Space Vector Modulation of Multi-level and Multi-module Converters for High Power Applications
Space Vector Modulation of Multi-level and Multi-module Converters for High Power Applications
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发表时间：
2009-02
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通讯作者：
M. Saeedifard;R. Iravani
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作者：
M. Saeedifard;R. Iravani
本文提出并研究了用于(I)多电平二极管钳位变流器(DCC)和(Ii)多模块电压型变流器(VSC)系统的空间矢量调制(SVM)开关策略，其中每个模块都是一个常规的两电平VSC。虽然支持向量机策略是通用的，适用于n级DCC和n模块VSC系统，但本文仅针对五级DCC和四模块VSC系统，针对五级DCC，提出了一种计算效率较高的支持向量机算法。该算法基于分类器神经网络(NN)，减少了支持向量机实现的计算时间。因此，在支持向量机的每个采样周期中，充分节省了处理器执行时间，以执行其他功能，例如直流电容电压平衡任务所需的计算。本文还提出了一种直流电容电压平衡策略来抵消(I)无源-前端五电平DCC和(Ii)背靠背连接五电平DCC系统的电压漂移现象。所提出的平衡策略基于改进的支持向量机算法，利用冗余的开关状态最小化与直流电容器电压偏差相关的二次代价函数。该平衡策略的显著特点是：(1)在线计算支持向量机以选择最佳开关状态；(2)最小化开关频率；(3)最小化交流侧电压的THD含量；(4)不需要额外的电源电路。所提出的策略(I)在多模块VSC系统的交流侧电压下提供谐波消除/最小化，(Ii)为每个VSC模块提供较低的开关频率。研究并提出了所提出的支持向量机策略在五电平DCC和四模块VSC系统作为STATCOM和背靠背高压直流输电系统的技术可行性。研究是在PSCAD/EMTDC软件环境下进行的。
This thesis presents and investigates Space Vector Modulation (SVM) switching strategies for (i) a multi-level Diode-Clamped Converter (DCC) and (ii) a multi-module Voltage-Sourced Converter (VSC) system in which each module is a conventional two-level VSC. Although the SVM strategies are general and applicable for n-level DCC and n-module VSC systems, this text only concentrates on five-level DCC and four-module VSC systems.For a five-level DCC, a computationally efficient SVM algorithm is proposed. The algorithm, that is based on a classifier Neural Network (NN), reduces the computational time for the SVM realization. Therefore, adequate saving of processor execution time, in each sampling period of SVM, is provided to carry out other functions, e.g. the calculations required for DC-capacitor voltage balancing task. The thesis also proposes a DC-capacitor voltagebalancing strategy to counteract the voltage drift phenomenon of (i) a passive-front-end five-level DCC, and (ii) a back-to-backconnected five-level DCC system. The proposed balancing strategy, that is based on augmenting the proposed SVM algorithm, takes advantage of the redundant switching states to minimize a quadratic cost function associated with voltage deviations of theDC-capacitors. The salient features of the proposed balancing strategy are (i) online calculation of SVM to select the bestswitching states, (ii) minimization of switching frequency, (iii) minimization of the THD content of the AC-side voltage, and (iv) no requirement for additional power circuitry.For a four-module VSC system a sequential sampling SVM strategy is proposed. The proposed strategy (i) provides harmonic cancellation/minimization at the net AC-side voltage of the multi-module VSC system, and (ii) offers a low switching frequencyfor each VSC module.Technical feasibility of the proposed SVM strategies for a five-level DCC and a four-module VSC system, as a STATCOM and aback-to-back HVDC system, are investigated and presented. The studies are conducted in the time-domain, in the PSCAD/EMTDCsoftware environment.