【作者】 李莉；

【导师】 刘玉田；

【作者基本信息】 山东大学 ， 电力系统及其自动化， 2009， 博士

【摘要】 电力是国民经济的支柱行业,电力系统能否安全稳定运行关系到国家安全、社会稳定与人民安居。然而,受到自身原因和外部干扰的影响,在电力系统中事故时有发生,特别是造成系统稳定性破坏和不可控恶性连锁反应的故障,不但使电力企业本身蒙受经济损失,而且对电力用户乃至整个社会都会造成严重的影响。因此,保证大规模互联电力系统的安全稳定,防止大面积停电事故的发生是电力系统所面临的一项迫切而重大的任务。失步解列控制作为保证系统安全运行的重要措施,是防止电网崩溃的重要手段。当互联电力系统之间发生失步振荡时,采取合理的解列控制方案,可以有效地防止事故的蔓延,以免系统大停电事故的发生。但是,不合理的解列往往给系统带来更大的混乱,促使系统崩溃。各国电力系统的运行实践表明:针对安全稳定破坏事故,无论采取如何严密的防范措施,都难以完全避免,尤其对于由多种不可预计的偶然因素叠加而导致的事故更是防不胜防。针对小概率的罕见事故,在防御措施上,应从防止事故发生向提高事故后的处置能力倾斜,最大程度地减少事故危害。当安全稳定破坏事故发生之后,如何阻止事故的扩大与发展,尽可能减少对用户的不良影响,并为电力系统恢复提供有利的条件,是事故处置方案应予以解决的问题。当电力系统遭受大扰动而失去同步时,恰当的解列措施能够将相互失步的各部分断开,阻止事故蔓延,减少停电范围,防止系统崩溃。因此,失步解列方案是常规安全稳定控制与保护措施的坚强后备。失步解列的关键是能够在系统被动解列之前,准确、及时地把系统解列为若干个各自保持同步运行的子系统。目前,电力系统所采用的各种失步解列方案存在若干问题,包括:1)基于等值两机系统模型,不能准确地刻画大规模互联电力系统的失步特点;2)采用单端测量捕捉失步中心,不能跟踪失步振荡中心的转移;3)难以适应运行方式与故障形态的变化,对未知的失步模式不能可靠地响应。针对上述问题,本文在分析电力系统失步后的电气量变化特征与比较多种现有失步解列方案的基础上,提出了基于广域测量信息的失步解列判据与控制系统方案。所提出的解列判据与方案,采用多端量测量,能够准确地跟踪失步振荡中心、识别系统失步状态,对运行方式与故障形态的变化具有较好的自适应性,对不同的失步模式可靠地响应。所采用的分层分布控制结构计及了大规模互联电力系统的特点,具有较强的实用性。论文主要的研究工作和创新性成果如下:1.提出了一种基于PMU量测量的改进失步判据。基于单端量的ucosφ判据可以根据振荡中心电压的变化规律来区分失步振荡、同步振荡和短路故障。通过对系统失步时各电气量变化规律和振荡中心特征的分析,可知当系统可以等值为幅值相等的两机系统且各处阻抗角一致时,ucosφ实质上反映了系统振荡电压的最低值。但是,当等值的两机系统幅值不相等时,有可能出现ucosφ没有物理意义的情况,从而无法确定失步振荡中心位置。利用PMU测量的联络线两端电压相角差,辅助识别系统的失步状态,确定失步振荡中心的位置,弥补基于单端量的ucosφ判据的不足。对新英格兰10机39节点系统和山东电网进行仿真。利用同调分群结果设置解列点,执行基于PMU量测量的改进失步判据,识别系统的失步状态。仿真结果表明该改进失步判据准确地跟踪失步振荡中心,识别系统失步状态。2.提出了一种适用于系统断面的自适应复合解列判据。系统从遭受扰动后发生摇摆到失步是一个复杂的过程,各种参数在不同阶段的特性不同,不同的判据各有利弊。可用不同的判据构成复合判据,互为补充,扬长避短。将系统按失步断面解列是一种有效的方法,它的优点是能根据不同的失步模式按不同的失步断面解列。在分析电力系统失步振荡过程和各种失步解列判据的基础上,提出了一种适用于失步断面的自适应复合解列判据。该复合判据不仅利用主判据ucosφ反映振荡中心电压的变化规律,而且以动作特性独立于振荡中心位置的电流变化量作为辅助判据,可及时检测系统是否失步。主判据与辅助判据相辅相成,可靠地实施解列。以山东电网为例进行仿真。根据电力系统调度分层、分区的特点,依照调度分区在线搜索解列断面,即在线搜索失稳部分与剩余部分之间的联络线。利用PMU测量解列断面的多端信息,把基于单端量针对等值两机系统单一线路ucosφ判据转化为系统失步状态判据。仿真结果表明系统断面复合判据对运行方式与故障形态的变化具有较好的自适应性,可靠地响应复杂多机系统的失步模式,准确性高。3.提出了一种基于广域测量信息的失步解列控制系统方案。在对现有失步解列方案和电力系统分层分区结构进行分析的基础上,对失步解列措施的协调与配合进行了探讨,指出目前存在的主要问题,提出了一种基于广域测量系统(WAMS)和多Agent的失步解列控制系统方案,着重解决多区域互联电力系统的复杂失步模式。该控制系统采用分层分布结构,由控制中心层、区域控制层和就地执行层三层协调合作,完成失步解列控制的协调优化,保证整个电网的稳定运行。控制中心层收集和处理涉及全系统的综合信息,识别整个电网的运行状况,搜索解列断面,识别区域系统之间的失步振荡,与紧急控制措施协调,并将有关运行方式的信息和解列控制方案下传到区域控制层和就地执行层。根据电网的结构和特点,将整个系统分成若干区域,而区域控制层包括若干区域控制子站,负责采集区域内系统运行信息,进行失步断面的协调优化和断面的失步状态识别,并把必要的信息向就地执行层传送;就地执行层有若干本地解列子站,采集就地信息,实施传统的就地解列控制,同时也可以从主站接收实时的解列控制策略和正确的解列装置动作信息。从而实现各层次既能相对独立工作又能协调一致的分层解列控制方案,较好地解决大规模互联电力系统的解列控制问题。针对新英格兰10机39节点系统和“三华“电网进行仿真,结果表明该控制系统方案能够从电力系统全局出发,实时监控系统状态,在线搜索合理的解列策略,实现失步状态的快速识别和解列断面之间解列措施的协调与配合,自动适应系统电网结构与运行方式的变化。更多还原

【Abstract】 The advancement of interconnected power grids provides strong supports for improvement of socioeconomic situation. Meanwhile, it also brings new challenges to security and stability of power systems. Huge efforts have been made to avoid blackouts worldwide but cascading outages which evolved into catastrophic blackouts still happened. As a result, more and more research on how to deal with unstable conditions of interconnected power system is necessary and resonable. Out-of-Step splitting control is one of important means to defend power systems blackouts, ensure stability and reliability of power systems. When oscillation occurs in interconnected power systems, if proper automatic control actions or operator intervention are not taken decisively, the system may be susceptible to further failures and subsequent cascading. It is imperative to develop new strategies of splitting control schemes to detect instability and take remedial actions to prevent power system from worldwide blackout emergency.The long time experiences for power system operation have shown that no matter how strict the requirements for power system stability, and how perfect the measures are, there would be some unpredictable casual faults working together to cause instability. However, the expense for too strict security requirements is very high. When the stability of power system is destroyed, the key question is how to detect and prevent oscillations rationally and quickly, and how to restoration rapidly. In China, when an interconnected grid is subjected to large disturbances and becomes out-of-step, out-of-step splitting control has been used widely as the last resort for preventing widespread blackout. But there are some problems of out-of-step splitting controls: 1) most of the criterions are designed based on equivalent two-machine system model, splitting controls will not be suitable to the interconnected power grids; 2) a lot of conventional out-of-step criterions are based on local signals, which can not follow drift of the dynamics oscillation center and can not be adaptive to the change of system network topology; 3) out-of-step splitting schemes are not able to adjust to complex oscillation conditions. In this paper, though analysising the charateristics of electrical parameters of out-of-step interface and current splitting schemes in the actual field, new out-of-step splitting criterions and splitting control schemes based on WAMS information are proposed. The splitting criterion and splitting control scheme of power system have correct functions of initiating the separation equipment, capturing the oscillation center and out-of-step interface, coordinating splitting controls and splitting the out-of-step area from the main system timely and accurately when the out-of-step happens in the interconnected system. The main research work and innovative fruits of the dissertation are as follwing.1. Based on the Phasor Measurements Units (PMUs), an adaptive ucosφimproving criterion for out-of-step splitting to obtain quick and selectable disconnecting actions is proposed in the paper. The ucosφout-of-step splitting criterion can identify out-of-step oscillation, short-circuit fault and synchronous oscillation which based on the changing track of the voltage of oscillation center. However, in practical system ucosφmay not able to represent voltage at any location of the out-of-step center and has no specific physical meaning. On the other hand, the ucosφcriterion based on local information may be misjudged because amplitudes of equivalent electric potential of both sides are different in practical system, so the power system might be in a dangerous condition. The change of angle difference of voltage phasor based on PMUs can reflect the out-of-step condition directly. It can help to confirm the location of the oscillation center. The reliability of ucosφsplitting criterion and the accuracy of splitting action are ensured with the assistant of angle difference of voltage phasor.In the simulations of the 10 machines 39 buses New England system and a practical Shandong power system, the splitting spots are set by the identification and aggregation of coherent generators and according to the active power balance. The improving out-of-step splitting criterion identifies out-of-step condition of system. Simulation results demonstrate the effectiveness of the proposed approach.2 . An adaptive out-of-step detecting composite criterion for out-of-step splitting interface is proposed. When the synchronization loss takes place, disconnecting the interface of out-of-step is considered the main solution to prevent power system from collapse. Through the analysis of the process of asynchronous oscillation and systematic researches on existing out-of-step criterions of power system, making several criterions work together and reusable and taking fully advantage of every criterion are possible. An adaptive out-of-step composite criterion for splitting interface based on WAMS includes the main criterion and the auxiliary criterion. The main ucosφcriterion which reflects the changing track of oscillation center voltage detects the synchronism loss. The auxiliary criterion reflecting changes of three-phase currents ensures the reliability of splitting action which is independent of the oscillation center. These two criterions are used together for determining out-of-step accurately and duly.In the simulations of Shandong power system in China, the islanding interface is determined based on power system dispatching area and generator coherency. And the composite criterion can be operated based on the confirmed interface. Simulation results have demonstrated that the proposed criterion can adapt to the changes of operating conditions, capture the position of out-of-step center dynamically and cope with the shortcoming of a single criterion.3. An out-of-step splitting control system scheme based on wide area measurement information for power system is proposed in this paper. This system scheme based on WAMS and multi-agent is designed to prevent worldwide collapse of interconnected power system. This system which has distributed hierarchical control structure includes control center level, region control level and local execute level. Three levels are coordinated and cooperated, so the splitting control system can observe power system more comprehensively, identify out-of-step condition correctly, split the out-of-step system duly and ensure the stability of the whole system. The control center level collects and processes the overall informations, searches splitting interfaces online, identifies the out-of-step oscillation between region power systems and coordinates with emergency control. The region control level which includes region splitting stations, identifies the out-of-step oscillation in the region power system and coordinates with out-of-step interfaces. The local execute level which includes local splitting stations, splitting control measures are carried out. Three control levels can work both independently and coordinately to maintain stability of the whole system.Simulation results for the 10 machines 39 buses New England system and the practical Huabei-Huazhong-Huadong interconnected power system have demonstrated that the splitting scheme which is easy to be applied in the engineering field can identify the out-of-step condition hierarchically, split the instability area cutting off from the whole system timely and correctly. So the asynchronous oscillation between interconnected power systems will be eliminated and the widespread outages will be averted.更多还原