多端直流输电系统控制策略的研究

发布时间：2018-08-22 12:39

【摘要】：随着分布式发电并网和孤岛供电等需求的增加,多端直流输电技术逐渐受到人们的重视,并在多项工程中得到了应用。而基于模块化多电平变流器的多端直流输电系统(Multi-terminal Direct Current based on Multilevel Converter,MMC-MTDC)不仅拥有MMC高电压、大容量的技术优势,同时也具有直流输电系统运行灵活、稳定性好、可实现多电源供电和多落点受电的特点。因此,基于MMC的MTDC系统已经成为人们研究的热点之一,研究的内容主要集中在协调控制策略、故障保护、分布式发电并网、潮流优化以及附加控制等方面。本文对多端直流输电系统的控制策略进行了研究,主要的研究内容包括:(1)针对MMC-MTDC系统,分析了其上层控制、站级和阀级等各级控制系统的需求,并按照需求对各级的控制系统进行了设计,使各级控制系统能够实现相应的控制功能。同时,设计了远程和本地两级的监控系统,实现对整个系统运行状态的监控。(2)对MMC-MTDC输电系统的阀级、站级和各换流站间的协调控制等控制策略进行了研究。并对适用于阀级、站级和各换流站间的协调控制等控制策略进行了对比分析,根据各换流站的运行方式选取合适的控制策略,从而确保系统能够稳定运行。利用仿真和实验对各级控制策略的正确性和有效性进行了验证。(3)考虑了利用多端直流输电系统向孤岛供电的情况,若负载不对称时,会使系统中出现波动功率,而该波动功率会进一步引起主换流站的交流侧电流和直流电压的电能质量问题。本文对负载不对称条件下的运行特性进行了分析,然后通过对环流的控制,实现了由子模块承担因负载不对称而产生的二倍频波动功率,从而避免了负载不对称引起的直流电压和主换流站的交流电流的电能质量的恶化。(4)考虑了负载不对称条件下,传统的定交流电压控制策略无法实现交流电压的平衡控制。因此,本文对PI调节器和R调节器的幅频特性进行了分析,并对传统的定交流电压控制策略进行改进,采用PI调节器和R调节器并联的结构,确保在负载不对称情况下,换流站能够输出对称的交流电压,从而使供电质量得到提高。
[Abstract]:With the increasing demand of distributed generation and island power supply, multi-terminal DC transmission technology has been paid more and more attention, and has been applied in many projects. The Multi-terminal Direct Current based on Multilevel converter MMC-MTDC based on modularized multilevel converter not only has the technical advantages of high voltage and large capacity of MMC, but also has the advantages of flexible operation and good stability of HVDC system. It can realize the characteristics of multi-power supply and multi-point power supply. Therefore, the MTDC system based on MMC has become one of the hot research topics. The research focuses on coordinated control strategy, fault protection, distributed generation grid connection, power flow optimization and additional control. In this paper, the control strategy of multi-terminal HVDC transmission system is studied. The main research contents are as follows: (1) for MMC-MTDC system, the requirements of the upper control system, station level and valve level control system are analyzed. The control system of each level is designed according to the requirement, so that the control system can realize the corresponding control function. At the same time, a remote and local monitoring system is designed to monitor the operation state of the whole system. (2) the control strategies of valve level, station level and coordinated control between converter stations of MMC-MTDC transmission system are studied. The control strategies suitable for valve level, station level and converter station are compared and analyzed. According to the operation mode of each converter station, appropriate control strategies are selected to ensure the stable operation of the system. Simulation and experiments are used to verify the correctness and effectiveness of the control strategy. (3) considering the use of multi-terminal HVDC system to supply power to isolated islands, if the load is asymmetric, the fluctuating power will appear in the system. The fluctuating power will cause the power quality problems of AC side current and DC voltage in the main converter station. In this paper, the operating characteristics under the condition of load asymmetry are analyzed, and by controlling the circulation, the double frequency fluctuation power caused by the load asymmetry is realized by the sub-module. Therefore, the deterioration of DC voltage and AC current quality caused by load asymmetry is avoided. (4) considering the load asymmetry, the traditional constant AC voltage control strategy can not realize the balance control of AC voltage. Therefore, this paper analyzes the amplitude-frequency characteristic of Pi regulator and R regulator, and improves the traditional constant AC voltage control strategy. The parallel structure of Pi regulator and R regulator is adopted to ensure the load asymmetry. The converter station can output symmetrical AC voltage, thus improving the quality of power supply.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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