【作者】 王丹；

【导师】 王兴成；

【作者基本信息】 大连海事大学 ， 控制科学与工程， 2017， 硕士

【摘要】 柔性直流输电技术现如今在高压直流输电领域的地位是传统技术无法替代的。但是若将基于两、三电平的柔性直流输电系统应用在实际直流输电系统中,则存在诸多缺陷,尤其在电压等级以及耗损和占地面积等问题上困难重重。经过缜密的调研,本文研究了基于模块化多电平换流器(Modular Multilevel Converter,MMC)的直流输电系统,具有很高的输出电平,且其电平可以灵活调节,因为采用模块化设计,可以有效的降低开关频率,应用在直流输电系统尤其是功率较大的情况下,能带来巨大的经济效益。本文研究了 MMC的拓扑结构与工作原理,主要工作内容如下:1.研究基于子模块和子模块组的拓扑结构以及闭锁、半闭锁和解闭锁状态,提出了子模块和子模块组的等效电路以及数学模型,通过其等效电路及数学模型,可以模拟子模块和子模块组的闭锁、半闭锁和解闭锁工作状态,并对其等效电路和数学模型进行了简化。在此基础上,根据四种不同程度的简化模型,搭建MMC的仿真模型,可以根据不同的需求,在具体研究MMC的各项指标时,选用不同的模型进行简化仿真。2.基于MMC的不同简化程度的仿真模型,研究载波移相电压调制,分组调制算法以及最近电平逼近调制,基于以上算法,提出取整修正量移位算法。这种算法首先对大规模的子模块进行分组以便简化仿真建模,对每个组进行不同的阶梯波调制,每个组的阶梯波采用不同的修正量进行取整,最后进行整合,可达到类似载波移项的效果。取整修正期间,用独立的可控电压源代替每个子模块组。同时,因为此过程需要添加直流分量,子模块组之间的电压还可以得到均衡。3.对MMC中桥臂之间环流的产生进行了详细分析,并进行一系列的数学计算和坐标变换,通过变换的坐标,推倒出等效电路,进而设计倍频负序环流抑制控制器。最后对所设计的控制器搭建模型进行验证,结果表明了其有效性。更多还原

【Abstract】 The status of flexible HVDC in the field of HVDC transmission technology now is the traditional technology can not be replaced.But if applicate flexible HVDC system based on two or three level in the actual HVDC system,there are many defects,especially in the problem of voltage levels,loss and covering area.After carefully research,the modular multilevel converter--MMC based on DC transmission system.It has many advantages such as high output level and flexible level regulation.With the modular design,it can reduce switching frequency effectively.It can bring huge economic benefits when used in HVDC transmission system especially in the large power condition.The topology and mathematical model of MMC are studied.Main works are as follows:1.The block,half block and de-block states are studied based on the topology of sub-module and sub-modules group.The equivalent circuit and mathematical model of the sub-module and sub-module group are put forward.On this basis,the block,half block and de-block states can be simulated using the equivalent circuit and mathematical model of the sub-module and sub-module group.Furthermore,four types of simulation models with different simplification degrees are set up.In the study of the MMC,the simulation model with different simplification degrees can be chose according to the different simulation purpose.2.Based on the simulation model with different simplification degree,Carriage Phase Shift PWM(CPS-PWM),Nearest Level Modulation(NLM)and the modulation of sub-models grouping control are studied.One this basis,the floor modify number shift algorithm are put forward.It can realize the grouping step control.With using different modify numbers,the similar effect of the Carriage Phase Shift PWM can be achieved.Every sub-module group can be regarded as an independent controlled voltage source by this method.Using the DC component added by the floor modify number shift algorithm,the voltage balance control between the sub-module groups can be achieved.3.The cause of circulation current is studied particularly.The circulating current suppression controller is designed based on the equivalent circuit of this double frequency component.The simulation proves that the designed controller can restrain the circulating current effectively.更多还原