Youyun Wang’s research while affiliated with Tianjin Design & Research Institute of Electric Drive and other places

The circulating current, the DC current fluctuation and DC fault current suppressing are important issues for modular multilevel converter (MMC). In order to enhance the suppressing effect of the system on the above three, the arm coupling inductor based natural current limiting MMC (ACINCL-MMC) is proposed in this paper. The operation principle analysis of ACINCL-MMC is carried out firstly. Based on the mathematical modeling of both the AC side and DC side, the relationship between the arm inductor coupling degree and the circulating current, the DC current fl uctuation and the DC fault current is studied. The natural current limiting effect of arm coupling inductor is analyzed in detail. Moreover, it further reveals the possibility of using arm coupling inductor instead of DC smoothing reactance. Finally, simulation results show the effectiveness of the proposed theory.

This paper proposes an enhanced modular multilevel converter based battery energy storage system (EMMC-BESS) for interfacing low voltage batteries to the medium or high voltage grids. Besides the distributed battery integration functionalities and the inherited advantages of traditional MMCs, EMMC-BESS also provides the DC fault handling capability. Based on analysis of operation principles, the control algorithms are developed for power control and the balancing of battery state of charge (SOC). Moreover, typical DC fault is taken into consideration for further analyzing the DC fault blocking mechanism. Feasibility of the proposed topology and the control strategies are verified by test results.

This paper proposes a super capacitor energy storage-based modular multilevel converter (SCES-MMC) for mine hoist application. Different from the conventional MMCs, the sub-modules employ distributed super capacitor banks, which are designed to absorb the regenerative energy of mine hoist and released in the traction condition, so as to improve energy utilization efficiency. The key control technologies are introduced in detail, followed by analysis of the configuration and operation principles. The feasibility of the proposed SCES-MMC topology and the control theory are also verified. Simulation results show that SCES-MMC can adapt to the variable frequency speed regulation of the motor drive, which shows good application prospects in the future for medium- and high-voltage mine hoist systems.