模块化多电平换流器型直流输电系统的稳态运行解析和控制技术研究

发布时间：2018-03-11 21:39

本文选题：模块化多电平换流器　切入点：直流输电　出处：《浙江大学》2014年博士论文　论文类型：学位论文

【摘要】：模块化多电平换流器(Modular Multilevel Converter,MMC)作为新一代柔性直流输电技术的核心设备,在新能源并网、电力系统互联、大城市供电以及海岛供电、海上钻井平台供电等场合具有广阔的应用前景。经过十几年的发展,MMC的研究工作已经取得一定进展,但依然尚有许多问题亟待解决,如大规模MMC的控制系统设计问题、直流双极短路故障的处理方式,等等。本文在总结前人研究成果的基础上,从以下几个方面对半桥子模块型MMC进行了深入研究： (1)研究了MMC的基本工作原理,在忽略了MMC各个子模块开关过程的基础上建立了MMC的交直流解耦模型,该模型将MMC等效为相互解耦的交流回路和直流回路两部分。在直流回路中,将桥臂不平衡电压进一步分解为固有分量和修正分量两部分；固有分量在根源上是MMC与交流系统之间的交换功率引起的,而修正分量是通过一定控制策略产生的用以调节MMC内部特性的电压分量。 (2)分析了理想工况下MMC的桥臂电流以及子模块电压波动的基本成分。在直接调制法的作用下,深入研究了谐波环流与子模块电压波动通过调制函数相互作用的机理；在此基础上,详细建立了谐波环流、内部虚拟电动势以及子模块电压波动的数学模型,尤其重点讨论了MMC的2次谐波环流成分,随后讨论了谐波环流的主要危害以及治理问题。针对实际运行中可能出现的上、下桥臂不对称运行工况,分别分析了上、下桥臂阻抗不对称和子模块数不一致对MMC运行带来的影响。 (3)研究了交流系统对称情况下MMC-HVDC控制系统的基本构成。根据交直流解耦模型,将换流站级控制系统分割为交流回路控制器、环流抑制控制器和阻尼控制器三部分。交流回路控制器负责调节MMC与交流系统之间的功率交换,环流抑制控制器负责抑制负序2倍频环流,阻尼控制器主要调节直流电流的动态响应过程。提出了MMC的启停控制方案。将MMC的启动过程分为不控启动阶段和可控启动阶段；讨论了限流电阻与最大交流充电电流峰值之间的数学关系,为限流电阻的选取提供依据。将MMC的停机过程分为能量反馈阶段和放电阶段,所提出的停机方案有助于提高能量利用率、缩短停机时间和降低放电电阻的选取要求。 (4)针对交流系统不对称情况下MMC-HVDC直流侧电压的2倍频波动问题,同时针对传统直流电压波动抑制算法存在矩阵奇异的缺陷,提出适用于MMC-HVDC的新型直流电压波动抑制方法。该方法利用MMC子模块能够储能的特性,在交流侧负序电流被抑制的同时,完全消除了直流电压的2倍频波动。建立了静止坐标系下3相MMC交流回路和直流回路的数学模型,同时设计了基于内模原理的交流回路控制器、环流抑制控制器和直流电压波动抑制控制器。 (5)研究了几种用于平衡MMC子模块电压的单级直接均压法,包含传统直接均压法、引入最大电压偏差控制的直接均压法和引入保持因子的直接均压法,重点从开关频率和死区效应两方面分析了传统直接均压法的缺陷。讨论了MMC的控制系统架构问题,提出适用于大规模MMC的“主控制单元+阀组控制单元”型控制系统。为了解决单级直接均压法中子模块电压排序耗时的问题,同时为了解决单级直接均压法给控制系统带来的通讯压力,提出了两级直接均压法,将一个桥臂的子模块均压过程分解为阀组间均压和阀组内均压两部分,二者可并行完成。研制了一台3相41电平MMC实验样机,重点介绍了控制系统的软件和硬件设计情况,为大规模MMC控制系统的协调控制、子模块的组织与独立控制等问题提供解决思路。通过动模实验验证了：引入最大电压偏差控制的直接均压法有效降低了MMC的开关频率和死区效应；所提出的“主控制单元+阀组控制单元”型控制系统是可行的,所提出的两级直接均压法是有效的。
[Abstract]:Modular multilevel converter (Modular Multilevel Converter, MMC) as the core equipment of a new generation of HVDC flexible technology, in the new energy grid, power system interconnection, power supply and large city island power supply, offshore drilling platform, power supply etc. has broad application prospects. After ten years of development, the research work of MMC have made some progress, but there are still many problems to be solved, such as large-scale MMC control system design problems, processing method, DC bipolar short-circuit fault and so on. In this paper, based on the results of previous studies, conducted in-depth research from the following aspects of half bridge sub module type MMC:
(1) study on the basic principle of MMC, ignoring the process based MMC sub module switch on the decoupling of the MMC model, the MMC model will be equivalent to the two part of the decoupling circuit and AC DC circuit. In DC circuit, the unbalanced voltage bridge arm is further decomposed into the two part of a natural component and a correction component; component is the inherent power exchange between MMC and AC system caused by the root, and the correction component is the voltage component adjustment MMC internal characteristics through the control strategy used to produce.
(2) the bridge arm current ideal condition of MMC and the basic components of sub module voltage fluctuation is analyzed. The direct modulation method under the action of in-depth study of the mechanism of harmonic circulation and sub module voltage fluctuation through the modulation function of interaction; on this basis, with a harmonic circulation, the mathematical model of virtual internal electric potential and sub module voltage fluctuation, especially focus on the 2 harmonic circulation component of MMC, then discusses the harmonic circulation major hazards and governance problems. Aiming at the possible in the actual operation, under the bridge arm asymmetry of operating condition, were analyzed, under the influence of bridge arm impedance asymmetry and sub module number no consistent operation of MMC brings.
(3) the basic structure of MMC-HVDC control system of symmetry under AC system. Based on the decoupling model, the converter control system is divided into communication loop controller, circulation suppression controller and a damping controller three. AC loop controller is responsible for regulating the power exchange between MMC and AC system, circulation inhibition controller is responsible for negative sequence 2 harmonic circulation, dynamic response of damping controller mainly adjust the DC current.
Put forward the MMC on-off control scheme. The startup process of MMC is divided into control start-up and controllable start-up stage; discusses the limit of the mathematical relationship between flow resistance and maximum AC charging peak current limit, provide the basis for the choice of the flow resistance. The shutdown process of MMC consists of the energy feedback stage and discharge stage. Stop the scheme helps to improve energy efficiency, reduce downtime and reduce discharge resistance selection requirements.
(4) for the 2 frequency fluctuation of the DC side of MMC-HVDC communication system under asymmetric voltage, while the traditional DC voltage fluctuation suppression algorithm of matrix singular defect suppression method is proposed for the new DC voltage fluctuation of MMC-HVDC. This method uses MMC module to characteristics of energy storage, the AC side negative sequence current is inhibition at the same time, the complete elimination of the 2 harmonic voltage fluctuation. Established a mathematical model of 3 phase MMC AC circuit and DC loop in the stationary coordinate system, and the design of AC loop controller based on the internal model principle, circulation inhibition controller and DC voltage fluctuation suppression controller.
(5) studied for several single-stage balanced MMC sub module voltage direct pressure method, including traditional direct pressure method, introducing the maximum voltage deviation control direct pressure method and introducing the direct pressure maintaining factor method, analyzes the shortcomings of the traditional direct pressure method from two aspects of switching frequency and dead time the effect is discussed. The control system architecture of MMC, which is suitable for large-scale MMC "main control unit + valve control unit" type control system. In order to solve the problem of single level direct pressure method of sub module voltage and time consuming, in order to solve the communication pressure single level direct pressure method were brought to the control system. This paper proposes two level direct pressure method, a bridge arm module is divided into pressure groups and pressure valve within the valve pressure two, two can be done in parallel. Developed a 3 phase 41 level MMC experimental prototype, point introduction The software and hardware design of control system for large-scale, coordinated control of MMC control system, and provide the solutions of sub module organization and independent control problem. Through dynamic simulation experiment proves that introducing the maximum voltage deviation control method can effectively reduce the direct pressure of MMC switching frequency and dead time effect; the proposed "the main control unit and control unit type valve control system is feasible, the proposed two level direct pressure method is effective.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM721.1

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