准Z源级联多电平光伏逆变器控制方法的研究

发布时间：2018-11-24 11:06

【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。
[Abstract]:With the development of the support policy of the PV industry, the global solar PV power generation technology is developing rapidly. However, the photovoltaic power generation is easy to be influenced by natural conditions such as temperature and light, and has the characteristics of randomness, instability, and seasonality. The voltage of a single photovoltaic cell is low, and a plurality of batteries in series are required to meet the requirements of the voltage level of the user. For such a direct series configuration, the local shading and mismatch of the photovoltaic panel will significantly reduce the power generation efficiency of the overall system. In order to overcome this problem, a large number of cascaded multilevel inverters (CMI) are used to distribute the photovoltaic panel to a plurality of independent H-bridge modules, and the modules are respectively subjected to the maximum power tracking to reduce the disadvantages caused by the local shading and the mismatch of the photovoltaic cell panel, so as to improve the power generation efficiency. However, the traditional H-bridge inverter module lacks the step-up function, and the difference of the maximum power point voltage of the photovoltaic cell panel will lead to an unbalanced DC bus voltage; and in the case of the variation of the wide range of the photovoltaic voltage, the requirement of the capacity of the inverter is multiplied. In recent years, it has been proposed to balance the DC bus voltage by embedding the DC-DC converter in each H-bridge module, but the additional large number of DC-DC converters not only increases the complexity of the power circuit and control, increases the cost, but also reduces the system efficiency. A new quasi-Z-source cascaded multilevel inverter (qZS-CMI) is proposed to embed the quasi-Z-source network into the traditional CMI, which not only improves the shortage of the H-bridge module, but also has a quasi-Z-source inverter (qZSI). The invention is characterized in that when applied to the photovoltaic power generation, each H-bridge module realizes the step-up and direct current-alternating current conversion with a single-stage power conversion, and independently controls the DC bus voltage; the upper and lower switching tubes of the same bridge arm of the inverter bridge can be simultaneously conducted without damage; and the distributed maximum power can be realized. tracking; a module that reduces 1/ 3 of the conventional CMI; and the like. These all contribute to the reduction of the cost of the photovoltaic power generation system, the improvement of the reliability, However, the research on the new topology of qZS-CMI is still in the preliminary stage and lacks in-depth analysis and control. This paper mainly studies the control method of quasi-Z-source cascade multi-level photovoltaic inverter, and puts forward two pulse-width modulation strategies and the system. Network control method. Specific as follows: First, a more detailed quasi-Z-source H-bridge is established PV inverter module model. At present, there is no system complete model to guide its parameters in the photovoltaic system composed of qZS-CMI in this paper, a quasi-Z-source H-bridge photovoltaic inverter module is used as an object, and a unified state space equation is established, and a double-frequency ripple component model and a system are derived, taking into account the influence of the capacitance of the photovoltaic panel terminal and the double-frequency ripple power, and establishing a uniform state space equation. The dynamic transfer function model is based on the two-frequency ripple component model, the influence of the impedance parameter on the low-frequency ripple component is analyzed, the whole set of impedance element parameters are designed to suppress the double-frequency ripple, and the dynamic model is a design independent DC bus voltage. Balance control provides a basis. Second, qZ is proposed The SVM method of S-CMI is proposed. By comparing the current two-level three-phase qZSI space vector modulation (SVM), an SVM method for qZSI is proposed to reduce the ripple of the inductor current and improve the efficiency. On the basis of this, the SVM of two-level three-phase qZSI is extended to qZS-CMI, and qZ is proposed. The SVM method of S-CMI and simulation and simulation Compared with the existing phase-shift sinusoidal pulse-width modulation (PS-SPWM) of qZS-CMI, the new modulation method has the advantages of high voltage utilization ratio, less occupied resources, modularization and easy expansion. Exhibitions to any of the advantages of any cascade. Again, a phase shift pulse width amplitude modulation (PS-PWAM) for qZS-CMI is proposed to reduce qZS-C The power loss is reduced by the switching action of the MI. The loss evaluation method in this modulation mode is studied. The two methods of PS-PWAM and PS-SPWM are compared. The power loss of qZS-CMI is verified by simulation and experiment, which shows that the PS-PWAM method in addition, a novel wide-gap silicon carbide (SiC) diode is used as a quasi-Z-source diode, Finally, the grid control strategy of the photovoltaic qZS-CMI is put forward, including the distributed MPPT and the independent DC bus. The system-level transfer function model is established based on the single-phase system, and each regulator is designed in detail so as to meet the wide range of PV voltage change and realize high quality and network; and then the proposed control method In this paper, the control strategy of the three-phase system is studied and the control strategy of the three-phase system is studied in this paper. The power of the three-phase system is studied from the aspects of the topological level, the modulation stage, the control level and the device level, and the control method proposed by the simulation and the experimental verification is carried out respectively. The research results will promote the new type of solar light
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM464

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