无隔离变压器光伏并网逆变器的研究

发布时间：2018-08-09 08:05

【摘要】：摘要：随着分布式发电的发展,小功率光伏并网逆变器有着广泛的应用。为了起到电气隔离,电压变换等作用,传统的光伏并网逆变器通常带有工频变压器或高频变压器。但是工频变压器的存在使得系统体积增大,损耗增加,同时提高了系统的安装难度；高频变压器的存在使得系统发电效率降低。去掉变压器可以弥补上述缺点,因此无隔离变压器光伏并网逆变器成为了当前的研究热点。由于光伏池板对地等效寄生电容的存在,将导致无隔离变压器光伏并网逆变系统产生对地漏电流,危及人身安全,因此研究如何抑制甚至消除对地漏电流对其发展与应用具有重要意义。本文从以下五个方面对无隔离变压器光伏并网逆变器展开研究： (1)介绍了无隔离变压器光伏并网发电系统的工作原理,分析了无隔离变压器光伏并网发电系统中对地漏电流产生的机理。 (2)从器件数量、滤波效果、以及系统损耗三个方面分析对比了多种能够抑制系统对地漏电流的单相全桥无隔离变压器光伏并网逆变器,并进行仿真验证,得出H5拓扑更适合在实践中发展。 (3)由于传统双级无隔离变压器NPC型拓扑存在中点电位的低频脉动,仍有对地漏电流问题。本文采用了一种新型双级无隔离变压器NPC型拓扑,相对于传统NPC型拓扑,该拓扑能够完全消除对地漏电流,抑制中点电位脉动以及降低直流侧电容值,通过仿真验证了理论分析的正确性。 (4)对新型双级无隔离变压器NPC型拓扑的控制策略进行了研究,前级采用单电流环控制以实现光伏池板的最大功率点跟踪；后级采用直流电压外环,并网电流内环的双闭环控制,比较分析了电流内环采用PI、PR、准PR三种控制器时的优缺点,指出了准PR控制器更适合单相光伏并网逆变器的控制,通过仿真验证了理论分析的正确性。 (5)搭建了5kW新型双级无隔离变压器NPC型光伏并网逆变器的实验样机,对传统NPC型拓扑与新型NPC型拓扑进行实验对比,对比结果验证了新型拓扑的可行性与优越性。
[Abstract]:Abstract: with the development of distributed generation, low-power photovoltaic grid-connected inverter has been widely used. Traditional photovoltaic grid-connected inverters usually have power frequency transformers or high frequency transformers for the purpose of electrical isolation and voltage conversion. However, the existence of power frequency transformer increases the volume and loss of the system, and increases the installation difficulty of the system. The existence of high-frequency transformer reduces the efficiency of power generation. Removing the transformer can make up for the above shortcomings, so the photovoltaic grid-connected inverter without isolating transformer has become a hot research topic. Because of the existence of equivalent parasitic capacitance of photovoltaic cell plate to the ground, it will lead to the generation of leakage current in the photovoltaic grid-connected inverter system without isolating transformer, which endangers the personal safety. Therefore, it is of great significance to study how to suppress or even eliminate the current of floor drain for its development and application. In this paper, the following five aspects of the photovoltaic grid-connected inverter without isolation transformer are studied: (1) the working principle of the photovoltaic grid-connected generation system without isolating transformer is introduced. The generation mechanism of floor drain current in photovoltaic grid-connected generation system without isolation transformer is analyzed. (2) from the number of devices, filtering effect, And three aspects of system loss are analyzed and compared, and the simulation results show that many single-phase full-bridge photovoltaic grid-connected inverters without isolating transformers can suppress the floor drain current. It is concluded that H5 topology is more suitable for development in practice. (3) due to the low frequency pulsation of midpoint potential in the traditional NPC topology of two-stage non-isolating transformer, there is still the problem of floor drain current. In this paper, a new two-stage unisolating transformer NPC topology is used. Compared with the traditional NPC topology, this topology can completely eliminate the floor drain current, suppress the pulsation of the midpoint potential and reduce the DC side capacitance. The correctness of the theoretical analysis is verified by simulation. (4) the control strategy of the NPC topology of a new two-stage unisolating transformer is studied. The single current loop control is used in the front stage to realize the maximum power point tracking of the photovoltaic cell plate; The back stage adopts the double closed loop control of the DC voltage outer loop and the grid-connected current inner loop. The advantages and disadvantages of the three kinds of controllers are compared and analyzed. It is pointed out that the quasi-PR controller is more suitable for single-phase photovoltaic grid-connected inverter control. The correctness of the theoretical analysis is verified by simulation. (5) the experimental prototype of NPC photovoltaic grid-connected inverter with 5kW two-stage non-isolating transformer is built, and the experimental comparison between the traditional NPC topology and the new NPC topology is carried out. The results verify the feasibility and superiority of the new topology.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464;TM615

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