• Title/Summary/Keyword: DC grid

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Improved DC Offset Error Compensation Algorithm in Phase Locked Loop System

  • Park, Chang-Seok;Jung, Tae-Uk
    • Journal of Electrical Engineering and Technology
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    • v.11 no.6
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    • pp.1707-1713
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    • 2016
  • This paper proposes a dc error compensation algorithm using dq-synchronous coordinate transform digital phase-locked-loop in single-phase grid-connected converters. The dc errors are caused by analog to digital conversion and grid voltage during measurement. If the dc offset error is included in the phase-locked-loop system, it can cause distortion in the grid angle estimation with phase-locked-loop. Accordingly, recent study has dealt with the integral technique using the synchronous reference frame phase-locked-loop method. However, dynamic response is slow because it requires to monitor one period of grid voltage. In this paper, the dc offset error compensation algorithm of the improved response characteristic is proposed by using the synchronous reference frame phase-locked-loop. The simulation and the experimental results are presented to demonstrate the effectiveness of the proposed dc offset error compensation algorithm.

A Novel DC Solid-State Circuit Breaker for DC Grid (DC Grid를 위한 새로운 구조의 DC Solid-State Circuit Breaker)

  • Kim, Jin-Young;Kim, In-Dong;Nho, Eui-Cheol
    • The Transactions of the Korean Institute of Power Electronics
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    • v.17 no.4
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    • pp.368-376
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    • 2012
  • According to developed distributed generators, Solid State Circuit Breaker(SSCB) is essential for high power quality of DC Grid. In this paper, a simple and new structure of DC SSCB with a fast circuit breaker and fault current limiter is proposed. It can help to choice low specification of elements because of the limiting of fault current and achieve economic efficiency for minimizing auxiliary SCRs. Also all of SCRs have little switching loss because they operate under ZVS and ZCS. Through simulations and experiments of short-circuit fault, the performance characteristic of proposed circuit is verified and a guideline is so suggested that the DC SSCB is applied for a different DC grid using formulas.

Load Characteristics of the DC GRID Connected to Small Fuel Cells (소형 연료전지 연계형 DC GRID 부하 특성)

  • Lee, Sang-Woo;Lee, Sang-Cheol;Kwon, O-Sung;Bae, Jun-Hyung;Park, Tae-Joon;Kang, Jin-Kyu;Lee, Dong-Ha
    • Journal of the Korean Solar Energy Society
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    • v.32 no.spc3
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    • pp.289-294
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    • 2012
  • In recent years, understanding the dynamics of DC distribution system has become critically important due mainly to the increasing needs for the interconnection of DC distributed generators and the (DC-based) electric vehicle (EV) charging systems. In this paper, the characteristics of the DC grid system connected to the compact proton exchange membrane fuel cell (PEMFC) has been studied. In particular, the voltage and current transient phenomena were measured by varying the load of the DC grid system. Also, the voltage and current ripple were measured at the different load conditions. Our experimental results clearly manifested that the study contributes to the establishment of fundamental method to characterize the small DC grid system including distributed generation.

Load Characteristics of the DC GRID Connected to Small Fuel Cells (소형 연료전지 연계형 DC GRID 부하 특성 실험)

  • Lee, Sang-Woo;Kwon, O-Sung;Lee, Sang-Cheol;Bae, Jun-Hyung;Park, Tae-Joon;Kang, Jin-Kyu;Lee, Dong-Ha
    • 한국태양에너지학회:학술대회논문집
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    • 2012.03a
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    • pp.414-418
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    • 2012
  • In recent years, understanding the dynamics of DC distribution system has become critically important due mainly to the increasing needs for the interconnection of DC distributed generators and the (DC-based) electric vehicle (EV) charging systems. In this paper, the characteristics of the DC grid system connected to the compact proton exchange membrane fuel cell (PEMFC) has been studied. In particular, the voltage and current transient phenomena were measured by varying the load of the DC grid system. Also, the voltage and current ripple were measured at the different load conditions. Our experimental results clearly manifested that the study contributes to the establishment of fundamental method to characterize the small DC grid system including distributed generation.

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Optimal Power Flow of DC-Grid Based on Improved PSO Algorithm

  • Liu, Xianzheng;Wang, Xingcheng;Wen, Jialiang
    • Journal of Electrical Engineering and Technology
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    • v.12 no.4
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    • pp.1586-1592
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    • 2017
  • Voltage sourced converter (VSC) based direct-current (DC) grid has the ability to control power flow flexibly and securely, thus it has become one of the most valid approaches in aspect of large-scale renewable power generation, oceanic island power supply and new urban grid construction. To solve the optimal power flow (OPF) problem in DC grid, an adaptive particle swarm optimization (PSO) algorithm based on fuzzy control theory is proposed in this paper, and the optimal operation considering both power loss and voltage quality is realized. Firstly, the fuzzy membership curve is used to transform two objectives into one, the fitness value of latest step is introduced as input of fuzzy controller to adjust the controlling parameters of PSO dynamically. The proposed strategy was applied in solving the power flow issue in six terminals DC grid model, and corresponding results are presented to verify the effectiveness and feasibility of proposed algorithm.

A Study on the Fault Tolerance and High Efficiency Control of 4 Leg DC/DC Converter for Battery Energy Storage System in Standalone DC Micro-grid (독립형 DC마이크로그리드 내 BESS용 4 LEG DC/DC 컨버터의 고장허용 및 고효율 제어에 관한 연구)

  • Choi, Jung-Sik;Oh, Seung-Yeol;Cha, Dae-Seak;Chung, Dong-Hwa
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.67 no.9
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    • pp.1239-1248
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    • 2018
  • This paper proposes a fault tolerant and high efficiency operation algorithm for a 4 LEG DC/DC converter for a battery energy storage system(BESS) forming a main power source in a standalone DC micro grid. The BESS for the main power supply in the stand-alone DC micro-grid is required to operate at high speed according to fault tolerant control and load by operating at all times. Fault-tolerance control changes the short-circuit fault to an open-circuit fault by using a fuse in case of leg fault in 4 legs, and operates stably through phase shift control. In addition, considering the loss of the power semiconductor, the number of LEG operation is adjusted to operate at high efficiency in the full load region. In this paper, fault tolerant control and high efficiency operation algorithm of DC/DC converter for BESS in standalone DC micro grid is presented and it is proved through simulation and experiment.

A Study on Energy Efficiency of Battery Charge/Discharge System based on DC μ-Grid (DC μ-Grid 기반 배터리 충/방전 시스템의 에너지 효율에 관한 연구)

  • Yeo, Sung-Dae;Kim, Jong-Un;Lee, Kyung-Ryang;Han, Cheol-Kyu;Ryu, Tae-Hyoung;Kim, Kyeong-Hwa;Kim, Seong-Kweon
    • The Journal of the Korea institute of electronic communication sciences
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    • v.10 no.12
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    • pp.1337-1344
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    • 2015
  • Formation process through charge/discharge operation is needed in manufacturing Li-ion battery. In the process battery is discharged by a load resistor of discharger. Here, energy losses happen. Therefore, in this paper, the efficient energy operation of battery is studied in the charge/discharge system based on DC ${\mu}-Grid$. A result of computer simulation shows that if in the charge/discharge system based on DC ${\mu}-Grid$, the number of discharge batteries in comparison with three charge battery sets exceeds 133%, voltage fluctuation that occurs while the grid voltage stabilizes, which makes the system fatal. Therefore, it was demonstrated that a remarkable energy saving effect could be achieved when the number of discharge battery set is maintained to be 133% in comparison with three charge battery sets.

A Second-order Harmonic Current Reduction with a Fast Dynamic Response for a Two-stage Single-phase Grid-connected Inverter

  • Jung, Hong-Ju;Kim, Rae-Young
    • Journal of Electrical Engineering and Technology
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    • v.9 no.6
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    • pp.1988-1994
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    • 2014
  • In a single-phase grid-connected power system consisting of a DC/DC converter and a DC/AC converter, the current drawn from renewable energy sources has a tendency to be pulsated and contains second-order frequency ripple components, which results in several drawback such as a power harvesting loss and a shortening of the energy source's life. This paper presents a new second-order harmonic current reduction scheme with a fast dc-link voltage loop for two-stage dc-dc-ac grid connected systems. In the frequency domain, an adequate control design is performed based on the small signal transfer function of a two-stage dc-dc-ac converter. To verify the effectiveness of proposed control algorithm, a 1 kW hardware prototype has been built and experimental results are presented.

Study of Self-excited Resonant DC Circuit Breaker in Future DC Grid (향후 DC 전력 계통에서의 자려 공진 DC 차단기에 관한 연구)

  • Guo, Qinglei;Yoon, Minhan;Jang, Gilsoo
    • Proceedings of the KIEE Conference
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    • 2015.07a
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    • pp.396-397
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    • 2015
  • With the increasing utilization of high-voltage, direct current (HVDC) transmissions in modern power systems, the DC grid is becoming a hot topic in academic and practical systems. In the DC grid, one of the urgent problems is the fast clearance of the DC fault in the DC network. One preferred method is to isolate the faulty point from the DC network in a short time. The DC circuit breaker is to interrupt the overcurrent after DC faults occur. In this paper, a self-excited resonant DC circuit breaker is an easy and cheap equipment to interrupt the DC fault current. The Mayr's arc model is utilized to simulate the self-excited DC circuit breaker in a DC test system in PSCAD/EMTDC.

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A Seamless Transfer Method of Bidirectional DC-DC Converter for ESS in DC Micro-grids (DC 마이크로그리드에서 에너지 저장장치를 위한 양방향 DC-DC컨버터의 무순단 절체 제어기법)

  • Kwon, Min-Ho;Park, Jung-Sung;Choi, Se-Wan
    • The Transactions of the Korean Institute of Power Electronics
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    • v.19 no.2
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    • pp.194-200
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    • 2014
  • In DC micro-grid system energy storage systems (ESS) are responsible for storing energy and balancing power. Also, control target of the bidirectional DC-DC converter(BDC) for ESS should be changed depending on the operating mode. During the grid connected mode, the BDC controls the battery current or voltage. When a grid fault occurs, the BDC should change the control target to regulate the DC-bus. The BDC with conventional control method may experience large transient state during the mode change. This paper proposes a control method of BDC for ESS. The proposed control method is able to provide autonomous and seamless mode transfer by a variable current limiter. To validate the proposed concept, simulation results using PSIM and experimental results from a 2kW prototype are provided.