【作者】 王昊；

【导师】 王洪涛；

【作者基本信息】 山东大学 ， 电气工程， 2022， 硕士

【摘要】 鉴于我国能源中心与负荷中心在地理位置上呈现逆向分布的特点,高压直流输电工程因其可远距离、跨区域大容量输电的优势而在我国被广泛应用。目前,我国华东、华南等地区负荷中心已有多回直流同时馈入,形成了直流多馈入系统。在缓解负荷中心供电压力的同时,由于直流多馈入受端系统中交、直流间存在强耦合作用会使系统运行风险增加,受端电网的局部故障可能引起交直流系统的连锁故障,导致整个区域电网发生大停电事故。因此有必要对直流多馈入系统的恢复过程进行研究。本文分别研究了直流参与电网黑启动进程对直流系统与受端交流系统的技术要求,直流系统参与网架重构过程的安全性,构建了直流多馈入系统解耦安全域模型和考虑负荷恢复安全裕度的交直流混联系统负荷优化决策等问题。论文的主要工作和创新点如下:1)分析了直流启动方式与控制模式对直流系统参与电网黑启动进程安全性的影响,从稳态频率稳定、动态频率稳定以及电压稳定三个角度分析了为支撑直流系统启动,受端交流电网应具备的技术要求。为适应系统恢复过程中直流出力不位于额定工况和直流控制模式与正常运行状态存在差别的情况,分析了多直流系统间相互作用的影响,并采用了一种新的综合短路比指标来反映直流多馈入系统受端电网的强度与恢复期间直流系统的静态电压稳定性。2)构建了网架重构双层优化模型与网架重构过程中直流多馈入系统解耦安全域模型。首先通过改进的电网节点重要度贡献矩阵对电网节点的重要度进行了评估,基于此建立了网架重构双层优化模型。分别以网架重构进程中常规机组发电量与直流输电量的总和与网架重构持续时间之比以及恢复路径中节点的平均重要度作为上、下层模型的目标函数,以改进的粒子群算法对该双层优化模型进行了求解。另一方面,考虑到系统恢复期间,受端交流系统强度较弱,直流进行功率支援时,容易使系统安全约束越限,建立了直流多馈入系统的解耦安全域模型,在得到的解耦安全域范围内,各直流功率可以进行解耦控制,提高了直流多馈入系统受端电网网架重构过程中直流系统运行的安全性。3)提出了一种计及恢复安全裕度的交直流混联系统负荷恢复优化决策方法。以加权负荷恢复量、系统电压稳定指标、系统潮流熵指标作为目标函数,然后通过对节点功率注入方程的线性化得到了系统静态安全约束的超平面组。基于此得到负荷恢复方案至各约束边界面的安全距离,并将此安全距离纳入约束条件中,提高了负荷恢复方案的安全裕度,然后通过非支配排序遗传算法NSGA-Ⅱ对该负荷恢复多目标优化模型进行了求解。进一步,通过改进的层次分析法、信息熵权法与最小二乘法得到各指标的综合权重,然后利用灰色关联度分析方法对得到的Pareto最优解集进行了多属性决策,最终得到了综合各个目标函数情况下最满意的负荷恢复方案。更多还原

【Abstract】 In view of the reverse distribution of energy centers and load centers in China,HVDC transmission engineering has been widely used in China because of its advantages of longdistance and trans-regional large capacity transmission.At present,the load centers in east China and South China have several DC feeds at the same time,forming a multi-infeed HVDC system.In addition to alleviating the power supply pressure of the load center,the strong coupling between AC and DC in the multi-infeed HVDC system will increase the risk of system operation,and the local failure of the receiving system may lead to the chain failure of the AC and DC system,resulting in a major blackout of the entire regional power grid.Therefore,it is necessary to study the power grid restoration process in which DC system participates.In this thesis,the technical requirements of the DC system and the ac system at the receiving end for the dc system participating in the black start process of the power grid,the security of the DC system participating in the network reconfiguration process,the decoupling security domain of the multi-infeed DC system and the coordination recovery of the AC and DC systems considering the safety margin of the system load recovery are respectively studied.The main work and innovations of the thesis are as follows:1)The influence of the DC start mode and control mode on the safety of the DC system participating in the black start process of the power grid is analyzed.In order to support DC start-up,the technical conditions that should be possessed by the AC system at the receiving end are analyzed from the perspectives of steady-state frequency stability,dynamic frequency stability and voltage stability.In order to adapt to the situation that the DC output is not in the rated working condition and the DC control mode is different from the normal operating state in the system recovery process,the influence of the interaction between multiple dc system are analyzed and adopted a new comprehensive short circuit ratio index to reflect the strength of the receiving grid of the multi-feed HVDC system and the static voltage stability of the dc system during recovery.2)The two-layer optimization model of grid reconfiguration and the decoupling safety domain of multi-infeed DC system in the process of grid reconfiguration are constructed.Firstly,the importance of grid nodes is evaluated through the improved grid node importance contribution matrix.Based on this,a two-layer optimization model for grid reconfiguration is established.The ratio of the sum of conventional unit power generation and DC transmission capacity to the duration of network reconfiguration in the process of network reconfiguration and the average importance of nodes in the restoration path are taken as the objective functions of the upper and lower models respectively,and then the improved particle swarm optimization algorithm is used to solve the two-layer optimization model.On the other hand,considering that during the system recovery period,the strength of the AC system at the receiving end is weak,and the safety constraints of the system are easily exceeded when the DC power is supported,a decoupling safety domain model of the multi-feed DC system is established.Within the safety domain,each DC power can be controlled decoupled,which improves the safety of the DC system participating in the grid reconfiguration process.3)A load restoration optimization decision method for AC-DC hybrid system considering restoration safety margin is proposed.The weighted load recovery index,system voltage stability index and system power flow entropy index are taken as the objective function,and then the hyperplane group of each static safety constraint is obtained by linearization of the node power injection equation.Based on this,the safe distance between the load recovery scheme and each constraint boundary surface was obtained,and the safe distance was incorporated into the constraint conditions to improve the recovery safety margin of the load recovery scheme.Then,the multi-objective optimization problem was solved by NSGA-Ⅱalgorithm.Furthermore,the comprehensive weight of each index is obtained by improved analytic hierarchy process,information entropy weight method and least square method,and then multi-attribute decision is made on the Pareto optimal solution set by grey relational degree analysis method.Finally,the most satisfactory load recovery scheme was obtained under the condition of integrating each objective function.更多还原