A high performance Si&SiC based hybrid asymmetrical multilevel cascaded H-bridge converter and its advanced control

中压大功率驱动广泛应用于石油化工、加工工业等领域。然而，大多数安装的中压电机都是以恒速运行的。因此，引入更高功率质量的更高效的变速驱动器是高度需要的。可控中压驱动器的设计面临着许多挑战，这些挑战与转换器的拓扑结构和控制以及功率半导体器件有关。通过从几个直流电压水平合成一个所需的电压，多电平变换器可以很容易地提供中压水平和高功率要求。目前，已有三种多电平变换器的拓扑结构作为商业工业产品。它们是中性点箝位（NPC）、飞行电容器（fc）和级联h桥（CHB）。在这些变换器拓扑中，CHB变换器由于采用多个单相变换器串联连接的结构，可以很容易地通过标准成熟技术元件达到更高的电压水平和更大的额定功率。不像传统的CHB变换器级联相同的单相逆变器具有相等的直流电压，混合非对称CHB变换器结合了各种不同拓扑的逆变器与不相等的直流源电压。通过这样做，转换器可以结合不同拓扑结构的优点，并以更少的电路和控制实现更高的电压水平。本课题旨在研究一种用于中压应用的混合非对称CHB变换器系统。系统的每一相由一个硅基5级NPC h桥（高压电池）和一个硅基3级h桥（低压电池）组成。将两个电池的直流母线电压按6:1的比例配置，将合成一个15级相位输出电压波形。近年来快速发展的碳化硅开关被认为是快速开关应用的理想候选者。然而，由于制造的复杂性，基于sic的功率器件的成本仍然很高。所提出的混合拓扑仅用SiC功率开关取代了低电压和快速开关单元，以合理的价格提高了整个系统的性能。该项目旨在研究混合转换器系统及其先进控制方法的实施。

Medium voltage and high power drives are widely used in various applications, such as in petrochemical or process industries etc. However most of the installed MV motors are running with a constant speed. Thus introducing more efficient variable-speed drives with higher power quality is highly demanded. The design of controlled MV drives is faced with a number of challenges that relate to the topologies and control of converters, as well as power semiconductor devices. By synthesizing a desired voltage from several levels of DC voltages, multilevel converters can easily provide the medium voltage level and high power requirements. Nowadays, three topologies of the multilevel converter are available as commercial industrial products. They are neutral point clamped (NPC), flying capacitors (FCs) and cascaded H-bridge (CHB). Among these converter topologies, CHB converters can easily reach higher voltage level and lager power rating by standard mature technology components because of its series connection structure of several single phase converters. Unlike the conventional CHB converters cascading identical single phase inverters with equal dc-link voltage, the hybrid asymmetrical CHB converters combine various different topologies of inverters with unequal DC source voltages. By doing this, the converter can combine the advantages of different topologies, and achieve higher voltage levels with less circuit and control. The proposed project is devoted to investigate a hybrid asymmetrical CHB converter system for MV applications. Each phase of the system is composed of one Si-based 5-level NPC H-bridge (HV cell) and one SiC-based 3-level H-bridge (LV cell). A 15-level phase output voltage waveform will be synthesized by configuring the dc-bus voltages of two cells in the ratio of 6:1. The resent fast developed SiC switches are considered as ideal candidates for fast switching applications. However due to the complexity of manufacturing, the cost of SiC-based power devices is still high. The proposed hybrid topology replaces only the low voltage and fast switching cells by using SiC power switches, which increases the performance of the whole system with a reasonable price. The project aims at investigating hybrid converter systems and implementation of their advanced control methodologies.