【作者】 马添翼；

【导师】 金新民；

【作者基本信息】 北京交通大学 ， 电力电子与电力传动， 2014， 博士

【摘要】 摘要：微网是由分布式电源、负荷、储能、监控和保护装置共同组成的小型发配电系统,它具有并网和孤岛两种运行模式,可提高负荷供电可靠性。微网中的分布式电源通常采用电力电子装置接入电网,电力电子装置惯性小且过载能力差,增加了微网系统的控制难度；而电力电子装置的灵活、可控特性则为微网系统电能质量改善提供了便利条件。基于电力电子装置的运行特性,本文对微网在孤岛模式下的稳定性提高和电能质量改善展开研究,主要工作如下：(1)围绕孤岛模式微网的小信号稳定性分析展开研究。基于李雅普诺夫第一法思想,对微网系统小信号模型计算及稳定性判定方法进行了描述。根据微源的控制特性,建立了单台下垂控制支撑微源(Droop-cntrol surpporting micro source, DSMS)状态方程,并对其小信号模型进行了计算。从多DSMS、供电微源(Feeding micro source, FMS)组网系统的拓扑结构出发,以特定系统为例,阐述了多DSMS、FMS组网系统的小信号模型计算方法。计算了负荷阻抗、下垂增益变化时特定多DSMS、FMS组网系统的特征值,确定了影响系统稳定性的关键参数,并采用时域仿真对关键参数计算结果的正确性进行了验证。(2)围绕虚拟阻抗对DSMS控制性能的影响展开研究。从等效电路出发,分析不同线路阻抗对DSMS输出功率解耦控制性能的影响,确定了导致DSMS输出功率耦合的原因。给出基于虚拟阻抗实现DSMS功率解耦的控制方法,通过对DSMS实际输出功率的计算,阐述了虚拟阻抗实现DSMS输出功率解耦控制的机理,明确了不同功率耦合程度下虚拟阻抗选取的原则。根据虚拟阻抗的实现方法和线性化模型,分析了虚拟阻抗控制对DSMS输出电压和稳定性的影响。(3)围绕多DSMS、FMS组网系统的电能质量改善策略展开研究。基于FMS系统的等效电路计算,确定了影响FMS系统谐振频率等效阻抗的关键参数,并对FMS系统的有源阻尼实现方法进行了讨论。从DSMS的谐波等效电路出发,推导了DSMS系统输出电压的谐波分量表示,提出了降低DSMS输出电压谐波分量的控制方法。对DSMS与公共耦合点(Point of common coupling, PCC)电压的基波负序矢量关系进行了分析,确定了导致PCC与DSMS的输出电压基波负序分量差异的原因,提出了基于二次控制降低PCC不平衡电压的控制策略,并分析了二次控制延时对系统稳定性的影响。(4)围绕含多DSMS微网系统的负荷合理分担问题展开研究。给出了集中式负荷工况下的多DSMS微网系统等效电路,对线性不平衡负荷、非线性负荷工况下DSMS的负荷分担原理进行了分析,确定了线路阻抗对DSMS负荷分担性能的影响。对基于虚拟负序导纳实现负荷合理分担的控制原理进行了分析,提出了采用虚拟阻抗实现多DSMS系统负荷分担性能改善的控制策略。从DSMS基波负序、谐波分量等效电路出发,对DSMS输出电压的基波负序、谐波分量表达式进行了推导,分析了DSMS负荷分担性能改善控制策略对输出电压基波负序、谐波分量的影响。更多还原

【Abstract】 ABSTRACT:Microgrid is a small electric power system with distributed generations, load, energy storage, monitoring and protecting devices. It can operate in both grid-connected and islanded mode, which can enhance the reliability of electrical energy supply. Distributed genetations are always connected to grid through power electronic devices. The power electronic devieces have bad overload ability and small inertia character, which pose difficulty to the control of microgrid. The flexible and controllable charcter of power electronics devices provide convenience to micro-grid power quality improving. Based on the characteristics of power electronic devices, this thesis concentrates on the stability enhancement and power quality improvement of microgrid islanded mode. The main jobs of the thesis are as the following.Firstly, small signal stability analysis of islanding mode microgrid is investigated. The small signal modeling and stability judging method is discribed based on Lyapunov first method. State equation of single droop-control supporting micro source (DSMS) is derived from its control character, and the small signal model is also caculated. The small signal modeling method of microgrid with multiple DSMS and feeding micro source (FMS) is proposed based on the particular system example. The droop parameters and load changing eigenvalue are calculated. Key factors related to the example system stability are given, and the theoretical results are verified by time domain simulations.Secondly, the effect of virtual impedance on DSMS control performance has been discussed. The analysis of relationship between different line impedance and DSMS power decoupling performance is carried out. Key parameters caused DSMS power coupling are determined. Virtual impedance method for power decoupling-is proposed. DSMS output power is calculated, and the mechanism of power decoupling is also described. Virtual impedance selection principle based on different power coupling level is determined. Based on virtual impedance implementation method and linearization model, the effect of virtual impedance on DSMS output voltage and stability is analyzed.Thirdly, the power quality improvement control strategy of multiple DSMS and FMS networking system are investigated. The equivalent circuit of FMS system is calculated, and key parameters that influence the FMS system resonance pointequivalent impedance are determined. The achievement method of active damping control of FMS system is given. The expression of harmonic output voltage in the DSMS system is calculated, and the influence of DSMS output impedance to harmonic output voltage is confirmed. Then harmonic reduction control method of DSMS output voltage is presented. The fundamental negative sequence of output voltage relationship between DSMS and point of common coupling (PCC) is calculated, and the fundamental negative sequence of output voltage difference between-DSMS and PCC is investigated. Based on the secondary control, the control strategy of unbalanced voltage reduction on PCC is proposed, and the influence of secondary control delay on system stability is analyzed.Fourthly, the load sharingcontrol strategy of multiple DSMS microgrid system is investigated. The equivalent circuit of multiple DSMS microgrid system with centralized load is calculated, and the load sharing principles of DSMS with linear unbalance load and nonlinear load are analyzed. Then the effect on line impedance to the load sharing performance of DSMS is clarified. The principle on the control of virtual negative sequence admittance to achieve reasonable load sharing is analyzed, and then control strategy to improve load sharing performance of multiple DSMS microgrid system is presented. The expressions of fundamental negative sequence and harmonic output voltage are calculated, and the influence of DSMS load sharing control strategy on fundamental negative sequence and harmonic output voltage is also analyzed.更多还原