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Title: Modular multilevel converter : submodule dimensioning, testing method, and topology innovation
Author: Yuan, Tang
ISNI:       0000 0004 5915 9171
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2015
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The modular multilevel converter (MMC) is being developed as a core technology for the next generation of high-power, voltage source converters (VSCs). The focus of this thesis lies in the SM dimensioning, testing method and topology innovation for the MMC. First, the thesis presents a new submodule (SM) capacitor selection method, considering the three main voltage requirements: the maximum capacitor voltage, the voltage ripple and the SM voltage capability. The effect of the arm inductor is included. A quick way to estimate the capacitor ripple current stress is also provided to check the selection. Second, the thesis proposes two model assisted SM testing schemes for the MMC. The prototype SM can be thoroughly tested according to the targeted operating modes without having to build a complete MMC. During the test, the converter arm current can be faithfully achieved, which contains not only the fundamental frequency component, but also dc offset and harmonic circulating current components. One scheme is the uncompensated testing scheme, which uses fewer devices, and has simpler control and faster transient dynamics. The other is the compensated testing scheme, which requires much lower dc supply voltage, smaller coupling inductance, and provides higher current tracking accuracy in steady state. Both testing schemes have been verified through simulation and experiments. Third, the thesis proposes a compact SM topology for the MMC based on stacked switched capacitor (SSC) architecture. Feasibility study shows that the total physical volume of all capacitors in each SM can be reduced by more than 40% without significantly increasing the power loss. Design concept and control principles are presented. Practical considerations for a high-voltage, high-power system are also provided, which are demonstrated through experiments on a scaled down laboratory prototype SM. Finally, this thesis evaluates the offshore 50/3 Hz ac power transmission and the use of back-to-back (B2B) MMC for frequency conversion. The high-level design of a B2B MMC is presented. System performance is briefly evaluated using computer simulation.
Supervisor: Not available Sponsor: School of Engineering
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering