大容量光伏逆变系统接入弱电网运行可行域研究

发布时间：2018-06-21 06:55

本文选题：弱电网 + 光伏逆变系统　；参考：《华北电力大学》2014年博士论文

【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。
[Abstract]:With the depletion of fossil energy and the environmental hazards caused by fossil energy, renewable energy generation is increasing rapidly. Solar energy is rich in resources and can be exploited in many ways. Photovoltaic power generation is one of the main renewable energy generation methods. Photovoltaic network operation is an important way to realize large-scale development and utilization of solar energy. However, due to the constraints of resource endowment, large-scale photovoltaic power plants are located in weak areas of power grid structure. In the early stage of photovoltaic development, the scale of photovoltaic network is very small compared with the capacity of access grid, and the influence of grid constraints on the operation of photovoltaic power system can be ignored, but with the increase of the capacity of photovoltaic power station, the connected grid will show the characteristics of weak grid. Photovoltaic power generation is usually connected to the power grid through the inverter system, that is, the photovoltaic inverter system. The inverter not only converts the DC generated by photovoltaic cells into AC into the power grid, but also takes on the task of regulating the operating state of photovoltaic cells to achieve maximum power tracking. When the grid structure is relatively strong, the conventional photovoltaic inverter system has better control performance, and the control performance of the photovoltaic inverter system will deteriorate when the larger PV inverter system is connected to the weak grid. There is even the risk of system instability. Under the background of the rapid development of photovoltaic network, the influence of weak grid on the performance of PV inverter system is evaluated, and the corresponding improvement measures are studied to improve the operation quality and security of PV inverter system connected to weak grid. It has important theoretical and practical significance. In this paper, the basic mathematical model of photovoltaic inverter system including photovoltaic array and inverter is established, and the output characteristics of photovoltaic array are analyzed. The design method of the main circuit parameters is given, and the structure of the non-closed loop control system which combines MPPT control and inverter power control is constructed. Based on the PSCAD / EMTDC platform, a networked photovoltaic inverter simulation system is built. It provides an effective tool for the research of operation analysis and control of PV inverter system connected to weak power grid. On the basis of analyzing the reality scene of PV inverter system connecting to power grid, this paper gives the index to describe the power grid strength, and gives the definition of weak current network based on this index, and establishes the concept of feasible region for PV inverter system to connect to weak grid operation. The boundary of access to weak grid operation constraints for PV inverters can be quantitatively described by the corresponding interimpedance unitary values, i.e., the stability region is surrounded by satisfying the controller stability margin constraints and satisfying the access point voltage regulation quality constraints. A method for calculating the boundary of feasible region is presented. Aiming at the stability margin constraint boundary of the controller in the operational feasible region, this paper analyzes the adverse effect of the weak current network on the stability margin of the controller, and puts forward a scheme to improve the structure of the controller by eliminating the voltage feedforward. In order to extend the feasible region of the PV inverter system connecting to the weak power grid, the optimal design method of controller parameters is constructed on the basis of structural optimization. Aiming at the voltage regulation constraints of the access point in the operational feasible region, the bottleneck of power transmission caused by the weak current network is analyzed, and the influence of different reactive power control modes on the operational feasible region is compared. A reactive power control strategy for access point voltage regulation is proposed to improve the voltage regulation quality of the PV inverter system connected to the weak grid and to avoid the potential voltage instability risk during the access of the PV inverter system to the weak grid.
【学位授予单位】：华北电力大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM615

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