交直流混联系统协调控制下的故障特征分析  

Fault Characteristics Analysis of the AC/DC Hybrid System Under Coordinated Control

作　　者：杨炳元[1] 杨志勇 任永峰[1] 杨帅 康海珍[1] Yang Bingyuan;Yang Zhiyong;Ren Yongfeng;Yang Shuai;Kang Haizhen(Inner Mongolia University of Technology,Hohhot 010051,China;Inner Mongolia Electric Power Economic Research Institute,Hohhot 010090,China)

机构地区：[1]内蒙古工业大学电力学院,呼和浩特010051 [2]内蒙古电力经济技术研究院,呼和浩特010090

出　　处：《天津大学学报（自然科学与工程技术版）》2021年第12期1258-1268,共11页Journal of Tianjin University：Science and Technology

基　　金：国家自然科学基金资助项目(51967016,51567020);内蒙古自治区科技重大专项(2019ZD027).

摘　　要：交直流混联电网场景下交直流线路发生短路会产生新的故障特征.为此,构建了永磁直驱风电经柔性直流并网的交直流混联系统模型,系统的协调控制有助于提升其故障穿越能力,保障其安全稳定运行.故而,在借助于直流断路器(DCCB)、卸荷电阻以及改进的模块化多电平换流器(MMC)控制策略基础上,提出一种无需换流站间通信的交直流故障穿越协调控制方案,进而探讨了不同因素对故障特征的影响.研究结果表明:交流并网联络线故障时,MMC具有非线性、幅值受限和输出电流受控于电压等特征的电源输出特性;当发生不对称短路故障时,故障线路柔直侧的负序电流可被完全抑制;当并网点电压三相有效值跌落到0.9 p.u.以下时,MMC优先发出无功功率;当直流系统不平衡功率积累出现直流过电压现象时,在主从电压裕度控制策略起主要作用下仅三相短路故障导致直流电压超过1.05 p.u.,此时风场侧MMC凭借降压法及卸荷电阻的投切可使直流电压控制在1.05~1.10 p.u.范围内.针对直流故障时的低电压问题,采用就地检测就地保护的故障隔离方案实现了5~6 ms切除直流故障.最后,通过RTDS仿真实验验证了该交直流故障穿越方案的有效性,证实了此控制方案下故障特征与理论分析结论的一致性.The short circuit on the AC/DC line produces new fault characteristics in the AC/DC hybrid grid.For this reason,the AC/DC hybrid system model of direct-driven permanent-magnet wind power was constructed by connecting the flexible DC to the grid.The coordinated control of the system helps to improve the fault ride-through capability and ensures its safe and stable operation.Therefore,a coordinated control scheme of AC/DC fault ride-through without communication between converter stations is presented with the help of a DC circuit breaker(DCCB),dissipation resistance,and an improved modular multilevel converter(MMC)control strategy.The influence of different factors on the fault characteristics is also discussed.The results show that the MMC has the nonlinear and limited amplitude characteristics of power supply output,of which the output current is controlled by the voltage when there is a fault in the AC grid-connected tie.The negative sequence current on the flexible DC side of the fault line can be completely suppressed under the coordinated control strategy when an asymmetric short circuit occurs on the AC grid-connected tie.The MMC prioritizes reactive power when the effective value of the three-phase voltage of the parallel node falls below 0.9 p.u..The unbalanced power accumulation of the DC system causes the DC overvoltage phenomenon,and the DC voltage exceeds 1.05 p.u.only when the three-phase short circuit occurs under the influence of the control strategy of the master and slave voltage margin.The DC voltage can be controlled within the range of 1.05—1.10 p.u.through the step-down method of MMC on the side of the wind farm and the switching of the dissipative resistor.The fault isolation scheme of local detection and local relaying is adopted to remove the fault within 5—6ms,when the voltage drop is caused by the DC fault.Finally,the effectiveness of the fault ride-through scheme is verified through RTDS,and the fault characteristics under this control scheme are consistent with the theoretical anal

关 键 词：交直流混联系统 模块化多电平换流器 故障穿越协调控制 故障特征 RTDS仿真实验 

分 类 号：TM711[电气工程—电力系统及自动化]