Title: Circulating current suppression in low frequency operation of modular multi-level converters

Authors: Divyesh J. Vaghela; Nilesh J. Patel; Mukesh M. Bhesaniya

Addresses: Gujarat Technological University, Gujarat, India ' Gujarat Technological University, Gujarat, India ' G.H. Patel College of Engineering and Technology, Gujarat India

Abstract: The modular multi-level converters (MMCs) have become hugely popular for high or medium power applications. One of the major challenges associated with MMC is large capacitor voltage ripple with higher circulating current (i_circ) during medium and low frequency operation. In this paper, circulating current control technique is proposed for MMC for the entire frequency range operation. Voltage balance between the arms is achieved by controlling the upper and lower arm voltages. The proposed technique uses the linear current regulator to eliminate the lower order fundamental frequency current harmonic (I_2f) from each arm. This leads to reduction in the arm current peak and the dc link current ripple. In addition, overall rating of switching device and switching losses are significantly reduced with the proposed method. A detailed simulation study with professional software MATLAB is carried out. A down-scaled laboratory prototype of MMC is prepared and tested with the proposed method.

Keywords: modular multi-level converter; MMC; circulating current; sub-module capacitor voltage ripple; low frequency operation; current harmonics; arm voltage balancing.

DOI: 10.1504/IJPELEC.2023.134429

International Journal of Power Electronics, 2023 Vol.18 No.4, pp.415 - 434

Received: 22 Oct 2022
Accepted: 28 Dec 2022
Published online: 23 Oct 2023 *

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