Title :
Modeling, Control Design, and Analysis of a Startup Scheme for Modular Multilevel Converters
Author :
Xiaojie Shi ; Bo Liu ; Zhiqiang Wang ; Yalong Li ; Tolbert, Leon M. ; Fei Wang
Author_Institution :
Dept. of Electr. Eng. & Comput. Sci., Univ. of Tennessee, Knoxville, TN, USA
Abstract :
Featuring modularity and high efficiency, a modular multilevel converter (MMC) has become a promising topology in high-voltage direct-current transmission systems. However, its distributed capacitors lead to a more complicated startup process than that of a two-level converter. To fully understand this issue, the charging loops of an MMC rectifier and an MMC inverter during an uncontrolled precharge period are analyzed in this paper, with special focus on the necessity of additional capacitor charging schemes. Moreover, a small-signal model of a capacitor charging loop is first derived according to the internal dynamics of the MMC inverter. Based on this model, a novel startup strategy incorporating an averaging capacitor voltage loop and a feedforward control is proposed, which is capable of an enhanced dynamic response and system stability without sacrificing voltage control precision. The design considerations of the control strategy are also given in detail. Simulation results from a back-to-back MMC system supplying passive loads and experimental results from a scaled-down MMC prototype are provided to support the theoretical analysis and the proposed control scheme.
Keywords :
HVDC power convertors; HVDC power transmission; capacitors; feedforward; invertors; power transmission control; rectifying circuits; voltage control; MMC inverter; MMC rectifier; back-to-back MMC system; capacitor charging loop scheme; capacitor voltage loop; distributed capacitor; dynamic response; feedforward control; high-voltage direct current transmission system; modular multilevel converter; passive load supply; small-signal model; startup scheme; uncontrolled precharge period; voltage control; Capacitors; Integrated circuits; Inverters; Modulation; Process control; Rectifiers; Voltage control; High-voltage direct-current (HVDC) transmission systems; Modular multilevel converter (MMC); highvoltage direct-current (HVDC) transmission systems; modular multilevel converter (MMC); startup;
Journal_Title :
Industrial Electronics, IEEE Transactions on
DOI :
10.1109/TIE.2015.2436354