计及可行解恢复的高载能负荷-新能源有功-无功协调调度

高载能负荷具有较强的用电调节能力,可通过与新能源协调促进新能源消纳。考虑节点电压约束和内部电网潮流方程的高载能负荷自调度问题是一个混合整数非线性非凸问题,现有的求解器难以求解。而采用线性潮流等简化方法求得的自调度结果不够精确,无法保证实际运行时的节点电压约束。针对以上问题,首先采用二阶锥松弛方法对原问题进行凸化以降低问题求解难度,进而采用基于交流潮流的可行解恢复过程以保证二阶锥松弛后的自调度结果精确合理。通过对比线性潮流自调度结果、基于二阶锥松弛的自调度结果、采用可行解恢复的自调度结果和原始自调度模型的结果,证明采用可行解恢复过程的自调度结果避免了基于线性潮流或基于二阶锥松弛的自调度解不精确问题。同时,相比利用现有商业求解器直接求解原问题,采用该方法可以在较短的时间内快速求得一组优化结果,有效地降低了原问题求解的难度。     

静态电压稳定分析的故障筛选和排序方法

提出一种新的故障筛选和排序方法。首先,定义一种负荷裕度阈值,用连续潮流法计算此裕度下的潮流工况,在此工况下,利用最优乘子法依次求解所有的开断潮流,将有解的大部分开断作为安全故障筛选掉,少量无解的则为不安全故障。然后,在基态下利用最优乘子法依次求解不安全故障的开断潮流。有解则为危险故障,并用连续潮流法求解负荷裕度,按裕度给出排序;无解则为失稳故障,结合最小二乘潮流解失配量中隐含的校正控制灵敏度信息,使用序列线性规划法给出使潮流恢复有解的最小切负荷代价,据此代价来排序失稳故障。新英格兰10机39节点系统的仿真结果验证了所提出的方法能快速、可靠、全面地实现电压稳定的故障筛选和排序。     

基于混合编码方式的配电网故障恢复算法研究

为提高遗传算法求解配电网故障恢复问题的效率,提出了一种染色体混合编码模型。对配电网的网络拓扑进行节点深度法编码,通过相应的交叉变异操作,产生可行的配电网生成树。非故障失电区的可中断负荷采用0-1编码,实现切负荷控制,增加故障恢复的灵活性。这种混合编码方式可以大大降低不可行解的数量,加快算法收敛速度。采用多目标优化算法NSGA-Ⅱ,减少权重系数主观性对最优解的影响,实现各个优化目标的协同进化,可以为调度人员提供多个最优恢复方案。算例计算结果验证了所提出的模型和算法的正确性和有效性。     

基于加权最小绝对值的大电力系统潮流可行解优化恢复方法

电力系统基本潮流无可行解时,通常只能根据经验以人工对可调的负荷出力进行反复调试才能获得一个较接近初始状态的新可行解。为了在恢复潮流可行解的同时,找到原运行方式中导致无解的症结,以节点注入偏差量绝对值最小为目标,提出了一种新的潮流恢复实用模型,并采用原—对偶内点法求解。对IEEE标准系统及实际超大电网系统的仿真表明该模型有效,优化结果可以较好地辨识出导致原运行方式无潮流可行解的节点出力和负荷,计算效率已达到实际应用水平。     

一种快速恢复潮流解的联动切负荷算法

电力系统运行过程中的某些严重故障可能导致静态电压崩溃,即潮流方程无解,此时需要采取紧急控制措施恢复潮流解。针对此问题,提出了一种快速恢复潮流解的切负荷算法。将无解故障模拟成断线支路两端节点的注入功率,利用故障前的潮流方程切向量识别故障后的薄弱节点,将恢复潮流解问题转换为薄弱节点电压幅值优化问题,避免了潮流方程无解导致的薄弱节点无法辨识和静态电压稳定裕度灵敏度信息的复杂计算。实际系统的仿真结果表明,该算法可快速恢复潮流解,适合在线应用。     

静态电压稳定分析的故障筛选和排序方法

提出一种新的故障筛选和排序方法。首先,定义一种负荷裕度阈值,用连续潮流法计算此裕度下的潮流工况,在此工况下,利用最优乘子法依次求解所有的开断潮流,将有解的大部分开断作为安全故障筛选掉,少量无解的则为不安全故障。然后,在基态下利用最优乘子法依次求解不安全故障的开断潮流。有解则为危险故障,并用连续潮流法求解负荷裕度,按裕度给出排序;     

失稳故障支路拟裕度评估及控制的虚拟支路法

为评估失稳故障支路的严重程度及解决故障后系统失去潮流可行解的问题,提出了失稳故障支路拟裕度评估及控制的虚拟支路法。该方法将待切除的故障支路用一条含参数的虚拟支路置换,使虚拟支路开断问题转换为故障支路两端点注入功率增长的裕度问题,并用拟裕度大小评估故障支路的严重程度。算法利用最小控制代价的过程控制法,使虚拟支路完全切除后系统获得可行潮流解;故障后优化控制是在可行解上优化系统,以满足稳定裕度要求。通过IEEE算例验证了方法的可行性和有效性。     

基于凸包理论的含风电电力系统负荷恢复方案优化

大停电事故后,合理的负荷恢复策略对加快电力系统恢复、减少停电损失具有重要意义。针对标准交流潮流方程的非凸性导致负荷恢复模型求解效率低的问题,提出了基于凸包理论的含风电电力系统负荷恢复方案优化方法。首先,简要介绍了凸包理论以及非线性函数的凸包构建方法。其次,针对风电出力的不确定性,采用条件风险价值理论处理风电波动带来的风险,进而建立了直角坐标系下基于凸包理论的电力系统负荷恢复二阶锥优化模型,其中,交流潮流方程中的非线性项采用凸包表达。针对无法精确确定凸包参数的问题,提出了基于迭代更新的参数优化方法,减少因凸包引入的松弛误差。所提出的模型为混合整数二阶锥规划模型,可采用商业求解器高效求解。最后,采用IEEE 39节点系统和改进的广东电力系统验证了所提出模型的有效性。     

静态安全分析中的联动切负荷算法

将导致潮流无解的故障的联动切负荷方案分解成恢复潮流解和切负荷量优化2个子问题。为恢复故障后的潮流可解性,提出了一种快速恢复潮流解的切负荷算法,进而利用基于灵敏度的线性优化消除恢复潮流解后的系统越限现象;若恢复潮流解后系统不存在越限现象则通过扩展潮流方程减少切负荷量。IEEE24节点和我国某实际682节点系统的算例表明本文所提方法简单、有效。     

电力系统恢复后期网架重构和负荷恢复的两阶段优化方法

电力系统恢复后期的网架重构和负荷恢复是一个复杂的多步混整非线性规划问题。为了降低其求解难度和提高求解效率,提出一种适用于网架重构和负荷恢复的两阶段优化方法,该方法将网架重构及负荷恢复问题解耦为基于直流潮流的混整线性规划和基于交流潮流的连续非线性规划两阶段优化问题。在第1阶段优化中,利用计及频率影响的直流潮流模型确定最优线路投运及负荷开关投切状态这些离散变量的值,再将其作为第2阶段基于增广交流潮流的连续非线性规划的系统运行条件,通过优化发电机出力及端电压,在确保系统安全的前提下确定最短的恢复耗时。在10机39节点系统下进行了算法验证,计算得到单步和全过程下的计算效率和恢复方案,结果表明,所提算法的计算效率远高于启发式算法,同时所得方案也具有更快的恢复速度。最后,以湖北电网鄂东南子网为例验证该算法用于实际电网恢复决策的可行性。     

Determination of load shedding to provide voltage stability

A computationally simple algorithm is developed for studying the load shedding problem in emergencies where an ac power flow solution cannot be found for the stressed system. The proposed algorithm is divided into two sub-problems: restoring solvability sub-problem and improving voltage stability margin (VSM) sub-problem. Linear optimization (LP)-based optimal power flow (OPF) is applied to solve each sub-problem. In restoring solvability sub-problem, rather than taking restoring power flow solvability as direct objective function, the objective function of maximization of voltage magnitudes of weak buses is employed. In VSM sub-problem, the traditional load shedding objective is extended to incorporate both technical and economic effects of load shedding and the linearized VSM constraint was added into the LP-based OPF. Case studies with a real 682 bus system are presented. The simulation results show that the proposed load shedding algorithm is effective, fast in finding the load shedding scheme to solve the problem of restoring solvability and improving VSM.     

A new formulation for FACTS allocation for security enhancement against voltage collapse

This paper proposes a new formulation for reactive power (VAr) planning problem including the allocation of flexible ac transmission systems (FACTS) devices. A new feature of the formulation lies in the treatment of security issues. Different from existing formulations, we directly take into account the expected cost for voltage collapse and corrective controls, where the control effects by the devices to be installed are evaluated together with the other controls such as load shedding in contingencies to compute an optimal VAr planning. The inclusion of load shedding into the formulation guarantees the feasibility of the problem. The optimal allocation by the proposed method implies that the investment is optimized, taking into account its effects on security in terms of the cost for power system operation under possible events occurring probabilistically. The problem is formulated as a mixed integer nonlinear programming problem of a large dimension. The Benders decomposition technique is tested where the original problem is decomposed into multiple subproblems. The numerical examinations are carried out using AEP-14 bus system to demonstrate the effectiveness of the proposed method.     

发输电组合系统可靠性评估中的最优负荷削减模型分析

介绍了基于直流潮流的负荷削减线性规划模型和基于交流潮流的负荷削减非线性规划模型的基本原理,对它们各自的优缺点进行了分析,并使用它们对 RBTS(RoyBillinton Test System)可靠性测试系统进行了评估.计算结果表明,直流潮流的负荷削减线性规划模型由于忽略了节点电压约束的影响,存在较大的模型误差,要得到精确的可靠性指标,应该使用基于交流潮流的负荷削减非线性规划模型.     

Planning of multi-type FACTS devices in restructured power systems with wind generation

Many electrical power systems are changing from a vertically integrated entity to a deregulated, open-market environment. This paper proposes an approach to optimally allocate multi-type flexible AC transmission system (FACTS) devices in restructured power systems with wind generation. The objective of the approach is to maximize the present value of long-term profit. Many factors like load variation, wind generation variation, generator capacity limit, line flow limit, voltage regulation, dispatchable load limits, generation rescheduling cost, load shedding cost, and multilateral power contracts are considered in problem formulation. The proposed method accurately evaluates the annual costs and benefits obtainable by FACTS devices in formulating the large-scale optimization problem under both normal condition and possible contingencies. The overall problem is solved using both Particle Swarm Optimization (PSO) for attaining optimal FACTS devices allocation as main problem and optimal power flow as sub optimization problem. The efficacy of the proposed approach is demonstrated for modified IEEE 14-bus test system and IEEE 118-bus test system.     

一种基于有序二元决策图的低频减载新方案

为控制电力系统大容量机组跳闸时频率下降的问题,需要设计可靠的低频减载方案。针对传统方案存在的不足,设计了一种考虑负荷模型和系统有功备用的低频减载方案。该方案通过故障后系统频率变化率来估算系统功率缺额,充分考虑负荷模型、系统备用的影响,确定切负荷量;根据负荷的频率调节特性确定切除的优先级;利用有序二元决策图(ordered binary decision diagram,OBDD)搜索切除方案可行解,针对可行解,考虑负荷的控制代价,确定最优的控制策略。该方案经在IEEE9节点系统上测试验证,能准确估算故障大小,并能快速得到最优切负荷方案,相比于传统的低频减载方案,具有自适应性强、控制代价小等优势。     

A comprehensive strategy for transmission switching action in simultaneous clearing of energy and spinning reserve markets

There is a great resolution calling for smart grids in recent years. Introduction of new technologies, that make the network flexible and controllable, is a main part of smart grid concept and a key factor to its success. Transmission network as a part of system network has drawn less attention. Transmission switching as a new transmission service can release us from load shedding and remove the constraints’ violations.Transmission switching can provide economic benefits compared to other control methods such as generation unit rescheduling or load shedding for contingency management.Utilizing a stochastic mix-integer nonlinear programming (SMINLP) model, transmission switching is used during contingencies and steady state to determine optimal required energy and reserve values.Stochastic joint energy and reserve markets with transmission switching considering dynamic constraints has been proposed to minimize the cost of supplying load, security expenses.Considering dynamic constraints in proposed model avoid the occurrence of transient instability when opening the line in transmission switching action.A network reduction method based on modified Jacobean AC Newton–Raphson technique power flow considering switchable line in technique is used for speeding up the calculation, efficiency and simplicity.To investigate the efficiency of the proposed strategy IEEE 14 bus test and IEEE 57 bus test system are studied. According to the obtained results, this strategy decreases energy and reserve marginal prices, as well as security cost.     

电力系统在线主动解列控制算法

对在线主动解列策略的判定及控制框架进行简要介绍,提出电力系统在线主动解列算法:借助机组分群情况确定各个孤岛的主要电源,按照发电机和负荷的功率分配关系,研究负荷分群算法和设计解列断面搜索算法,实现负荷分群;考虑孤岛中功率调节特性,计算各个孤岛的不平衡功率情况,确定进一步切机、切负荷控制措施;在IEEE标准系统及实际电力系...     

基于轨迹灵敏度的紧急切负荷优化算法

超/特高压直流远距离、大容量输电使受端电网发生大功率缺额的概率增加。为防御失去大电源导致的电网安全稳定破坏,提出了一种兼顾暂态安全性和经济性的紧急切负荷优化模型,并设计了高效求解方法。优化模型以总切负荷代价最小为目标,计及暂态电压安全、暂态频率安全和切负荷量约束。暂态安全性均基于时域轨迹严格评估,是带时域参数约束的大规模非线性规划问题。分析了问题最优解的特征,针对带时域参量约束的非线性规划无法直接求解的问题,利用轨迹灵敏度将安全约束线性化,将问题转化为线性规划求解,并通过逐次迭代保证解的一致性。以实际省级电网为例进行仿真分析,验证了算法的有效性。     

Optimal allocation of shunt Var compensators in power systems using a novel global harmony search algorithm

In this paper, a novel global harmony search algorithm (NGHS) is used to determine the optimal location and size of shunt reactive power compensators such as shunt capacitors, static Var compensators (SVCs), and static synchronous compensators (STATCOMs) in a transmission network. The problem is decomposed into two subproblems. The first deals with the optimal placement of shunt Var compensation devices using the modal analysis method. The second subproblem is the optimization of the load flow using the NGHS algorithm. A multi-criterion objective function is defined to enhance the voltage stability, improve the voltage profile, and minimize power loss while minimizing the total cost. The results from a 57-bus test system show that the NGHS algorithm causes lower power loss and has better voltage profile and greater voltage stability than the improved harmony search algorithm (IHS) and particle swarm optimization (PSO) techniques in solving the placement and sizing problem of shunt Var compensators. Finally, a comparison of the convergence characteristics of three optimization methods demonstrates the greater accuracy and higher speed of the proposed NGHS algorithm in finding better solutions compared with PSO and IHS.