三相非隔离三电平并网逆变器的研究

发布时间：2018-01-07 07:42

本文关键词：三相非隔离三电平并网逆变器的研究　出处：《扬州大学》2014年硕士论文　论文类型：学位论文

【摘要】：随着社会的发展、科技的进步、能源需求量的增大和化石能源的日益短缺,开发使用新能源已成为当今社会的主题。太阳能以其独特的优势,扮演着越来越重要的角色,而光伏并网发电作为太阳能利用的一种形式,已成为研究和应用的热点。光伏并网发电系统中能量转换的核心装置是逆变器,它的成本和效率是整个光伏发电系统的关键。因此,开发低成本、高效率的光伏并网逆变器是各国研究人员追求的目标。本文对NPC-I型三相三电平并网逆变器和NPC-T型三相三电平并网逆变器的原理进行了详细分析,并给出了中点钳位(Neutral Point Clamped, NPC)T型三相三电平主电路的控制方法。论文详细研究了空间矢量调制策略(Space Vector Pulse Width Modulation, SVPWM),给出了SVPWM算法的实施步骤。通过仿真研究了改进型三平SVPWM与传统三电平SVPWM算法下主电路的共模特性,仿真结果表明改进型SVPWM调制策略能有效抑制电路的共模漏电流。但在软起动实验中,改进型SVPWM算法会导致桥臂中点电压畸变,主要原因是为了抑制电路的共模漏电流,该调制方法没有采用冗余小矢量,故在起动过程中,当调制比较小时,小矢量的作用导致了桥臂中点的电压畸变,针对这种情况本文提出了一种基于十二扇区的SVPWM调制策略,由于这种调制方法没有使用小矢量,故解决了软起动过程中桥臂中点电压出现的畸变问题,同时本文提出的十二扇区SVPWM调制策略可有效的抑制共模漏电流。本文针对NPC-I型和NPC-T型三相三电平电路拓扑,详细分析了这两种电路拓扑的动态换流过程,在此基础上归纳总结了各种换流模态下开关器件的损耗情况,然后在NPC-I型和NPC-T型三相三电平电路中通过采用相同的开关器件,对NPC-I型和NPC-T型三相三电平电路进行了损耗分析,结果表明对于本文设计的功率等级和选用的开关频率而言,NPC-T型三相三电平电路的效率优于NPC-I型三相三电平电路。本文在仿真的基础上研制了一台17KW非隔离NPC-T型三相三电平并网逆变器样机。对NPC-T型三相三电平并网逆变器的硬件进行了设计并给出了主要参数的计算方法,给出了输出滤波器的详细设计过程,开关器件的选型依据和直流侧电容的选取方法。最后给出了NPC-T型三相三电平并网逆变器的实验和仿真波形,绘制并对比了NPC-I型和NPC-T型三相三电平并网逆变器的效率曲线。仿真和实验验证了本文提出的调制策略和设计方法的有效性。
[Abstract]:With the development of society, the progress of science and technology, the increase of energy demand and the increasing shortage of fossil energy, the development and use of new energy has become the theme of today's society. Solar energy has its unique advantages. Photovoltaic grid-connected generation, as a form of solar energy utilization, has become a research and application hotspot. Inverter is the core device of energy conversion in photovoltaic grid-connected generation system. Its cost and efficiency are the key of the whole photovoltaic power generation system. Therefore, developing low-cost and high-efficiency photovoltaic grid-connected inverter is the goal pursued by researchers all over the world. In this paper, the principle of NPC-I three-level grid-connected inverter and NPC-T three-level grid-connected inverter are analyzed in detail. Neutral Point Clamped is given. The control method of NPC)T three-phase three-level main circuit. The space vector modulation strategy is studied in detail in this paper. Space Vector Pulse Width Modulation. The implementation steps of the SVPWM algorithm are given. The common mode characteristics of the main circuit under the improved three-level SVPWM algorithm and the traditional three-level SVPWM algorithm are studied by simulation. Simulation results show that the improved SVPWM modulation strategy can effectively suppress the common mode leakage current of the circuit, but in the soft start experiment, the improved SVPWM algorithm will lead to the midpoint voltage distortion of the bridge arm. The main reason is that in order to suppress the common mode leakage current of the circuit, the modulation method does not use redundant small vectors, so in the starting process, when the modulation comparison is small, the effect of the small vector leads to the voltage distortion in the midpoint of the bridge arm. In this paper, a SVPWM modulation strategy based on sector 12 is proposed. Because this modulation method does not use small vectors, it solves the distortion of the midpoint voltage of the bridge arm during soft start. At the same time, the 12 sector SVPWM modulation strategy proposed in this paper can effectively suppress the common mode leakage current. In this paper, the dynamic commutation process of NPC-I and NPC-T three-phase three-level circuit topologies is analyzed in detail. On this basis, the losses of switching devices in various commutation modes are summarized, and then the same switching devices are used in NPC-I and NPC-T three-phase three-level circuits. The loss analysis of NPC-I and NPC-T three-phase three-level circuits is carried out. The results show that the power level and switching frequency of the designed circuit are discussed in this paper. The efficiency of NPC-T type three-phase three-level circuit is better than that of NPC-I three-phase three-level circuit. In this paper, a 17KW unisolated NPC-T three-phase three-level grid-connected inverter prototype is developed on the basis of simulation. The hardware design of NPC-T three-level three-level grid-connected inverter is presented. The calculation method of main parameters. The detailed design process of output filter, the selection basis of switching device and the selection method of DC side capacitance are given. Finally, the experimental and simulation waveforms of NPC-T three-phase three-level grid-connected inverter are given. The efficiency curves of NPC-I and NPC-T three-phase three-level grid-connected inverters are drawn and compared. The effectiveness of the proposed modulation strategy and design method is verified by simulation and experiments.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464

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