Control strategy for hybrid LCC-C-MMC HVDC system under AC fault at rectifier side

• Published in: Journal of engineering (Stevenage, England) Vol. 2019; no. 16; pp. 3259 - 3263
• Main Authors: Xue, Yinglin, Ge, Fenglei, Zhao, Zheng, Zhang, Zheren, Xing, Facai
• Format: Journal Article
• Language: English
• Published: The Institution of Engineering and Technology 01.03.2019; Wiley
• Subjects: AC grid fault; AC voltage drop; backup constant voltage control; C-MMC valve group; clamp double sub-modules; combined modular multilevel converter; control strategy; half-voltage mode; harmonic injection modulation; healthy converter unit; high voltage terminal; HVDC power convertors; HVDC power transmission; hybrid HVDC system; hybrid LCC-C-MMC HVDC system; inverter side; invertors; low DC voltage ride; modulation range; power grids; power system stability; power transmission control; reactive power dynamic adjusting method; rectifier DC voltage; rectifier side; rectifiers; The 14th IET International Conference on AC and DC Power Transmission (ACDC 2018); voltage control; HVDC power convertors; rectifier DC voltage; control strategy; AC voltage drop; combined modular multilevel converter; rectifiers; reactive power dynamic adjusting method; hybrid HVDC system; modulation range; HVDC power transmission; invertors; AC grid fault; backup constant voltage control; inverter side; power grids; clamp double sub-modules; harmonic injection modulation; hybrid LCC-C-MMC HVDC system; power system stability; healthy converter unit; C-MMC valve group; power transmission control; high voltage terminal; half-voltage mode; low DC voltage ride; rectifier side; voltage control
• ISSN: 2051-3305; 2051-3305
• DOI: 10.1049/joe.2018.8705

This paper focus on the new hybrid HVDC system, whose rectifier side is traditional line commutated converter (LCC) and inverter side is made up of the series connected combined modular multilevel converter with clamp double sub-modules (C-MMCs). However, when the AC grid fault occurs at rectifier side, the DC voltage of LCC will drop; at this time, the DC voltage of C-MMC can not be decreased much since the modulation range is limited. Thus, the transmitted power may interrupt if the rectifier DC voltage is lower than the inverter side. To solve this problem, the paper proposed a new low DC voltage ride through control strategy. When the fault is very serious, which means the DC voltage will drop much, the converter unit at high voltage terminal is switched off to make the system operate under the half-voltage mode, then, the healthy converter unit is controlled to transmit power continuously. During the process, one arm is bypassed, and the other two arms are blocked. Finally, the PSCAD/EMTDC results show, the proposed control strategies achieve excellent operation characteristic under 10% and 50% ac voltage drop.