非理想电网条件下三电平光伏并网变换器控制研究

发布时间：2018-12-11 21:51

【摘要】：光伏并网发电作为太阳能利用的重要形式之一,其推广应用具有重大的现实意义。为了提高发电质量,目前三电平变换器仍为光伏并网变换器的主流。本文以非理想电网条件下三电平光伏并网变换器的控制作为研究对象,深入研究了三电平光伏并网变换器的关键技术及其不平衡控制策略。非理想电网条件下基波相位及基波正负序分量的准确提取是实现三电平光伏并网变换器不平衡控制策略的基础。本文在研究基于自适应陷波滤波器(adaptive notch filter,ANF)锁相方法的基础上,针对其锁相性能受直流偏移和谐波的影响,分别提出了基于改进自适应陷波滤波器和基于滑动平均-自适应陷波滤波器的锁相方法,实现了直流偏移和谐波次数未知情况下的准确锁相。研究了基于双二阶广义积分器-锁频环(dual second order general integrator-frequency locked loop,DSOG-FLL)的基波正负序提取方法,并对其进行改进,实现了谐波次数未知情况下基波正负序分量的快速准确提取。对所提改进方法进行了仿真和实验研究,验证了所提方法的有效性。深入分析了三电平光伏并网变换器的中点电位不平衡问题,通过研究各基本矢量对中点电位造成的不同影响,提出了基于矢量置换与平衡因子相结合的三电平中点电位平衡算法,在充分考虑各基本矢量有利于中点电位平衡的情况下结合平衡因子的有效控制,实现了中点电位的动态平衡,通过仿真验证了中点电位平衡控制的有效性。针对电网不平衡时三电平光伏并网变换器交流侧的负序电流和直流侧电压的二倍频波动,分别提出了电网不平衡条件下抑制交流侧负序电流和抑制直流侧电压二次纹波的控制策略,有效实现了不平衡电网条件下三电平光伏并网变换器的高性能运行,并通过仿真验证了所提控制策略的有效性。为降低成本、提高系统鲁棒性,引入虚拟电网磁链,并提出了基于DSOGI-FLL的虚拟电网磁链观测技术,实现了电网不平衡条件下虚拟电网磁链正负序分量的快速准确提取。应用虚拟电网磁链观测技术,提出了电网不平衡条件下三电平光伏并网变换器无电网电压传感器的不平衡控制策略,并通过仿真验证了所提控制策略的有效性。
[Abstract]:Grid-connected photovoltaic power generation as one of the important forms of solar energy utilization, its application has great practical significance. In order to improve generation quality, three-level converters are still the mainstream of PV grid-connected converters. In this paper, the key technology of three-level photovoltaic grid-connected converter and its unbalanced control strategy are studied in detail, taking the control of three-level photovoltaic grid-connected converter as the research object. The accurate extraction of the fundamental phase and the positive and negative sequence components of the fundamental wave is the basis of the unbalanced control strategy for the three-level photovoltaic grid-connected converter. In this paper, based on the study of the phase-locking method based on adaptive notch filter (adaptive notch filter,ANF), the phase-locking property can be affected by DC migration and harmonics. The phase-locking methods based on improved adaptive notch filter and sliding average adaptive notch filter are proposed respectively. The accurate phase-locked method is realized when the DC offset and harmonic frequency are unknown. In this paper, the method of extracting fundamental positive and negative sequence based on (dual second order general integrator-frequency locked loop,DSOG-FLL (double second order Generalized Integrator) is studied and improved. The fast and accurate extraction of the positive and negative sequence components of the fundamental wave is realized when the harmonic frequency is unknown. The effectiveness of the proposed method is verified by simulation and experimental research. In this paper, the unbalanced neutral point potential of three-level photovoltaic grid-connected converter is deeply analyzed, and the different effects of each basic vector on the neutral point potential are studied. A three-level neutral-point potential balance algorithm based on vector permutation and balance factor is proposed, which combines the effective control of the equilibrium factor with the full consideration of each basic vector in favor of the neutral-point potential balance. The dynamic equilibrium of midpoint potential is realized, and the effectiveness of the control is verified by simulation. Aiming at the double frequency fluctuation of negative sequence current and DC side voltage in AC side of three-level photovoltaic grid-connected converter when the power grid is unbalanced, The control strategies of suppressing the negative sequence current on the AC side and the secondary ripple of the DC side voltage under the unbalanced power grid are proposed respectively. The high performance operation of the three-level photovoltaic grid-connected converter is realized effectively under the unbalanced power grid condition. The effectiveness of the proposed control strategy is verified by simulation. In order to reduce the cost and improve the robustness of the system, the virtual grid flux is introduced, and the observation technology of the virtual grid flux based on DSOGI-FLL is proposed, which realizes the fast and accurate extraction of the positive and negative sequence components of the virtual grid flux under the condition of unbalanced power grid. The unbalanced control strategy of three-level photovoltaic grid-connected converter without grid voltage sensor is proposed by using the virtual grid flux observation technique. The effectiveness of the proposed control strategy is verified by simulation.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46;TM615

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