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Dv/dt Analysis and Its Mitigation Methods in Medium Voltage SiC Modular Multilevel Converters

Li, Xiao
http://orcid.org/0000-0002-0222-074X
http://rave.ohiolink.edu/etdc/view?acc_num=osu1658385557853035

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Modular multilevel converters (MMCs) are currently widely used in medium and high voltage applications. In recent years, with the rapid development of silicon carbide (SiC) devices, growing attention has been placed on adopting SiC devices in MMCs. Thanks to the device's superior electrical and thermal characteristics, the SiC devices, especially the emerging medium voltage ones, are promising to benefit MMC based systems in numerous specifications, such as improved power density, reduced thermal stress, and higher efficiency. However, medium voltage systems can also experience challenges brought about by devices' fast switching speed, including worse electromagnetic interference (EMI), reflected wave phenomenon, and partial discharge. To better utilize the SiC devices in MMCs, this dissertation seeks to evaluate the effects of applying SiC power modules in MMCs. The analysis and discussions include the influential factors of the dv/dt seen at the load terminal, the dv/dt reduction methods, and the effect of high dv/dt on EMI noise and the system insulation design. The analysis is based on a 1 MVA MMC built with the 1.7 kV rated SiC power modules. The influential factors are discussed in three aspects: the source of high dv/dt, the propagation loop, and the control methods. The effects of the three aspects are discussed and evaluated with mathematical models, spice simulations, and hardware tests. It is straightforward that the load terminal dv/dt would change along with the device terminal dv/dt, which is the source of the high switching speed noise. Moreover, the design of passive components in a MMC system also affects the dv/dt by introducing the filtering effect. That is, the parasitic components and the arm inductors would form R-L-C networks between the power modules and the load, and the high order networks would bring down the dv/dt along the propagation loop of the switching transients. Last but not least, the control methods also affect the dv/dts at the load terminal, and the effect is realized via coordinating the switching transients of the two arm voltages. The analysis follows with the dv/dt reduction methods. Corresponding to the factors that affect the dv/dts, the voltage slew rate can be reduced by changing the power devices' switching speed, the passive components design, and different control methods. It is proved via simulation and experiments that the three methods can relieve the dv/dt stress on the load terminal with no or minor loss penalty. At the same time, the high dv/dt also introduces more concerns about the EMI noise and insulation-related issues. In this work, the insulation design concerns and the EMI performance are discussed based on the common mode model of the system. The EMI noises are evaluated with three indicators, including the leakage current that goes through the dc link middle point to the ground, the common-mode voltage of the load side neutral point, and the equivalent voltage drop on the human impedance network. The tests are carried out under different operation conditions to analyze the impact of modulation index, control methods, and the common mode impedance of the power loop.
Jin Wang (Advisor)
Anant Agarwal (Committee Member)
Mahesh Illindala (Committee Member)
Longya Xu (Committee Member)
131 p.
Electrical Engineering
Modular multilevel converters, silicon carbide devices, dv/dt

Recommended Citations

Citations

  • Li, X. (2022). Dv/dt Analysis and Its Mitigation Methods in Medium Voltage SiC Modular Multilevel Converters [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1658385557853035

    APA Style (7th edition)

  • Li, Xiao. Dv/dt Analysis and Its Mitigation Methods in Medium Voltage SiC Modular Multilevel Converters. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1658385557853035.

    MLA Style (8th edition)

  • Li, Xiao. "Dv/dt Analysis and Its Mitigation Methods in Medium Voltage SiC Modular Multilevel Converters." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1658385557853035

    Chicago Manual of Style (17th edition)

osu1658385557853035
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This open access ETD is published by The Ohio State University and OhioLINK.