【作者】 王京景；

【导师】 丁明；

【作者基本信息】 合肥工业大学 ， 电力系统及其自动化， 2012， 博士

【摘要】 近年来,大功率电力电子设备被广泛应用到电力系统领域,特别是柔性交流输电和高压直流输电设备。它们在远距离大容量输电、不伺频率联网、提高交流电网的可控性和最大化电网的输送能力等方面起着不可替代的作用。做为新一代的直流输电技术,柔性直流输电采用全控型电力电子器件、电压源换流器和脉宽调制等技术,解决了传统直流输电存在的诸多问题。然而,由于电力电子设备结构复杂、与电网联系紧密等特点,其本身的可靠性以及电网对其可靠性的影响不容忽视。现有柔性直流输电设备的可靠性模型,尤其是换流阀等核心器件,尚不完善；基于恒定故障率和解析法的元件可靠性模型,很难完全反应变化的工作环境对电力电子器件可靠性的影响。本文将负载效应引入柔性直流输电换流阀的可靠性建模中,针对电压与电流负载效应的不同特性,提出了相应的处理方法。同时,本文提出的电流负载等效模型计及变化的电网潮流对换流阀可靠性的影响,因此在对电流负载进行等效时,需要进行概率潮流的蒙特卡罗仿真计算。由于蒙特卡罗仿真计算量过大,本文提出并研究了扩展拉丁超立方采样算法,提高计算效率,减小计算时间。本文围绕以上问题,做了以下研究工作：(1)基于电力电子设备可靠性研究理论,提出了柔性直流输电换流阀的可靠性评估模型,采用表决系统模型,讨论了换流阀冗余设置与可靠性指标之间的量化关系；(2)针对现有恒定故障率下可靠性建模的不足,提出了基于负载效应的换流阀可靠性模型,采用蒙特卡罗仿真求解；从不可修和可修两类模型的角度分析了电压负载效应的引入对可靠性指标的影响,并以此为基础,对换流阀的备件储备策略进行了研究计算；(3)针对现有VSC-HVDC换流站稳态模型的不足,引入了一般形式的交流侧等值电路方程和二次函数拟合的换流站损耗计算模型,在此基础上采用统一求解法进行含VSC-HVDC的交直流混合潮流计算；(4)在现有VSC-HVDC稳态潮流模型的基础上,对含VSC-HVDC的电力系统概率潮流进行计算分析,根据概率潮流的计算结果对变化的电流负载进行等效计算,获得考虑电网潮流变化时的阀模块可靠性模型：(5)针对现有拉丁超立方采样技术的计算只能基于固定采样数,无法在已有采样点的基础上扩展的不足,引入扩展技术,形成了扩展拉丁超立方采样技术；并在此基础上研究了拉丁超立方采样减小方差的机理；通过对现有误差分析和收敛判据工具的研究,指出方差系数不能作为收敛判据,提出了以输出变量数字特征变化的相对值作为拉丁超立方采样的收敛判据；(6)将扩展拉丁超立方采样技术应用于电力系统概率潮流计算,通过算例分析证明了算法的正确性和高效性,分析比较了直接蒙特卡罗仿真、固定采样数拉丁超立方采样和本文提出的扩展拉丁超立方采样在概率潮流计算产生的绝对误差的概率性,验证了本文提出的收敛判据的有效性：同时在单次扩展方案的基础上,提出了多扩展方案的思想,通过获取更为精确和详细的收敛趋势提高收敛判据的准确性。更多还原

【Abstract】 In recent years, high-power electronic devices become widely applied to the field of power system, especially for FACTS and HVDC technology. In long-distance large-capacity transmission, different frequencies interconnection, enhancement of the controllability of the AC power grid and maximize the power grid transmission capacity, etc., high-power electronic devices play an irreplaceable role. As a new generation of HVDC Transmission technology, VSC-HVDC introduced all-controlling power electronics device, voltage source converters and PWM control technology, solved many problems which exist in conventional HVDC. However, due to the immaturity in their own development, complex structure and the tie in closely with the grid, reliability of high-power electronic devices and the impact of the power system on its reliability should never be neglected. Existing VSC-HVDC reliability model, especially for converter valve, is not perfect and requires to be improved. It is difficult to reflect the impact of the changing work environment on the reliability of power electronic devices by the model based on fixed failure rate and analytic method. This paper introduces the load-sharing effect for reliability modeling of the VSC-HVDC converter valve, proposes the correspond disposal methods according to the characteristic between voltage and current load-sharing effect.Meanwhile, equivalent model proposed for current load-sharing effect takes the varying power flow into account. Therefore, probabilistic load flow (PLF) based on simulation is need for equivalent current load-sharing model. Due to large calculation quantities in Monte Carlo simulation (MCS) method, extended Latin hypercube sampling (ELHS) is proposed in this paper for PLF evaluation to improve computation efficiency and reduce calculation time.This paper conducts the following research based on the above:(1) Based on the theoretical basis of the existing research on reliability power electronic equipment, the reliability model of VSC-HVDC converter valve using the k-out-of-n:G model are presented, and the quantitative relationship between redundant set and reliability indicators is discussed.(2) Due to the disadvantages of the existing fixed failure rate reliability modeling, the proposed converter valve reliability model based on the load effect is presented. Instead of analytical algorithm, Monte monteCarlo simulation is used to solve the reliability model to explore the influence on the reliability indexes with the voltage load-sharing effect through the aspect of the unrepairable and repairable models. Calculation and study on the spare parts reserves strategy of the converter valve is presented.(3) Due to the disadvantages of the existing steady-state VSC-HVDC converter model, the converter equations are derived in the most general format and a generalized loss formula with the converter losses quadratically dependent on the converter current. This paper proposed a unified method for power flow calculation in the AC power systems with embedded VSC-HVDC system.(4) Based on the steady power flow model of VSC-HVDC, PLF evaluation with VSC-HVDC is proposed. According to the results, equivalent calculation of varying current is proposed to take varying power flow into account in reliability model of valve module.(5) In view of existing Latin Hypercube sampling (LHS) technique based on fixed sample sizes and the disadvantage that cannot be extended on the existing sampling points, the extended Latin hypercube sampling is presented. On the basis of the study of variance reduction mechanism of LHS, the existing error analysis and convergence criterion tool, this paper points out that the coefficient of variation cannot be used as convergence criterion for LHS, and proposes the relative change of the output variable estimator used as the convergence criterion for LHS.(6) ELHS is applied to the calculation of PLF. The numerical example has shown that the method is valid and effective. By comparing the probability of the absolute error in MCS, CLHS and ELHS, the efficiency of the proposed convergence criterion is validated. On the basis of a single expansion program, this paper presents the idea of multiple expansion programs for obtaining more accurate and detailed convergence trend to improve the accuracy of the proposed convergence criterion.更多还原