• Title, Summary, Keyword: Parallel-connected inverter

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Parallel Connected High Frequency AC Link Inverters Based on Full Digital Control

  • Sha, Deshang;Guo, Zhiqiang;Deng, Kai;Liao, Xiaozhong
    • Journal of Power Electronics
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    • v.12 no.4
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    • pp.595-603
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    • 2012
  • This paper presents a full digital control strategy for parallel connected modular inverter systems. Each modular inverter is a high frequency (HF) AC link inverter which is composed of a HF inverter and a HF transformer followed by a cycloconverter. To achieve equal sharing of the load current and to suppress the circulating currents among the modules, a three-loop control strategy, consisting of a common output voltage regulation (OVR) loop, individual circulating current suppression (CCS) loops and individual inner current tracking (ICT) loops, is proposed. The ICT loops are implemented with predictive current control from which high precision current tracking can be obtained. The effectiveness of the proposed control strategy is verified by simulation and experimental results from parallel connected two full-bridge HF AC link inverter modules.

Parallel Operation Characteristics of Two Linear Induction Motors (선형 유도전동기의 병렬 운전 특성 실험)

  • Park Seung-Chan;Kim Kyung-Min
    • Proceedings of the KSR Conference
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    • pp.44-48
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    • 2005
  • In general, the parallel-connected linear induction motors(LIM) are fed by one VVVF inverter in the magnetically levitated vehicle(MAGLEV) or linear motor subway drives. The air gap length of the parallel-connected linear induction motors operating at a grade or curved sections can be different each other. The air gap difference of the two motors attached to the same module causes unequal phase currents, asymmetic thrust and attraction force generation. In this paper, parellel-connected linear induction motors are operated by one IGBT inverter under the different air gap condition so that the phase current characteristics are examined experimentally.

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Islanding Detection for Grid-connected PV Inverter under Parallel Operation (계통연계형 태양광 인버터 병렬운전 상황에서의 단독운전 검출)

  • Jo, Yeong-Min;Kim, Dong-Gyun;Song, Seung-Ho;Choy, Ick;Lee, Young-Kwoun;Cho, Sang-Yoon;Choi, Ju-Yeop
    • The Transactions of the Korean Institute of Power Electronics
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    • v.21 no.4
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    • pp.283-289
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    • 2016
  • Islanding protection of a grid-connected photovoltaic (PV) inverter is a key function for standards compliance. Unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, many anti-islanding schemes have been examined. However, existing anti-islanding schemes have poor power quality and non-detection zone issues. Moreover, most schemes have problems that deteriorate the performance of islanding detection under parallel operation. Therefore, this paper proposes a novel anti-islanding scheme that has negligible power quality degradation and has no non-detection zone and islanding detection under a parallel operation. Both simulation and experimental results validate the proposed scheme.

Seamless Mode Transfer of Indirect Current Controlled Parallel Grid-Connected Inverters (간접전류제어방식 병렬형 계통연계 인버터의 무순단 모드절환)

  • Song, Injong;Choi, Junsoo;Lim, Kyungbae;Choi, Jaeho
    • The Transactions of the Korean Institute of Power Electronics
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    • v.24 no.5
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    • pp.334-341
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    • 2019
  • This study proposes the control strategy for the seamless mode transfer of indirect current controlled parallel grid-connected inverters. Under the abnormal grid condition, the grid-connected inverter can convert the operation mode from grid-connected to stand-alone mode to supply power to the local load. For a seamless mode transfer, the time delay problems caused by the accumulated control variable error must be solved, and the indirect current control method has been applied as one of the solutions. In this study, the design of control parameters for the proportional-resonant-based triple-loop indirect current controller and the control strategy for the seamless mode transfer of parallel grid-connected inverters are described and analyzed. The validity of the proposed mode transfer method is verified by the PSiM simulation results.

Instantaneous Current Control for Parallel Inverter with a Current Share Bus (전류공유버스를 이용한 병렬 인버터 순시 제어기 설계)

  • 이창석;김시경
    • Proceedings of the KIPE Conference
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    • pp.90-94
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    • 1998
  • The parallel inverter is popularly used because of its fault-tolerance capability, high-current outputs at constant voltages and system modularity. The conventional parallel inverter usually employes active and reactive power control or frequency and voltage droop control. However, these approaches have the disadvantages that the response time of parallel inverter control is slow against load and system parameter variation to calculate active, reactive power, frequency and voltage. This paper describes a novel control scheme for power equalization in parallel connected inverter. The proposed scheme has a fast power balance control response, a simplicity of implementation, and inherent peak current limiting capability since it employes a instantaneous current/voltage control with output voltage and current balance and output voltage regulation. A design procedure for the proposed parallel inverter controller is presented. Futhermore, the proposed control scheme is verified through the simulation in various cases such as the system parameter variation, the control parameter variation and the nonlinear load condition.

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A Current Sharing Circuit for the Parallel Inverter

  • Lee, Chang-Seok;Kim, Si-Kyung
    • Proceedings of the KIPE Conference
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    • pp.176-181
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    • 1998
  • The parallel inverter is popularly used because of its fault-tolerance capability, high-current outputs at constant voltages and system modularity. The conventional parallel inverter usually employs active and reactive power control of frequency and voltage droop control. However, these approaches have the disadvantages that the response time of parallel inverter control is slow against load and system parameter variation to calculate active, reactive power, frequency and voltage. This paper describes a novel control scheme for power equalization in parallel-connected inverter. The proposed scheme has a fast power balance control response, a simplicity of implementation, and inherent peak current limiting capability since it employees an instantaneous current/voltage control with output voltage and current balance and output voltage regulation. A design procedure for the proposed parallel inverter controller is presented. Furthermore, the proposed control scheme is verified through the experiment in various cases such as the system parameter variation, the control parameter variation and the nonlinear load condition.

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The Anti-islanding Scheme for a Number of Grid-connected Inverters Under Parallel Operation (병렬 연결된 다수 대 계통연계형 인버터를 위한 단독운전 방지 기법)

  • Kim, Dong-Kyune;Cho, Sang-Rae;Choy, Ick;Lee, Young-Kwoon;Choi, Ju-Yeop
    • Journal of the Korean Solar Energy Society
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    • v.37 no.3
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    • pp.13-22
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    • 2017
  • Anti-islanding scheme of grid-connected inverter is a key function of standards compliance, since unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, many anti-islanding schemes have been researched, however, most of them have problems, which deteriorate performance of islanding detection under parallel-operation. Therefore, this paper proves the reason of problems and proposes a new anti-islanding scheme that has precise islanding detection under parallel-operation in single-phase and three-phase system. Finally, both simulation and experimental result validate the proposed scheme.

Sensorless Active Damping Method for an LCL Filter in Grid-Connected Parallel Inverters for Battery Energy Storage Systems

  • Sung, Won-Yong;Ahn, Hyo Min;Ahn, Jung-Hoon;Lee, Byoung Kuk
    • Journal of Electrical Engineering and Technology
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    • v.13 no.1
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    • pp.280-286
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    • 2018
  • A sensorless active damping scheme for LCL filters in grid-connected parallel inverters for battery energy storage systems is proposed. This damping method is superior to the conventional notch filter and virtual damping methods with respect to robustness against the variation of the resonance of the filter and unnecessary additional current sensors. The theoretical analysis of the proposed damping method is explained in detail, along with the characteristic comparison to the conventional active damping methods. The performance verification of the proposed sensorless active damping method shows that its performance is comparable to that of the conventional virtual damping method, even without additional current sensors. Finally, simulation and experimental results are provided to examine the overall characteristics of the proposed method.

Performance Analysis of Anti-islanding Function for Grid-connected PV Inverter Systems under Parallel Connections (병렬운전하는 계통연계형 태양광 발전용 인버터의 단독운전 검출 성능 분석)

  • Jung, Young-Seok;Yu, Byung-Gyu;Kang, Gi-Hwa
    • Journal of the Korean Solar Energy Society
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    • v.33 no.5
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    • pp.34-40
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    • 2013
  • Islanding phenomenon of photovoltaic system is undesirable because it leads to a safety hazard to utility service personnel and may cause damage to power generation and power supply facilities as a result of unsynchronized re-closure. Anti-islanding protection is an important technical requirement for grid-connected PV system. Until now, various anti-islanding methods for detecting and preventing islanding of photovoltaic and other distributed generations have been proposed. Most of them are focusing on the anti-islanding performance of single PV system according to the related international and domestic standard test procedures. There are few studies on the islanding phenomenon for multiple photovoltaic operation in parallel. This paper presents performance analysis of anti-islanding function for grid-connected PV inverter systems when several PV inverters are connected in parallel.

Accurate Power Sharing in Proportion for Parallel Connected Inverters by Reconstructing Inverter Output Impedance

  • Huang, Shengli;Luo, Jianguo
    • Journal of Power Electronics
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    • v.18 no.6
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    • pp.1751-1759
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    • 2018
  • This paper presents parallel-connected inverters to achieve accurate proportional power sharing. Due to line impedance mismatch, reactive power cannot be distributed proportionally when using the conventional $P-{\omega}$ and $\mathcal{Q}-E$ droop. In order to realize reactive proportional power sharing, the ratio of the droop coefficients should be inversely proportional to their power-sharing ratios. Meanwhile, the ratio of the line impedance should be inversely proportional to the desired power-sharing ratio, which is very difficult to be met in practice. In order to deal with this issue, a practical control strategy is presented. By measuring the PCC voltage and using the virtual impedance, the output impedance of individual inverters is reconstructed to counteract the line impedance effect. In order to guarantee system stability, a low pass filter is designed to suppress the bandwidth of the line compensation. Finally, the simulation and experimental results are given to verify the effectiveness of the proposed control strategy.