链式STATCOM在不平衡工况下的控制策略研究

发布时间：2018-09-06 18:17

【摘要】：链式结构STATCOM具有体积小,造价低、易冗余等优势,有着极为广阔的工业应用前景。本文就链式STATCOM的主电路及其控制策略特别是在电网不平衡工况下的控制策略展开了研究。首先,总结了直流侧电容电压平衡控制、不平衡条件下链式STATCOM的控制研究两个方面的研究现状。通过分析链式STATCOM主电路结构及其运行工作原理,建立了 d-q同步旋转坐标系下解耦控制的数学模型,得出其在系统电压平衡条件下的稳态运行特性。其次,为发挥链式STATCOM易冗余的优势,本文搭建了链式STATCOM链节数可调的通用仿真模型,控制策略采用标幺化设计,以适应不同电压等级。并分析了链节变化对链式STATCOM参数选择的影响,为参数选择提供了选择依据。然后,根据链式STATCOM的拓扑结构和工作模型,详细讨论了其在平衡系统中的控制策略设计。为实现直流电容电压均衡控制,采取了分层协调控制方式。上层控制采用基于直接电流解耦控制的电压电流双环控制,下层控制采用两级稳压和改进的最近电平逼近法。通过上下两层系统的协调控制,最终实现装置和系统无功功率的传递和各链节直流电容电压的均衡。并在PSCAD中搭建了仿真模型予以验证。最后,本文对不平衡系统中链式STATCOM的运行特性进行分析,建立数学模型,改进了正负序双电流内环的控制策略,通过引入可控的负序电流平衡三相换流链功率,并使其负序电流参考值能快速追踪装置内外不平衡,解决了系统不平衡工况下链式STATCOM装置过流及换流链电压不均衡的问题。模型在PSCAD中进行仿真,通过控制系统负序电压改变不平衡度来模拟不同的不平衡工况,负序参考电流在200ms内达到稳定,三相换流链平衡效果显著,可以一定程度满足风机入网的不平衡需求。经过仿真验证,在不平衡度达到50%时装置仍可不退出运行并具有一定的无功补偿能力。
[Abstract]:Chain structure STATCOM has many advantages, such as small volume, low cost and easy redundancy. In this paper, the main circuit of chain STATCOM and its control strategy are studied, especially under the unbalanced condition of power network. Firstly, the research status of DC capacitive voltage balance control and chain STATCOM control under unbalanced condition is summarized. The mathematical model of decoupling control in d-q synchronous rotating coordinate system is established by analyzing the main circuit structure of chain type STATCOM and its operating principle. The steady state operation characteristics of the decoupling control system under the condition of voltage balance are obtained. Secondly, in order to give full play to the advantage of easy redundancy of chain STATCOM, a general simulation model with adjustable chain number of chain STATCOM is built, and the control strategy is designed to adapt to different voltage levels. The influence of the change of chain node on the selection of chain STATCOM parameters is analyzed, which provides the basis for parameter selection. Then, according to the topological structure and working model of chain STATCOM, the control strategy design in balanced system is discussed in detail. In order to realize DC capacitor voltage equalization control, a hierarchical coordinated control method is adopted. The upper control adopts the voltage and current double loop control based on direct current decoupling control, and the lower control adopts the two-stage voltage stabilizer and the improved nearest level approximation method. Through the coordinated control of the upper and lower layers of the system, the transfer of reactive power of the device and the system and the equalization of the DC capacitor voltage of each link are finally realized. The simulation model is built in PSCAD to verify it. Finally, this paper analyzes the operation characteristics of chain STATCOM in unbalanced system, establishes mathematical model, improves the control strategy of positive and negative sequence double current inner loop, and balances the power of three-phase commutation chain by introducing controllable negative sequence current. The negative sequence current reference value can quickly track the imbalance between inside and outside of the device, which solves the problem of over-current and voltage imbalance of the chain STATCOM device under the unbalanced condition of the system. The model is simulated in PSCAD, and different unbalance conditions are simulated by controlling the unbalance degree of negative sequence voltage. The negative sequence reference current is stable in 200ms, and the balance effect of three-phase commutation chain is remarkable. To a certain extent can meet the fan into the network imbalance demand. The simulation results show that the device can still not quit operation and has a certain reactive power compensation ability when the unbalance reaches 50.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM761.12

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