新型模块化多电平柔性直流输电技术及仿真研究

发布时间：2018-01-08 20:03

本文关键词：新型模块化多电平柔性直流输电技术及仿真研究　出处：《长沙理工大学》2014年硕士论文　论文类型：学位论文

【摘要】：柔性直流输电(High voltage direct current based on voltage source converter, VSC-HVDC)在清洁能源传输和海上供电等方面的巨大技术优势让它成为了近几年的研究热点。本文对VSC-HVDC的最新研究成果——模块化多电平换流器(Modular multilevel converter, MMC)的拓扑结构和控制方法展开研究。首先,文章对MMC三种最基本的子模块(Sub-module, SM)半桥子模块、全桥子模块及箝位双子模块进行分析,比较了它们的运行方式、工作原理以及各自的缺点。由半桥子模块组成的MMC使用电子元器件数量最少,开关频率最低,相对损耗小,是当前最主流的MMC拓扑,但由于不具备直流故障穿越能力一定程度限制了其发展；全桥子模块组成的MMC具备直流故障穿越能力,但需要的电子元器件数量多,损耗大,成本高；箝位双子模块组成的MMC优点在于,有直流故障穿越能力,相对于全桥MMC也减少了电子元器件使用量,但相比于半桥子模块组成的MMC,电子元器件使用量仍然较多,开关损耗较大。对此论文采用一种新的混合型MMC拓扑结构,MMC桥臂由半桥子模块和筘位双子模块共同组成,在保留了箝位双子模块直流故障穿越能力的同时,能进一步降低换流器电子元器件的使用数量和系统损耗。其次,论文对柔性直流输电的控制系统进行了研究。MMC控制系统中现有的调制策略主要有脉宽调制(Pulse width modulation, PWM)策略和阶梯波调制策略,对此论文介绍了现有工程中最主流的调制方法——载波移相脉宽调制(CPS-PWM)。MMC控制系统通常分为系统级控制、换流站级控制和换流阀级控制,但换流站级控制现有的直接电流控制策略在抑制MMC环流方面效果不佳且算法复杂。为了解决这个问题,论文提出一种新型MMC模型预测控制策略(Model predictive control, MPC),应用于MMC的环流抑制和子模块均压：根据MMC-HVDC系统的离散时间数学模型建立对应的预测模型,然后通过求解定义的成本函数最优化问题,得到每个MMC子模块的最佳开关状态,实现MMC子模块的电容电压平衡,达到抑制循环电流的目的。最后,论文在PSCAD/EMTDC中搭建MMC-HVDC系统仿真模型,对新型混合子模块MMC进行直流故障穿越仿真,仿真结果表明,新型混合子模块MMC在减少了电子元器件使用量的情况下,依然保留了直流故障穿越能力。文章对提出的新型MPC控制策略稳态仿真分析也证明了新型MPC控制策略具有良好的子模块电容均压效果和环流抑制作用,具有一定的工程使用价值。
[Abstract]:High voltage direct current based on voltage source converter. VSC-HVDC). Because of its great technical advantages in clean energy transmission and offshore power supply, it has become a research hotspot in recent years. In this paper, the latest research achievement of VSC-HVDC is modularized multilevel converter (. Modular multilevel converter. The topology and control methods of MMC) are studied. First of all, three basic sub-modules of MMC, Sub-Module (SM1) half-bridge sub-module, are studied in this paper. The whole bridge module and the clamped double module are analyzed, and their operation mode, working principle and their shortcomings are compared. The MMC composed of half bridge module uses the least number of electronic components. The switching frequency is the lowest and the relative loss is small. It is the most popular MMC topology at present, but its development is limited to a certain extent due to the lack of DC fault traversing capability. The MMC composed of the whole bridge module has the ability of DC fault crossing, but it needs a large number of electronic components, large loss and high cost. The advantage of the clamped two-submodule MMC is that it has the ability of DC fault traversing, compared with the full-bridge MMC, it also reduces the use of electronic components, but compared with the half-bridge sub-module of the MMC. The use of electronic components is still high, and the switching loss is high. In this paper, a new hybrid MMC topology is proposed, which consists of half bridge module and Reed twin module. At the same time, it can further reduce the number of electronic components of converter and the loss of the system. In this paper, the control system of flexible direct current transmission is studied. The main modulation strategies in the MMC control system are pulse width modulation. PWM) strategy and step wave modulation strategy. In this paper, the most popular modulation method-carrier phase-shifted pulse-width modulation (CPS-PWMU. MMC) control system is introduced, which is usually divided into system-level control. Converter station level control and converter valve level control, but the existing direct current control strategy of converter station level control in the suppression of MMC circulation is not good and the algorithm is complex, in order to solve this problem. In this paper, a new predictive control strategy for MMC model, Model predictive control (MPC), is proposed. It is applied to MMC circulation suppression and sub-module voltage equalization: according to the discrete time mathematical model of MMC-HVDC system, the corresponding prediction model is established, and then the optimization problem of cost function is solved by solving the defined cost function optimization problem. Get the best switching state of each MMC submodule, realize the capacitor voltage balance of MMC submodule, and achieve the purpose of restraining the cycle current. Finally. In this paper, the simulation model of MMC-HVDC system is built in PSCAD/EMTDC, and the DC fault traversing simulation of a new hybrid sub-module MMC is carried out. The simulation results show that. The new hybrid sub-module MMC can reduce the usage of electronic components. The steady-state simulation analysis of the proposed new MPC control strategy also proves that the new MPC control strategy has a good effect of capacitor voltage equalization and circulation suppression. Has certain engineering use value.
【学位授予单位】：长沙理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM721.1

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