• Journal of Communications and Networks
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• 제12권1호
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• pp.30-42
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• 2010

In this work we consider the problem of downlink resource allocation for proportional fairness of long term received rates of data users and quality of service for real time sessions in an OFDMA-based wireless system. The base station allocates available power and subchannels to individual users based on long term average received rates, quality of service (QoS) based rate constraints and channel conditions. We formulate and solve a joint bandwidth and power optimization problem, solving which provides a performance improvement with respect to existing resource allocation algorithms. We propose schemes for flat as well as frequency selective fading cases. Numerical evaluation results show that the proposed method provides better QoS to voice and video sessions while providing more and fair rates to data users in comparison with existing schemes.

• Journal of Electrical Engineering and Technology
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• 제7권1호
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• pp.1-8
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• 2012

The current paper presents a novel control strategy of a three-phase, four-wire Unified Power Quality (UPQC) to improve power quality. The UPQC is realized by the integration of series and shunt active power filters (APF) sharing a common dc bus capacitor. The realization of shunt APF is carried out using a three-phase, four-leg Voltage Source Inverter (VSI), and the series APF is realized using a three-phase, three-leg VSI. To extract the fundamental source voltages as reference signals for series APF, a zero-crossing detector and sample-and-hold circuits are used. For the control of shunt APF, a simple scheme based on the real component of fundamental load current (I $Cos{\Phi}$) with reduced numbers of current sensors is applied. The performance of the applied control algorithm is evaluated in terms of power-factor correction, source neutral current mitigation, load balancing, and mitigation of voltage and current harmonics in a three-phase, four-wire distribution system for different combinations of linear and non-linear loads. The reference signals and sensed signals are used in a hysteresis controller to generate switching signals for shunt and series APFs. In this proposed UPQC control scheme, the current/voltage control is applied to the fundamental supply currents/voltages instead of fast-changing APF currents/voltages, thus reducing the computational delay and the required sensors. MATLAB/Simulink-based simulations that support the functionality of the UPQC are obtained.

• 산업공학
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• 제11권3호
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• pp.155-166
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• 1998

The productivity and quality are most challenging problems facing all companies. This paper presents a process improvement of the SMPS(switching mode power supply) assembly line through elimination of unnecessary operations, a proper factory layout, motion study, and line balancing techniques. The proposed assembly line increases the productivity by 23.9%, and decrease the proportion of nonconforming items by 48.9%.

• Journal of Power Electronics
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• 제17권4호
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• pp.983-990
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• 2017

This paper proposes a model predictive control based on the discrete Lyapunov function to improve the performance of power electronic converters. The proposed control technique, based on the finite control set model predictive control (FCS-MPC), defines a cost function for the control law which is determined under the Lyapunov stability theorem with a control error compensation. The steady state and dynamic performance of the proposed control strategy has been tested under a single phase AC/DC voltage source rectifier (S-VSR). Experimental results demonstrate that the proposed control strategy not only offers global stability and good robustness but also leads to a high quality sinusoidal current with a reasonably low total harmonic distortion (THD) and a fast dynamic response under linear loads.

• 품질경영학회지
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• 제35권3호
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• pp.75-87
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• 2007

This paper deals with an integration model of three major quality management systems. The well known global standards such as ISO 9001 quality system, Malcolm Baldrige model, and EFQM model are integrated as a prototype quality system. The proposed model is then applied to help a power generation company to select improvement tasks for enhancing quality management. Here, we discuss three quality management systems, an integration process of the three systems, the integrated model, and a real world application case.

• 한국통신학회논문지
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• 제39B권2호
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• pp.61-74
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• 2014

In recent years, development of femtocells are receiving considerable attention towards increasing the network coverage, capacity, and improvement in the quality of service for users. In 3GPP LTE-Advanced (LTE-A) system, to efficiently utilize the bandwidth, femtocell and macro cell uses the same frequency band, but this deployment poses a technical challenge of cross-tier interference to macro users. In this paper, the novel quality of service based fractional power control (QoS-FPC) scheme under the heterogeneous networks environment is proposed, which considers the users priority and QoS-requirements during the power allocation. The proposed QoS-FPC scheme has two focal points: firs, it protects the macrocell users uplink communication by limiting the cross-tier interference at eNB below a given threshold, and second, it ensures the optimization of femtocell users power allocation at each power adjustment phase. Performance gain is demonstrated with extensive system-level simulations to show that the proposed QoS-FPC scheme significantly decreases the cross-tier intereference and improves the overall users throughput.

• 환경영향평가
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• 제9권1호
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• pp.61-74
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• 2000

This study compares the results of environmental impact assessment with the results of post-environmental investigation, using the case of Taean thermal power plant construction. The atmospheric and water qualities were not greatly changed before and after the construction of the power plant. However, the site of the highest concentration predicted by the atmospheric quality modeling in environmental impact assessment was different from that after operation of 4 power plants. There was also a difference in the diffusion range of thermal discharge water between the measured result(1km) and the predicted value(1.5km) with the model. Thus, environmental impact evaluation should be based on long-term (more than a year) environmental monitoring data. For the modeling of atmospheric quality and numerical thermal discharge water diffusion, appropriate models for each plant should be selected and the numerical modeling should be accompanied by computer simulation, wind tunnel test, etc. Moreover, environmental evaluation should focus more on the degree of impact on surroundings than the prediction of changes in surroundings caused by operation of plants.

• 항공우주시스템공학회지
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• 제13권5호
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• pp.24-31
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• 2019

본 연구에서는 항공기용 전원분배장치에서 발생한 소손현상의 원인을 분석하고 개선 방안을 제안하였다. 항공기용 전원분배장치는 교류와 직류로 분류하며, 두 장비 사이에 정류기가 존재한다. 전원분배 장치의 전원이 켜지고 꺼질 때 전원 보드내의 커패시터가 소손되었다. 주요 원인은 정류기에 내장되어 있는 인덕턴스로 인해 과도한 전압이 발생했기 때문이다. 고장이 발생 할 수 있는 경우를 분류하였다. 그리고 그에 따른 영향성을 분석하였으며, 실험적인 방법을 통해서 해결책을 수립하였다.

• 정보처리학회논문지D
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• 제11D권3호
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• pp.571-576
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• 2004

국내의 정보화 프로젝트 개발 소프트웨어가 대형화되고 복잡화됨에 따라 개발 업체의 소프트웨어 프로젝트 품질이 매우 중요해지고 있다. 프로젝트 품질 평가 심사 모형인 CMM 등으로 개발 사업자의 프로젝트 수행능력이 평가되고 있다. 따라서 개발 사업자들은 CMM 등급 인증획득 또는 등급을 올리기 위한 노력을 기울이고 있다. 그러나 인증의 신뢰성에 대하여 논란이 되고 있는 시점에서 프로젝트 품질 인증의 제도가 프로젝트 품질에 차이를 나타내는지에 대한 연구와 CMM등급 인증과 기업 문화의 적합이 프로젝트 품질 성과에 차이를 나타내는지에 대하여 연구를 수행하였다. 연구 결과, CMM인증 등급이 높고 기업문화의 개방성이 높은 조직이 프로젝트 품질 성과가 높은 것으로 나타났다. 프로젝트 품질 성과를 높이기 위해서는 CMM인증 등급도 중요하지만 품질을 위한 기업 문화의 개방성을 높여나가는 것이 매우 중요한 것으로 나타났다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.166-169
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• 2003

In this paper, a PWM Buck-Boost AC-AC converter for improvement of power quality of custom power is presented. The PWM Buck-Boost AC-AC converter is modelled by using circuit DQ transformation whereby the design guideline is obtained. Based on the analysis, the converter system is implemented with the design criteria and the experimental results show the validity of modelling and analysis.