【作者】 杨向真；

【导师】 丁明； 苏建徽；

【作者基本信息】 合肥工业大学 ， 电力电子与电力传动， 2011， 博士

【摘要】 微网是整合各种分布式能源优势、减弱分散的分布式发电对大电网的不利影响、充分挖掘分布式发电经济效益的有效方式,已经成为分布式发电领域的研究热点和重要发展方向。本文针对微网逆变器及其协调控制展开研究,借鉴同步发电机组的运行特性、控制策略以及电力系统的电压、频率控制结构,建立了微网逆变器的数学模型、各种运行模式下的控制器以及微网分层控制结构,本文的主要研究内容有：(1)深入调研了微网产生和发展的背景、概念以及国内外发展现状；基于现有各国建立的多个微网实验平台和示范工程,归纳总结了微网的控制结构和微网逆变器的控制策略；(2)重点提出了一种统一的微网逆变器接口一虚拟同步发电机(virtual synchronous generator, VSG);详细阐述了VSG的基本原理和实现方法,提出了瞬时无功理论和准谐振滤波器两种提取基波分量的方法来模拟同步电抗：基于VSG和同步发电机定子电气部分的数学模型,详细对比了它们的等效输出阻抗特性、外特性、动态特性以及功角特性；(3)借鉴电力系统调速器和励磁控制器的基本原理,设计了VSG的数字调速器和励磁控制器,有效模拟了同步发电机组的功频特性和电压调节特性：VSG以PQ.模式联网运行时,详细分析了有功功率闭环控制的稳定性、动态性能和抗扰性能；无功功率控制方面,在励磁调节器的基础上,提出了一种前馈补偿和闭环控制器相结合的无功功率复合校正系统,快速准确的达到无功功率无差控制的目的；为了满足微网逆变器按照调度经常切入切出的需要,设计了VSG独立运行模式下的频率控制器和电压控制器,以及独立运行模式向并网模式切换的预并列控制单元；(4)借鉴电力系统分层控制思想,提出了一种适宜于微网的分层控制结构；阐述了将电力系统分层调频方法引入到微网的可行性,侧重研究了微网一次调频和二次调频。根据经济调度对功率分配的影响,提出了一种变频率调节系数的调速器,以便最大限度的利用现有发电容量参与一次调频；对比分析了分散式和集中式两种二次调频的实现方式,揭示了分散式频率无差控制无法实际应用的原因；(5)研究了微网孤岛模式下电压分层控制策略。为了方便的实现并联组网模式下电压控制与PQ模式下无功功率控制之间的平滑切换,提出了一种调差系数可调的新型励磁调节器,阐述了不考虑线路阻抗情况下VSG间无功功率分配的原理；一次电压控制中,提出了一种在线计算一次电压控制器参考输入电压的新算法,用以解决无功功率分配精度和母线电压跌落问题；设计了微网二次电压控制器,在matlab/simulink仿真平台上验证了一次电压控制器改进算法的效果和孤岛运行时微网分层控制的正确性；(6)介绍了基于实验平台的微网系统整体结构,给出了微网逆变器实验样机的硬件结构和软件架构,详细进行了单台微网逆变器惯性时间常数的模拟、独立运行、PQ并网、两台微网逆变器并联组网以及电压频率恢复等各种实验。更多还原

【Abstract】 Microgrid is an effective approach to integrate the advantages of all kinds of distributed resources, to take less impact on distribution grid and improve the economic profits of distributed generations. It has become a hot topic and important direction in distributed generation area. Research on microgrid inverter and coordinated control of multiinverter was focus on in this paper. According to the behavior and control strategy of synchronous generator and control structure of utility, the mathematic model of microgrid inverter, controllers for different operation modes and hierarchical control structure of microgrid were established. The main content of this paper are as follow:First of all, a survey of the background, concept and development at home and broad of microgrid were provided; Control structures of microgrid and operation strategies of inverters were summarized based on many experimental platforms and projects in many countries.Secondly, a new kind of unified microgrid inverter was proposed—virtual synchronous generator (VSG in short); fundamental theory and implemental method of VSG were expatiated. Instantaneous reactive power theory and quasi-resonant filter were adopted to imitate the synchronous reactance; Equivalent output impedance, external characteristic, dynamic performance and power angle feature were compared relatively between synchronous generator and VSGThirdly, a digital governor and an excitation controller, extracting from the essence of governor and excitation controller of synchronous generator, were designed to embody as same power-frequency characteristic and voltage regulating characteristic as synchronous generator set. When PQ control of VSG operated in grid-connected mode, stability, dynamic performance and anti-disturbance characteristic of the active power control system were analyzed in detail relatively. A reactive power controller composing of a feedforward loop and a close loop was proposed to achieve the aim of no steady error of reactive power fast and accurately. VSG often switches in and off from grid according to the economic dispatching, so a frequency controller and voltage controller of VSG for independent operation and a resynchronous unit from independent operation to grid-connected mode were designed.Fourthly, a hierarchical control structure suitable for microgrid was presented according to the hierarchical control of utility; the possibility of employing the hierarchical frequency regulation of utility was described. Both the first frequency regulation and the second frequency regulation were focus on. Economic dispatching had a significant impact on the power distribution among the microgrid inverters, so a governor with variable frequency regulation coefficient was proposed. In this way, more generation capacity of inverters would participate in the first frequency regulation of microgrid; the second frequency regulation both in decentralized and centralized way were compared and analyzed. The reason why the decentralized way was unpractical was revealed.Then, the hierarchical voltage control was researched. A new excitation controller with adjustable voltage regulation coefficient was developed to satisfy the switching requirement between parallel control in islanded mode and reactive power control in grid-connected mode. A new online algorithm of reference voltage for the first voltage controller of VSG was proposed to solve the problem of distribution accuracy of reactive power and voltage drop; the second voltage controller of microgrid was designed. This new algorithm of the first voltage controller and hierarchical control of microgrid in islanded operation were testified on Matlab/simulink platform.Finally, the framework of microgrid based on experimental platform was introduced. The hardware scheme and software flow chart of the experimental prototype of microgrid inverter were provided. Many experiments of single inverter, such as the effect of inertia time constant, independent operation, PQ control, and two inverters in parallel control including voltage/frequency restoration were verified on experimental prototype of microgrid inverter.更多还原