• Title/Summary/Keyword: Grid connected

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A Seamless and Autonomous Mode Transfer Method of Grid-connected Inverter in Microgrid (마이크로그리드에서 계통연계 인버터의 자율적이며 끊김없는 모드전환 기법)

  • Park, Sung-Youl;Kwon, Min-Ho;Choi, Se-Wan
    • The Transactions of the Korean Institute of Power Electronics
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    • v.24 no.5
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    • pp.349-355
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    • 2019
  • A grid-connected inverter with critical loads should be able to supply a stable voltage to critical loads at mode change and during clearing time while detecting unintentional islanding. This study proposes a mode transfer method for a grid-connected inverter with critical loads. The proposed method, which integrates the grid-connected and islanded mode control loops into one control block, provides an autonomous and seamless mode transfer from the current control to the voltage control. Therefore, the proposed scheme can supply a stable voltage to critical loads at mode change and during clearing time. Experimental results are provided to validate the proposed method.

Grid Current Control Scheme at Thee-Phase Grid-Connected Inverter Under Unbalanced and Distorted Grid Voltage Conditions (계통전압 왜곡 및 불평형시 3상 계통연계인버터의 계통전류제어 기법)

  • Tran, Thanh-Vu;Chun, Tae-Won
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.11
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    • pp.1560-1565
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    • 2013
  • This paper proposes the control method for compensating for unbalanced grid current and reducing a total harmonic distortion (THD) of the grid current at the three-phase grid-connected inverter systems under unbalancd and distorted grid voltage conditions. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and magnitude attenuation due to the hardware low-pass filter (LPF). The Cauchy-Schwarz inequality theory is used in order to search more easily for a minimum point of THD. Both the gain and angle of a compensation voltage at the minimum point of THD of the grid current are derived. The negative-sequence components in the three-phase unbalanced grid voltage are cancelled in order to achieve the balanced grid current. The simulation and experimental results show the validity of the proposed control methods.

Modeling and Control of a Grid Connected VSI using a Delta Connected LCL Filter ($\Delta$-결선 LCL 필터를 사용하는 삼상 계통 연계 인버터의 모델링과 제어)

  • Lee, Sang-In;Lee, Kui-Jun;Hyun, Dong-Seok
    • The Transactions of the Korean Institute of Power Electronics
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    • v.14 no.1
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    • pp.1-7
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    • 2009
  • There are two ways to connect an LCL filter in a grid-connected VSI. A wye connected LCL filter is general way, and the other is a delta connected LCL filter. While a model of a system with a wye connected LCL filter is calculated, a model of a system with a delta connected LCL filter is not formulated. Thus, we propose a mathematical model of a system with a delta connected LCL filter. Also, a comparative study of capacitor current harmonics of a delta connected LCL filter and a wye connected LCL filter is included. Experimental results exhibit that it is advantageous to control grid currents for a system with a delta connected LCL filter.

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.

Loss Calculation Method of Grid-Connected Photovoltaic System (계통연계형 태양광발전시스템의 손실 산출방법)

  • So, Jung-Hun;Lim, Hyun-Mook;Wang, Hye-Mi;Jung, Young-Seok;Ko, Suk-Whan;Ju, Young-Chul
    • Journal of the Korean Solar Energy Society
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    • v.33 no.5
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    • pp.18-23
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    • 2013
  • This paper presents a simple but valid loss calculation method of grid-connected photovoltaic system based on normalized yield model. The proposed method can be represented as a quantitative value for five losses and performance of grid-connected photovoltaic system with three years monitored data. These results will indicate that it is useful to investigate various loss factors causing the performance obstruction, enhance the lifetime yield for changing meteorological conditions, and determine the optimal design and performance improvement of grid-connected photovoltaic system.

Control Method for Reducing the THD of Grid Current of Three-Phase Grid-Connected Inverters Under Distorted Grid Voltages

  • Tran, Thanh-Vu;Chun, Tae-Won;Lee, Hong-Hee;Kim, Heung-Geun;Nho, Eui-Cheol
    • Journal of Power Electronics
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    • v.13 no.4
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    • pp.712-718
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    • 2013
  • This paper proposes a control method for reducing the total harmonic distortion (THD) of the grid current of three-phase grid-connected inverter systems when the grid voltage is distorted. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and magnitude attenuation due to the hardware low-pass filter (LPF). The Cauchy-Schwarz inequality theory is used in order to search more easily for the minimum point of the THD. Both the gain and angle of the compensation voltage at the minimum point of the THD of the grid current are derived with the variation of cut-off frequencies of the hardware LPF. Simulation and experimental results show the validity of the proposed control methods.

Assessment on Power Quality of Grid-Connected PV System Based on Incremental Conductance MPPT Control (증분컨덕턴스 MPPT제어 기반 계통연계형 태양광발전시스템의 전력품질 평가)

  • Seol, Jae-Woong;Jang, Jae-Jung;Kim, Dong-Min;Lee, Seung-Hyuk;Kim, Jin-O
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.56 no.1
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    • pp.8-13
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    • 2007
  • During the last years, there has been an increased interest in the new energy such as photovoltaic(PV) system from the viewpoint of environmental pollution. In this regard, this paper estimates the power quality of grid-connected PV system. As the maximum power operating point(MPOP) of photovoltaic(PV) power systems alters with changing atmospheric conditions, the efficiency of maximum power point tracking(MPPT) is important in PV power systems. Moreover, grid-connected PV system occurs some problems such as voltage inequality and harmonics. Therefore, this paper presents the results of a grid-connected PV system modeling that contains incremental conductance MPPT controller by PSCAD/EMTDC simulator and investigates the influence that can occur in the grid-connected PV system from aspect of power quality, i.e. voltage drop, total harmonic distortion(TDD) and total demand distortion(TDD). For the case study, the measured data of the PV way in Cheongwadae, Seoul, Korea is used.

Dual-Loop Power Control for Single-Phase Grid-Connected Converters with LCL Filter

  • Peng, Shuangjian;Luo, An;Chen, Yandong;Lv, Zhipeng
    • Journal of Power Electronics
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    • v.11 no.4
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    • pp.456-463
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    • 2011
  • Grid-connected converters have widely adopted LCL filters to acquire high harmonic suppression. However, the LCL filter increases the system order so that the design of the system stability would be complicated. Recently, sole-loop control strategies have been used for grid-connected converters with L or LC filters. But if the sole-loop control is directly transplanted to grid-connected converters with LCL filters, the systems may be unstable. This paper presents a novel dual-loop power control strategy composed of a power outer loop and a current inner loop. The outer loop regulates the grid-connected power. The inner loop improves the system stability margin and suppresses the resonant peak caused by the LCL filter. To obtain the control variables, a single-phase current detection is proposed based on PQ theory. The system transfer function is derived in detail and the influence of control gains on the system stability is analyzed with the root locus. Simulation and experimental results demonstrate the feasibility of the proposed control.

BPF-based Grid Voltage Feedforward Control of Grid-connected Converters for Improving Robust Stability

  • Yang, Shude;Tong, Xiangqian;Yin, Jun;Wang, Haiyan;Deng, Yaping;Liu, Le
    • Journal of Power Electronics
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    • v.17 no.2
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    • pp.432-441
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    • 2017
  • Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter's robust stability against grid impedance variations. The selection method of the BPF's bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system's robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

Adaptive Neural PLL for Grid-connected DFIG Synchronization

  • Bechouche, Ali;Abdeslam, Djaffar Ould;Otmane-Cherif, Tahar;Seddiki, Hamid
    • Journal of Power Electronics
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    • v.14 no.3
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    • pp.608-620
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    • 2014
  • In this paper, an adaptive neural phase-locked loop (AN-PLL) based on adaptive linear neuron is proposed for grid-connected doubly fed induction generator (DFIG) synchronization. The proposed AN-PLL architecture comprises three stages, namely, the frequency of polluted and distorted grid voltages is tracked online; the grid voltages are filtered, and the voltage vector amplitude is detected; the phase angle is estimated. First, the AN-PLL architecture is implemented and applied to a real three-phase power supply. Thereafter, the performances and robustness of the new AN-PLL under voltage sag and two-phase faults are compared with those of conventional PLL. Finally, an application of the suggested AN-PLL in the grid-connected DFIG-decoupled control strategy is conducted. Experimental results prove the good performances of the new AN-PLL in grid-connected DFIG synchronization.