基于模块化多电平的柔性直流输电控制策略研究

发布时间：2018-01-13 19:06

本文关键词：基于模块化多电平的柔性直流输电控制策略研究　出处：《西南交通大学》2014年硕士论文　论文类型：学位论文

【摘要】：模块化多电平换流器(MMC)是近年来提出的应用于VSC-HVDC的新型拓扑结构。与传统VSC-HVDC采用的两电平、三电平换流器拓扑结构相比,MMC不仅具有其原有优点,而且采用的是模块化设计。针对不同的电压等级场合,可通过调节串联的子模块数来改变输出电平的大小。在电平数很大的情况下,不但使子模块的开关频率得到下降,而且大大降低输出谐波的大小而无需交流滤波器,十分适用于VSC-HVDC系统。本文对模块化多电平换流器的拓扑结构及工作原理进行了详细分析。从桥臂能量平衡的角度推导分析了子模块电容电压不平衡的原因。定义了平均开关状态,对子模块直流电容电流及桥臂电压波动原理进行了分析,得到了相间二倍频环流产生的原因以及表达式。设计了结合排序法的最近电平调制策略实现子模块电容电压的均衡控制,并进行了仿真验证。对桥臂电流及环流进行了傅里叶分析,通过其频谱图验证了对桥臂电流中环流大小及组成成分的分析。设计了叠加了三相桥臂能量均分控制分量的基于载波移相的均压调制策略,该策略在实现子模块均压控制的同时有效的抑制了环流。通过交流侧单相接地故障仿真,验证了采用三相桥臂能量均分控制比单相桥臂能量均分控制具有更好的抗干扰能力。对比了采用最近电平调制和载波移相调制策略下MMC电平数及控制器频率与MMC输出电压谐波含量的关系。分别建立了MMC-HVDC在三相静止坐标系及dq旋转坐标系下的数学模型,并在dq坐标系下对直接电流控制器的外环及内环控制器进行了设计。利用PSCAD仿真软件,建立了两端21电平的MMC-HVDC仿真模型,仿真验证了控制器具有良好的解耦特性及快速的动态响应能力。根据MMC-HVDC数学模型的特点以及无差拍控制在数字控制中的优点,对MMC-HVDC系统换流站的数学模型进行离散化,设计了在三相静止坐标系下的无差拍解耦控制策略。仿真验证该策略在具有良好的解耦特性及快速的动态响应特性的同时,由于减少了控制器的坐标变换次数及PI调节环节,控制器的运算量及复杂程度得到降低,便于数字控制器的设计与实现。根据多端MMC-HVDC的连接方式和控制原则,分析了主从控制策略和结合直流电压偏差的主从控制策略各自的原理和优劣,在PSCAD中搭建21电平的三端MMC-HVDC仿真模型,对两种控制策略进行了仿真,仿真结果表明了结合直流电压偏差的主从控制策略无需高速通信就能实现换流站模式的切换,提高了多端MMC-HVDC的灵活性和可靠性,应用范围更广。
[Abstract]:Modular multilevel converter (MMC) is a new topology proposed in recent years. Based on VSC-HVDC and traditional VSC-HVDC with two level, three level converter topology is compared, MMC not only has its original advantages, and modular design. According to the voltage level of different occasions, by the number of sub modules in series regulate the output voltage levels change size. In the case of a large number of level, not only the switch frequency of sub modules are decreased, and greatly reduce the size of output harmonic without AC filter, which is suitable for VSC-HVDC system.
The topological structure and working principle of the modular multilevel converter is analyzed in detail. From the viewpoint of energy balance arm is analyzed by reason of the sub module capacitor voltage unbalance. The definition of average switching state, sub module and DC capacitor current bridge arm voltage fluctuation principle is analyzed, and two reasons double circulation and expression are designed. The nearest level modulation strategy with sorting method to achieve a balanced control sub module capacitor voltage, and the simulation is conducted. The bridge arm current and circulation are analyzed by Fourier analysis, the spectrum analysis is verified on the bridge arm current flows in the size and composition of the design. The superposition of the three-phase bridge voltage was based on arm carrier phase shift modulation strategy of equipartition of energy control components, at the same time, the strategy of pressure control on module implementation effectively Circulation. Through the AC single phase to ground fault simulation, verified by the three-phase bridge arm of equipartition of energy control than the single-phase bridge arm of equipartition of energy control has better anti-jamming ability. Compared with the relationship between MMC level and MMC controller frequency and harmonic content of the output voltage of the nearest level modulation and carrier phase shift modulation strategy.
The mathematical model in three-phase static coordinate and DQ coordinates of MMC-HVDC were established, and in the DQ coordinates of the outer ring and the inner loop controller of direct current controller was designed. By using PSCAD simulation software, the simulation model was established in MMC-HVDC at 21 level, the simulation shows that the controller has good decoupling property and fast dynamic response.
According to the characteristics of the MMC-HVDC mathematical model and deadbeat control advantages in digital control system, the mathematical model of MMC-HVDC converter is discretized, designed in three-phase coordinates deadbeat decoupling control strategy. The simulation results show that the strategy has good decoupling characteristics and fast dynamic response characteristics at the same time because of the reduced number of coordinate transformation, and the PI controller control link, controller and the complexity of computation is reduced, the design and Implementation for digital controller.
According to the connection mode and control principle of multi terminal MMC-HVDC, analysis of the master-slave control strategy and combined DC voltage deviation of the master-slave control strategy principle and their quality, builds the simulation model of three terminal MMC-HVDC 21 level in PSCAD, the two control strategies are simulated, the simulation results show that the combination of master-slave DC voltage error control no communication can realize switching mode converter, improve the flexibility and reliability of multi terminal MMC-HVDC, a wider range of applications.

【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM721.1

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