节点文献
多端直流配电网协同控制研究
【作者】 周敏；
【作者基本信息】 南京师范大学 ， 电力电子与电力传动， 2021， 硕士
【摘要】 电力电子技术的蓬勃发展和分布式电源的大规模接入推动了多端直流配电网的研究和发展。和传统的交流配电网相比,多端直流配电网在供电容量、线路损耗、控制策略方面具有一定的优势,理论上直流系统没有三相不平衡、电网谐波、无功补偿等问题,因此极大地提高了配电网的可靠性和可控性,成为未来配电网建设的重要方向。然而,由于多端直流配电网拓扑复杂,运行方式多样,且分布式发电具有不确定性,配电网系统的稳定、可靠和经济运行都面临着全新挑战。因此,需要深入研究多端直流配电网各控制单元之间的协同控制策略。基于此,本文从以下四个方面展开研究:(1)首先,总结了直流配电网典型拓扑结构,确定本文研究对象为750V低压环状直流配电网。选取电压源型换流器(voltage source converter,VSC)作为换流站关键装置,并给出了其详细数学模型;分析了光伏和储能模块的输出外特性,并给出关键设备的典型控制策略;针对多端直流配电网协同控制研究,总结了直流配电网协同控制的分级结构和目前典型的协同控制方法。(2)其次,基于直流配电网换流站初级控制策略-斜率偏差控制,提出一种改进的协同控制策略。该策略将换流站分为主换流站和辅助换流站,同时将直流系统的电压进行分区,分为正常运行区间和临界运行区间,给出了各区间各换流站和储能的外环控制策略。将该控制策略在PSCAD/EMTDC软件中进行仿真,验证了该策略的有效性,并将其与斜率偏差控制比较,验证了所提策略的优越性。(3)再次,针对直流配电网二级控制的局限性,提出了一种分布式二级优化控制策略。该策略基于相邻换流站间的稀疏通信,利用分布式一致性算法实现电压和功率的双重控制,在提高换流站利用率的同时减少端口平均电压偏差。仿真验证了该策略的有效性和可靠性,并将其与下垂控制比较,验证所提策略的优越性。(4)最后,基于本文所提的分布式二级优化控制策略,研究该控制策略下直流配电网的小扰动稳定性分析。利用模块化建模的思想建立系统整体小信号模型,并利用特征根分析法和主要参与因子分析法研究了直流配电网稳定运行的影响参数,并得出重要参数的影响规律,为参数选取提供理论依据。仿真验证了小信号模型的准确性。
【Abstract】 The vigorous development of power electronics and the large-scale access of distributed generation have promoted the research and development of multi-terminal DC distribution network.Compared with the traditional AC distribution network,the multiterminal DC distribution network has certain advantages in power supply capacity,line loss,and control strategy.Theoretically,the DC system can be developed without many complicated problems such as three-phase imbalance,grid harmonics and reactive power compensation.Therefore,it greatly improves the reliability and controllability of the distribution network and becomes a significant direction for the construction of future distribution system.However,apart from the uncertainty of distributed generation in the system,as DC distribution network can be divided into different complex topologies and operate in diverse modes,it is confronted with new challenges in stable and economic operation.Hence,it is necessary to deeply study the cooperative control strategy of control units in the multi-terminal DC system.Based on this,this dissertation conducts research from the following four aspects:(1)Firstly,the typical topology of DC distribution network is summarized.750 V ring DC distribution network is determined as the research object.The voltage source converter(VSC)is selected as the key device of converter station,and its detailed mathematical model is given.The output characteristics of photovoltaic and energy storage system are analyzed.The typical control strategies of critical devices are given.In terms of the collaborative control of multi-terminal DC distribution network,the hierarchical structure and the current collaborative control method are concluded.(2)Secondly,based on the primary control strategy of VSC-slope deviation control,an improved collaborative control method is proposed.This method divides converter stations into main converter station and auxiliary converter stations.The voltage of the DC system is divided into normal operation intervals and critical operation intervals.The outer-loop control strategy of converter stations and energy storage system in each interval are given.The effectiveness of the proposed strategy is verified through simulations in PSCAD/EMTDC software,and the slope deviation control strategy is compared to verify the superiority of the proposed strategy.(3)Thirdly,based on the limitations of secondary control,a distributed secondary optimal control strategy is proposed.This strategy is based on sparse communication between adjacent converter stations.It mainly adopts a distributed consensus algorithm to achieve voltage control and active power control simultaneously,which improves the utilization of converter stations while reducing the average voltage deviation.The effectiveness and reliability of the strategy are verified through simulations.Droop control is compared to verify the superiority of the proposed distributed secondary optimal control strategy.(4)Finally,based on the proposed distributed secondary optimal control strategy,the small disturbance stability analysis is studied.The idea of modular modeling is employed to establish the small signal model of entire system.Moreover,the eigenvalue analysis method and major participant analysis method are employed to study the impacts on system stability with the variation of important parameters.The design rules of these parameters are obtained,which provides an academic guideline for the selection of the parameters.The simulation verifies the accuracy of the established small signal model.