断线故障为常见的直流故障类型之一,研究该场景下海上风电经柔性直流送出系统的暂态响应特性对于系统的保护方案设计有着重要参考价值。首先,分析了直流母线正极断线故障下短路电流产生机理,推导了非故障极短路电流表达式,并分析了接地阻抗参数对该短路电流特性的影响。其次,研究了故障期间风电场侧与电网侧换流站交直流侧暂态电压演变特性。研究表明:故障期间风电场侧直流电压与其有功输出正相关,且两端换流站交流阀侧电压产生了一对大小相等、方向相反的直流偏置分量;此外,采用较大的接地阻抗参数可有效降低短路电流对系统运行性能的影响。最后,基于PSCAD/EMTDC仿真平台搭建了全系统的电磁暂态仿真模型,通过仿真验证了暂态特性分析的正确性与参数选择的合理性,对于大规模海上风电经柔性直流系统并网的规划设计具有一定的指导意义。

双极短路故障作为最严重的直流系统故障,研究该场景下海上风电模块化多电平换流器型高压直流输电(modular multilevel converter-high voltage direct current,MMC-HVDC)并网系统的暂态运行特性对于系统的断路器配置与控制方案设计有着重要意义.首先分析了直流断路器(direct current circuit breaker,DCCB)未动作时换流站短路电流的产生机理,并提出了风电场侧与电网侧交、直流短路电流的计算方法.其次,研究了计及DCCB控制作用下换流站交、直流侧暂态电压、电流特性,并考虑了风电场运行工况和限流电抗参数对其暂态特性的影响.最后,基于PSCAD/EMTDC仿真平台搭建了全系统的电磁暂态模型,通过仿真分析了双极短路故障下有无DCCB控制时换流站的暂态电压、电流特性.研究表明:所提短路电流计算方法具有良好的精度,且DCCB动作后风电场侧交、直流电压恢复速率与其输出有功功率呈正相关关系.该研究工作可为系统的电气设计、断路器选型提供理论依据,也可为系统故障恢复阶段控制方案的制定奠定基础.

当高压直流输电系统送端换流站发生单极闭锁故障时,换流站交流侧将出现无功功率过剩,导致换流站交流侧电压骤升,进一步会引起送端电网各发电设备端电压骤升.因此,需要在送端交流侧附近加装适当的暂态无功补偿装置以提高系统的稳定性.为此,当先从运行原理、响应特性等多个角度对同步调相机和静止同步补偿器两类暂态无功补偿装置进行分析.然后,对比分析单极闭锁故障下两者在高压直流输电送端系统的应用效果.最后,结合单极闭锁故障下切除部分无功补偿装置的措施,得出同步调相机具有更强的暂态无功支撑能力和暂态电压调节能力的结论.

The high voltage direct current (HVDC) transmission technology based on modular multilevel converter (MMC) is widely used in the offshore grid-connected wind power generation projects, and the small signal stability problems of the grid-connected system have been attracted great attention. This paper focused on the influence of the zero-sequence circulating current (ZSCC) controller on the stability of the offshore wind power generation MMC-HVDC grid-connected system. The closed-loop frequency domain model was derived by means of complex vectors and harmonic state space firstly. Then the paper developed the single-input-single-output (SISO) impedance model of MMC which considering the ZSCC controller. In addition, the impedance model of the offshore wind farm and the distribution network were established. Based on the impedance model, the influence law and mechanism of the ZSCC controller on the stability of the offshore wind power generation MMC-HVDC grid-connected system were explored. The analysis results show that when the output power of wind is too large, the system is prone to oscillation. The application of the ZSCC controller equivalently increases the bridge arm resistance and enhancing the system damping, which effectively suppressing the resonant peaks of MMC impedance in island control mode. Finally, from the point of view of enhancing the damping of the system, the parameter optimization scheme for ZSCC controller was designed, and the correctness of the theory and the feasibility of the scheme were verified by simulations.

Normal sequencing rules for collaborative design task do not take disjunctive relationship and weight into account. Therefore, the independency logic of task based on collaborative business rules is proposed by independency analysis method in Coordination Theory (CT) and digraph definition in Graph Theory (GT). Furthermore, sequencing model for collaborative design task based on disjunctive constrains is presented. Then weighting collaborative tasks are ordered in a weighted shortest processing time (WSPT) sequence rule. Case study is demonstrated to illustrate the feasibility and applicability.