基于模塊化多電平換流器的直流輸電系統(tǒng)研究
發(fā)布時間：2019-04-22 20:09
【摘要】：柔性直流輸電技術(shù)在解決異步電網(wǎng)互聯(lián)、遠距離孤立負荷供電等問題上有著傳統(tǒng)直流輸電技術(shù)不可比擬的優(yōu)勢。然而基于兩電平、三電平的柔性直流輸電系統(tǒng)存在電壓等級低、損耗較大、濾波器體積龐大等不足，在一定程度上限制了其在直流輸電工程中的進一步應用。基于模塊化多電平換流器的直流輸電系統(tǒng)采用模塊化設(shè)計，輸出電平數(shù)高且可靈活調(diào)節(jié)，以適應不同電壓等級和功率等級的要求，省去了大功率交流濾波器，降低了子模塊的開關(guān)頻率，適用于大功率直流輸電場合。 本文在介紹了模塊化多電平換流器工作原理的基礎(chǔ)上，，闡述了模塊化多電平換流器的調(diào)制策略；提出了一種改進的基于排序法的電容電壓均壓策略，該方法可以有效地實現(xiàn)電容均壓，降低器件的開關(guān)頻率；通過分析換流器內(nèi)部環(huán)流產(chǎn)生機理，設(shè)計了負序二倍頻環(huán)流抑制控制器，仿真證實了所設(shè)計的控制器可以有效地抑制換流器的相間環(huán)流分量。 本文在兩相旋轉(zhuǎn)坐標系下建立了基于模塊化多電平換流器的直流輸電系統(tǒng)的數(shù)學模型；分析設(shè)計直流輸電系統(tǒng)的雙閉環(huán)控制策略，與閥組級控制策略相結(jié)合，實現(xiàn)了對模塊化多電平換流器及直流系統(tǒng)的有效控制；通過對兩端有源和向無源系統(tǒng)供電的直流系統(tǒng)的電壓、電流、有功、無功、子模塊各電量的仿真分析，直觀地證明了直流系統(tǒng)的優(yōu)質(zhì)特性。 考慮了負序電流分量對直流輸電系統(tǒng)及換流器的影響，本文建立了三相電壓故障工況下直流輸電系統(tǒng)的數(shù)學模型；考慮了負序分量對傳統(tǒng)鎖相環(huán)的影響，設(shè)計了故障狀態(tài)下的相位檢測法；以抑制交流側(cè)負序電流為目標，提出與負序電壓補償控制相結(jié)合的雙閉環(huán)控制方法；通過對換流器的子模塊電容電壓波動、內(nèi)部環(huán)流變化的仿真分析，驗證了雙閉環(huán)控制方法、子模塊電容電壓均衡策略、環(huán)流抑制策略在三相不平衡故障條件時的有效性。
[Abstract]:Flexible HVDC technology has unparalleled advantages over traditional HVDC technology in solving the problems of asynchronous grid interconnection and long-distance isolated load power supply. However, the flexible HVDC system based on two-level and three-level has some disadvantages, such as low voltage grade, large loss and huge volume of filter, which limits its further application in HVDC engineering to a certain extent. The DC transmission system based on modular multilevel converter adopts modular design with high output level and flexible adjustment to meet the requirements of different voltage levels and power levels, thus eliminating the need of high-power AC filters. The switching frequency of the sub-module is reduced, which is suitable for high-power HVDC transmission. On the basis of introducing the working principle of modular multilevel converter, the modulation strategy of modular multilevel converter is described in this paper. An improved capacitance voltage equalization strategy based on sorting method is proposed. This method can effectively achieve capacitance voltage equalization and reduce the switching frequency of devices. By analyzing the internal circulation mechanism of the converter, a negative sequence double-frequency loop suppression controller is designed. The simulation results show that the designed controller can effectively suppress the phase-to-phase circulation component of the converter. In this paper, the mathematical model of HVDC transmission system based on modular multilevel converter is established in two-phase rotating coordinate system. The double closed loop control strategy of HVDC transmission system is analyzed and designed. Combined with the valve group control strategy, the effective control of modular multilevel converter and DC system is realized. By simulating and analyzing the voltage, current, active power, reactive power and electric quantity of each sub-module of the DC system, the high-quality characteristics of the DC system are proved intuitively. Considering the influence of negative sequence current component on HVDC system and converter, the mathematical model of HVDC system under three-phase voltage fault condition is established in this paper. Considering the influence of the negative sequence component on the traditional phase locked loop, the phase detection method under the fault condition is designed, and a double closed loop control method combining with negative sequence voltage compensation control is proposed in order to restrain the negative sequence current on the AC side. Through the simulation analysis of the capacitance voltage fluctuation and internal circulation variation of the sub-module of the converter, the validity of the double closed loop control method, the capacitor voltage equalization strategy of the sub-module and the loop suppression strategy under the three-phase unbalanced fault condition is verified.
【學位授予單位】：重慶大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TM721.1;TM46
本文編號：2463159
[Abstract]:Flexible HVDC technology has unparalleled advantages over traditional HVDC technology in solving the problems of asynchronous grid interconnection and long-distance isolated load power supply. However, the flexible HVDC system based on two-level and three-level has some disadvantages, such as low voltage grade, large loss and huge volume of filter, which limits its further application in HVDC engineering to a certain extent. The DC transmission system based on modular multilevel converter adopts modular design with high output level and flexible adjustment to meet the requirements of different voltage levels and power levels, thus eliminating the need of high-power AC filters. The switching frequency of the sub-module is reduced, which is suitable for high-power HVDC transmission. On the basis of introducing the working principle of modular multilevel converter, the modulation strategy of modular multilevel converter is described in this paper. An improved capacitance voltage equalization strategy based on sorting method is proposed. This method can effectively achieve capacitance voltage equalization and reduce the switching frequency of devices. By analyzing the internal circulation mechanism of the converter, a negative sequence double-frequency loop suppression controller is designed. The simulation results show that the designed controller can effectively suppress the phase-to-phase circulation component of the converter. In this paper, the mathematical model of HVDC transmission system based on modular multilevel converter is established in two-phase rotating coordinate system. The double closed loop control strategy of HVDC transmission system is analyzed and designed. Combined with the valve group control strategy, the effective control of modular multilevel converter and DC system is realized. By simulating and analyzing the voltage, current, active power, reactive power and electric quantity of each sub-module of the DC system, the high-quality characteristics of the DC system are proved intuitively. Considering the influence of negative sequence current component on HVDC system and converter, the mathematical model of HVDC system under three-phase voltage fault condition is established in this paper. Considering the influence of the negative sequence component on the traditional phase locked loop, the phase detection method under the fault condition is designed, and a double closed loop control method combining with negative sequence voltage compensation control is proposed in order to restrain the negative sequence current on the AC side. Through the simulation analysis of the capacitance voltage fluctuation and internal circulation variation of the sub-module of the converter, the validity of the double closed loop control method, the capacitor voltage equalization strategy of the sub-module and the loop suppression strategy under the three-phase unbalanced fault condition is verified.
【學位授予單位】：重慶大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TM721.1;TM46
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