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The Control And Experimental Platform Design Of Modular Multilevel Converter

Posted on:2016-09-07Degree:MasterType:Thesis
Country:ChinaCandidate:Q WuFull Text:PDF
GTID:2308330503977800Subject:Software engineering
Abstract/Summary:PDF Full Text Request
Modular multilevel converter topology is based on modular design, and each of its components (modules) is an independent control unit. It has the ability of extending different output levels by adjusting the number of sub modules. Compared with the traditional AC converter, modular multilevel converter has the advantages of reducing the switching frequency and the unnecessary of filtering device. Due to the characteristics of its own topology structure, Modular multilevel converter is proposed a good application prospect in the high power application such as HVDC flexible, which means great engineering significance.This paper has investigated the working principle of the topological structure of the modular multilevel converter and several key technologies which improve the working performance of the converter. Based on two methods as the carrier phase shift modulation and the nearest level modulation, the primary objective of the paper has analyzed the design of the experimental platform and the control effect of the system. The main contents of this paper is as follows:Firstly, the mathematical model of the main circuit is established by analyzing the working principle and the modulation method of the modular multilevel converter.After that, three key controlling methods such as the capacitor voltage balancing technology, the bridge arm circulating current suppressing technology and the capacitor pre charging technology are analyzed respectively. The matlab experiments are initiated to investigate the effects on the bridge arm circulation inhibition and the capacitor voltage balancing by two kinds of MMC’s controlling methods, which are the carrier phase shift (PWM) controlling method and the nearest voltage level modulation (NLM) controlling method. The findings suggest that the nearest voltage level modulation method is simpler and more effective than carrier phase shift pulse width modulation method, thus it can be much easier to apply the former method into the large capacity VSC-HVDC application.Finally, a MMC experimental platform of two voltage level are designed for the survey based on the the NLM control method. DSP controler is adopted to generate the action of each sub module(SM) switching by the data collection of the energy storage capacitor voltage value and the bridge arm current phase. FPGA controler is set to receive the command from DSP controler of switching each SM and transform it to PWM signals with proper dead zone time to drive two IGBTs of each SM.In conclusion, the study of the control theories of the modular multilevel converter and the design scheme of the experimental platform play significant roles for further studies.
Keywords/Search Tags:MMC, PWM control, NLM control, capacitor voltage balance, circulating current suppress
PDF Full Text Request
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