• Title/Summary/Keyword: Grid connected

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Droop Control Scheme of a Three-phase Inverter for Grid Voltage Unbalance Compensation

  • Liu, Hongpeng;Zhou, Jiajie;Wang, Wei;Xu, Dianguo
    • Journal of Power Electronics
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    • v.18 no.4
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    • pp.1245-1254
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    • 2018
  • The stability of a grid-connected system (GCS) has become a critical issue with the increasing utilization of renewable energy sources. Under grid faults, however, a grid-connected inverter cannot work efficiently by using only the traditional droop control. In addition, the unbalance factor of voltage/current at the common coupling point (PCC) may increase significantly. To ensure the stable operation of a GCS under grid faults, the capability to compensate for grid imbalance should be integrated. To solve the aforementioned problem, an improved voltage-type grid-connected control strategy is proposed in this study. A negative sequence conductance compensation loop based on a positive sequence power droop control is added to maintain PCC voltage balance and reduce grid current imbalance, thereby meeting PCC power quality requirements. Moreover, a stable analysis is presented based on the small signal model. Simulation and experimental results verify the aforementioned expectations, and consequently, the effectiveness of the proposed control scheme.

A Study on the Characteristic Analysis of a Grid-connected Induction Generator for Wind Power Systems on Simulink (Simulink에서 계통연계 유도형 풍력발전시스템의 특성해석에 대한 연구)

  • An, Hae-Joon;Kim, Hyun-Goo;Jang, Moon-Seok;Jang, Gil-Soo
    • 한국신재생에너지학회:학술대회논문집
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    • 2010.06a
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    • pp.184.3-184.3
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    • 2010
  • This study suggests a modeling of grid-connected wind turbine generation systems and performs simulation according to increase/decrease of real wind speed. MATLAB & SIMULINK implemented modeling of grid-connected wind turbine generation system. Terminal voltage, grid voltage, and active/reactive power shall be observed following the performance of simulation.

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Grid-connected Wind Turbine Generation System Modeling and Simulation Using MATLAB/Simulink (MATLAB/Simulink를 이용한 계통연계 풍력발전 시스템 모델링 및 시뮬레이션)

  • An, Hae-Joon;Kim, Hyun-Goo;Jang, Gil-Soo;Jang, Moon-Seok;Ko, Seok-Whan
    • 한국신재생에너지학회:학술대회논문집
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    • 2008.10a
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    • pp.321-323
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    • 2008
  • This study suggests a modeling of grid-connected wind turbine generation systems and performs simulation according to increase/decrease of real wind speed. MATLAB/Simulink implemented modeling of grid-connected wind turbine generation system. Terminal voltage, grid voltage, and active/reactive power shall be observed following the performance of simulation.

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Simulation for voltage fluctuations of Grid-connected Wind Turbine Generators by Simulink (Simulink에서 풍력발전 연계시스템의 전압변동 시뮬레이션)

  • Ahn, Duck-Keun;Ho, Kyoung-Soo
    • Proceedings of the KIEE Conference
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    • 2003.07b
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    • pp.1389-1391
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    • 2003
  • The development of wind turbine power generation has grown during the past ten years. An important question, when installing wind turbines with the generator connected directly to the grid, is holt much the voltage quality will be affected by the uneven power production and by the connection of the wind turbine to the grid. This paper presents the voltage fluctuation of grid-connected WTG(wind turbine generators) by MATLAB/Simulink.

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Power Quality Improvement for Grid Connected Inverters under Distorted and Unbalanced Grids

  • Kim, Hyun-Sou;Kim, Jung-Su;Kim, Kyeong-Hwa
    • Journal of Power Electronics
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    • v.16 no.4
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    • pp.1578-1586
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    • 2016
  • A power quality improvement scheme for grid connected inverters, even in the presence of the disturbances in grid voltages due to harmonic distortions and three-phase imbalance, is presented for distributed generation (DG) power systems. The control objective is to force the inverter currents to follow their references with robustness even under external disturbances in grid voltages. The proposed scheme is realized by a disturbance observer (DOB) based current control scheme. Since the uncertainty in a system can be effectively canceled out using an estimated disturbance by the DOB, the resultant system behaves like a closed-loop system consisting of a disturbance-free nominal model. For experimental verification, a 2 kVA laboratory prototype of a grid connected inverter has been built using a digital signal processor (DSP) TMS320F28335. Through comparative simulations and experimental results under grid disturbances such as harmonic distortion and imbalance, the effectiveness of the proposed DOB based current control scheme is demonstrated.

A Novel Harmonic Compensation Method for the Single Phase Grid Connected Inverters (단상 계통연계 인버터를 위한 새로운 고조파 보상법)

  • Khan, Reyyan Ahmad;Ashraf, Muhammad Noman;Choi, Woojin
    • Proceedings of the KIPE Conference
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    • 2018.07a
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    • pp.144-146
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    • 2018
  • In order to meet the harmonics standards such as IEEE 519 and P1547 the output quality of a grid connected inverter should satisfy a certain level of Total Harmonic Distortion (THD) value. However, the output quality of an inverter gets degraded due to the grid voltage harmonics, the dead time effects and the nonlinearity of the switches, which all contributes to a higher THD value of the output. In order to meet the required THD value for the inverter output under the distorted grid condition the use of harmonic controller is essential. In this paper a novel feedforward harmonic compensation method is proposed in order to effectively eliminate the low order harmonics in the inverter current to the grid. In the proposed method, unlike the conventional harmonic control methods, the hamonic components are directly compensated by the feedforward terms generated by the PR controller with the grid current in the stationary frame. The proposed method is simple in implementation but powerful in eliminating the harmonics from the output. The effectiveness of proposed method is verified through the PSIM simulation and the experiments with a 5kW single phase grid connected inverter.

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Mode Switching Smooth Control of Transient Process of Grid-Connected 400 Hz Solid-State Power Supply System

  • Zhu, Jun-Jie;Nie, Zi-Ling;Zhang, Yin-Feng;Han, Yi
    • Journal of Power Electronics
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    • v.16 no.6
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    • pp.2327-2337
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    • 2016
  • The mode-switching control of transient process is important to grid-connected 400 Hz solid-state power supply systems. Therefore, this paper analyzes the principle of on-grid and islanding operation of the system with or without local loads in the grid-connected process and provides a theoretical study of the effect of different switching sequences on the mode-switching transient process. The conclusion is that the mode switch (MS) must be turned on before the solid-state switch (STS) in the on-grid process and that STS must be turned off before the MS in the off-grid process. A strategy of mode-switching smooth control for transient process of the system is proposed, including its concrete steps. The strategy utilizes the average distribution of peak currents and the smooth adjustment of peak currents and phases to achieve a no-shock grid connection. The simulation and experimental results show that the theoretical analysis is correct and that the method is effective.

An Improved Harmonic Compensation Method for a Single-Phase Grid Connected Inverter (단상 계통연계 인버터를 위한 개선된 고조파 보상법)

  • Khan, Reyyan Ahmad;Choi, Woojin
    • The Transactions of the Korean Institute of Power Electronics
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    • v.24 no.3
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    • pp.215-227
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    • 2019
  • Grid-connected inverters should satisfy a certain level of total harmonic distortion (THD) to meet harmonics standards, such as IEEE 519 and P1547. The output quality of an inverter is typically degraded due to grid voltage harmonics, dead time effects, and the device's turn-on/turn-off delay, which all contribute to increasing the THD value of the output. The use of a harmonic controller is essential to meet the required THD value for inverter output under a distorted grid condition. In this study, an improved feedforward harmonic compensation method is proposed to effectively eliminate low-order harmonics in the inverter current to the grid. In the proposed method, harmonic components are directly compensated through feedforward terms generated by the proportional resonant controller with the grid current in a stationary frame. The proposed method is simple to implement but powerful in eliminating harmonics from the output. The effectiveness of the proposed method is verified through simulation using PSIM software and experiments with a 5 kW single-phase grid-connected inverter.

Development of Low-voltage Seamless Transfer Microgrid on Grid-connected Type Islands by Autonomous Operation (자율운전에 의한 계통연계형 도서의 저압 무순단 마이크로그리드 구축)

  • Kim, Jeong Hun;Kwon, Jung-Min;Yun, Sang-Yun
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.66 no.4
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    • pp.169-176
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    • 2017
  • This paper presents research on low-voltage microgrids to maintain a continuous power supply to critical loads on grid-connected islands in Korea. The low-voltage microgrids of this paper focused on that changes public office buildings into uninterrupted microgrids by autonomous operation. For this, a microgrid controller (MGC) and a power conditioning system (PCS) that allow a seamless transfer between grid-connected and grid-isolated operation are proposed. The proposed PCS operates with a silicon controlled rectifier (SCR) switch and employs a simple structure. It supplies power continuously without operators through a coordinated operation between MGC and PCS. In addition, proposed MG has a schedule operation for minimizing electricity charges and provides ancillary services that enable the utilization of resources according to the operation purpose of utility distribution networks. To demonstrate the uninterrupted low-voltage microgrid proposed in this study, a microgrid was implemented and tested in a public office building in Anjwa Island, Jeollanam-do in Korea. A seamless, autonomous operation history, despite system disturbances, was obtained through a long-term demonstration of operation. The results showed that the proposed microgrid technology can be used to achieve energy resilience in grid-connected island areas.

A Synthetical Study on Power Quality Measurement of Grid-Connected Wind Turbine Generating System based on the IEC International Standards (IEC 국제표준에 따른 계통연계형 풍력터빈 발전기계통의 전력품질 측정방법에 관한 심화연구)

  • Cho, Soo-Hwan
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.63 no.2
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    • pp.197-204
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    • 2014
  • As more and more renewable energy resources are connected into the existing power system and their generation capacities are increasing, the need for regulations to minimize their impacts on the power grid is increasingly growing. And minimizing the irregular impacts made by grid-connected wind generators is important, since the output power generated by renewable energy resources can be changed easily by the weather condition and surrounding environment. In South Korea, an operational technical standard for distributed generation is used as a regulation, in which renewable energy sources including wind power are considered as a kind of distributed generation. In this paper, an international standard, IEC 61400-21, for the grid-connected wind turbine generating system(WTGS) will be introduced and a comprehensive and detailed review on the measuring methods of power quality characteristic parameters for WTGS based on the related IEC standards will be presented. Additionally, some prerequisites for applying the international standards to KEPCO system will be proposed.