• 대한전기학회논문지
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• 제35권1호
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• pp.26-35
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• 1986

In this paper, non-linear state equations for a 3-phase, 220V, 0.4 KW, squirrel cage induction motor have been derived using the d-q transformation and then these equations have been linearized around an operating point by a small perturbation method. Root loci on the s-plane with repect to the changes of slip S and supply frequency f have been studied. Based on the above results, the derived linear state equations have been augmented to the 6th order, including the output velocity feedback and a discrete PI speed controller. Using the new state equations, stability regions on the Kp-Kl plane have been investigated for slip S and sampling time T. In designing a discrete PI controller, the coefficients Kp and Kl around the normal operating point (220V,1,692rpm,60Hz)have been chosen under the assumptions that each response to a perturbation input of reference speed and load torque be underdamped and dominated by a pair of complex poles. Step responses in the experimental system using an Intel SDK-86 and an optimized PWM inverter show satisfactory results that the maximum overshoots and damped frequency are well coincided with ones from the computer simulation.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.170-178
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• 1999

In general, an impeller of centrifugal turbomachinery is designed at isolated condition without considering the presence of a volute, but when the impeller is operating with its volute, the performance of impeller can be different. This is largely caused by the interaction between the impeller and volute flow fields. The magnitude of distortion is increased as the operating point is away from the design point and, as a result, the interaction between the impeller and volute is stronger. In the present calculation, the flow through the impeller is simulated using coarse grids. The flow within the impeller and the volute is naturally unsteady, but the flow is assumed to be steady across the interface between the volute and impeller flow fields. Under the assumption of steady three-dimensional incompressible turbulent flow, the time averaged N-S equations involving standard k-$\epsilon$ turbulent model was solved by the F.V.M. The calculation results are compared with the experimental results obtained for an industrial fan by Sakai etc. and the Hood agreement is demonstrated. And the effects of the impeller-volute interaction are studied.

• 전력전자학회논문지
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• 제25권2호
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• pp.118-126
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• 2020

A solar array simulator is a special power supply that regulates the output voltage and current to simulate the characteristics of a photovoltaic panel. The operating point of the panel is difficult to control with a single controller because of the non-linearity of the output curve, which is determined by the amount of irradiation, temperature, and panel material. In the conventional method, the output curve is divided into sections through the current and the voltage mode controls. It reduces the overall performance of the system due to the interchanging control mode. By using the single mode controller, the noise interference of the measured value and the stability of the control around the maximum power point were demonstrated. To solve these issues, this study proposes a new unified controller. The stability of the controller was analyzed along with operating principles, and performance improvement was experimentally verified.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.541-551
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• 2020

Based on the trend, there have been numerous researches analysing the ship collision risk. However, in this scope, the navigational conditions and external environment are ignored or incompletely considered in training or/and real situation. It has been identified as a significant limitation in the navigational collision risk assessment. Therefore, a novel algorithm of the ship navigational collision risk solving system has been proposed based on basic collision risk and vulnerabilities of marine accidents. The vulnerability can increase the possibility of marine collision accidents. The factors of vulnerabilities including bad weather, tidal currents, accidents prone area, traffic congestion, operator fatigue and fishing boat operating area are involved in the fuzzy reasoning engines to evaluate the navigational conditions and environment. Fuzzy logic is employed to reason basic collision risk using Distance to Closest Point of Approach (DCPA) and Time of Closest Point of Approach (TCPA) and the degree of vulnerability in the specific coastal waterways. Analytical Hierarchy Process (AHP) method is used to obtain the integration of vulnerabilities. In this paper, vulnerability factors have been proposed to improve the collision risk assessment especially for non-SOLAS ships such as coastal operating ships and fishing vessels in practice. Simulation is implemented to validate the practicability of the designed navigational collision risk solving system.

• Journal of Biosystems Engineering
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• 제15권2호
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• pp.99-109
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• 1990

Rough rice is subjected to a series of static and dynamic forces during mechanical harvesting, handling and processing operations. The mechanical properties such as bioyield point, compressive strength, and deformations at the bioyield point and rupture point are important engineering data needed to develop processing machines and to determine reasonable operating conditions for these machines. The objectives of this study were to determine the mechanical properties of the rough rice kernel at loading rate of 0.664 mm/min and 1.673 mm/min and at various moisture contents, and to examine the effect of the moisture content and the loading rate on these mechanical properties. The follwing results were obtained from the study. 1. Bioyield point, rupture point, bioyield strength and ultimate strength of the rough rice kernel generally decreased in magnitude with an increase in moisture content. A little larger values of these mechanical properties were obtained at the higher loading rate. The rough rice variety and the loading rate affected significantly these mechanical properties at low moisture content, but not at the higher moisture levels. 2. Bioyield point of the sample grains varied from 20 to 80 N, and rupture point varied from 45 to 130N. Bioyield point for Japonica-type rough rice was a little higher than that for Indica-type rough rice, but there were little differnces in rupture point between two types of rough rice. 3. Bioyield strength and ultimate strength of the Japonica-type rough rice varied from 10 MPa. to 39 MPa., and from 13 MPa. to 45 MPa. respectively. Those of the Indica-type rough rice varied from 12 MPa. to 42 MPa., and from 15 MPa. to 53 MPa. respectively. 4. Deformations at bioyield point and rupture point ranged from 0.18 mm/min to 0.26 mm, and from 0.28 mm to 0.53 mm respectively. These deformations decreased with an increase in moisture content up to moisture content of approximately 17% (w.b.) and increased again thereafter. 5. Regression equations were developed to predict these mechanical properties for the rough rice kernel as a function of moisture content.

• 한국산학기술학회논문지
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• 제15권5호
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• pp.3074-3078
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• 2014

본 논문은 무선 근거리 네트워크(WLAN)대역의 Access Point(AP)용 이중대역 슬롯결합 패치(SCP) 안테나에 관한 것이다. 본 논문의 안테나는 세 개의 적층 구조로 구성되었고, 두 개의 방사체로 이루어져있다. 첫 번째 방사체는 2.4-2.483 GHz 대역에서 동작하는 슬롯형태의 나비넥타이(bow-tie) 안테나이다. 두 번째 방사체는 4.095-5.845 GHz에서 동작하는 기생 소자(parasitic element)들을 포함한 패치안테나이다. 높은 이득과 넓은 대역폭은 우수한 무선 접속의 중요한 요소이다. 대역폭을 넓히기 위해서 첫 번째 방사체에서 커플링 급전(coupling feed)이 사용되었고, 두 번째 방사체에 기생 패치(parasitic patch)를 사용하였다. 그리고, 지향성(directivity)과 격리도(isolation)를 향상시키기 위해 기생 패치(parasitic patch)와 초크(chock)를 고안하였다. EM 시뮬레이션을 통하여 분석하였고, 측정하여 결과를 확인하였다. 동작 주파수에서 -11dB 이하의 반사계수(S11)를 보여준다. 최대이득은 첫 번째 안테나에서 6 dBi이상, 두 번째 안테나에서 8 dBi이상이다.

• 한국대기환경학회지
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• 제17권1호
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• pp.51-56
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• 2001

This study was carried out to interpret mathematically hydraulic behaviour in packing tower which packed 50 mm plastic Hiflow-ring with a dimension of 300 mm wide and 1,400 mm high. In view of energy saving, the recent packing. 50 mm plastic Higlow-ring was superior to conventional packings because of low pressure drop in high loads. As relative error between numerically predicted and experimentally obtained values was less then 6% in the loading and flooding point, it found that therir results appeared to be adequate. Comparison of hose two values in both dry and wet packing conditions. relative errors amount to 3.96 and 5.6%, respectively. In order to evaluate the operating characteristics of packing, the type, size, and material for packings must be estimated in various system and loads. This study is able to calculated pressure drop, hold-up, gas and liquid loads using mathematical interpretation. For these calculation, the specific constants of each packings must be calculated first all. The method of mathematical interpretation in this study turned out to be superior to the existing methods because of reduced errors at loading and flooding point.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 F
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• pp.2177-2180
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• 1997

The solar cell has an optimum operating point to be able to got maximum power. To obtain maximum power from Photovoltaic array, hotovoltaic power system usually requres maximum power point c tracking controller. The output characteristics of solar cell are nonlinear, and these characteristics vary with load solar insolation, solar cell temperature. Therefore the tracking control of maximum power point is the com-plicated problem. This paper presents power characteristics of residential Photovoltaic system applying a buck-boost conversion system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.626-630
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• 2001

MPPT (maximum power point tracking) control is very important for the practical PV (photovoltaic) systems to maintain efficient power generating conditions irrespective of the deviation in the PV array insolation or/and temperature conditions. Although a plenty of researches have been done so far, most of them are too costly because of being too dependant on expensive sensors for measuring photovoltaic power and micro-processors for achieving elaborate and complicated control strategies. From this point of view, authors have been researching on sensor-less approaches for MPPT control, and have proposed two types of new control schemes 'Power Equilibrium Scheme' and 'Limit Cycle Scheme'. This paper summarises these two schemes with focussing on their :- operating principles and some results of simulation and experiments.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.622-625
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• 2001

Photovoltaic generation systems need MPPT (Maximum Power Point Tracking) control because the output power depends on the operating voltage and current. Therefore, many researchers propose various types of MPPT control methods. A new MPPT control scheme is proposed in this paper in order to realize higher efficiency with simple calculation. The line search algorithm with fibonacci sequence which is one of the optimizing method is employed for the MPPT. The line search method is modified for real-time operation. The method is verified by simulations and experiments. It is concluded that the scheme can respond fast variation of irradiance.