【作者】 刘钰山；

【导师】 葛宝明；

【作者基本信息】 北京交通大学 ， 电气工程， 2014， 博士

【摘要】 随着光伏产业扶持政策的不断出台,全球太阳能光伏发电技术正持续快速发展。然而,光伏发电易受温度和光照等自然条件影响,具有随机性、不稳定性、季节性等特点。单个光伏电池电压较低,需要串联很多个电池满足用户电压等级要求。对于这种直接串联的结构,光伏电池板局部阴影和失配将严重降低整个系统的发电效率。为了克服这个问题,已有大量研究采用级联多电平逆变器(CMI),将光伏板分配给多个独立的H桥模块,对各模块分别进行最大功率跟踪来降低光伏电池板局部阴影和失配导致的不利,以改善发电效率。但传统H桥逆变模块缺少升压功能,光伏电池板最大功率点电压的不同将导致不平衡的直流母线电压；并且在光伏电压宽范围变化的情况下,对逆变器容量的要求倍增。近年,有研究提出在每个H桥模块嵌入DC-DC变换器来平衡直流母线电压,但是,附加的大量DC-DC变换器,不仅增加了功率电路和控制的复杂性,增加了成本,而且降低了系统效率。新近提出的准Z源级联多电平逆变器(qZS-CMI),将准Z源网络嵌入传统CMI,不仅改善了H桥模块无法升压的不足,且具有准Z源逆变器(qZSI)的特点。将其应用于光伏发电时,各H桥模块均以单级功率变换实现升压及直流-交流转换,独立地控制直流母线电压；逆变桥同一桥臂的上下开关管可同时导通而不损坏；可实现分布式最大功率跟踪；比传统CMI减少1/3的模块；等等。这些都有助于光伏发电系统成本的降低、可靠性的提高,受到了越来越多的关注。然而,对qZS-CMI这一新型拓扑的研究尚处于初步阶段,缺乏较深入的分析与控制设计。本文重点研究准Z源级联多电平光伏逆变器的控制方法,提出了两种脉宽调制策略,以及系统并网控制方法。具体如下：首先,建立了较详细的准Z源H桥光伏逆变模块模型。目前,在由qZS-CMI构成的光伏系统方面,尚无系统完整的模型来指导其参数选取和控制器设计。本文以准Z源H桥光伏逆变模块为对象,考虑光伏板终端电容和两倍频脉动功率影响,建立其统一的状态空间方程,推导了两倍频脉动分量模型和系统动态传递函数模型。依据两倍频脉动分量模型,分析了阻抗参数对低频脉动分量的影响,设计了抑制两倍频脉动的整套阻抗元件参数；动态模型则为设计独立的直流母线电压平衡控制提供依据。其次,提出了qZS-CMI的SVM方法。通过比较现有两电平三相qZSI的空间矢量调制(SVM),提出一种qZSI的SVM方法,以降低电感电流脉动、提高效率；依此为基础,结合qZS-CMI模块化特点,将两电平三相qZSI的SVM扩展到qZS-CMI,提出qZS-CMI的SVM方法,并以仿真和实验验证了所提出的方法。与qZS-CMI已有的移相正弦脉宽调制(PS-SPWM)相比,新调制方法具有电压利用率高、占用资源少、模块化、易于扩展至任意级联数目的优点。再次,提出了qZS-CMI的移相脉冲宽度幅值调制(PS-PWAM),以减少qZS-CMI的开关动作,降低功率损耗。研究了该调制方式下的损耗评估方法,比较了PS-PWAM和PS-SPWM两种方法控制时qZS-CMI的功率损耗。仿真与实验验证了所提出的PS-PWAM方法,表明PS-PWAM可有效降低系统损耗,改善效率。此外,分析了以新型宽能隙碳化硅(SiC)二极管作准Z源二极管,进一步从器件上减少损耗的情况。最后,提出了光伏qZS-CMI的并网控制策略,包括分布式MPPT、独立的直流母线电压平衡控制,及单位功率因数并网控制。先以单相系统为对象,建立了其系统级传递函数模型,详细设计了各调节器,以适应宽范围的光伏电压变化与实现高质量并网；再将所提出的控制方法进行扩展,研究了三相系统的控制策略。本文力从拓扑级、调制级、控制级和器件级等方面,对准Z源级联多电平光伏逆变系统进行研究,分别以仿真和实验验证提出的控制方法,其研究成果将促进新型太阳能光伏逆变器的应用,满足高质量的供电用电需求。更多还原

【Abstract】 The global solar Photovoltaic (PV) technology is experiencing a sustained and rapid development with the continuous introduction of supporting policies in PV industry. However, PV power generation is stochastic, instable, and susceptible to natural conditions, such as irradiation and temperature variations. Moreover, partial shading and mismatching of PV panels are also one of the main reasons of power loss. Researches have been dedicated on cascade multilevel inverter (CMI) that can allocate PV panels to several independent H-bridge inverter modules and each module tracks their own maximum power points distributedly, thus to weaken those defects of PV power generation. Nevertheless, traditional H-bridge inverter (HBI) module lacks of boost function so that different PV panel output voltages result in imbalanced dc-link voltages and the inverter KVA rating requirement has to be increased twice with a PV voltage range of1:2. More recently, extra dc-dc boost converter was added into each HBI module to handle PV panel voltage variations. However, such topology is with a two-stage inverter for each module, and many extra dc-dc converters will make the whole system complex, bulky, high cost, and low efficiency.The quasi-Z-source cascade multilevel inverter (qZS-CMI), coupling the quasi-Z-source network into each HBI’s dc link, not only improves advantages of traditional CMI, but also inherits characteristics of quasi-Z-source inverter (qZSI). When applied to PV power generation, this topology presents promising features that: the ability of dc-link voltage balance because each of qZSI module can handle the wide PV panel voltage variation through single-stage power conversion; the power switches in the same bridge leg can conduct together without damage; the modular structure that each H-bridge inverter can be seen as a module with the same circuit topology, modulation, and control; the distributed MPPT that to maximize solar energy; etc. Therefore, the higher reliability, lower cost, and smaller volume can be brough in to PV power systems.The main contribution of this reseach is to investigate control of qZS-CMI based PV power system. Two pulse-width modulation (PWM) methods and the grid-tie control of the entire system are proposed accordingly. The details are as follows.Firstly, a double-line-frequency (2ω) ripple model of qZS network with PV panel terminal capacitance is established for qZS-HBI based PV module, which is used to analyze the influences of impedance parameter to2ω ripples and design impedance parameter to effectively buffer the low-frequency ripples. A small-signal model with stray resistance is established for designing the dc-link voltage control.Secondly, a simple extended, less-resource, and modular multilevel space vector modulation (SVM) for qZS-CMI is proposed on the basis of overview for two-level three-phase qZSI’s SVM. Simulation and experiments verify the proposed method.Moreover, a phase-shifted pulse-width-amplitude modulation (PS-PWAM) is proposed for qZS-CMI, aiming at reducing the power loss of existing PS-SPWM of qZS-CMI. Simulation and experimental results demonstrate its validation, and the qZS-CMI presents lower power loss in the PS-PWAM than PS-SPWM.Finally, a grid-tie control scheme of the qZS-CMI based PV system is proposed, including distributed MPPT, indenpedent dc-link voltage balance control, and grid-tie control with unity power factor. Completed system-level modeling and regulator design process are presented for single-phase qZS-CMI based PV system. The proposed control is then extended to three-phase PV qZS-CMI system.This research aims at investigating the qZS-CMI based PV system in terms of topological level, modulation level, control level, and material level, etc. Simulation and experimental results verify the proposed control, which will promote the application of novel PV inverters and satisfy the high-quality power supply demands.更多还原