一种混合桥臂的MMC研究及物理实现

发布时间：2018-08-09 07:02

【摘要】：随着电力电子技术的发展,基于电压源换流器的高压直流输电(Voltage Source Converter based HVDC,VSC-HVDC)在世界范围内得到了快速发展。在远距离大容量直流输电领域,考虑到经济性因素需要采用架空线输电。这样,柔性直流输电系统的直流故障保护问题就变得十分重要。在采用交流断路器、直流断路器、新型拓扑换流器几种隔离直流故障的方法中,采用可箝位直流故障的换流器拓扑具有响应速度快、投资少、不需额外附加设备等优点,非常适用于两端或多端直流输电系统。在各种新型拓扑中,由半桥和全桥子模块组成的混合桥臂模块化多电平换流器(Modular Multilevel Converter,MMC)拓扑,结合使用了目前最成熟的两种子模块拓扑,既降低了损耗,又保证了直流故障箝位的可靠性。论文通过对通用MMC拓扑和半桥、全桥子模块工作原理的分析,引出了桥臂混合MMC的拓扑;根据其等效电路的数学模型,分析了基于旋转坐标系下的站级解耦控制策略和阀级调制及均压策略,并计算了实现直流故障闭锁所需的最小全桥子模块比例;在PSCAD/EMTDC中搭建了双端混合桥臂MMC仿真模型,验证了稳态和暂态控制策略的合理性。为更好地验证混合桥臂MMC拓扑的工作特性,设计并搭建了一台低压原理性实验样机。首先,根据柔性直流输电系统的分层控制原理,结合实际需求,将控制系统分为了数据采集系统、站控层、阀控层和子模块层,根据各层功能划分,确定功能实现的性能要求,选定合适的主控芯片及外围辅助电路,设计并制作控制器板卡。然后,根据控制器功能要求和数学模型,画出程序流程图,并采用硬件描述语言实现相应算法,仿真验证各子程序模块的全工况执行情况。之后,对系统在各种运行状态下的控制器时序配合进行了分析,并采用计算深度的估算方法,对通讯速率提出了要求。最后,设计混合桥臂MMC一次系统参数并选定主设备型号,搭建实验样机。为验证混合桥臂MMC的工作特性,对低压物理样机进行了稳态和暂态控制实验。在稳态实验中,对直流电压、子模块电容电压、阀出口侧电压特性进行了分析;在功率阶跃实验中,验证了控制器的快速响应特性;在直流双极短路实验中,验证了拓扑的故障自清除能力,为混合桥臂MMC拓扑的工程化应用奠定了基础。
[Abstract]:With the development of power electronics technology, (Voltage Source Converter based HVDC VSC-HVDC based on voltage source converter has been developed rapidly in the world. In the field of long distance and large capacity direct current transmission, overhead transmission is needed to take account of economic factors. In this way, the DC fault protection of flexible DC transmission system becomes very important. Among the methods of isolating DC faults by AC circuit breaker, DC circuit breaker and new topology converter, the converter topology with clamped DC fault has the advantages of fast response speed, less investment and no additional equipment. Very suitable for both ends or multi-terminal HVDC transmission systems. Among the new topologies, the hybrid bridge arm modularized multilevel converter (Modular Multilevel converter MMC), which consists of half-bridge and full-bridge sub-modules, combines the two most mature submodule topologies to reduce the loss. The reliability of DC fault clamping is ensured. Based on the analysis of the general MMC topology and the working principle of the half-bridge and full-bridge sub-modules, the topology of the bridge arm hybrid MMC is introduced, and the mathematical model of the equivalent circuit is given. The decoupling control strategy and valve level modulation and voltage equalization strategy based on rotating coordinate system are analyzed, and the minimum ratio of full bridge module required to realize DC fault locking is calculated, and the MMC simulation model of two-ended hybrid bridge arm is built in PSCAD/EMTDC. The rationality of steady-state and transient control strategies is verified. In order to better verify the working characteristics of the hybrid MMC topology, a low-voltage experimental prototype is designed and built. Firstly, according to the hierarchical control principle of the flexible direct current transmission system and the actual demand, the control system is divided into data acquisition system, station control layer, valve control layer and sub-module layer. According to the function division of each layer, the performance requirements of the function realization are determined. Select suitable main control chip and peripheral auxiliary circuit, design and manufacture controller card. Then, according to the functional requirements and mathematical model of the controller, the program flow chart is drawn, and the corresponding algorithm is implemented by using the hardware description language. After that, the timing coordination of the controller in various operating states is analyzed, and the communication rate is required by calculating the depth of the controller. Finally, the MMC primary system parameters of the hybrid arm are designed and the main equipment model is selected, and the experimental prototype is built. In order to verify the working characteristics of the hybrid bridge arm MMC, the steady and transient control experiments of the low voltage physical prototype were carried out. In the steady state experiment, the characteristics of DC voltage, capacitor voltage of submodule and outlet voltage of valve are analyzed. In the power step experiment, the fast response characteristic of controller is verified. The fault self-clearing capability of the topology is verified, which lays a foundation for the engineering application of the hybrid MMC topology.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1;TM46

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