多端柔性直流输电系统直流电压控制无缝切换策略研究

发布时间：2019-03-19 16:09

【摘要】：随着能源紧缺和环境污染等问题的日益严峻,世界各国逐渐开展对可再生能源的大规模开发与利用,柔性直流输电技术受到广泛应用。基于模块化多电平换流器的多端柔性直流输电系统(Multi-Terminal Flexible DC Transmission System Based on Modular Multi-level Converter,MMC-MTDC)因同时具备了MMC氋电压、大容量的技术优势和MTDC系统灵活、可靠以及经济的运行特性而备受关注。MMC-MTDC系统需要在各换流站内实现基本控制功能的基础上,必须要有站间的协调控制策略,以应对系统在正常状态、潮流扰动、网架结构变动等情况,最大限度地维持系统稳定运行。本文主要对MMC-MTDC系统换流站间的协调控制策略进行研究。首先分析了MMC的工作原理及其特性,并依据MMC的等效电路以三端系统为例建立了多端柔性直流输电系统的数学模型;然后阐述了MMC-MTDC系统的分层控制结构体系,详细介绍了换流器级和换流阀级控制中的各个环节;接着论述了MMC-MTDC系统换流站间协调控制的特性,并着重分析了电压裕度控制策略和电压倾斜控制策略的机理、控制器结构以及优缺点;最后,在以上研究的基础上,提出了适用于多端柔性直流输电系统的直流电压控制无缝切换策略,该策略将定直流电压控制、定有功功率控制、以及下垂控制三种外环有功量控制模式结合起来,在各种情形下可利用相应的控制器通过一定的原则只需改变控制模式选择系数即可及时切换特定换流站的控制模式,来维持系统直流电压稳定和保证各换流站功率平衡,具有很强的灵活性和适应性。另外,研究过程中在RT-LAB环境下搭建了基于MMC的五端柔性直流输电系统仿真模型,验证了所提出策略的正确性与有效性。
[Abstract]:With the increasingly serious problems of energy shortage and environmental pollution, the large-scale development and utilization of renewable energy has been carried out in various countries in the world, and flexible DC transmission technology has been widely used. The multi-terminal flexible DC transmission system (Multi-Terminal Flexible DC Transmission System Based on Modular Multi-level Converter,MMC-MTDC) based on modular multilevel converter has the advantages of MMC voltage, large capacity and flexibility of MTDC system at the same time. MMC-MTDC system needs to realize the basic control function in each converter station, and must have coordinated control strategy between stations in order to deal with the system in normal state and power flow disturbance. Grid structure changes and other circumstances, to maximize the stability of the system operation. This paper mainly studies the coordinated control strategy between converter stations in MMC-MTDC system. Firstly, the working principle and characteristics of MMC are analyzed. According to the equivalent circuit of MMC, the mathematical model of multi-terminal flexible HVDC transmission system is established by taking the three-terminal system as an example. Then the hierarchical control structure system of MMC-MTDC system is described, and every link in converter stage and converter valve stage control is introduced in detail. Secondly, the characteristics of coordinated control between converter stations in MMC-MTDC system are discussed, and the mechanism of voltage margin control strategy and voltage tilt control strategy, the structure of controller, the advantages and disadvantages of the control strategy are emphatically analyzed. Finally, on the basis of the above research, a seamless switching strategy of DC voltage control for multi-terminal flexible HVDC transmission system is proposed, which is composed of constant DC voltage control and constant active power control. Combined with the three external loop active power control modes, the corresponding controller can be used to switch the control mode of a particular converter station in time by changing the control mode selection coefficient only by changing the selection coefficient of the control mode, under various circumstances, the corresponding controller can be used to change the control mode of a particular converter station in time by changing the control mode selection coefficient. In order to maintain the DC voltage stability of the system and ensure the power balance of each converter station, it has strong flexibility and adaptability. In addition, the simulation model of five-terminal flexible DC transmission system based on MMC is built in RT-LAB environment, and the correctness and effectiveness of the proposed strategy are verified.
【学位授予单位】：东北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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