考虑系统电压影响的低频减载新策略

低频减载（Under Frequency Load Shedding, UFLS）是电力系统中普遍采用的技术,它通过在系统的某些地点切除过负荷量,达到维护系统稳定的目的。为了改进和提高传统的策略,很多研究者都考虑采用频率变化率作为指示器,用于确定系统的有功功率缺额。重点研究了影响频率变化率测量值的因素,分析了频率变化率在使用中遇到的相关问题,在此基础上,得出系统扰动后不平衡功率的准确求解表达式。一个综合利用电压信息量来确定切负荷地点和切负荷量的新UFLS策略被提出,仿真结果表明,新的切负荷策略更具有优越性。     

基于WAMS的自适应低频减载动态优化策略

在《电力安全事故应急处置和调查处理条例》(599号令)中,提出了在故障处理过程中的负荷切除量等同于故障损失负荷量,这要求电网在安全稳定运行的前提下尽可能地少切或不切负荷,以降低事故控制代价。因此,提出计及负荷频率调节效应、P-V特性和负荷重要度的减载贡献因子来有效指导低频减载过程中的选址定容。通过分析电压突变因素对不平衡功率的影响以提高功率缺额计算式精度,依据系统频率变化率的梯度变化逐轮次地动态优化减载量,以期充分发挥系统频率的自恢复调节能力。IEEE 39节点系统仿真分析表明,所提出的低频减载动态修正优化策略,能够在减少切负荷控制代价的同时改善系统频率恢复水平,从而兼顾频率紧急控制的经济性与可靠性要求。     

基于潮流追踪算法的自适应低频减载策略研究

低频减载（under frequency load shedding,UFLS）是防止电力系统频率崩溃的有效手段之一,它通过在系统的某些地点切除过负荷量,达到维护系统稳定的目的。为此,计及负荷的电压调节效应,提出一种改进的功率不平衡量计算方法,针对不同的扰动在线计算系统的减载总量;并利用邻接矩阵的稀疏性,结合邻接矩阵和比例分配原则提出了一种潮流追踪新算法,提高了潮流追踪算法的计算效率,将其应用于在线确定减载地点与分配减载量。仿真结果表明,新的自适应减载策略可靠性更高,能够有效防止欠切或过切,改善受扰系统减载后的频率恢复效果,并提高系统的电压稳定水平,对实际电力系统紧急控制研究具有重要意义。     

自适应低频减载装置的研究

介绍一种自适应型低频减载装置的方案,它依据频率和频率的变化率,动态的确定减负荷装置的动作情况。自动减负荷装置与旋转备用容量的作用相协调。利用微型计算机这一方案是完全可行的。     

低频减载（UFLS）的重要性

电力系统稳定主要包括功角稳定、电压稳定和频率稳定等几个方面。对功角稳定的研究较多，相应地有许多控制手段。在法国电网和日本电网相继发生大停电事故之后，电压稳定问题受到了更多的重视。由于现代电力系统运行点都很接近临界点，当系统发生一个小的故障扰动或出现缓慢的负荷增长变化时，就可能使系统进入不稳定状态。目前，已经有许多预测手段和控制方法（如FACTS）来防止电压崩溃事故的发生。     

自适应型低频减载装置的研究

介绍一种自适应型低频减载装置的方案 ,它依据频率和频率的变化率 ,动态的确定减负荷装置的动作情况。自动减负荷装置与旋转备用容量的作用相协调。利用微型计算机实现这一方案是完全可行的     

电力系统低频减载控制优化算法

讨论了电力系统低频集中减载控制算法,基于系统出现功率缺额时的频率动态快速分析,提出了确定减载量 和减载地点的优化算法。该算法将保证频率稳定的减载控制表述成一个线性规划问题,充分考虑了负荷的频 率电压特性。应用于某68节点系统,取得了满意的效果。     

电力稳定控制系统低频低压减载的最优策略实现

对电力稳定控制系统中母线低频低压减载这一运行故障处理的控制策略进行了分析。以18条运行负荷线路为例,列出其最优策略数学模型。分别用穷举法、过切法、动态规划法加以实现,比较各自运算过程、计算分析次数以及特点和不足。结果显示:动态规划法相比于穷举法计算量少、计算结果丰富;相比于过切法,计算量没有大的增加且计算结果准确。     

计及负荷频率特性的低频减载方案研究

低频减载是电力系统抑制频率下降、维持系统频率稳定的有效方法。该文针对目前低频减载方案中忽略了负荷频率特性的不足，提出了一种新的计及负荷频率特性的低频减载方案，该方案充分利用了频率下降时，负荷自身吸收的功率也下降的特点，优先切除频率调节系数小的线路，此举有利于系统频率的快速恢复和系统稳定，文中对方案的实现进行了详细的介绍，并采用单机系统进行了数字仿真，仿真结果验证了该方案的合理性。     

A new under‐voltage load shedding scheme for islanded distribution system based on voltage stability indices

Under‐voltage load shedding (UVLS) is an important technique to maintain the voltage stability and frequency of a power system network. UVLS has been applied widely in transmission systems to avoid system blackouts. However, with increasing penetration of distributed generation such as photovoltaic (PV) systems, the application of UVLS becomes important for islanded distribution systems. Under this condition, the network does not have a frequency reference as when it is connected to the grid. In this condition, when the load demand exceeds the PV capacity, UVLS is the only option to stabilize the system by shedding the load based on the changes of the voltage magnitude. In this work, a new UVLS scheme based on voltage stability indices is proposed. Four voltage stability indices are used as indicators for load shedding. Based on the stability indices, the loads that have the highest tendency of voltage collapse shall be the first ones to be shed. The proposed scheme is tested on a practical distribution network energized by a grid, a mini hydro generator, and a PV system. The test results on various scenarios prove that the proposed method is able to restore the system stability. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

频率安全分段控制下轮次切负荷协调优化策略

区外来电和大规模新能源发电比例的迅速提升使得电力系统频率安全问题日益严峻,精准负荷控制为源荷的瞬时平衡提供了新途径。提出了频率安全分段控制下,毫秒级负荷控制(FC-Ⅰ段)和秒级/分钟级负荷控制(FC-Ⅱ段)的用户侧轮次切负荷协调优化策略。根据FC-Ⅰ段控制策略确定的节点负荷控制量,以控制代价最小为目标,以负荷重要程度、负荷控制精确度为约束,基于McCormick松弛和内点法,快速求解该节点下底层用户的毫秒级负荷切除策略;对于FC-Ⅱ段的秒级/分钟级负荷控制,综合考虑FC-Ⅰ段控制后的剩余可控量与用户的参与意愿,建立多用户非合作博弈模型,并采用多目标粒子群优化算法求解秒级/分钟级负荷切除方案。通过实例分析,验证了所提策略的有效性。     

暂态稳定分析中低压切负荷对仿真结果的影响

负荷模型对电力系统仿真的结果有重要影响,随着系统中电压敏感负荷的增多,短暂低电压发生时负荷的切除对系统仿真结果的影响不可忽略。东北某变电站记录的大扰动实验时的实测数据表明,系统在低电压发生时存在负荷切除现象。10机39节点系统的仿真说明,切负荷现象对系统仿真结果影响巨大。在分析实测数据和原来综合负荷模型的基础上,通过增加有关低压切负荷因子,成功地模拟了电力系统在低压暂态过程中的掉负荷现象,所提出的新模型为研究电网大电压扰动下的动态稳定提供了借鉴。     

基于动态负荷特性指标化的集中式低压减载方案

针对考虑负荷模型的最优减载问题,在戴维南等值电路的基础上指出传统依据静态负荷指标考虑低压减载问题可能导致分析不准确的原因.推导了基于本地量测信息的动态电压稳定裕度指标,该指标考虑节点负荷特性,能够通过本地量测量信息实时得出,不用进行复杂的节点戴维南等值,在电压变化的关键区域能够近似线性地反映出该点的负荷裕度,从而降低优...     

基于相量测量的电压稳定裕度计算及减载方案

根据变电站实时测量的相量信息,计及数据量测误差,建立考虑等效电动势相角变化的外网最小二乘等值模型,求解精确的实时电压稳定裕度。提出一种基于实时电压稳定裕度的低压减载方案,建立了变电站紧急切负荷综合策略,实现在线动态计算切负荷量。设计了新型低压减载控制装置,软硬件平台设计采用标准化、模块化,通过高精度采样和实时数据处理,有效实现了提出的低压减载方案,保证了系统的安全稳定运行。     

电力系统静态电压稳定性在线监控(一)--一种可在线应用的计及负荷静态特性的电压稳定指标

基于局部量测数据和负荷静态特性．提出了一种可在线应用的节点静态电压稳定指标。首先介绍了ZIP负荷模型,然后用戴维南等值电路简化系统,将线路电流表达式整理成实部和虚部．消去负荷有功后代入ZIP负荷模型中的无功表达式得二次方程式．用根判别式得到以无功表示的电压稳定指标VSIQ;同理得以有功表示的电压稳定指标VSIP;取两者中的较小值作为节点电压稳定指标VSI。比较各节点VSI,最小值对应的节点即为系统最薄弱节点。以IEEE14节点和IEEE30节点系统为例,仿真系统在不同负荷特性下VSI的变化曲线。结果显示：恒定功率分量所占比例越大则节点VSI越小,电压稳定性越差;恒定功率比重相等情况下,恒定电流分量比重越大．节点电压稳定性越差．     

考虑负荷静态电压特性的重负荷节点静态电压稳定分析

首先从理论上论述了负荷静态电压特性对静态电压稳定的影响作用。在功率供求关系紧张状态下,电压稳定临界区域电压陡降时负荷静态电压特性影响显著,应计及阻抗负荷和恒电流负荷对静态电压稳定的作用,使用综合负荷进行计算。同时,接近分岔点时采用负荷导纳描述负荷功率需求,使用负荷导纳模型法计算电压稳定极限值及PV曲线下半部分的值。对IEEE30节点系统进行仿真计算分析,结果证明了所提出方法的有效性,同时快速性和精确性得到了保证。     

Application of active power sensitivity to frequency and voltage variations on load shedding

The occurrence of a large disturbance in a power system can lead to a decline in the system frequency and bus voltages due to a real and reactive power deficiency or due to the formation of islands with generation–load imbalance. Load shedding is an emergency control action that can prevent a blackout in the power system by relieving the overload in some parts of the system. This paper shows that rate of change of frequency can be utilized to determine the magnitude of generation–load imbalance, while the rate of change of voltage with respect to active power can be utilized to identify the sensitive bus for load shedding. The frequency, voltages and their rate of change can be obtained by means of measurements in real-time from various devices such as digital recorders or phasor measurement units or these parameters can be estimated from the voltage data by other means such as an optimal estimation method like Kalman filtering. The rate of change of system frequency, along with the equivalent system inertia may be used to estimate the magnitude of the disturbance prior to each load shedding step. The buses with a higher rate of change of voltage may be identified as the critical ones for load shedding and load can be first shed at these buses, depending on the change in the power flow at each bus. This application is tested on the IEEE 30 bus system and the preliminary results demonstrate that it is feasible to be used in load shedding to restore system voltage and frequency.     

Scheme design considering network topology and multi-attribute decision-making for under frequency load shedding

Power system emergency control is one key defense strategy in contingencies for protecting the system from cascading blackout. Under Frequency Load Shedding (UFLS) is one such strategy to ensure system stability by shedding load to retrieve balance between power supply and demand. Novel UFLS scheme design and a scheme optimization approach are proposed in this paper to find the optimal load-shedding schemes for different network partition resulted from contingencies. To obtain all possible UFLS schemes for a certain area, a candidate scheme set design algorithm based on value assigning of scheme parameters is proposed and then a relatively complete candidate scheme set is constructed. Considering network splitting caused by protection, several subsystems may exist from the reconstruction of independent network areas. The concept of homological area is defined and a graph-based method is used to analyse system topology change. Then, a multi-attribute decision-making (MADM) algorithm is introduced for order preference by similarity to an ideal solution (TOPSIS) for global optimizing candidate schemes. Optimal schemes for an area in both isolated area and homological area cases can be derived from all feasible UFLS schemes by MADM method. Simulation results demonstrate that the UFLS schemes can effectively restore system frequency in different network topologies.     

A new integer-value modeling of optimal load shedding to prevent voltage instability

This paper presents a novel integer-value modeling for optimal under voltage load shedding (UVLS) problem. The real-value modeling of UVLS is encountered to some drawbacks which lead to an ineffective practical solution. The proposed integer-value modeling overcomes these drawbacks by considering the load feeders of load buses in the modeling as well as assigning interruption penalty factors and participation penalty factors to feeders and buses respectively. Applying these factors to the proposed UVLS integer-value modeling result achieving objectives such as minimizing the total number of participating feeders in the load shedding, minimizing the total number of participating buses in the load shedding, minimizing the total amount of load to be shed, minimizing the total interruption cost and combination sets of the objectives. Without any limitation of applying the proposed modeling to large scale networks, it is implemented on IEEE 14-bus and 30-bus test systems and the results verify the effectiveness of the proposed method.