【作者】 李辉；

【导师】 孙向东；

【作者基本信息】 西安理工大学 ， 电气工程， 2023， 硕士

【摘要】 模块化多电平变换器(Modular Multilevel Converter,MMC)具有输出电能质量高,模块化结构易于实现冗余控制等优势,目前已经在柔性直流输电、电力电子变压器等高压大功率应用领域得到了广泛认可。然而MMC电路拓扑通常所需级联的子模块数量相对较多,子模块运行状态对系统的正常运行起着重要的作用,一旦有子模块发生故障,若不及时检测,则会对变换器整体性能造成严重影响。为此,本文以电力电子变压器中的三相半桥型MMC为研究对象,对其子模块开关器件故障检测及定位展开较为深入的研究。主要研究内容如下:首先,分析了MMC的工作原理、调制策略以及子模块电容均压方法等。考虑MMC的应用场景以及后续研究的故障检测及定位方法的普适性,本文最终选用载波移相调制策略结合经典排序均压算法以实现变换器的调制和电容电压的均衡控制。其次,分析了MMC在子模块开关器件故障状态下的行为特性,阐述了开关器件的开路和短路故障原理,研究了不同电容均压算法在子模块开关器件开路故障时对桥臂电流及子模块电容电压的影响。对于子模块下管VT2开路故障,本文研究了一种基于改进滑模观测器(Sliding Mode Observer,SMO)的故障检测及定位方法,该方法能有效地抑制系统抖振,提高故障诊断的准确性。针对子模块上管VT1开路故障,当采用排序均压算法时,通常存在同桥臂中正常子模块的电容电压随着故障子模块的电容电压同步上升难以定位的问题,本文研究了一种基于子模块放电能量累积的方法来实现故障检测及定位。最后,搭建了Matlab/simulink仿真模型和三相低压小功率MMC实验平台,仿真和实验结果表明了本文所研究的故障检测及定位方法的有效性和正确性,且方法简单易实现,具有良好的工程应用参考价值。更多还原

【Abstract】 Modular Multilevel Converter(MMC)has the advantages of high output power quality and modular structure for easy redundancy control,and it has been widely recognized in high voltage and high power applications such as flexible DC power transmission and power electronic transformers.However,the MMC circuit topology usually requires a relatively large number of cascaded sub-modules,and the operation status of the sub-modules plays an important role in the normal operation of the system.Once a sub-module fails,if it is not detected in time,it will have a serious impact on the overall performance of the converter.Therefore,the three-phase halfbridge MMC in power electronic transformer is taken as the research object in this thesis,and a more in-depth study on the fault detection and location of its sub-module switching devices is conducted.The main research contents are as follows:Firstly,the working principle,modulation strategy and sub-module capacitance voltage equalization method of the MMC are analyzed.Considering the application scenarios of the MMC and the universality of the subsequent fault detection and location methods,the carrierphase-shifted modulation strategy combined with the classical sequential voltage equalization algorithm is finally chosen to realize the modulation and capacitance voltage equalization control of the converter..Secondly,the behavioral characteristics of the MMC in the fault state of sub-module switching devices are analyzed,the principles of open-circuit and short-circuit faults of switching devices are described,and the effects of different capacitance voltage equalization algorithms on bridge arm currents and sub-module capacitance voltages during open-circuit faults of submodule switching devices are studied.For the submodule lower tube VT2 open-circuit fault,an improved sliding mode observer(SMO)for fault detection and localization is studied,which can effectively suppress the system jitter and improve the accuracy of fault diagnosis.For the opencircuit fault of sub-module upper tube VT1,when the sequencing voltage equalization algorithm is used,there is usually a problem that the capacitance voltage of normal sub-module in the same bridge arm rises synchronously with the capacitance voltage of the faulty sub-module,so a method based on sub-module discharge energy accumulation is studied to achieve fault detection and location.Finally,the Matlab/simulink simulation model and the three-phase low-voltage low-power MMC experimental platform are built.The simulation and experimental results show the effectiveness and correctness of the fault detection and localization method studied in this thesis,The method is simple and easy to implement,and has good reference value for engineering applications.更多还原