. This paper presents a reclosing scheme to reduce the shaft torsional torques of turbine generators by inserting an additional reactor. A novel method to determine optimal reactor capacity to minimize the torsional torque generated in a turbine generator is also proposed. In this paper, the turbine generator shaft is represented by a multi-mass model to measure torsional torques generated in the shaft between the turbine and the generator. Transmission systems based on actual data from Korea are modeled to verify the proposed scheme using ElectroMagnetic Transient Program (EMTP) software. The simulation results clearly show the effectiveness of the proposed scheme and torsional torque can be minimized by applying the proposed scheme.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.71-76
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• 2017

선박 및 해양구조물 설계에 있어 롤댐핑에 관한 문제는 유체점성과 현상자체의 비선형성으로 인해 공학자들에게 있어 난제로 남아있다. 본 연구에서는 강제동요방법을 이용하여 원형실린더의 점성 롤감쇠에 관한 연구를 수행하였다. 토크 센서를 이용하여 강제동요 시 발생하는 롤모멘트(roll moment)를 강제동요 주기별로 계측하였고 이를 실험식(empirical formula)과 비교 검토 하였다. 점성에 의한 전단력으로부터 계측된 토크의 크기가 상대적으로 작은 값임에도 불구하고 실험식으로부터 얻어진 계산값들과 정성적으로 유사한 결과를 보였고, 일부 주기에서는 정량적으로도 잘 일치하는 결과를 보였다. 또한, PIV 계측기법을 통해 원형실린더 벽면주위의 유동을 면밀히 관찰하였으며, 유체점성으로 인해 원형실린더 벽면근처에서 경계층이 형성되고 자유수면에서 원형실린더의 주기적인 강제회전동요로 인해 미소한 크기의 파가 생성(wave making)됨을 PIV 계측결과의 분석을 통해 확인하였다. 본 연구에서는 점성 롤감쇠로 인한 실험식의 적합성을 모형시험을 통해 확인하였고, PIV 계측기법을 통해 벽면주위의 유체점성으로 인한 조파현상을 입증하였다.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2008년도 Asian Magnetics Conference
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• pp.261.2-261.2
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• 2008