大型光伏电站逆变器并网控制策略及稳定性分析

发布时间：2018-06-09 21:45

本文选题：大型光伏电站 + 并网逆变器　；参考：《重庆大学》2014年博士论文

【摘要】：在能源紧缺和环境污染日益严重的新形势下，建设大型光伏电站是大规模利用太阳能的有效方式，也是优化能源配置和缓解雾霾天气的重要途径。但大型光伏电站通常建立在远离负荷中心、光照资源丰富的荒漠地区，光伏发电系统经过长距离输电线路与负荷连接。光伏电站存在并网电能质量低、电网电压波动越限等问题，而且当变压器与长距离输电线路等构成的电网阻抗较大时或者装机容量增加时，易引起光伏发电系统产生谐振，限制了光伏电站的规模化应用。为提高光伏电站的并网电能质量，增强光伏电站并网稳定性，论文围绕光伏电站和电网之间的相互影响机理，以光伏电站中的并网逆变器为研究对象，从光伏电站的等效建模以及并网逆变器在非理想电网下的控制、无功调压控制和并网稳定性方面探讨了并网逆变器面临的技术难题，并提出了相应的分析方法及解决方案。论文首先以863课题“大型光伏电站并网关键技术研究”所依托的国电蒙电40MWp光伏发电项目为例，通过对光伏阵列、并网逆变器以及输电网络电路模型的分析，建立了光伏电站的等效电路模型，指出光伏电站和电网之间以及各并网逆变器之间相互影响的关键因素在于电网阻抗。在此基础上，针对光伏电站并网逆变器LCL滤波器谐振和直流侧电压波动等问题，研究了并网逆变器在正常电网下的电流环优化方案，为并网逆变器后续问题的深入研究奠定了基础。实际上各并网逆变器的接入点电压并不是理想的，为提高并网电能质量，论文分别从电网畸变不平衡和电网基频偏移角度进行了分析。针对电网畸变不平衡，分析了传统正序电流控制和有功恒定控制之间的矛盾，提出了并网逆变器在静止坐标系下的协调控制策略以及相应的正负序基波分量提取算法。针对电网基频偏移，分析了电流控制器谐振带宽抑制能力不足的缺点，并给出了相应的改进方案。在上述基础上，提出了并网逆变器在非理想电网下的控制策略，即在保证并网电能质量前提下，通过调节电流控制指令中负序分量的权重，实现并网电流幅值不平衡和瞬时有功波动之间的协调控制。仿真与实验结果也验证了所提控制策略的可行性和有效性。针对光伏电站电网电压波动越限的无功调压问题，论文从电网电压稳定性角度出发，对光伏电站有功输出变化对并网电压的影响进行了量化分析。此外，归纳总结了并网逆变器在不同控制方式下的无功容量及其无功补偿局限性，提出了无功补偿装置为主、并网逆变器为辅的无功输出模式。在此基础上，依据电力系统无功与电压控制的基本思想，提出了适用于光伏电站的并网逆变器无功调压控制策略，并对具体实现方式、无功分配方案、光伏发电单元无功优化等关键问题进行了阐述。算例仿真也验证了所提无功调压控制策略的可行性和有效性。最后，针对光伏电站装机容量增加时或者电网阻抗较大时光伏发电系统的稳定性问题，论文将电网阻抗因素考虑到光伏电站并网逆变器电流控制中，通过对电网阻抗在各并网逆变器之间耦合效应的分析，建立了考虑电网阻抗影响的光伏电站等效电路模型。在此基础上，利用传统的频域分析法，，从系统阻尼和开环传递函数两个角度，分析了电网阻抗对并网逆变器电流控制的影响，理论分析表明：等效电抗的影响要远大于等效电阻，等效电阻的增加会降低系统的稳态性能，而等效电抗的增加会严重减小系统的截止频率和稳定裕度，进而降低系统的动态性能甚至导致不稳定。对此，论文分别从光伏电站规划和并网逆变器电流控制角度给出了初步的解决思路。算例仿真和相关实验也验证了上述理论分析的正确性。
[Abstract]:Under the new situation that the energy shortage and environmental pollution are increasingly serious, the construction of large photovoltaic power stations is an effective way to utilize the solar energy in large scale. It is also an important way to optimize the energy allocation and alleviate the haze weather. However, the large photovoltaic power stations are usually built in the desert areas which are far from the load center, the light resources are rich, and the photovoltaic power generation system passes through. The long distance transmission line is connected with the load. There are some problems in the photovoltaic power station, such as the low quality of the grid connected power and the limit of the voltage fluctuation of the power grid. And when the transformer and the long distance transmission line are more impedance and the installed capacity increases, it will easily cause the resonance of the photovoltaic power generation system, which restricts the scale application of the photovoltaic power station. In order to improve the grid connected power quality of the photovoltaic power station and enhance the stability of the grid connected photovoltaic power station, the paper focuses on the interaction mechanism between the photovoltaic power station and the power grid, taking the grid connected inverter in the photovoltaic power station as the research object, from the equivalent modeling of the photovoltaic power station, the control of the grid connected inverter under the non rational power grid, the reactive voltage control control and the grid connected stability. The technical difficulties faced by grid connected inverters are discussed qualitatively, and corresponding analysis methods and solutions are proposed.
The paper first takes the 863 subject "the key technology of large photovoltaic power station to be connected to the grid" as an example. Through the analysis of the photovoltaic array, the grid connected inverter and the transmission network circuit model, the equivalent circuit model of the photovoltaic power station is set up, and the inverse of the photovoltaic power station and the grid and the converse of each grid are pointed out. The key factor of the interaction between the transformers lies in the impedance of the power grid. On this basis, the current loop optimization scheme of the grid connected inverter under the normal power grid is studied for the problems of the LCL filter resonance and the DC side voltage fluctuation of the grid connected inverters of the PV power station.
In fact, the access point voltage of the grid connected inverters is not ideal. In order to improve the quality of grid connected power, the paper analyzes the unbalanced power grid distortion and the basic frequency offset of the power grid respectively. In view of the unbalanced grid distortion, the contradiction between the traditional positive sequence current control and the active power constant control is analyzed, and the grid connected inverter is put forward in the static state. The coordination control strategy under the check coordinate system and the corresponding positive negative sequence fundamental wave component extraction algorithm. In view of the basic frequency offset of the power grid, the shortcomings of the current controller's lack of resonant bandwidth suppression ability are analyzed, and the corresponding improvement scheme is given. On the premise of grid connected power quality, by adjusting the weight of the negative sequence component in the current control instruction, the coordinated control between the unbalanced current amplitude and the instantaneous active power fluctuation is realized. The simulation and experimental results also verify the feasibility and effectiveness of the proposed control strategy.
In view of the reactive voltage regulation of the voltage fluctuation limit of the power grid of the photovoltaic power station, this paper quantifies the influence of the active output change of the photovoltaic power station on the grid voltage from the angle of the voltage stability of the power grid, and summarizes the reactive power capacity and the limitation of the reactive power compensation of the grid connected inverter under different control modes. On the basis of the basic thought of power system reactive power and voltage control, the reactive power control strategy for grid connected inverters suitable for photovoltaic power stations is proposed on this basis, and the key questions of specific realization mode, reactive distribution scheme and reactive power optimization of photovoltaic power unit are also discussed. The simulation results also verify the feasibility and effectiveness of the proposed reactive power voltage regulation strategy.
Finally, in view of the increase of the capacity of the photovoltaic power plant, or the stability of the power system with a large impedance time, the paper takes the impedance factor of the power grid into consideration in the current control of the grid connected inverters of the photovoltaic power station. Through the analysis of the coupling effect between the grid impedance and the grid inverters, the light of the grid impedance is established. On the basis of the equivalent circuit model of the volt power station, the influence of the electric network impedance on the current control of the grid connected inverter is analyzed from two angles of the system damping and the open loop transfer function. The theoretical analysis shows that the effect of the equivalent reactance is far greater than the equivalent resistance, and the increase of the equivalent resistance will reduce the steady state of the system. The performance, and the increase of the equivalent reactance will seriously reduce the cut-off frequency and stability margin of the system, and then reduce the dynamic performance of the system and even lead to instability. This paper gives a preliminary solution to the current control of the PV power station planning and the grid connected inverter. The correctness of the analysis.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM464

【参考文献】