【作者】 王伟；

【导师】 徐殿国；

【作者基本信息】 哈尔滨工业大学 ， 电力电子与电力传动， 2013， 博士

【摘要】 随着风电在电网中比例快速提高，具有随机性和间歇性特点的风电并网将给系统的无功电压稳定运行带来较大影响。2011年以来，中国西北、华北等大规模风电基地发生了多起风电机组连锁脱网事故。初步分析表明这几起大面积风电脱网事故与风电机组的低电压穿越能力、高电压穿越能力以及无功电压控制等密切相关。当前双馈风电机组（Doubly-Fed Induction Generator, DFIG）已成为世界上风电装机的主流机型，也是在系统故障时发生连锁脱网最多的机组类型。为研究机组连锁脱网原因和提出相应措施，本文研究了电网电压跌落下DFIG运行控制与保护技术，主要研究内容包括：分析表明了在电网不对称电压跌落下提高DFIG控制能力是应对脱网的技术关键。提出了用于快速分离正负序分量的瞬时对称分量计算法，并将其扩展到分离转子中非工频的正负序分量。仿真对比表明大幅提高了不对称电压跌落下的控制响应速度。提出将DFIG电网电压跌落下的控制过程分为四个阶段，并给出了机/网侧变流器不同阶段相应的控制目标和控制策略。提出了以转子功率变化量为网侧控制前馈项的控制策略，实现了机网侧联合统一控制，仿真结果表明显著改善了电压深度跌落下DFIG的控制性能。研究了电网电压恢复过程中DFIG连锁脱网重要原因。深入分析了电压跌落和恢复过程中的机端电压相角跳变机理及其对矢量定向控制的影响。提出了机端电压相角补偿控制原理，改进了现有的DFIG电压跌落下控制策略：正常运行及Crowbar退出阶段，采用定子磁链定向控制；在Crowbar投入阶段，封闭转子侧变流器的脉冲，网侧变流器保持正常工作；在电网电压恢复阶段采用相角补偿控制。仿真和动模试验结果表明电压恢复阶段，改进的控制策略能够有效抑制转子过电流，从而降低机组脱网的风险。撬棒（Crowbar）保护是DFIG实现低电压穿越的主要方式。为研究集成Crowbar保护的DFIG交互影响及其连锁脱网原因，分析了对称电压跌落下定转子电流的计算方法，给出了投入Crowbar后定转子电流峰值估算式以及Crowbar电阻取值方法。分析了Crowbar保护风电场无功功率特性和低电压穿越特性。仿真研究表明风电机组和风电场之间存在较强暂态耦合，Crowbar保护对系统动态特性具有重要影响，Crowbar保护电阻取值和投切控制需要综合考虑机组电气应力约束和系统无功支撑的需求。针对基于SCR的三相交流结构和基于IGBT的三相整流结构的Crowbar保护方案，进行了风电场现场测试，数据表明Crowbar保护投入后应在故障清除后1~2周期内切出，避免在故障恢复期间，因风电机组异步运行从系统吸收大量无功，对系统恢复产生不利影响；有源Crowbar保护具有较好的可控性，可以达到更加优异的系统特性，并保有足够的可靠裕度，能有效增强风电场对电网故障的应对能力。基于实际风电外送电网拓扑和参数建模，仿真重演了某实际风电场的风电机组连锁脱网事故的暂态过程。基于仿真结果分析了该暂态过程中风电机组和无功补偿装置的动态无功响应能力，并提出了综合考虑以上动态无功响应能力的大规模风电场全过程无功电压紧急控制策略：在电压跌落期间风电机组网侧变流器基于电压变化量提供实时动态无功支撑缓解电压跌落；在故障切除之前主动切除部分无功补偿装置来抑制暂态过电压；在故障恢复阶段根据电压判据重新投入无功补偿装置为系统提供无功调节能力，并通过仿真验证了所提策略的可行性和有效性。更多还原

【Abstract】 With the increasing share of the wind power in the power system, the impact of its integration is becoming more widespread. Random and intermittence of wind has more and more influence on the stability of power system. Since2011, the cascad-ing disconnection failures of power system caused by disturbance frequently occur in large-scale wind power base of China’s North and Northwest. The preliminary analysis shows that the cascading disconnection closely related to low voltage ride through (LVRT) and high voltage ride through (HVRT) capability of the wind pow-er generation system and its reactive power control system. Based on its merit, doubly-fed induction generator (DFIG) has become one of mainstream model of wind-driven generator which connected with grid directly, and also the most com-mon types in all of the cascading disconnection. In order to explore the causes, op-eration and protection technology under the grid voltage dip were proposed in view of the existing problems.The analysis states that improving the control ability of DFIG under the volt-age dip is the key to deal with cascading disconnection. The method of instaneous sequence component to get the positive and negative sequence was improved and expanded to non-power frequency. The simulation result shows that this algorithm is more effective and efficient compared with the traditional method. The imple-mentation is broken down into four phases, and different objectives and strategies are presented during the voltage dip. Base on the rotor power variation, a novel feed forward control strategy is proposed for DIFG. The simulation results show that the proposed strategy can significantly improve control performance and realize unified control of grid side and rotor side converter.The cascading disconnection was revealed in the grid voltage recovering peri-od. The sudden changes of the phase angle and its impact on the vector orientation under grid voltage dip and recover, was deeply analyzed. The phase angle compen-sation theory and improved control strategy is proposed under voltage dip. In nor-mal operation stage (without crowbar), stator flux oriented control is used. In volt-age dip stage (with crowbar), deactive the rotor side converter and active grid-side converter. The phase angle compensation theory is adopted in grid voltage recover-ing period. The simulations and dynamic test shows that the improved control strategy effectively can decrease the rotor over-current and reduce the risk of cas-cading failures. Consequently, the crowbar is the most commonly method for DFIG to realize low voltage ride through. In order to study the reason of cascading disconnection and the influence among the DFIGs with crowbar, the resistance of crowbar was calculated based on the estimation formula of peak current on the stator and rotor side. The simulations show that complexity and tight coupling between DFIGs and the wind farms. Crowbar circuit has significant influence on dynamic feature of system. The resistance value and switching control strategy should account for the needs of electrical constraints and the reactive compensatory requirement for power system. The measurement of field-tests are carried out based on the SCR’s three-phase ac structure and IGBT’s three-phase rectifier structure of crowbar cir-cuit protection scheme. These data indicate that crowbar circuit should be disabled after1~2periods at the fault clearance, because its negative effects of reactive power consuming in the grid voltage recovering period. Active crowbar circuit can effectively strengthen the ability to resist grid failures, for its good controllability and enough stability margins.The real wind power delivery case with detailed power network topology and parameters is modeled, and based on it the transient process of large-scale wind turbines cascading disconnection is recurred. The dynamic reactive power response capabilities of wind turbines and reactive power compensation devices during the transient process are analyzed. A reactive power and voltage emergency control strategy with the consideration of above dynamic reactive power response capabili-ties is proposed. In the proposed emergency control strategy, the grid-side convert-ers of wind turbines are utilized to dynamically provide reactive power to the grid to mitigate voltage drop in real time. In addition, reactive power compensation devices are actively disconnected to the grid before fault removal to restrain the transient overvoltage, and then reconnected to the grid according to voltage level in recover-ing period to provide reactive power support. The simulation validates the feasibil-ity and effectiveness of the proposed control strategy.更多还原