• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권7호
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• pp.430-436
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• 2004

This paper presents an advanced control technique for power density maximization of the Brushless DC (BLDC) generator by using the linear tracking method. In a generator of given rating, the weight and size of the system affect the fuel consumption directly. Therefore, power density is one of the most important issues in a stand-alone generator. BLDC generator has high power density in the machine point of view and additional increases of power density by control means can be expected. Conventional rectification methods cannot achieve the maximum power possible because of hon-optimal current waveforms. The optimal current waveform to maximize power density and minimize machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation and experimental work. A new simple algebraic method has been proposed to accomplish the proposed control without an FFT which is time consuming and complicated.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제4B권3호
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• pp.108-113
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• 2004

This paper presents methods to improve performance of the power supply system in a NASA deep space explorer. In the Stirling engine driven reciprocating Brushless DC (BLDC) generator, the accurate position information of the prime mover is important to diagnose the performance of the engine and prevent distortion of the output power. Since sensors to detect the position are fragile and unreliable, and conventional sensorless techniques have drawbacks in the low speed region, a novel sensorless position detection technique for the prime mover has been proposed and verified. Another major issue of the generator for the spacecraft is power density maximization. The mass of the power system is important to the mass of the satellite. Therefore, the components of the spacecraft should be lightweight. Conventional rectification methods cannot achieve the maximum power possible due to non-optimal current waveforms. The optimal current waveform for maximizing power density and minimizing machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation work.

• 한국통신학회논문지
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• 제34권2A호
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• pp.85-90
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• 2009

In this paper, as an alternative to constant modulus algorithm based on MSE, maximization of the probability that equalizer output power is equal to the constant modulus of the transmitted symbols is introduced. The proposed algorithm using the gradient ascent method to the maximum probability criterion has superior convergence and steady-state MSE performance, and the error samples of the proposed algorithm exhibit more concentrated density functions in blind equalization environments. Simulation results indicate that the proposed training has a potential advantage versus MSE training for the constant modulus approach to blind equalization.

• 지구물리와물리탐사
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• 제19권1호
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• pp.11-19
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• 2016

나머지 정적보정 기법중에서 가장 많이 쓰이는 주행시간 분해기법과 겹쌓기제곱 최대화기법의 적용성을 육상 탄성파자료에서 비교 검토하였다. 모든 발파점과 수신점에 대한 임의의 나머지 정적보정값(시간차이)과 무작위 잡음이 포함된 모델자료에서 겹쌓기제곱 최대화기법은 주행시간 분해기법에 비해 흐트러진 반사 이벤트를 정확히 정렬시키고 보정과정에서 출력된 발파점과 수신점의 정적보정 그래프가 입력된 값과 거의 같은 진폭으로 역전된다는 점에서 신호대잡음이 작은 자료의 반사면 향상에 보다 효과적이었다. 나머지 정적보정에 적합한 입력인자(최대허용 시간차이, 상관창, 반복횟수)들은 공통중간점 자료외에 공통발파점 겹쌓기자료와 공통수신점 겹쌓기자료에 대한 연속 테스트를 거쳐 효과적으로 진단할 수 있었다. 나머지 정적보정에 앞서 송수신점의 높이보정 및 풍화대 깊이보정을 실시하여 장파장 시간차이를 제거하고 진동수-파수 필터링, 예측곱풀기, 시간변화 빛띠흰색화로 잡음을 줄여 교차상관의 오차를 최소화시킨다. 또한 나머지 정적보정후 수직시간차 역보정을 거쳐 속도를 재분석하여 겹쌓기한 결과 저류층을 포함한 반사면들의 향상된 연속성 및 분해능을 확인할 수 있었다.

• Journal of Communications and Networks
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• 제12권5호
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• pp.459-465
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• 2010

A new blind equalization algorithm that is based on maximizing the probability that the constant modulus errors concentrate near zero is proposed. The cost function of the proposed algorithm is to maximize the probability that the equalizer output power is equal to the constant modulus of the transmitted symbols. Two blind information-theoretic learning (ITL) algorithms based on constant modulus error signals are also introduced: One for minimizing the Euclidean probability density function distance and the other for minimizing the constant modulus error entropy. The relations between the algorithms and their characteristics are investigated, and their performance is compared and analyzed through simulations in multi-path channel environments. The proposed algorithm has a lower computational complexity and a faster convergence speed than the other ITL algorithms that are based on a constant modulus error. The error samples of the proposed blind algorithm exhibit more concentrated density functions and superior error rate performance in severe multi-path channel environments when compared with the other algorithms.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1383-1388
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• 2010

The latest generation of tram is low-floor design, various nations in europe and japan have developed battery driven hybrid trams that combine battery and wiring. Battery driven tram system is achieved by contactless power supply system, thus system is needed high efficiency, high power and low weight traction motor for maximization of energy efficiency. Research from abroad is still in induction motor(IM) application, and it is not meet the efficiency and the power per unit volume in IPMSM. In this paper, we design compare IM and IPMSM to apply battery driven tram, and then compare these motors. To design the motor, we estimate the loading condition at first. Loading condition includes rolling resistance, air-drag resistance, and slope resistance. Based on the loading condition by estimation, we determine the power and compute rated voltage and rated current. In this paper, voltage is limited by battery voltage level. As a result, volume about IM is 1.98 times bigger than IPMSM under same condition. Even though IPMSM is bigger than IM in power density per volume, we consider more factors for actual application because there are demagnetization of permanent magnet in IPMSM and so on by external environment conditions.

• Journal of Advanced Marine Engineering and Technology
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• 제35권6호
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• pp.796-801
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• 2011

본 논문은 고도로 발전된 군사과학 기술의 영향과 급변하는 해양전장환경의 디지털화, 함정생존성 극대화를 위한 고출력 센서체계 등 고출력 에너지 사용 체계 플랫폼 실현을 위한 해군함정의 통합 동력 시스템 발전 경향을 분석하는데 초점을 두었다. 함정에서 전자기를 이용하는 항공기 출격 시스템, 200NM(370km) 이상 원거리에서 정밀타격이 가능한 전자기 포 등 고출력 에너지를 사용하는 각종 무기체계가 탑재되기 위해서는 추진동력을 포함한 함정에 공급되는 모든 동력이 단일화 되어야하는 통합 동력 시스템으로 변화하는 것이 가장 이상적이다. 선진국을 중심으로 통합 동력 시스템을 실현하기 위해서 기계식 추진시스템에서 하이브리드 및 완전전기추진시스템으로 변화하고 있는 추세이며 이러한 노력은 연료사용의 절감, 함정 탑재 장비의 고출력화, 함정 총 수명주기 비용 절감 등을 포함하고 있다.

• Structural Engineering and Mechanics
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• 제63권6호
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• pp.809-824
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• 2017

The accurate evaluation of wind characteristics and wind-induced structural responses during a typhoon is of significant importance for bridge design and safety assessment. This paper presents an expectation maximization (EM) algorithm-based angular-linear approach for probabilistic modeling of field-measured wind characteristics. The proposed method has been applied to model the wind speed and direction data during typhoons recorded by the structural health monitoring (SHM) system instrumented on the arch Jiubao Bridge located in Hangzhou, China. In the summer of 2015, three typhoons, i.e., Typhoon Chan-hom, Typhoon Soudelor and Typhoon Goni, made landfall in the east of China and then struck the Jiubao Bridge. By analyzing the wind monitoring data such as the wind speed and direction measured by three anemometers during typhoons, the wind characteristics during typhoons are derived, including the average wind speed and direction, turbulence intensity, gust factor, turbulence integral scale, and power spectral density (PSD). An EM algorithm-based angular-linear modeling approach is proposed for modeling the joint distribution of the wind speed and direction. For the marginal distribution of the wind speed, the finite mixture of two-parameter Weibull distribution is employed, and the finite mixture of von Mises distribution is used to represent the wind direction. The parameters of each distribution model are estimated by use of the EM algorithm, and the optimal model is determined by the values of $R^2$ statistic and the Akaike's information criterion (AIC). The results indicate that the stochastic properties of the wind field around the bridge site during typhoons are effectively characterized by the proposed EM algorithm-based angular-linear modeling approach. The formulated joint distribution of the wind speed and direction can serve as a solid foundation for the purpose of accurately evaluating the typhoon-induced fatigue damage of long-span bridges.

• Structural Engineering and Mechanics
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• 제50권5호
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• pp.653-664
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• 2014

Wind fragility analysis provides a quantitative instrument for delineating the safety performance of civil structures under hazardous wind loading conditions such as cyclones and tornados. It has attracted and would be expected to continue to attract intensive research spotlight particularly in the nowadays worldwide context of adapting to the changing climate. One of the challenges encumbering efficacious assessment of the safety performance of existing civil structures is the possible incompleteness of the structural appraisal data. Addressing the issue of the data missingness, the study presented in this paper forms a first attempt to investigate the feasibility of using the expectation-maximization (EM) algorithm and Bayesian techniques to predict the wind fragilities of existing civil structures. Numerical examples of typical linear or hysteretic shear frames are introduced with the wind loads derived from a widely used power spectral density function. Specifically, the application of the maximum a posteriori estimates of the distribution parameters for the story stiffness is examined, and a surrogate model is developed and applied to facilitate the nonlinear response computation when studying the fragilities of the hysteretic shear frame involved.

• 항공우주시스템공학회지
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• 제15권4호
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• pp.11-20
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• 2021

The estimation of hovering flight time of multicopters using the battery power propulsion system is important for the development and design of the aircraft and its operation. For a given operational weight, the maximum possible battery weight can be decided using both a conventional energy density method and a new Peukert law. In the present study, the hovering flight time is predicted using both methods. The specific data of multicopters in the published literatures were employed for the computation of the hovering flight time. The results were validated with the measured data. The effect of figure of merit of propeller, battery discharging process on the hovering flight time was evaluated, Finally, the effect of the battery cell and package connection types on the hovering time was investigated. It was found that the combination of serial battery cell connections and parallel package connection is the bast in the endurance maximization aspect. As the cell number increases in a package, the hovering flight time is increased. There exists the max. battery ratio for the given takeoff gross weight.