• Title/Summary/Keyword: Accurate power sharing

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A Droop Method for High Capacity Parallel Inverters Considering Accurate Real Power Sharing

  • Kim, Donghwan;Jung, Kyosun;Lim, Kyungbae;Choi, Jaeho
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.38-47
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    • 2016
  • This paper presents DG based droop controlled parallel inverter systems with virtual impedance considering the unequal resistive-inductive combined line impedance condition. This causes a reactive power sharing error and dynamic performance degradation. Each of these drawbacks can be solved by adding the feedforward term of each line impedance voltage drop or injecting the virtual inductor. However, if the line impedances are high enough because of the long distance between the DG and the PCC or if the capacity of the system is large so that the output current is very large, this leads to a high virtual inductor voltage drop which causes reductions of the output voltage and power. Therefore, the line impedance voltage drops and the virtual inductor and resistor voltage drop compensation methods have been considered to solve these problems. The proposed method has been verified in comparison with the conventional droop method through PSIM simulation and low-scale experimental results.

Digital Load Sharing Method for Converter parallel Operation (컨버터 병렬운전을 위한 디지털 부하분담 기법)

  • Yoo, Kwang-Min;Kim, Won-Yong;Park, Seung-Hee;Lee, Dong-Hoo;Kim, Yun-Sung;Jeong, Yu-Seok;Lee, Jun-Young
    • The Transactions of the Korean Institute of Power Electronics
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    • v.17 no.2
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    • pp.150-157
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    • 2012
  • This paper presents CAN-based parallel-operation and load-sharing techniques for the communication server power supply. With the load information obtained through CAN communication, each modules performs its current control independently and the power unbalance caused by impedance differences of converter modules can be reduced. In conventional method, slave modules are controlled by master module. On the other hand, the proposed load share algorithm uses the Multi-Master method. Therefore, accurate load sharing can be accomplished by the reference structure of each module's average current. Each converter has two stages and it is separated into PFC, which is responsible for harmonic regulation, and LLC resonant converter, which controls output voltage. To verified the performance of the proposed method, two 2KW prototypes has been implemented and experimented.

An Enhanced Instantaneous Circulating Current Control for Reactive Power and Harmonic Load Sharing in Islanded Microgrids

  • Lorzadeh, Iman;Abyaneh, Hossein Askarian;Savaghebi, Mehdi;Lorzadeh, Omid;Bakhshai, Alireza;Guerrero, Josep M.
    • Journal of Power Electronics
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    • v.17 no.6
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    • pp.1658-1671
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    • 2017
  • To address the inaccurate load demand sharing problems among parallel inverter-interfaced voltage-controlled distributed generation (DG) units in islanded microgrids (MGs) with different DG power ratings and mismatched feeder impedances, an enhanced voltage control scheme based on the active compensation of circulating voltage drops is proposed in this paper. Using the proposed strategy, reactive power and harmonic currents are shared accurately and proportionally without knowledge of the feeder impedances. Since the proposed local controller consists of two well-separated fundamental and harmonic voltage control branches, the reactive power and harmonic currents can be independently shared without having a remarkable effect on the amplitude or quality of the DGs voltage, even if nonlinear (harmonic) loads are directly connected at the output terminals of the units. In addition, accurate load sharing can also be attained when the plug-and-play performance of DGs and various loading conditions are applied to MGs. The effects of communication failures and latency on the performance of the proposed strategy are also explored. The design process of the proposed control system is presented in detail and comprehensive simulation studies on a three-phase MG are provided to validate the effectiveness of the proposed control method.

A Study on the Evaluation of Structural Properties of Wind Turbine Blade-Part1 (풍력터빈의 구조특성 평가에 관한 연구-Part1)

  • Lee, Kyoung-Soo;Huque, Ziaul;Kommalapati, Raghava;Han, Sang-Eul
    • Journal of Korean Association for Spatial Structures
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    • v.14 no.4
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    • pp.47-54
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    • 2014
  • This paper presents the structural model development and verification processes of wind turbine blade. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. The wind turbine assembled by blades, rotor, nacelle and tower. The wind blade connected to rotor. To make the whole turbine structural model, the mass and stiffness properties of all parts should be clear and given. However the wind blade, hub, nacelle, rotor and power generating machinery parts have difficulties to define the material properties because of the composite and assembling nature of that. Nowadays to increase the power generating coefficient and cost efficiency, the highly accurate aerodynamic loading evaluating technique should be developed. The Fluid-Structure Interaction (FSI) is the emerging new way to evaluate the aerodynamic force on the rotating wind blade. To perform the FSI analysis, the fluid and structural model which are sharing the associated interface topology have to be provided. In this paper, the structural model of blade development and verifying processes have been explained for Part1. In following Part2 paper, the processes of whole turbine system will be discussing.

Parallel Operation Control Method of Grid-connected Inverters with Seamless Transfer for Energy Storage System in Microgrid (마이크로그리드에서 에너지 저장시스템을 위한 무순단 절체 기능을 갖는 계통연계형 인버터의 병렬운전 제어기법)

  • Park, Sung-Youl;Kim, Joo-Ha;Jung, Ah-Jin;Choi, Se-Wan
    • The Transactions of the Korean Institute of Power Electronics
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    • v.21 no.3
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    • pp.200-206
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    • 2016
  • In the microgrid, inverters for energy storage system are generally constructed in a parallel structure because of capacity expandability, convenience of system maintenance, and reliability improvement. Parallel inverters are required to provide stable voltage to the critical load in PCC and to accurately share the current between each inverter. Furthermore, when islanding occurs, the inverters should change its operating mode from grid-connected mode to stand-alone mode. However, during clearing time and control mode change, the conventional control method has a negative impact on the critical load, that is, severe fluctuating voltage. In this study, a parallel operation control method is proposed. This method provides seamless mode transfer for the entire transition period, including clearing time and control mode change, and has accurate current sharing between each inverter. The proposed control method is validated through simulation and experiment.

Frequency Estimation Method using Recursive Discrete Wavelet Transform for Fault Disturbance Recorder (FDR를 위한 RDWT에 의한 주파수 추정 기법)

  • Park, Chul-Won;Ban, Yu-Hyeon
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.60 no.8
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    • pp.1492-1501
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    • 2011
  • A wide-area protection intelligent technique has been used to improve a reliability in power systems and to prevent a blackout. Nowadays, voltage and current phasor estimation has been executed by GPS-based synchronized PMU, which has become an important way of wide-area blackout protection for the prevention of expending faults in power systems. As this technique has the difficulties in collecting and sharing of information, there have been used a FNET method for the wide-area intelligent protection. This technique is very useful for the prediction of the inception fault and for the prevention of fault propagation with accurate monitoring frequency and frequency deviation. It consists of FDRs and IMS. It is well known that FNET can detect the dynamic behavior of system and obtain the real-time frequency information. Therefore, FDRs must adopt a optimal frequency estimation method that is robust to noise and fault. In this paper, we present comparative studies for the frequency estimation method using IRDWT(improved recursive discrete wavelet transform), for the frequency estimation method using FRDWT(fast recursive discrete wavelet transform). we used the Republic of Korea 345kV power system modeling data by EMTP-RV. The user-defined arbitrary waveforms were used in order to evaluate the performance of the proposed two kinds of RDWT. Also, the frequency variation data in various range, both large range and small range, were used for simulation. The simulation results showed that the proposed frequency estimation technique using FRDWT can be the optimal frequency measurement method applied to FDRs.

Designing Smart-tag based Logistics System with Intelligent Track and Trace Service

  • Oh, Se-Won;Park, Joo-Sang;Lee, Yong-Joon
    • Proceedings of the Korean Institute of Intelligent Systems Conference
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    • 2003.09a
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    • pp.244-247
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    • 2003
  • All over the value chain, a logistics information system must satisfy several requirements about gathering and sharing related information. For example, distributors or forwarders need up-to-date information for scheduling and managing their logistics resources. Meanwhile, consignors or consignees want to know the dynamic information about current states or location of their goods. Such information is dependent upon the quality of data sets collected throughout the logistics processes. Thus, gathering accurate data promptly is the essential factor for the success of a logistics information system. However, there are limits in reducing both time-gap and man-power for datn sourcing, since this process is done manually or by using bar codes and scanning devices. Smart-tag can be the alternative to such n time-consuming and inefficient operation, especially for handling piles of goods. The tag includes a micro-chip containing data which is remotely readable by readers with antenna. Logistics system with Smart tag can provide all the information anywhere and anytime, and it will increase the efficiency of logistics and satisfaction of users. In this paper, we propose a conceptual architecture for smart-tag based logistics system and describe its functions.

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Basic principles of intellectual property protection agreements and strategies about traditional knowledge in WIPO (WIPO의 전통지식 등 지적재산권 보호 논의 동향 및 대응 전략의 기본 원칙)

  • Ahn, Sang-Woo;Kim, Hong-Jun;Choi, Hwan-Soo
    • Korean Journal of Oriental Medicine
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    • v.9 no.1
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    • pp.51-63
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    • 2003
  • The international government committee is progressing their agreements about intellectual property protection of traditional knowledge(TK), gene resource(GR), folklore(FL) in WIPO. It is in the course of selection with precedence of TK, GR, FL in WlPO, focused on discussions about listing of TK documents, standardization of DB construction, sharing and profit distribution of GR. Their are disagreements between developed countries and underdeveloped countries about intellectual property protection agreements of TK, GR. The developed countries insist on using, the existing intellectual property protections, but the underdeveloped countries ask new ones on character of TK, GR, It causes intangible assets to be valuable trade properties in future world trade. We have to make national plans to face agreements about IP of TK, GR in WIPO with our own TK, GR. We must have a basic attitude about laying down these plans such as raising national economy, considering our TK, GR to be relics of mankind culture. In addition to these, it needs accurate analysis about agreements in WIPO, our TK, GR, scientific mechanical level and capital power.

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Intelligent Phase Plane Switching Control of Pneumatic Artificial Muscle Manipulators with Magneto-Rheological Brake

  • Thanh, Tu Diep Cong;Ahn, Kyoung-Kwan
    • 제어로봇시스템학회:학술대회논문집
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    • 2005.06a
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    • pp.1983-1989
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    • 2005
  • Industrial robots are powerful, extremely accurate multi-jointed systems, but they are heavy and highly rigid because of their mechanical structure and motorization. Therefore, sharing the robot working space with its environment is problematic. A novel pneumatic artificial muscle actuator (PAM actuator) has been regarded during the recent decades as an interesting alternative to hydraulic and electric actuators. Its main advantages are high strength and high power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source, inherent safety and mobility assistance to humans performing tasks. The PAM is undoubtedly the most promising artificial muscle for the actuation of new types of industrial robots such as Rubber Actuator and PAM manipulators. However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. In addition, the nonlinearities in the PAM manipulator still limit the controllability. Therefore, it is not easy to realize motion with high accuracy and high speed and with respect to various external inertia loads in order to realize a human-friendly therapy robot To overcome these problems a novel controller, which harmonizes a phase plane switching control method with conventional PID controller and the adaptabilities of neural network, is newly proposed. In order to realize satisfactory control performance a variable damper - Magneto-Rheological Brake (MRB) is equipped to the joint of the manipulator. Superb mixture of conventional PID controller and a phase plane switching control using neural network brings us a novel controller. This proposed controller is appropriate for a kind of plants with nonlinearity uncertainties and disturbances. The experiments were carried out in practical PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with phase plane switching control using neural network and without regard for the changes of external inertia loads.

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Context Sharing Framework Based on Time Dependent Metadata for Social News Service (소셜 뉴스를 위한 시간 종속적인 메타데이터 기반의 컨텍스트 공유 프레임워크)

  • Ga, Myung-Hyun;Oh, Kyeong-Jin;Hong, Myung-Duk;Jo, Geun-Sik
    • Journal of Intelligence and Information Systems
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    • v.19 no.4
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    • pp.39-53
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    • 2013
  • The emergence of the internet technology and SNS has increased the information flow and has changed the way people to communicate from one-way to two-way communication. Users not only consume and share the information, they also can create and share it among their friends across the social network service. It also changes the Social Media behavior to become one of the most important communication tools which also includes Social TV. Social TV is a form which people can watch a TV program and at the same share any information or its content with friends through Social media. Social News is getting popular and also known as a Participatory Social Media. It creates influences on user interest through Internet to represent society issues and creates news credibility based on user's reputation. However, the conventional platforms in news services only focus on the news recommendation domain. Recent development in SNS has changed this landscape to allow user to share and disseminate the news. Conventional platform does not provide any special way for news to be share. Currently, Social News Service only allows user to access the entire news. Nonetheless, they cannot access partial of the contents which related to users interest. For example user only have interested to a partial of the news and share the content, it is still hard for them to do so. In worst cases users might understand the news in different context. To solve this, Social News Service must provide a method to provide additional information. For example, Yovisto known as an academic video searching service provided time dependent metadata from the video. User can search and watch partial of video content according to time dependent metadata. They also can share content with a friend in social media. Yovisto applies a method to divide or synchronize a video based whenever the slides presentation is changed to another page. However, we are not able to employs this method on news video since the news video is not incorporating with any power point slides presentation. Segmentation method is required to separate the news video and to creating time dependent metadata. In this work, In this paper, a time dependent metadata-based framework is proposed to segment news contents and to provide time dependent metadata so that user can use context information to communicate with their friends. The transcript of the news is divided by using the proposed story segmentation method. We provide a tag to represent the entire content of the news. And provide the sub tag to indicate the segmented news which includes the starting time of the news. The time dependent metadata helps user to track the news information. It also allows them to leave a comment on each segment of the news. User also may share the news based on time metadata as segmented news or as a whole. Therefore, it helps the user to understand the shared news. To demonstrate the performance, we evaluate the story segmentation accuracy and also the tag generation. For this purpose, we measured accuracy of the story segmentation through semantic similarity and compared to the benchmark algorithm. Experimental results show that the proposed method outperforms benchmark algorithms in terms of the accuracy of story segmentation. It is important to note that sub tag accuracy is the most important as a part of the proposed framework to share the specific news context with others. To extract a more accurate sub tags, we have created stop word list that is not related to the content of the news such as name of the anchor or reporter. And we applied to framework. We have analyzed the accuracy of tags and sub tags which represent the context of news. From the analysis, it seems that proposed framework is helpful to users for sharing their opinions with context information in Social media and Social news.