【摘要】：隨著電力電子技術的發(fā)展,基于電壓源換流器的高壓直流輸電(Voltage Source Converter based HVDC,VSC-HVDC)在世界范圍內得到了快速發(fā)展。在遠距離大容量直流輸電領域,考慮到經(jīng)濟性因素需要采用架空線輸電。這樣,柔性直流輸電系統(tǒng)的直流故障保護問題就變得十分重要。在采用交流斷路器、直流斷路器、新型拓撲換流器幾種隔離直流故障的方法中,采用可箝位直流故障的換流器拓撲具有響應速度快、投資少、不需額外附加設備等優(yōu)點,非常適用于兩端或多端直流輸電系統(tǒng)。在各種新型拓撲中,由半橋和全橋子模塊組成的混合橋臂模塊化多電平換流器(Modular Multilevel Converter,MMC)拓撲,結合使用了目前最成熟的兩種子模塊拓撲,既降低了損耗,又保證了直流故障箝位的可靠性。論文通過對通用MMC拓撲和半橋、全橋子模塊工作原理的分析,引出了橋臂混合MMC的拓撲;根據(jù)其等效電路的數(shù)學模型,分析了基于旋轉坐標系下的站級解耦控制策略和閥級調制及均壓策略,并計算了實現(xiàn)直流故障閉鎖所需的最小全橋子模塊比例;在PSCAD/EMTDC中搭建了雙端混合橋臂MMC仿真模型,驗證了穩(wěn)態(tài)和暫態(tài)控制策略的合理性。為更好地驗證混合橋臂MMC拓撲的工作特性,設計并搭建了一臺低壓原理性實驗樣機。首先,根據(jù)柔性直流輸電系統(tǒng)的分層控制原理,結合實際需求,將控制系統(tǒng)分為了數(shù)據(jù)采集系統(tǒng)、站控層、閥控層和子模塊層,根據(jù)各層功能劃分,確定功能實現(xiàn)的性能要求,選定合適的主控芯片及外圍輔助電路,設計并制作控制器板卡。然后,根據(jù)控制器功能要求和數(shù)學模型,畫出程序流程圖,并采用硬件描述語言實現(xiàn)相應算法,仿真驗證各子程序模塊的全工況執(zhí)行情況。之后,對系統(tǒng)在各種運行狀態(tài)下的控制器時序配合進行了分析,并采用計算深度的估算方法,對通訊速率提出了要求。最后,設計混合橋臂MMC一次系統(tǒng)參數(shù)并選定主設備型號,搭建實驗樣機。為驗證混合橋臂MMC的工作特性,對低壓物理樣機進行了穩(wěn)態(tài)和暫態(tài)控制實驗。在穩(wěn)態(tài)實驗中,對直流電壓、子模塊電容電壓、閥出口側電壓特性進行了分析;在功率階躍實驗中,驗證了控制器的快速響應特性;在直流雙極短路實驗中,驗證了拓撲的故障自清除能力,為混合橋臂MMC拓撲的工程化應用奠定了基礎。
[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.
【學位授予單位】：華北電力大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM721.1;TM46

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