【作者】 撖奥洋；

【导师】 张哲； 尹项根；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2010， 博士

【摘要】 随着我国能源短缺、能源安全以及节能减排等方面的问题日益突出,以风能为代表的可再生能源利用已成为重要的发展战略之一。风电场的大规模并网将给电力系统在规划设计、调度运行、保护控制等方面带来许多新的问题。尤其是当高渗透率接入时,对配电网的故障特性、保护构建模式带来了深刻的影响,从而使传统的故障检测和保护模式难以满足电网安全运行要求,已成为制约风能大规模高效利用的重要技术屏障。在此背景下,论文对变速恒频风力发电系统及所接配电网复杂故障特性进行了研究,并提出相关保护的构建方案,实现原理等。本文是针对含有高渗透率风电场的配电网安全运行的一项基础性工作,对我国新能源的高效利用具有重要的理论意义和实用价值。结合我国新能源大规模利用、智能化电网研究所取得的成果,论文首先概括了风电行业的发展现状,指出在风机制造、风场运行和风能消纳等方面存在的问题。随后分析了以风电场为典型的分布式电源(DG)接入大电网后,对电网安全稳定运行造成的影响,提出需要开展的研究课题。特别就DG接入配电网后,继电保护面临的主要问题和目前的研究进展进行了综述分析。在变速恒频风电场的控制和低压穿越方面,研究了双馈式发电机的稳态、暂态运行机理,并建立较为完备的可用于故障暂态分析的仿真模型。重点就其转子侧功率解耦控制机理及风速变化下的小扰动下转子逆变器的调节过程进行了分析并进行了仿真；对风电机组低电压穿越问题,深入研究了机组在外部电网故障时,导致机组转子回路产生过流、过压的机理,及目前多种提升双馈风电机组低压穿越运行能力的控制和保护技术。在此基础上,建立了主动crowbar保护的仿真模型,并考虑了其中释能电阻大小的选取,启动值的整定原则等因素,对风机低压运行范围和外部故障特征的影响进行了分析讨论和仿真验证。在双馈式风电场的故障特性的研究方面,首先针对变速恒频机组转子侧交流励磁的特点,理论分析了电网发生故障时定子短路电流呈现的“多态”故障特征,论述了故障点距离、crowbar保护动作门槛值以及励磁逆变器控制系数等因素对双馈电机短路电流特性的影响,并给出了各种条件下的故障电流仿真波形。最后从继电保护的角度分析了双馈电机故障电流对保护性能的影响,提出在为风电场构建保护时应注意的关键问题。以构建双馈风力发电系统并网处的保护为研究目标,从提高双馈电机故障穿越能力的角度出发,提出了一套适合于双馈电机“多态”故障电流特征的新型复合式电流-电压保护方案。通过对传统电流保护的改进和构建低故障穿越运行特性的电压保护,使其能够满足风场联络线上故障的可靠切除及配电系统内故障时风电场的低压穿越运行,对实现含双馈风电机组的电网稳定及故障后的快速恢复具有重要意义。为防止由于风电接入引起电网保护误动和非同期合闸,进一步增加风电系统的低压穿越能力,对电网侧馈线保护及重合闸提出了多种改进措施。为防止风电场接入后可能引起的馈线保护反向故障误动,提出了以校验所接入的风电场的最大短路电流水平为主,增设功率方向元件为辅的应对策略。从防止非同期合闸的角度,提出了重合闸与风电场并网处保护的配合原则以及实现该原则的两种技术方案。最后通过仿真计算验证了所提出的技术措施的有效性。针对DG的高渗透率接入,传统电流保护存在重新调整动作值和时限配合关系,整定工作复杂困难这一问题。构建了一种利用广域信息进行故障定位的保护系统。详细介绍了此保护系统的结构和功能划分,重点论述了保护系统的核心-基于广域信息的故障定位算法。算例结果表明,基于广域信息的保护系统能够在高渗透DG接入配电网时,实现故障元件的可靠识别与切除,保证电网的安全稳定运行。最后,总结了论文的主要研究工作,并阐述了有待进一步研究的主要问题。更多还原

【Abstract】 Accelerate the development of renewable clean energy and its efficient utilization has become one of the key national policies in China. Wind power generation, as a representative of the renewable energy utilization, has become one of the important developing strategies. High penetration of wind farm integration will have an impact on short circuit capacity, protection coordination, system transient stability, voltage control and power quality, which can significantly cause deterioration of relay performance, safety and stability of the whole utility (large power) grid. Many technical measures need to be adopted to mitigate the negative effeteness.In this background, the paper study on the external fault characteristic of doubly-fed induction generator (DFIG) and related protection technology. This is a basic work for the grid-connected wind power’s stable operation in our country, which has certain theoretical significance and practical value.With the new energy utilization development and intelligent large-scale network research achievements, the first summarize the present status of wind industry; then combining the impact of typical wind farms connected into the gird, some questions that should be further studied are provided in the thesis. And in particular, the details and issues of protection technology for grid integrated with DFIG are reviewed.For variable-speed constant-frequency operation and low voltage ride through (LVRT), the operational mechanism of DFIG in steady-steady and transient-stated were studied, and a complete set of simulation system was established for fault analysis. Focus on its rotor side power decoupling control mechanism and the wind changes under the small disturbance regulation of rotor inverter process is analyzed and simulated.For LVRT operation, the over-current and over-voltage induced in the rotor were researched in the external fault. On this basis, the simulation model of active crowbar protection, with considered the release resistance and set values of crowbar circuit, were installed.This paper also discussed how the fault locations, action of crowbar protection and the proportional and integral coefficient of rotor side inverter affect the magnitude and decay time of doubly-fed induction generator (DFIG)’s short-circuit current. The simulation experiments verifies the "multi-waveform" fault characteristics of DFIG current fed into the grid, which is due to the multi rotor exciting models. Based on this, a grid connecting-point protection scheme for wind farm is proposed. The scheme was composed of advanced current protection and low voltage protections, which can not only reliably remove the fault, happened on the tie line, but also ensure the wind farm to operate under fault condition. The proposed protection scheme is of great significance to realizing the reliable operation and fast fault restoration of the grid with high penetration wind generators.To further increase the wind turbine’s LVRT ability from the grid side, feeder protection and reclose action strategies were improved. For preventing wind farm caused mis-operation, this paper proposes that check the maximum wind short-circuit current level, or add complementary elements of the direction for feed current relay. From the Angle of feeder to prevent overvoltage, two kinds of technology solutions were puts forward, for help realizing the cooperate principle between reclosing and interconnection of wind power. At last the simulation results verify the effectiveness of the proposed measures, can make full use of wind power.With The high penetration of DG integration, traditional current protection operation condition could be more complicated and security and stability problem would be more austere in large-scale interconnected power source. The paper constructs a new protection system using the wide-area information to indentify the fault location. Introduced the protection system structure and function division, discussed the core of protection system-based on wide area information for fault location algorithm.a numerical example is given to illustrate the wide-area protection system based on the information can be more effectively determine the fault location, and this methods can guarantee the safe and stable operation of power grid under high permeability DG access.Finally the achieved research is concluded and further prospective on development of limited wide area intelligent protection is highlighted.更多还原