基于二阶广义积分器的高压直流输电系统控制策略研究

发布时间：2018-10-12 11:22

【摘要】：近年来,我国经济高速发展,社会电气化水平持续提高,国家整体电力需求呈现高速增长。然而,从我国的能源禀赋来讲,无论是传统的化石能源还是新兴的清洁能源,其主要分布均位于西南部地区,而我国能源需求的重心则位于中东部地区。因此,在中国这样一个幅员辽阔、经济高速发展的大国中,高压交直流输电必将获得快速发展。一方面,相比与交流输电系统,高压直流输电系统具有输送容量大、线路走廊窄、灵活性强、运行经济环保等优点,适合应用于大功率、远距离输电的场合;另一方面,高压直流输电技术可以实现大区电网异步互联,增强风能、太阳能等清洁能源的并网消纳能力,提高电力系统的稳定性。模块化多电平换流器高压直流输电系统(MMC-HVDC)作为一种极具发展前景的输电方式,已经在很多工程实际中得到了应用。MMC换流站模块化的拓扑结构决定了其可应用容量较小的电力电子器件实现很高的电压等级和功率水平;电平数较多,输出波形畸变小,无需加装交流滤波装置,可实现冗余控制;系统损耗小,无功功率可控,开关频率可控;具有更好的稳态和暂态性能。MMC-HVDC采用子模块级联结构,这种含有大量器件的模块化结构也带来了相应的控制问题,例如,平稳的预充电与启动环节,子模块电容电压均衡控制,相间环流的抑制以及需要比低电平VSC-HVDC更复杂的故障保护策略。因此,MMC-HVDC的优化控制是当前研究的一大热点,专家学者们提出了很多具有优良特性的控制算法。本文从以下两方面对MMC-HVDC的优化控制进行研究:一方面利用二阶广义积分器(DSOGI-QSG)进行网侧交流电压的估算,提高锁相环节与电压测量环节的精度与可靠性;另一方面采用改进的模型预测方法来减少预测环节的计算量,使模型预测方法可以用于更多电平的MMC-HVDC系统。最后,在PSCAD/EMTDC仿真实验平台上对所提方法进行了验证,仿真结果显示所提方法有良好的动态响应,能够达到预期的控制目标。
[Abstract]:In recent years, with the rapid development of our economy, the level of social electrification continues to improve, and the overall power demand of the country is growing at a high speed. However, in terms of the energy endowment of our country, both the traditional fossil energy and the emerging clean energy are mainly distributed in the southwest region, and the center of energy demand in China lies in the central and eastern regions. Therefore, high voltage AC / DC transmission is bound to develop rapidly in a large country with a vast territory and rapid economic development. On the one hand, compared with AC transmission system, HVDC system has the advantages of large transmission capacity, narrow line corridor, strong flexibility, economic and environmental protection and so on. On the other hand, it is suitable for high power and long distance transmission. High voltage direct current (HVDC) transmission technology can realize asynchronous interconnection of large area power grid, enhance the grid and absorption capacity of clean energy, such as wind energy and solar energy, and improve the stability of power system. Modular multilevel converter high voltage direct current transmission system (MMC-HVDC) as a very promising transmission mode, The modularization topology structure of MMC converter station determines that the power electronic devices with small capacity can be used to achieve high voltage level and power level, the number of level is more, and the distortion of output waveform is small. Without adding AC filter device, redundant control can be realized; system loss is small, reactive power is controllable, switching frequency is controllable; and better steady-state and transient performance is achieved. MMC-HVDC adopts submodule cascade structure. This modular structure with a large number of devices also brings about the corresponding control problems, such as steady precharge and startup, capacitor voltage equalization control of sub-modules. The suppression of interphase circulation and the need for a more complex fault protection strategy than low level VSC-HVDC. Therefore, the optimization control of MMC-HVDC is a hot topic in the current research. Many control algorithms with excellent characteristics have been proposed by experts and scholars. In this paper, the optimal control of MMC-HVDC is studied in the following two aspects: on the one hand, the second order generalized integrator (DSOGI-QSG) is used to estimate the AC voltage on the grid side to improve the accuracy and reliability of PLL and voltage measurement; On the other hand, the improved model prediction method is used to reduce the computational complexity of the prediction link, so that the model prediction method can be used in multi-level MMC-HVDC systems. Finally, the proposed method is verified on the PSCAD/EMTDC simulation platform. The simulation results show that the proposed method has a good dynamic response and can achieve the desired control objectives.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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