【作者】 魏军强；

【导师】 李庚银；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2013， 博士

【摘要】 随着智能电网的建设和电力市场的竞争日益激烈,电力系统越来越接近于其极限运行,这给电力系统的安全稳定运行带来了严峻的挑战。电网可用输电能力是电力市场环境下的一项重要技术指标,其计算的准确性、快速性对电力系统的可靠运行、市场交易各方的利益分配具有至关重要的影响。随着大区电网互联和高压直流输电的广泛应用,亟需研究关于交直流混合电网输电能力的理论和方法。本论文在充分调研已有研究成果的基础上,从输电能力的定义和计算要求出发,对交直流混合系统可用输电能力的评估与计算模型和方法等问题展开深入研究,主要工作如下：首先考虑直流系统接入对交流系统的影响,建立了交直流混合系统静态可用输电能力评估的数学模型,并提出了基于蒙特卡罗模拟的评估方法。综合考虑不确定性因素、.直流系统及其灵活的控制方式对交流系统的影响,通过对交流系统输电能力的数学模型进行改造,完善目标函数和约束条件,提出了包含直流系统的混合电网可用输电能力评估模型,并基于蒙特卡罗方法对静态可用输电能力进行评估,提出了有效蒙特卡罗模拟次数的概念和基于核函数的可用输电能力概率分布密度估计。在计算环节,考虑到系统的安全性与经济性,将最优潮流模型应用到重复潮流法的每次求解潮流中。在不考虑系统输电裕度的情况下,可用输电能力在数值上等于最大输电能力减去现有输电协议所占用的输电能力,因此对可用输电能力的评估所提模型和方法对于最大输电能力的评估同样适用。然后针对传统蒙特卡罗模拟方法计算耗时的缺点,提出了基于广义蒙特卡罗方法的交直流混合系统可用输电能力或／和最大输电能力的评估方法。在评估方法的选取过程中,针对多次蒙特卡罗方法模拟需要做大量潮流计算,非常耗时以及相应可用输电能力或／和最大输电能力评估指标受极端值影响严重的特征,提出了将传统蒙特卡罗模拟方法和重采样法、并行计算以及稳健性统计方法相结合的广义蒙特卡罗方法,这类方法能显著提高交直流混合电网的输电能力评估效率,不但为可用输电能力或／和最大输电能力评估的实时化奠定基础,而且也为蒙特卡罗方法在其他领域的使用提供了方法支撑。接着,提出了适用于交直流混合系统动态可用输电能力计算的最优潮流法。针对交直流混合电网可用输电能力计算中考虑暂态稳定约束的必要性及复杂性,在静态可用输电能力计算的基础上,通过引入影响暂态稳定性的微分代数约束,提出了适用于交直流混合系统动态可用输电能力计算的最优潮流法,并且针对最严重故障计算可用输电能力。最后,提出了基于非线性分岔理论的交直流混合系统可用输电能力的计算模型。在借鉴传统电压稳定分析的非线性分岔方法的基础上,考虑将负荷作为参数,通过扩张系统方法计算得到鞍结分岔和霍普夫分岔分别对应的静态和动态可用输电能力。从理论上验证了直接法确定鞍结分岔和霍普夫分岔与最优化方法的等价性,指出了相应方法的优劣,为快速、准确的可用输电能力计算提供理论依据和算法支撑。更多还原

【Abstract】 Under the competitive power market environment and in the smard grid era, the power grid has been extensively used and operated close to its limit. This results in a new challenging task for power system engineers in managing the security of the power system. Available Transfer Capability (ATC) is a significant technical index in the power market environment. The precise and fast computation or evaluation of ATC is crucial to reliable operation of the power system and fair distribution of the power market participants’benefits. Along with the interconnection of bulk power grid and extensively used of high voltage direct current (HVDC) in modern transmission network, there is an urgent need to study the theory and methods on ATC assessment problems arising from AC/DC interconnection modes of bulk power grid. Based on thoroughly researching of the existing literature, this dissertation deeply focuses on the computation and evaluation problems of ATC in AC/DC hybrid systems from the definition and computation requirements of ATC, the main aspects are as following.Considering the uncertainties, DC system and its flexible control modes, and their effects on the AC system, a novel mathematical model is constructed to assess ATC in the AC/DC hybrid systems. The objective function and corresponding constraints are modified according to the electricity transfer profile selected and the control and operation of DC systems. Because of time and space varying of ATC, the probabilistic methods are suitable for ATC evaluation. The non-sequential Monte Carlo simulation based methods are presented to calculate the five-number summary and other statistical indices of ATC for the long time transfer capability assessment of the network. Effective numbers of Monte Carlo simulations can be obtained by the given acceptable error and the confidence level. A kernel density estimation based method is proposed to approximate the probability density function of ATC. In the process of calculation, the optimal power flow model is added into the repeated power flow method to ensure both safe and economical operation. In general, the ATC is the difference between the Total Transfer Capability (TTC) and the Existing Transfer Capability (ETC) without considering system margins since various operating margins can be accounted for separatedly. When using such a definition, all the models and methods applicable to evaluation of ATC are also applicable to the evaluation of the TTC.In order to avoid too many times of Monte Carlo simulations and promote the efficiency of the assessment, generalized Monte Carlo methods are proposed to deal with the stochstic behavior of the power system by incorporating the traditional Monte Carlo method and resampling, parallel computing, and robust statistics methods. All of these methods can not only establish the basis for realtime assessment of ATC/TTC, but also provide methodology support for applications of Monte Carlo method in other fields.Based on the analysis to the traditional modeling of available transfer capability, one method is proposed to calculate ATC for AC/DC hybrid power grid considering transient stability constraints. The optimal power flow (OPF) model is employed to solve the problem. In this method, different kinds of constraints including voltage limit, transient stability limit, generator operation limit, etc. can be considered comprehensively. Some contingency states are considered. Furthermore, the flexible control functions of DC systems were involved in the calculation by rationality and security principles.Numerical bifurcation analysis techniques are very powerful and efficient in physics, biology, engineering, and economics. Power system engineering has become a classical application field of bifurcation theory since1990’s. Local bifurcations are readily evident in power systems as important elements of voltage instability. Apart from considering the static limits, application of bifurcation analysis would be a novel idea in the computation of dynamic ATC. By integrating the saddle-node bifurcation (SNB) and Hopf bifurcation (HB) into the ATC model, both the static and transient security are considered. For ATC determination, the static and dynamic ATC corresponding to SNB and HB respectively and they are obtained by the extended systems with respect to specific singular points. Furthermore, the direct method and the optimization method to determine the bifurcation point are compared and the equivalency of them is proved from a mathematical viewpoint. All of these can act as theoretical and technical support for fast and accurate computation of ATC.更多还原