【作者】 顾卓远；

【导师】 汤涌；

【作者基本信息】 中国电力科学研究院 ， 电力系统及其自动化， 2014， 博士

【摘要】 电力系统的安全稳定运行对于国家经济发展和社会稳定具有重要意义,历来受到电力学术界和工业界的高度重视。近年来国内外发生了多起大停电事故,造成了巨大的经济损失和严重的社会影响,同时也暴露出传统安全稳定控制系统在应对小概率意外事故方面的不足。相对于传统的安全稳定控制系统,基于响应的安全稳定控制摆脱了电力系统元件模型和参数的影响,无需预想运行方式和故障集合,可以全面、客观的评估电网暂态安全稳定水平、制定适宜的控制措施,为电力系统构筑一道新的综合防线抵御大规模停电事故。本文从此为切入点,重点研究基于响应的电力系统暂态稳定判别与控制技术,主要做了如下工作：(1)在基于响应的电力系统暂态功角稳定性判别方面,提出了一种基于转速差—功角差变化趋势的判别方法。该方法根据电力系统功角失稳过程一般首先表现为两群失稳模式的特点,以其在相平面运动轨迹的变化特征为基础,判断暂态过程中电网机群间是否能够保持同步运行。为克服虚拟的等效惯量中心计算得到的运动轨迹并不平滑的缺点,采用最小二乘法曲线拟合的方式判断运动轨迹走势,进而判断系统暂态功角稳定性。该方法依赖于发电机功角和转速的响应信息,计算方便快捷,可以作为暂态功角稳定紧急控制的启动判据。最后通过算例验证了所提方法的有效性。(2)在基于响应的电力系统暂态功角稳定实时紧急控制方面,提出了一种基于相对动能概念的紧急控制方案。以暂态功角稳定判别结果作为启动判据,通过相对动能衡量两机系统消纳暂态冲击能量的能力,再根据等面积准则计算切机措施量,形成完整的闭环实时紧急控制方案。为了考虑控制措施执行过程中存在的时间延迟的影响,在控制决策的制定中引入延迟时间来提高准确性。该方案摆脱了电力系统的元件模型和参数的影响,无需预想运行方式和故障集合,仅利用系统的实时动态响应曲线,可以适应复杂的运行方式和故障形式。最后通过算例验证了所提方案的有效性,表明所提方案可以防止系统进一步恶化甚至造成大停电事故。(3)为了全面防御电力系统暂态电压稳定与暂态功角稳定问题,以暂态功角稳定实时紧急控制方案为基础,提出了一种综合实时紧急控制方案。研究了暂态电压失稳的实时判别方法,建立了集中切负荷的控制方案。考虑到两种稳定问题具有相同的时间尺度,难以从失稳过程中电压、功角的变化中区分出到底是电压失稳还是功角失稳。采用并行判断的方法,同时监测系统的电压与功角稳定性,当判断出系统可能出现失稳现象时,立即采取相应失稳模式的紧急控制措施。最后通过算例验证了所提方案的有效性,表明所提方案能够准确抓住影响系统稳定的关键因素并采取相应措施,丰富了原有的电力系统暂态稳定实时紧急控制方案,将系统电压稳定问题纳入综合防御体系中,解决电网安全运行面临的稳定问题。(4)针对我国互联电网仿真分析中发现的新特性,研究了区域电网远端故障引发互联系统稳定破坏现象和影响互联电网稳定特性的关键因素。指出系统的网络结构和运行方式均会影响互联电网暂态失稳表现形式。在此基础上,重点研究了区域电网内机群间摆动对互联电网暂态稳定性的影响。从区域内部发电机群摆动对等值电势的影响入手,探讨研究大区互联电网暂态稳定新特征。分析表明,扰动后区域内部机群会相互摆动,导致等效电势幅值变动,使互联系统功率特性产生变化,从而影响到系统暂态稳定能力。最后对实际算例进行了仿真研究,该研究结果有助于掌握大区互联系统暂态稳定特性,加深对大区互联电力系统运行特性的理解。更多还原

【Abstract】 The security and stability of power system is significant to the national economic development and social stability, which attract more attentions from academics and industries in the world. In these years some serious blackouts occurred which have caused huge economic losses, and revealed that the traditional stability control system cannot handle the contingency with low probability. Compared with the traditional method, the response-based control is free from the influence of power system component models and parameters with no requirement to making planned operational mode and contingency set. It can comprehensively and objectively evaluate power system security and stability level and provide appropriate control measures to prevent blackouts. Thus, the response-based power system real-time transient stability identification and control strategy is mainly studied in this dissertation, which mainly includes:(1) Firstly, an identification method based on the variation trend of rotor speed difference-rotor angle difference is proposed to estimate the power system transient angle stability based on response. According to the characteristics that the power system often behaves as the two-group instability mode and based on the variation characteristics of the motion trajectory on the phase plane, whether the two machine groups can keep synchronization in the transient process will be estimated by this method. In order to overcome the defect that the trajectory of the virtual equivalent inertia center is unsmooth, the least square method is adopted to judge the trajectory tendency and the system transient angle stability. This method only needs the response information of generator’s power angle and speed. It is convenient and fast, which can be used as starting criterion of transient stability emergency control. Finally the effectiveness of the proposed method is verified by simulation.(2) In the aspect of response-based power system transient stability real-time emergency control, an emergency control scheme based on the relative kinetic energy is proposed. The transient stability identification result estimated from (1) is used as the starting criterion; the capability of the two-machine system absorbing transient energy is evaluated by relative kinetic energy. The machine tripping amount is calculated according to the equal area criterion to form a complete closed-loop real-time emergency control scheme. In order to take into account the impact of the time delay of the emergency control, the delay time is considered in the control strategy to enhance the accuracy. This method only depends on the system dynamic response curves, is free from the influence of power system component models and parameters, and doesn’t need to preset operational mode and contingency set. Thus it is suited to complex operational modes and contingency types. Finally the effectiveness of the proposed method is verified by simulation, showing that the proposed scheme can prevent the system from further deteriorating and even widespread blackout.(3) In order to comprehensively defend power system transient voltage instability and transient angle instability, a new comprehensive real-time emergency control scheme based on the transient angle stability real-time emergency control scheme is proposed. A transient voltage instability real-time identification method is developed, and a load shedding control scheme is proposed. These two stability problems have the same time scale, so it is difficult to identify voltage instability or angle instability from the variation of voltage and angle in the unstable process. The parallel judging method is applied to monitor both system voltage and angle stability problems. When it is detected that the system will be unstable, a corresponding emergency control measure is implemented to enhance the system stability. Finally the effectiveness of the proposed method is verified by simulation, showing that the proposed method can correctly detect the key factors influencing system stability and can implement corresponding measures. The power system transient stability real-time emergency control scheme can be enriched, and the system voltage stability can be introduced into the comprehensive defense system, solving the main problems of power systems.(4) Based on the new characteristics discovered in the simulation analysis of interconnected power systems in our country, the phenomenon of interconnected power system instability caused by fault occurred in the remote end of regional power grid and the key factors influencing the interconnected power system stability characteristics is studied. It shows that both the network topology and the operational mode can influence the transient instability mode of interconnected power systems. The impact of angle swing between machine groups in the regional power grid on the transient stability is mainly studied. This paper provides new transient stability characteristics of interconnected power systems through the point of the impact of machine group angle swing on the equivalent potential in the regional grid. The analysis indicates that the post-disturbance angle swing between generator groups in the regional grid can affect the amplitude of equivalent potential, which lead to variation of transient stability of interconnected systems and influence the capability of system transient stability. The conclusions are verified by the simulation to the actual power grid. The work in this paper contributes the mastery of transient stability characteristics of large-region interconnected power systems, and the mining of operation characteristics of large-region interconnected power systems.更多还原