【作者】 黄亚峰；

【导师】 穆钢； 严干贵；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2014， 博士

【摘要】 随着化石能源的枯竭及其造成的环境危害日趋严重,各种方式的可再生能源发电快速增长。太阳能资源丰富,可多方式开发利用,光伏发电是现今的主要可再生能源发电方式之一。光伏发电联网运行是实现太阳能大规模开发利用的重要途径。但由于受资源禀赋的约束,大规模光伏电站多位于电网结构薄弱地区。在光伏发展初期,光伏联网规模与接入电网容量相比很小,可不考虑电网约束对光伏发电系统运行的影响；但随着光伏电站容量的增大,所接入电网将呈现弱电网特征。光伏发电通常经逆变系统接入电网,即光伏逆变系统。逆变器不仅将光伏电池产生的直流变换为交流送入电网,还承担着调控光伏电池运行状态以实现最大功率跟踪的任务。在电网结构相对较强时,常规设计的光伏逆变系统具有较好的运行控制性能；当较大容量的光伏逆变系统接入弱电网时,光伏逆变系统的控制性能将会恶化,甚至存在系统运行失稳的风险。在光伏入网规模快速发展的背景下,评估弱电网对光伏逆变系统运行性能的影响,研究相应的改进措施以提高光伏逆变系统接入弱电网的运行品质和安全性,具有重要的理论意义和现实意义。本文以单级式三相联网光伏逆变系统为研究对象,建立了包括光伏阵列,含(?)L滤波器逆变器的光伏逆变系统基础数学模型,分析了光伏阵列的输出特性.给出了主电路参数的设计方法,构建了MPPT控制与逆变器功率控制结合的不闭环控制系统结构,并基于PSCAD/EMTDC平台搭建了联网光伏逆变仿真系统,为光伏逆变系统接入弱电网运行分析与控制研究提供有效的工具。在分析光伏逆变系统接入电网现实场景的基础上,给出了描述电网强弱的指标,并基于此指标给出了弱电网的定义；建立了光伏逆变系统接入弱电网运行可行域的概念,光伏逆变系统接入弱电网运行约束的边界可以用相应的电网阻抗际幺值来定量描述,即稳定域由满足控制器稳定裕量约束和满足接入点电压调节品质约束围成。提出了可行域边界的计算方法。针对运行可行域的控制器稳定裕量约束边界,分析了弱电网对控制器稳定裕量的不利影响,提出了取消电压前馈的控制器结构改进方案,以拓展光伏逆变系统接入弱电网运行的可行域,在结构优化的基础上构建了控制器参数优化设计方法。针对运行可行域的接入点电压调节约束,分析了弱电网引起的功率传输瓶颈,比较了不同无功控制方式对运行可行域的影响。提出了一种面向接入点电压调节的无功控制策略,以改善光伏逆变系统接入弱电网的电压调节品质,并规避光伏逆变系统接入弱电网运行中潜在的电压失稳风险。更多还原

【Abstract】 With the depletion of fossil fuels and the increasingly serious environment pollution, the demand for the utilization of renewable energy sources to generate electricity is increasing. Due to the advantages of decreasing cost and flexible installation, solar energy has become one of the dominating renewable energy sources. Solar energy can be utilized on a large scale through the integration into the existing power distribution infrastructure. However, restricted by the geographical conditions, most large-scale PV power plants are located in desert or semi-desert regions where the grid infrastructure is weak. Under this scenario, the network equivalent impedance of long transmission lines cannot be ignored. For systems with low PV penetration the connected grid can be regarded as a strong power grid because of the small capacity of the PV power plants. With the expansion of the PV power plants to a level comparable to the reference utility power generation capability, the connected grid should be treated as a weak grid.PV power generation systems are connected into the grid through PV inverters. PV inverters change the DC energy into AC to feed into the grid. Additional functionality of the grid-tie PV inverter includes operating the PV modules at the conditions where the maximum power is captured. When PV systems are connected to a grid which is relatively strong, the PV systems can be well controlled. With the expansion of PV inverter systems, the grid has the potential of being overcome by the PV systems. The inconsistency of power generation of PV systems, combined with its dominate position over a weak utility infrastructure could eventually bring the system into collapse. Therefore, it has important theoretical significance and practical value to evaluate the impacts of the high penetration of PV systems on a weak grid. New methods to improve the operation quality and maintain the safety margin of the system with high P V penetration need to be investigatedBased on a single-stage three-phase PV inverter system, the mathematical model including the PV array, LCL filter and DC/AC inverter is established. The output characteristic of the PV array is analyzed, the design method of main circuit parameters is given. A dual closed-loop control structure combined with maximum power point tracking (MPPT) and inverter power controls is built. Using the PSCAD/EMTDC platform, a PV inverter simulation system is created. This provides effective tools for the study of operation analysis and control of PV inverter systems, which are connected with the weak grid.Based on the field test of PV inverter systems connected with the grid, the index to evaluate the fragility of power grid and the definition of a weak grid are given. Then the concept of the feasible operation region of PV inverter system is established. Per unit value of the grid impedance on the boundary of feasible operation regions are used to measure the adaptability of PV inverter systems connected to the weak grid. The methods to analyze the boundary of the feasible region to meet the controller’s stability margin constraints and voltage regulation constraints are also presented.For the controller’s stability margin constraints the adverse effects of weak network on controller stability margin are analyzed. An improved control structure without using voltage feedforward is presented, which can significantly extend the feasible operation regions. The methods to optimize the controller parameters are presented.In the end with regard to the voltage regulation constraints on the access point, the impact of weak power grid on power transmission constraints is analyzed. Comparisons between the operation regions of PV inverter systems with different reactive power control methods show that it is necessary to improve the reactive power control strategy under weak grid conditions. Based on the simulation and field test results, the reactive adjustability of the single stage P V inverter is studied. The reactive control strategy to regulate the access point voltage is derived, which can be used to improve the voltage level of PV inverter systems to avoid the potential risk of voltage instability in the system.更多还原