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Level Selection Algorithm with Fixed Sampling Frequency for Modular Multilevel Converter

고정 샘플링 주파수에서의 모듈형 멀티레벨 컨버터 레벨 선택 알고리즘

  • Kim, Chan-Ki (Power Transmission Laboratory, KEPCO Research Institut) ;
  • Park, Chang-Hwan (Dept. of Electrical Eng., Pusan National University) ;
  • Kim, Jang-Mok (Dept. of Electrical Eng., Pusan National University)
  • Received : 2018.07.20
  • Accepted : 2018.10.01
  • Published : 2018.12.20

Abstract

This study uses a level selection algorithm with fixed sampling frequency for modular multilevel converter (MMC) systems. Theoretically, the proposed method increases the level infinitely while the sampling time remains the same. The proposed method called cluster stream buffer (CSB) consists of several clusters, wherein each cluster is composed of 32 submodules that depend on the level of the submodules in the MMC system. To increase the level of the MMC system, additional clusters are used, and the sampling time between clusters is determined from the sampling time between levels needed for utilizing the entire level from the MMC system. This method is crucial in the control of MMC-type HVDC systems because it improves scalability and precision.

Keywords

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Fig. 1. Basic structure of MMC.

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Fig. 2. ABB’S Group Module based MMC.

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Fig. 3. Pole voltage of ABB’s MMC using group module topology.

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Fig. 4. Single-phase equivalent circuit of MMC.

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Fig. 5. MMC Control Diagram with NLC Modulation.

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Fig. 6. Output voltage of NLC with small sampling interval.

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Fig. 8. Actual implementation of the proposed “Cluster stream buffer” method for MMC.

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Fig. 7. Output voltage of NLC with large sampling interval.

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Fig. 9. Cluster module based MMC arm.

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Fig. 10. Cluster module based MMC controller H/W structure.

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Fig. 11. Output voltage level of MMC based VSC-HVDC without cluster stream buffer method.

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Fig. 12. Output voltage level of MMC based VSC-HVDC using cluster stream buffer method.

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Fig. 13. Simulation result of the proposed algorithm: Cluster stream buffer.

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Fig. 14. Simulation result of conventional method. (a) Upper and lower arm voltages, (b) Three phase output current.

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Fig. 15. Simulation result of proposed method. (a) Upper and lower arm voltages, (b) Three phase output current.

TABLE I SIMULATION PARAMETER OF GRID CONNECTEDMMC SYSTEM

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