多光伏发电单元并联接入弱电网时的运行控制策略研究

As the energy density of photovoltaic panels is relatively low，the large-scale grid-connected PV stations usually adopt multiple parallelled-inverter for multiple photovoltaic generation units connected to the grid. Due to the restriction of resource endowment, large scale photovoltaic power stations are mostly located in deserts/semideserts where the grid structure is relatively weak.With the increasing capacity of grid-connected photovoltaic power generation,the equivalent impedance of photovoltaic generation system is gradually reducing. When the equivalent impedance reduce to the value that can not be ignored compared with the weak grid impedance, the generation power fluctuation of photovoltaic power station will seriously affect the voltage quality of the public connection point(PCC) to the grid, and then influence the operation performance of paralleled-inverters, and even may lead to the operation instability of parallelled-inverters for multiple photovoltaic generation units. This proposal is aimed to the problem "Study on the control strategy of multiple paralleled-inverters for photovoltaic generation units connected to the weak grid", and to study the following four problems: 1)the power-voltage dynamic regulation performance of an inverter for photovoltaic generation governed by the maximum power point track control;2)Coupling mechanism of multiple parallelled-inverters due to different photovoltaic power injection from photovoltaic cell arrays;3)Stability analysis of multiple parallelled-inverters for photovoltaic generation connected to weak grid when the output power of solar station approaches to the transmission bottleneck capacity;4) Control strategy designing for multiple parallelled-inverters for photovoltaic generation units connected to weak grid; These reaserch results will provide theoretical supports to improve the operation stability of paralleled-inverters for multiple photovoltaic generation units connected to the weak grid, and therefore contribute to promote the large-scale exploitation and utilization of solar energy.

大规模联网型光伏电站通常采用经逆变器并网的多光伏发电单元并联结构。受资源禀赋约束，大规模光伏电站多位于电网结构薄弱的沙漠/半沙漠地带。随着光伏发电系统并网容量的增加，光伏发电系统的等值阻抗减小，当其等值阻抗降至与弱电网等值阻抗相比不可忽视时，光伏电站的发电功率波动将严重影响并网点的电压质量，进而影响光伏逆变器的并联运行性能，甚至可能导致多光伏发电单元并联运行的不稳定。本申报书拟针对"多光伏发电单元并联接入弱电网时的运行控制策略设计"问题，深入研究4个科学问题：1）既有控制策略下光伏逆变器功率-电压动态特性；2）连接波动特性各异光伏电源时多光伏逆变器并联运行的耦合机理；3）接近电网输电瓶颈工况时多光伏逆变器并联接入弱电网运行稳定性分析；4）多光伏逆变器并联接入弱电网时的运行控制策略设计及效益评估。为提高大规模光伏电站并联接入弱电网时运行的稳定性提供理论指导，促进太阳能的大规模开发利用。

光伏发电是推进能源转型和应对环境挑战的重要途径。近年来，全球光伏发电装机规模大幅增长，但由于受资源禀赋约束，大规模光伏电站多位于电网结构薄弱的沙漠/半沙漠地带，经光伏逆变单元联网。随着光伏并网发电容量的增加，所接入电网呈弱电网特性，大规模光伏电站联网运行稳定性问题突出。. 本项目围绕多光伏发电单元并联接入弱电网失稳机理问题，开展了光伏电站建模、运行失稳机理分析及控制策略设计等研究，提出了基于短路容量比概念（光伏逆变系统容量与所接入电网短路容量之比来）刻画电网强弱的定量表征方法；基于频域阻抗模型与时域状态空间模型，揭示电网阻抗参数、控制器参数对光伏逆变系统接入弱电网稳定性的影响机理；构建松弛稳定裕量约束的光伏逆变系统控制器结构和控制器参数的优化方法，提高光伏逆变系统接入弱电网的运行控制性能；提出一种改进电压调节性能的光伏逆变系统无功优化控制策略，改善光伏逆变系统接入弱电网的电压调节能力。. 研究成果为大规模光伏电站联网运行分析与控制、大规模光伏电站接入规划提供了理论依据，有助于促进太阳能大规模开发利用。