| Modular multilevel converter (MMC) has a special topology which ischopper-cells cascaded. Such topology gives MMC distinctiveperformance and makes it different from traditional multilevel converters.Since the good scalability and low requirements for power electronicdevices, MMC provides new ideas for applications in field of high voltageand large capacity, and has a good research prospect. In this dissertation,research on modulation methods and control strategy of MMC isconducted in depth. The main contests are as follows:(1) Basic theories included topology structure and working principlesare introduced. Its current and voltage characteristic is discussed.(2) Applicable multilevel modulation methods are compared andresearch on their capacitor voltage balancing control is conducted.Mathematical model of circulating current is built and circulating currentsuppressing control is designed. Mathematical model of MMC in boththree phase coordinates and two phase synchronous coordinates is built.Current indirect control strategy based on status feedback decoupling isdesigned.(3) HVDC simulation platform based on MMC is built to validate andcompare modulation method and control strategy. Key simulation modulesare introduced and explained.(4) Based on traditional MMC topology, a novel topology withH-bridge cells cascaded is presented. Research on modulation method andcontrol strategy of novel topology is conducted in depth to increase outputvoltage levels. Maximum voltage deviation is presented to improve voltage balancing control by sorting and reduce switch loss.(5) Hardware experiment platform based on VME-Bus is designedand built. Its software and hardware architectures are discussed. |
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