【作者】 张静；

【导师】 任碧莹； 高永军；

【作者基本信息】 西安理工大学 ， 能源动力（专业学位）， 2025， 硕士

【摘要】 随着全球工业化迅猛发展,能源与环境双重危机日益凸显为制约可持续发展的关键瓶颈。在此背景下,基于可再生能源的微电网系统凭借其灵活组网与清洁发电特性,逐渐成为新型电力系统建设的重要技术路径。然而受限于分布式电源(Distributed Generation,DG)占比高、系统惯量储备有限等固有特性,微电网的抗扰动能力变差,特别是在孤岛运行模式下,脱离主网电网频率支撑的微电网,更容易出现稳定性的问题。本文以并联中点箝位(Neutral Point Clamped,NPC)逆变器为研究对象,基于小信号模型对输出功率低频振荡及功率均分控制策略进行研究,以提升孤岛微电网运行的暂态稳定性与分布式电源的功率均分性能。逆变器模块是孤岛微电网的核心单元,本文首先建立NPC逆变器数学模型,接着针对下垂功率环参数、电压/电流双闭环控制系统,从稳定性与跟踪特性角度展开控制参数优化设计。为后续展开并联NPC逆变器系统的小信号建模及动态稳定性分析提供了研究依据和技术支撑。其次,针对并联NPC逆变器在dq旋转坐标系下出现功率低频振荡的问题,本文建立了功率下垂环、电压/电流双闭环、单/多台逆变器、阻感负载的小信号模型,进而得到孤岛微电网并联系统的小信号模型;进一步,基于并联系统的状态空间模型进行特征值计算,绘制根轨迹图并进行分析,明确低频振荡的重要特征,定量分析低频段主要状态变量对系统稳定性影响,为振荡抑制提供理论基础。然后,为抑制并联系统的低频振荡,提出了一种增加系统阻尼的改进下垂控制策略,并对该方法建立并联系统的小信号模型,通过特征值分析法验证其可行性;本文还针对并联NPC逆变器线路阻抗不一致导致的无功不均分问题,通过逆变器等效阻抗分析环流原因,研究基于二阶广义积分(Second Order Generalized Intrgral,SOGI)的虚拟电感功率均分控制策略。在不同工况下进行仿真验证,结果表明改进下垂控制能够有效抑制低频振荡,功率均分控制能够有效提高功率均分精度。最终,在孤岛运行模式下的微电网中,通过RT Box实验平台搭建两台50kW NPC型逆变器并联系统,分别进行了单台逆变器运行试验、并联逆变器低频振荡及抑制实验、并联逆变器功率均分实验,验证了本文所研究的抑制功率低频振荡的改进下垂控制及功率均分控制策略的正确性与可行性。更多还原

【Abstract】 With the rapid development of global industrialization,the double crises of energy and environment are increasingly highlighted as key bottlenecks constraining sustainable development.In this context,renewable energy-based microgrid system has gradually become an important technology path for the construction of new power system by virtue of its flexible network organization and clean power generation characteristics.However,due to the high proportion of distributed generation(DG),limited system inertia reserve and other inherent characteristics,the anti-disturbance ability of the microgrid is poor,especially in the islanding operation mode,the microgrid,which is separated from the main grid frequency support,is more likely to have stability problems.In this paper,we take the shunt neutral point clamped(NPC)inverter as the research object,and study the low-frequency oscillation of the output power and the power equalization control strategy based on the small-signal model,in order to improve the transient stability of the islanded microgrid operation and the power equalization performance of the distributed power supply.The inverter module is the core unit of an islanded microgrid.This paper first establishes a mathematical model of the NPC inverter.Subsequently,focusing on droop power loop parameters and the voltage/current dual closed-loop control system,it conducts optimization design of control parameters from the perspectives of stability and tracking characteristics.This provides both research basis and technical support for subsequent small-signal modeling and dynamic stability analysis of parallel NPC inverter systems.Secondly,to address the low-frequency power oscillation issues of parallel NPC inverters in the dq rotating coordinate system,this paper establishes small-signal models for the power droop loop,voltage/current dual closed-loop control,single/multiple inverters,and resistive-inductive loads.thereby obtaining the small-signal model of the islanded microgrid parallel system.Furthermore,based on the state-space model of the parallel system,eigenvalue calculations are performed by plotting root locus diagrams and analyzing them,which clarifies the key characteristics of low-frequency oscillations.A quantitative analysis is conducted on the influence of major state variables in the low-frequency range on system stability,providing theoretical foundations for oscillation suppression.Next,to suppress low-frequency oscillations in the parallel system,an improved droop control strategy that enhances system damping is proposed.A small-signal model of the parallel system incorporating this method is established,and its feasibility is validated through eigenvalue analysis.Additionally,to address reactive power sharing inaccuracy caused by inconsistent line impedances among parallel NPC inverters,this paper analyzes circulating current mechanisms via inverter equivalent impedance and investigates a virtual inductance-based power sharing control strategy utilizing the Second Order Generalized Integral(SOGI).Simulation verifications under various operating conditions demonstrate that the improved droop control effectively mitigates low-frequency oscillations,while the power sharing control significantly enhances power distribution accuracy.Finally,within a microgrid operating in islanded mode,a parallel system consisting of two50kW NPC inverters was constructed using the RT Box experimental platform.Experimental tests were conducted,including single-inverter operation tests,parallel inverter low-frequency oscillation and suppression tests,and parallel inverter power sharing tests.These experiments validated the correctness and feasibility of the improved droop control for suppressing low-frequency power oscillations and the power sharing control strategies studied in this paper.更多还原