柔性多端直流对交流系统的故障穿越控制研究

发布时间：2018-04-28 08:41

本文选题：柔性多端直流输电系统 + 交流故障穿越控制　；参考：《华北电力大学(北京)》2017年硕士论文

【摘要】：随着传输功率和电压等级不断提升、新能源发电需求不断加大,高压柔性多端直流输电(Multi-terminal High Voltage Direct Current transmission based on Voltage Source Converter,VSC-MTDC)在经济性、互连性和控制性等方面都开始显现极大的优势。当柔性多端直流连接的交流电网发生一定程度的故障时,为了保持系统的稳定性,直流系统需要具备一定的故障穿越能力。本文针对这一需求,以模块化多电平换流器(Modular Multi-terminal Converter,MMC)柔性多端直流输电为对象,在研究其工作原理、拓扑结构和数学模型的基础上,分析交流系统侧故障对系统的主要影响,并结合仿真分析了交流电流、有功功率和直流电压等物理量的故障暂态特性。基于暂态分析,通过在阀级控制中增加调制比比例积分控制环节和反馈量,抑制故障时交流电流幅值的增大。通过对柔性多端直流系统的内环解耦控制的改进,实现正负序分量单独控制,抑制不对称故障下交流电流的负序分量。在故障较大需要切除故障换流站时,分析了电压下垂控制特性,并与电压裕度控制进行了对比,对下垂控制进一步改进,添加有功功率反馈环节,使非故障换流站灵活分配功率,在较小的电压偏差情况下迅速达到新的稳定。在PSCAD/EMTDC仿真软件中搭建了四端MMC-MTDC系统分别进行仿真验证,结果表明通过控制策略的设计,故障时交流侧电流的幅值减小,能保持三相对称性,在故障换流站退出运行后电压下垂控制特性灵活,而改进的下垂控制使有功功率分配更合理,直流电压偏差减小,一定程度上提高了柔性多端直流系统对交流系统侧故障的穿越能力。
[Abstract]:With the continuous improvement of transmission power and voltage, the demand for new energy generation is increasing, and the high voltage flexible multi-terminal High Voltage Direct Current transmission based on Voltage Source converter VSC-MTDCs are beginning to show great advantages in economy, interconnection and control. In order to maintain the stability of the system, the DC system needs to have a certain fault traversing ability when the flexible multi-terminal DC power grid has a certain degree of failure. In this paper, the flexible multiterminal DC transmission of modular multilevel converter, Modular Multi-terminal converter, is taken as an object. On the basis of studying its working principle, topological structure and mathematical model, the main influence of AC system side fault on the system is analyzed. The fault transient characteristics of AC current, active power and DC voltage are analyzed by simulation. Based on the transient analysis, the amplitude of AC current is restrained by increasing the modulation ratio, proportional integral control and feedback in the valve level control. By improving the internal loop decoupling control of flexible multi-terminal DC system, the positive and negative sequence components are controlled separately to suppress the negative sequence components of AC current under asymmetric faults. When the fault converter station needs to be removed, the characteristics of voltage sag control are analyzed, and compared with voltage margin control, the droop control is further improved and the active power feedback link is added. The power distribution of the non-fault converter station is flexible, and the new stability can be achieved quickly under the condition of small voltage deviation. A four-terminal MMC-MTDC system is built in the PSCAD/EMTDC simulation software for simulation verification. The results show that the amplitude of AC side current decreases and the three-phase symmetry can be maintained by the design of control strategy. The voltage droop control characteristic is flexible after the fault converter station exits from operation, but the improved droop control makes the distribution of active power more reasonable, and the DC voltage deviation decreases. To some extent, the ability of flexible multi-terminal DC system to pass through AC system side faults is improved.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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