【作者】 张强；

【导师】 石访；

【作者基本信息】 山东大学 ， 电气工程， 2021， 硕士

【摘要】 随着能源危机和环境污染问题的日益严重,我国已将可再生能源的开发与利用上升到国家战略层面。新能源集中并网、并通过大容量高压直流远距离输送,是我国现阶段新能源开发外送的典型场景之一。然而,针对光伏经高压直流送出时的稳定问题研究尚不充分。特征值分析法广泛应用于交直流混联系统的稳定性分析,然而通过电力电子装置实现并网的光伏电站是一个高阶系统,光伏电站的加入使特征值的求解遇到维数灾的问题,计算量大且精度难以保证。阻抗分析法建模简便,只需建立研究对象的输入或输出阻抗模型,根据阻抗之间的关系分析系统的稳定性,尤其适用于理论分析和实验测试相结合的情况,近年来广泛应用于新能源并网系统。然而,该方法在面对光伏并网经LCC-HVDC送出系统时,如何将系统的动态特性通过阻抗的形式完整的表现出来,使据此提出的稳定判据准确的判断系统的稳定性,是一个挑战。本文为解决这一问题,做了以下工作。首先,本文简单介绍了课题研究的理论基础。传统阻抗分析法适用于含两个子系统的单输入单输出系统,然而实际电力系统为含多个子系统的多输入多输出系统。部分学者认为,可以通过将多个子系统等效为电源子系统或负荷子系统这一方法将多输入多输出系统等效为单输入单输出系统。将该方法应用于光伏集中接入直流近区系统中,给出等效电源子系统和负荷子系统的思路,得到该系统的稳定判据,并在PSCAD仿真软件中设计仿真案例验证该方法的可行性。并且基于稳定性分析结果,通过计算参数相对灵敏度量化分析系统中部分参数对系统稳定性的影响,并据此优化光伏系统。其次,本文通过理论推导验证了传统阻抗分析法在光伏并网系统中的适用性和适用条件。首先在光伏单端口并网场景下,分别通过特征值分析法和阻抗分析法对该系统的稳定性展开分析研究,在验证二者一致性的基础上证明不正确地选择研究点,会使阻抗分析法构造的开环传递函数出现零极点对消,这导致该系统的部分特征值隐藏在被传统阻抗分析法忽略的那一项中,并最终导致传统阻抗分析法给出错误的稳定性分析结果。然后在光伏多端口并网场景下,证明“将多输入多输出系统等效为单输入单输出系统”的方法在该场景下需满足电源子系统和负荷子系统内部无不稳定极点的前提条件。最后,本文提出了适用于多输入多输出系统的阻抗分析法(MIMO-IMA),该方法基于广义奈奎斯特判据和系统的节点导纳矩阵。选择光伏和直流接入的节点作为研究对象,构造光伏并网经直流送出系统的多输入多输出的闭环表达形式。基于广义奈奎斯特判据,给出系统的稳定判据。并通过理论推导证明该方法和特征值分析法的一致性,且传统阻抗分析法可视作为该方法应用在单输入单输出系统中的特例。最后,在PSCAD仿真软件中设计光伏集中接入直流送端近区和光伏分散接入直流送端系统两个仿真案例,证明该方法的可行性和有效性。更多还原

【Abstract】 With the increasingly serious energy crisis and environmental pollution,China has raised the development and utilization of renewable energy to the national strategic level.The concentrated interconnection and long-distance power transmission of renewable energy through large-capacity HVDC is one of the typical scenarios of renewable energy development and transmission in China at the present stage.However,the research on the stability of photovoltaic(PV)power when it is transmitted through HVDC is not enough.The eigenvalue analysis method is widely used in the stability analysis of the AC/DC hybrid system.However,the PV station connected to the power grid by power electronic devices is a high-order system.The solution of the state matrix encounters the problem of dimension disaster,which results in a large amount of calculation and difficulty to guarantee accuracy.The impedance-based analysis method(IMA)is simple in modeling and only needs to establish the input or output impedance model of the research object.According to the relationship between the impedances,the stability of the system is analyzed,especially suitable for the combination of theoretical analysis and experimental test.In recent years,it is widely used in renewable energy grid-connected systems.However,when the method faces multiple-input and multi-output(MIMO)systems,it is a challenge that how to make stability criteria completely reflect not only the dynamic characteristics of subsystems but also the interaction among subsystems,to include all the unstable poles.This paper attempts to solve this problem,the main contributions of this paper are in the following.This paper firstly introduces the theoretical basis of the research.The traditional IMA is suitable for single-input and single-output(SISO)systems with two subsystems.However,the actual power system is mostly a MIMO system with multiple subsystems.Some scholars believe that the MIMO system can be equivalent to the SISO system by equivalent the multiple subsystems to the power supply subsystem or load subsystem.In this paper,it is applied to the grid-connected PV system.The idea of equivalent power supply subsystem and load subsystem is given,and the stability criterion of the system is obtained.Simulation cases are designed in the PSCAD to verify the feasibility of the method.Based on the results of impedance-based stability analysis,the influence of some parameters on the stability of the system is quantitatively analyzed by calculating the relative sensitivity of parameters,to guide the optimization of PV control parameters.Secondly,the applicability of traditional IMA in the grid-connected PV system is verified by theoretical derivation.At first,taking the scenario of single grid-connected PV as the research object,the stability of the system is analyzed by the eigenvalue analysis method and IMA respectively.Based on verifying the consistency of the two methods,it is proved that improper selection of research points will cause the zero-pole cancellation of the open-loop transfer function constructed by IMA.As a result,part of the eigenvalues of the system are hidden in the item ignored by the traditional IMA,and eventually,the traditional IMA gives wrong stability analysis results.Then,taking the scenario of multi grid-connected PVs as the research object,it is proved that the method of "equivalent MIMO system to SISO system"should satisfy the premise that there are no unstable poles in the power supply subsystem and load subsystem in this scenario.Finally,the impedance-based analysis method for MIMO systems(MIMO-IMA)is proposed,which is based on the generalized Nyquist criterion(GNC)and the node admittance matrix of the system.The PV and DC connected nodes are selected as the research objects,and the closed-loop expression of MIMO of the PV grid-connected and DC transmission system is constructed.Based on GNC,the stability criterion of the system is given.The consistency of MIMO-IMA and the eigenvalue analysis method is proved by theoretical derivation,and the traditional IMA can be regarded as a special case of MIMO-IMA applied in the SISO system.Finally,two simulation cases are designed in PSCAD,which are the PV grid-connected system with centralized connection to the near field of LCC-HVDC sending end and the PV grid-connected system with distributed connection to LCC-HVDC sending end system,to prove the feasibility and effectiveness of the proposed method.更多还原