• Title/Summary/Keyword: DC grid

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Power Loss and Junction Temperature Analysis in the Modular Multilevel Converters for HVDC Transmission Systems

  • Wang, Haitian;Tang, Guangfu;He, Zhiyuan;Cao, Junzheng
    • Journal of Power Electronics
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    • v.15 no.3
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    • pp.685-694
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    • 2015
  • The power loss of the controllable switches in modular multilevel converter (MMC) HVDC transmission systems is an important factor, which can determine the design of the operating junction temperatures. Due to the dc current component, the approximate calculation tool provided by the manufacturer of the switches cannot be used for the losses of the switches in the MMC. Based on the enabled probabilities of each SM in an arm, the current analytical models of the switches can be determined. The average and RMS currents can be obtained from the corresponding current analytical model. Then, the conduction losses can be calculated, and the switching losses of the switches can be estimated according to the upper limit of the switching frequency. Finally, the thermal resistance model of the switches can be utilized, and the junction temperatures can be estimated. A comparison between the calculation and PSCAD simulation results shows that the proposed method is effective for estimating the junction temperatures of the switches in the MMC.

The Economic Evaluation of Renewable Energy Penetration Based on Grid Parity According to the Ratio of DC Power Supply (Grid Parity를 고려한 DC 전원 공급율에 따른 신재생에너지 계통 연계의 경제성 평가)

  • Kim, Sung-Yul;Lee, Sung-Hun;Kim, Jin-O
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.61 no.1
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    • pp.16-21
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    • 2012
  • The growth in IT industry has brought a corresponding rise in the number of connected digital devices in the distribution network. These digital loads lead to AC to DC conversion losses in order to supply power to them. The more the renewable energies and plug-in electrical vehicles penetrated our lives, the more the electrical losses are caused by AC to DC conversion process. Hence, this paper suggests the methodology for evaluating the amount of power supplied according to the ratio of DC power supply and performs an economic analysis of DC distribution system considering grid parity. In here, the cost of carbon emission reduced by renewable energy is also concerned.

A Robust PLL Technique Based on the Digital Lock-in Amplifier under the Non-Sinusoidal Grid Conditions (디지털 록인앰프를 이용한 비정현 계통하에서 강인한 PLL 방법)

  • Ashraf, Muhammad Noman;Khan, Reyyan Ahmad;Choi, Woojin
    • Proceedings of the KIPE Conference
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    • 2018.11a
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    • pp.104-106
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    • 2018
  • The harmonics and the DC offset in the grid can cause serious synchronization problems for grid connected inverters (GCIs) which leads not able to satisfy the IEEE 519 and p1547 standards in terms of phase and frequency variations. In order to guarantee the smooth and reliable synchronization of GCIs with the grid, Phase Locked Loop (PLL) is the crucial element. Typically, the performance of the PLL is assessed to limit the grid disturbances e.g. grid harmonics, DC Offset and voltage sag etc. To ensure the quality of GCI, the PLL should be precise in estimating the grid amplitude, frequency and phase. Therefore, in this paper a novel Robust PLL technique called Digital Lock-in Amplifier (DLA) PLL is proposed. The proposed PLL estimate the frequency variations and phase errors accurately even in the highly distorted grid voltage conditions like grid voltage harmonics, DC offsets and grid voltage sag. To verify the performance of proposed method, it is compared with other six conventional used PLLs (CCF PLL, SOGI PLL, SOGI LPF PLL, APF PLL, dqDSC PLL, MAF PLL). The comparison is done by simulations on MATLAB Simulink. Finally, the experimental results are verified with Single Phase GCI Prototype.

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Development of Simulation Model for Grid-tied Fuel-Cell Power Generation with Digital Controlled DC-DC Converter (디지털제어 DC-DC컨버터로 구성된 계통연계 연료전지발전 시뮬레이션모델 개발)

  • Ju, Young-Ah;Cha, Min-Young;Han, Byung-Moon;Kang, Tae-Sub;Cha, Han-Ju
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.9
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    • pp.1728-1734
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    • 2009
  • This paper proposes a new power conditioning system for the fuel cell power generation, which consists of a ZVS DC-DC converter and 3-phase inverter. The ZVS DC-DC converter with a digital controller boosts the fuel cell voltage of 26-50V up to 400V, and the grid-tie inverter controls the active power delivered to the grid. The operation of proposed power conditioning system was verified through simulations with PSCAD/EMTDC software. The feasibility of hardware implementation was verified through experimental works with a laboratory prototype, which was built with 1.2kW PEM fuel-cell stack, 1kW DC-DC converter, and 3kW PWM inverter. The proposed system can be utilized to commercialize an interconnection system for the fuel-cell power generation.

Compensation Strategy to Eliminate the Effect of Current Measurement Offsets in Grid-Connected Inverters

  • Lee, Chang-Hee;Choi, Jong-Woo
    • Journal of Power Electronics
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    • v.14 no.2
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    • pp.383-391
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    • 2014
  • For the digital control of systems such as grid-connected inverters, measuring inverter output currents accurately is essential. However, current measurement offsets are inevitably generated by current measurement paths and cause DC current components in real inverter output currents. Real inverter output currents with DC components cause the DC-link capacitor voltage to oscillate at the frequency of a utility voltage. For these reasons, current measurement offsets deteriorate the overall system performance. A compensation strategy to eliminate the effect of current measurement offsets in grid-connected inverters is proposed in this study. The validity of the proposed compensation strategy is verified through simulations and experiments. Results show that the proposed compensation strategy improves the performance of grid-connected inverters.

Operational Analysis of DC Micro-grid using PSCAD/EMTDC Software (PSCAD/EMTDC를 이용한 DC Micro-grid의 동작 분석)

  • Lee, Ji-Heon;Kwon, Ki-Hyun;Han, Byung-Moon
    • Proceedings of the KIEE Conference
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    • 2009.07a
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    • pp.446_447
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    • 2009
  • This paper describes operational analysis results of the DC micro-grid using detailed model of distributed generation. Detailed model of wind power generation, photo-voltaic generation, fuel-cell generation was implemented with the user-defined model of PSCAD/EMTDC software that is coded with C-language. Various simulation results confirm that the DC micro-grid can operate without any problem in both the interconnected mode and the islanded mode. The operation analysis result confirms that the DC micro-grid make it feasible to provide power to the load stably.

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Improved Conditional Integrator Anti-Windup Method for Seamless Transfer of Bidirectional DC-DC Converter in Grid-Connected Battery Energy Storage System (계통연계형 배터리 에너지저장장치용 양방향 DC-DC 컨버터의 무순단 절체를 위한 조건부 적분 안티-와인드업 연구)

  • Eom, Jun-Yong;Choi, Sung-Jin;Lee, Hong-Hee
    • The Transactions of the Korean Institute of Power Electronics
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    • v.25 no.5
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    • pp.333-342
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    • 2020
  • Power exchanges between the grid and the battery through a bidirectional DC-DC converter are essential for DC microgrid systems. In general, the battery is charged when the grid is connected, and the system is powered by the battery when the grid is disconnected. In this mode transition, the saturation of the voltage controller slows down output response and produces large transient errors in DC link voltage. To solve this problem, a novel anti-windup design is proposed to improve anti-windup performance further. The proposed method stabilizes DC bus voltage through a wider range of battery voltage with faster transition compared with that of conventional methods. The proposed method is verified through an experimental setup composed of a 125 W laboratory-scale DC microgrid system.

Study on the Voltage Stabilization Technology Using Photovoltaic Generation Simulator in Three-Level Bipolar Type DC Microgrid

  • Kim, Taehoon;Kim, Juyong;Cho, Jintae;Jung, Jae-Seung
    • Journal of Electrical Engineering and Technology
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    • v.13 no.3
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    • pp.1123-1130
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    • 2018
  • Voltage stabilization is an essential component of power quality in low voltage DC (LVDC) microgrid. The microgrid demands the interconnection of a number of small distributed power resources, including variable renewable generators. Therefore, the voltage can be maintained in a stable manner through the control of these distributed generators. In this study, we did research on the new advanced operating method for a photovoltaic (PV) simulator in order to achieve interconnection to a bipolar LVDC microgrid. The validity of this voltage stabilization method, using the distributed generators, is experimentally verified. The test LVDC microgrid is configured by connecting the developed PV simulator and DC load, DC line, and AC/DC rectifier for connecting the main AC grid. The new advanced control method is applied to the developed PV simulator for the bipolar LVDC grid in order to stabilize the gird voltage. Using simulation results, the stabilization of the grid voltage by PV simulator using the proposed control method is confirmed the through the simulation results in various operation scenarios.

DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation

  • Lee, Ji-Heon;Kim, Hyun-Jun;Han, Byung-Moon;Jeong, Yu-Seok;Yang, Hyo-Sik;Cha, Han-Ju
    • Journal of Power Electronics
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    • v.11 no.3
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    • pp.350-359
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    • 2011
  • This paper describes the operational analysis results of a DC micro-grid using a detailed model of distributed generation. A detailed model of wind power generation, photo-voltaic generation and fuel cell generation was implemented with an userdefined model created with PSCAD/EMTDC software and coded in C-language. The operational analysis was carried out using PSCAD/EMTDC software, in which the power circuit is implemented by a built-in model and the controller is modeled by an user-defined model that is also coded in C-language. Various simulation results confirm that a DC micro-grid can operate without any problems in both the grid-tied mode and in the islanded mode. The operational analysis results confirm that the DC micro-grid makes it feasible to provide power to the load stably. It can also be utilized to develop an actual system design.

Optimized Design and Coordinated Control for Stand-alone DC Micro-grid (독립형 DC 마이크로그리드의 최적화 설계와 협조적 제어)

  • Han, Tae-Hee;Lee, Ji-Heon;Kim, Hyun-Jun;Han, Byung-Moon
    • The Transactions of the Korean Institute of Power Electronics
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    • v.18 no.1
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    • pp.63-71
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    • 2013
  • This paper describes the coordinated droop control method for stand-alone type DC micro-grid to improve reliability and utilization of distributed generations and energy storage. The stand-alone type DC micro-grid consists of several distributed generations such as a wind power generation, solar power and micro-turbine, and energy storage. The proposed method which is based on autonomous control method shows high reliability and stability through coordinated droop control of distributed generations and energy storage and also capability of battery management. The operation of stand-alone type DC micro-grid was analyzed using detail simulation model with PSCAD/EMTDC software. Based on simulation results, a hardware simulator was built and tested with commercially available components and performance of system was verified.