Optimal submodule capacitor sizing for modular multilevel converters with common mode voltage injection and circulating current control

• Published in: 2017 IEEE Energy Conversion Congress and Exposition (ECCE) pp. 1802 - 1808
• Main Authors: Ziwei Ke, Jianyu Pan, Potty, Karun, Perdikakis, William, Shanmuganaatham, Arvind, Al Sabbagh, Muneer, Zhang, Julia, Fang Luo, Jin Wang, Longya Xu
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01-10-2017
• Subjects: Capacitance; Capacitor Sizing; Capacitors; Current control; Fluctuations; Frequency control; Mathematical model; MMC; motor drives; ripple reduction technique; Voltage control
• DOI: 10.1109/ECCE.2017.8096013

Modular multilevel converters (MMCs), with the filter-less and transformer-less features, are considered as a promising topology for high-efficiency medium voltage (MV) high voltage (HV) drive systems. However, at low frequencies (<; 30 Hz), a large current ripple flowing through the capacitors of each submodule will cause significant capacitor voltage fluctuation. This paper proposes an optimal submodule capacitor selection based on the common mode voltage injection. The proposed sizing model includes two functions: a) accurately estimating the capacitor voltage ripple based on the drive system parameters; and b) identifying the minimum capacitance of the submodule capacitors based on the allowed maximum capacitor voltage fluctuations. Simulation and hardware-in-the-loop (HIL) test results show that the error between the actual and estimated values of the voltage fluctuation is within 3% using the proposed model.