光伏并网系统低电压穿越技术的研究

发布时间：2018-05-01 07:28

本文选题：光伏并网 + 有限控制集模型预测控制　；参考：《山东大学》2017年硕士论文

【摘要】：随着传统能源的短缺以及环境污染日渐严重,可再生能源的发展和利用成为人们研究的热点,太阳能光伏发电即为其中最具潜力、发展迅速的清洁能源之一。随着光伏渗透率的提高,其对电网造成的影响也越来越大,其中在电网扰动或者发生故障时,光伏系统突然脱网会给电网带来严重后果,而低电压穿越(low voltage ride through,LVRT)技术作为电网故障恢复的有力支撑也成为光伏发电发展所需解决的关键问题。为了保证发生电压暂降时光伏发电仍能保持并网,国内外的并网标准中都要求大中型的光伏电站需要具有一定的低电压穿越能力。本文首先介绍和建立了光伏电池、最大功率跟踪(maximum power point tracking,MPPT)控制模块、并网逆变器的数学模型,并在Matlab/Simulink软件中搭建了相关部分的仿真模型。通过仿真得出了光伏电池的特征曲线以及光伏电池的最大功率跟踪仿真结果图,验证了所建模型的有效性和正确性,为光伏并网系统LVRT技术的研究提供了基础。其次,研究了逆变器的有限控制集模型预测控制(finite control set-model predictive control,FCS-MPC)。通过分析FCS-MPC算法的基本原理,建立三相并网逆变器FCS-MPC的模型。该算法在每个采样周期,由逆变器的数学模型和系统的状态信息,预测将来一段时间所有开关状态所对应的控制变量以及系统输出,并由价值函数选出让系统性能最佳的开关状态作用到逆变器,预先对系统误差进行修正以取得期望的性能。此控制方法具有简单易理解、无需调制器、内部完全解耦和动态响应快等优点。通过仿真验证,该控制可以实现单位功率因数运行,使得输出电流跟电网电压频率相位均相同,能够满足并网要求。最后,针对光伏并网的低电压穿越问题,本文提出了基于FCS-MPC的LVRT控制策略。介绍了国内外的低电压穿越标准;分析了电网故障期间并网逆变器的运行特性,阐述了电网故障对光伏并网发电系统的影响,为低电压穿越控制提供了理论基础;并通过仿真验证了采用的dq锁相环电压暂降检测方法可以准确、迅速地检测到三相对称电压暂降,为低电压穿越控制的动作提供依据。当电网故障引起并网点电压暂降时,光伏电池不再使用MPPT控制,转换为一种参考功率跟踪控制模式,减小光伏电池输送到逆变器的有功功率;逆变器在有限控制集模型预测控制的基础上采取一种拥有无功补偿的控制策略,通过重新调整有功电流和无功电流参考值,限制逆变器过电流,且给电网输出定量的无功支撑并网点电压的恢复。仿真结果表明,当并网点发生电压暂降时,所采用的LVRT控制策略,可以抑制直流侧母线电压的升高,限制逆变器输出电流的增大,为电网电压的恢复输出一定的无功功率,实现了低电压穿越。
[Abstract]:With the shortage of traditional energy and the increasingly serious environmental pollution, the development and utilization of renewable energy has become a hot topic. Solar photovoltaic power generation is one of the most potential and rapidly developing clean energy. With the increase of photovoltaic permeability, the influence of photovoltaic system on the power network is becoming more and more serious. When the grid is disturbed or broken, the photovoltaic system will bring serious consequences to the power network. Low voltage traversing voltage ride through LVRTT technology as a powerful support for power grid fault recovery has become a key problem for the development of photovoltaic power generation. In order to ensure that photovoltaic generation can still be connected to the grid when voltage sag occurs large and medium-sized photovoltaic power plants are required to have a certain low voltage traversing capacity in the grid-connected standards at home and abroad. This paper first introduces and establishes the control module of photovoltaic cell, maximum power point tracking module, and the mathematical model of grid-connected inverter, and builds the simulation model of related parts in Matlab/Simulink software. The characteristic curve of photovoltaic cell and the simulation diagram of maximum power tracking of photovoltaic cell are obtained by simulation, which verify the validity and correctness of the model, and provide the foundation for the research of LVRT technology in photovoltaic grid-connected system. Secondly, finite control set-model predictive control (FCS-MPC) is studied. By analyzing the basic principle of FCS-MPC algorithm, the FCS-MPC model of three-phase grid-connected inverter is established. In each sampling period, the control variables corresponding to all switching states and the system output are predicted by the mathematical model of the inverter and the system state information. According to the value function, the switching state with the best system performance is selected for the inverter, and the system error is corrected in advance to obtain the desired performance. This control method has the advantages of simple and easy to understand, no modulator, complete internal decoupling and fast dynamic response. The simulation results show that the control can realize the operation of unit power factor and make the output current equal to the frequency phase of the grid voltage and can meet the requirements of grid connection. Finally, a LVRT control strategy based on FCS-MPC is proposed to solve the low voltage traversing problem of photovoltaic grid-connected system. This paper introduces the low voltage traversing standards at home and abroad, analyzes the operation characteristics of grid-connected inverters during power grid failure, and expounds the influence of grid faults on photovoltaic grid-connected generation system, which provides a theoretical basis for low-voltage traversing control. The simulation results show that the DQ phase-locked loop voltage sag detection method can accurately and rapidly detect the three-phase symmetrical voltage sag, which provides the basis for the low-voltage traversing control. When the grid fault is caused and the node voltage is temporarily dropped, the photovoltaic cell is no longer controlled by MPPT and converted into a reference power tracking control mode to reduce the active power of the photovoltaic cell to the inverter. Based on the finite control set model predictive control, the inverter adopts a control strategy with reactive power compensation. By adjusting the reference value of active current and reactive current, the inverter overcurrent is limited. And to the grid output quantitative reactive power support and network voltage recovery. The simulation results show that the LVRT control strategy can restrain the rise of DC bus voltage, limit the increase of inverter output current, and output a certain reactive power for the restoration of grid voltage. Low voltage traversing is realized.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM615

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