Stability-based minimization of load shedding in weakly interconnected systems for real-time applications

The transient stability of power systems is highly affected by the changes in the power generation and load levels. Due to the variability of the generating resources, the system stability can be provoked and the system stability limits can be reached as a result of certain sudden drop in the power generation. In these cases, the load shedding can act as an effective emergency corrective action for keeping system stability; however, over-shedding of loads results in severe economical as well as social security problems. Therefore, minimization of the load shedding required for the restoration of the system stability is one of the main objectives of this paper. Another critical issue related to successful load shedding is the fast assessment of the system stability, and the amount of the load shedding as well as the implementation of the load shedding corrective action. Therefore, this paper presents a fast method of stability assessment and load shedding requirements in the weakly interconnected power system. The method is an improved form of the extended equal area criterion (EEAC) where the required system equivalence is based on the availability of wide area monitoring (WAM) devices in modern power systems. The paper also investigates the impact of the implementation duration of the required load shedding. The results are verified through time domain simulations which confirm the accuracy of the presented method and its suitability for real-time applications.     

Method Combining ANNs and Monte Carlo Simulation for the Selection of the Load Shedding Protection Strategies in Autonomous Power Systems

This paper describes an efficient computational methodology that can be used for calculating the appropriate strategy for load shedding protection in autonomous power systems. It extends an existing method that is based on the sequential Monte Carlo simulation approach for comparing alternative strategies by taking into account the amount of load to be shed and the respective risk for the system stability. The extended methodology uses artificial neural networks (ANNs) for determining directly the parameters of the most appropriate load shedding protection strategy. For this purpose, the system inputs are the desirable probabilistic criteria concerning the system security or the amount of customer load interruptions. Using this methodology, the utility engineers can adopt a specific strategy that meets the respective utility criteria. The methodology was tested on a practical power system using a computer simulation for its operation, and the obtained results demonstrate its accuracy and the improved system performance     

市场环境下的负荷备用容量

经济利益是市场环境下电网公司所追求的重要目标之一。利用概率统计方法，对切负荷措施的可行性、保留负荷备用容量成本及切负荷赔偿费用进行了分析，提出市场环境下负荷备用容量的确定应在综合考虑保留备用容量成本和切负荷赔偿费用的基础上，求取经济上最优的负荷备用容量。数字份真结果表明方法可行，且具有较好的经济性。     

Optimal design of adaptive under frequency load shedding using artificial neural networks in isolated power system

The frequency and voltage stability is a basic principle in the power system operation. Different short circuits, load growth, generation shortage, and other faults which disturb the voltage and frequency stability are serious threats to the system security. The frequency and voltage instability causes dispersal of a power system into sub-systems, and leads to blackout as well as heavy damages of the system equipments. Optimum load shedding during contingency situations is one of the most important issues in power system security analysis. This paper presents a fast and optimal adaptive load shedding method, for isolated power system using Artificial Neural Networks (ANNs). By creating an appropriate data-base of contingencies for training the neural network, the proposed method is able to perform correct load shedding in various loading scenario. In this regard, the total power generation, the total loads in power system, the existing spinning reserved capacity value in the network and frequency reduction rate were selected as the ANN inputs. This method has been tested on the New-England power system. The simulation results show that the proposed algorithm is very fast, robust and optimal values of load shedding in different loading scenarios, related to conventional method.     

紧急切负荷网荷互动终端设计与实现

鉴于调控切负荷和营销负控切负荷控制手段都无法同时满足特高压直流线路闭锁故障时负荷紧急控制和保障大型用户重要负荷供电的需要,文中提出了通过改进专变用户终端实现负荷快速控制的方法,设计了一种可满足用户可切负荷精细化采集、实时通讯、多主站安全快速控制的通用型紧急切负荷网荷互动终端,并针对现场的负荷接入、功率计算、跳闸出口设计了一种可灵活配置的解决方案,最终实现终端在用户现场应用,通过实际切负荷测试验证了终端完全满足精准切负荷系统的要求。     

计及风险备用约束的含风电场电力系统动态经济调度

为解决风电的不确定性给电网调度带来的问题,必须开展含风电场的经济调度问题研究。通过引入风速和负荷预测误差的概率分布函数来描述系统中存在的不确定性因素,提出了一种基于风险备用约束的含风电场电力系统动态经济调度新模型。在目标函数中采用惩罚的方式对风电计划出力相对于实际出力的偏差所造成的备用成本加以考虑。该模型采用收敛特性稳定的非线性预估–校正原对偶内点法进行求解。通过含有一个风电场的10机组系统算例,验证了所提调度模型的可行性。分析表明,该模型可以在保证系统可靠性要求的基础上,实现经济性最优的目标。     

基于频率动态特性的电力系统频率失稳概率评估

提出一种电力系统频率失稳风险评估方法,该方法计及了旋转备用的频率动态特性,建立了低频减载作用下的频率稳定分析模型。基于非序贯蒙特卡洛仿真,计算分析了失稳概率、失稳频率、期望切负荷量和频率动态指标,实现了对频率稳定性的概率量化评估。探讨了旋转备用容量变化、低频切机容量变化对频率稳定性的影响,并计算了在多层负荷模型中计及和不计及不确定性两种情况下的频率稳定年度指标。IEEE RTS79系统算例分析表明所提方法能从概率角度全面深入评价电力系统的频率稳定性,可为低频减载配置方案的合理性和机-网的协调性提供一定参考依据。     

基于最优负荷削减的小世界电网连锁故障模拟

现有小世界电网连锁故障模型中,故障严重程度的评价指标不能很好地考虑故障后系统运行情况,且计算方法过于简化,为此,提出以最小失负荷百分比作为连锁故障发生后评价故障严重程度的指标,并运用基于直流潮流的负荷削减最优化模型计算最小失负荷量,从而对基于节点电气介数的连锁故障模型的模拟过程进行改进.系统受到攻击后,该方法通过重新调度系统中的发电功率来消除系统约束违限,在无法避免负荷削减时使负荷削减量最小.算例结果验证了该方法的有效性     

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。     

大电网可靠性影响分析的潮流跟踪方法

提出了大电网可靠性评估中削减负荷的潮流跟踪模型, 建立了节点和系统可靠性对元件的分配计算模型,基于此易于分析系统的薄弱环节。在负荷削减的潮流跟踪模型中,按负荷对发电机和线路利用系数的大小顺序削减负荷。基于潮流跟踪削减负荷能建立故障元件与削减负荷节点间的映射关系,该模型的核心在于找出所有元件中对削减负荷节点利用系数最大的元件。算例结果证明了所提出方法的有效性。     

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。     

基于BPA的电力系统低压减载的研究

低压减载作为电力系统的第三道防线,是维持电力系统安全稳定和经济运行,并保证电能质量的重要措施。依工程实际需求,在电力系统分析软件BPA的基础上,参考国内外现有研究成果,针对分散型低压减载方案,提出基于电压-无功灵敏度减负荷的方法确定低压减载量。采用连续潮流算法,确定薄弱区域的电压-无功灵敏度,最后通过时域仿真分析对所配置的方案进行校验。以河北南网2007年夏季高峰数据为例,验证了该方法具有很好的工程参考价值。     

考虑光伏功率相关性的随机潮流方法

光伏发电属于典型的间歇性能源,且同一地区的光伏出力相关性显著。在含光伏电站的系统随机潮流中,综合考虑多维光伏功率的相关性对于分析光伏电站接入对电力系统的影响具有重要意义。文中提出了计及多个光伏电站出力相关性的随机潮流方法,该方法采用了Pair Copula函数对多个光伏电站的出力进行相关性建模,综合考虑了电站出力两两之间不同的相依结构。同时,将数字交错技术融入拟蒙特卡洛法中,对现有的随机潮流方法进行了改进,有效提高了算法的收敛速度。以美国德克萨斯州光伏电站基地的出力历史数据为例,分别在IEEE 30节点系统和IEEE118节点系统中进行仿真计算,验证了所提方法的有效性。     

An enhanced cascading failure modelintegrating data mining technique

Under frequency load shedding is an effective approach to maintain or restore the steady-state operation of the power system when frequency accidents occur. An improved under frequency load shedding strategy based on dynamic power flow tracking is proposed. The expression of the kinetic energy theorem in power system is derived and combined with the power flow tracing method to analyze the relation between system energy distribution and its frequency. The power system frequency influencing factors are then constructed and applied to find the reasons of frequency decline and to quantify the contributions of the mechanical power of the generators, the load power and the transmission losses for the frequency deviation. Finally, considering a variety of unbalanced power scenarios in the system, the modified load shedding strategy is designed. Based on the results of dynamic power flow tracing, the strategy can choose the suitable load node to control, and the defined load frequency contribution indicator is utilized to determine the load shedding amount which each control object undertakes. The proposed methodology is verified by the fault scenarios when the generator sets mistakenly cut off and the trip of important tie-lines in the IEEE 39-bus system. Compared with the conventional strategies, the proposed strategy is more selective, can reduce the blackout range, and improve the effect of stable frequency recovery     

An improved under frequency load shedding strategy based on dynamic power flow tracing

Under frequency load shedding is an effective approach to maintain or restore the steady-state operation of the power system when frequency accidents occur. An improved under frequency load shedding strategy based on dynamic power flow tracking is proposed. The expression of the kinetic energy theorem in power system is derived and combined with the power flow tracing method to analyze the relation between system energy distribution and its frequency. The power system frequency influencing factors are then constructed and applied to find the reasons of frequency decline and to quantify the contributions of the mechanical power of the generators, the load power and the transmission losses for the frequency deviation. Finally, considering a variety of unbalanced power scenarios in the system, the modified load shedding strategy is designed. Based on the results of dynamic power flow tracing, the strategy can choose the suitable load node to control, and the defined load frequency contribution indicator is utilized to determine the load shedding amount which each control object undertakes. The proposed methodology is verified by the fault scenarios when the generator sets mistakenly cut off and the trip of important tie-lines in the IEEE 39-bus system. Compared with the conventional strategies, the proposed strategy is more selective, can reduce the blackout range, and improve the effect of stable frequency recovery.     

考虑微网充电站影响的输电网风险评估方法

微网充电站接入配电网后,传统的辐射型配电网中将存在电源,这就造成在传统的输电网风险评估方法中配电网不能够再简单等效为一个无源负荷点。为了分析这种影响,提出了考虑微网充电站影响的输电网风险评估方法。首先介绍了风险评估基础理论,然后重点分析了微网充电站概率模型,包括分布式电源出力概率模型和电动汽车(Electric Vehicles, EV)充电负荷概率模型。应用考虑了配电网层面影响的期望负荷削减量代替绝对负荷削减量。最后应用测试系统验证了所提方法的有效性,包括微网充电站中分布式电源容量配置比例以及反送电比例对于输电网风险指标的影响。分析结果表明,微网充电站能够有效降低输电网风险水平。     

基于新能源出力保证率轨迹灵敏度分析的储能配置方法

大规模新能源接入电网使得电源出力的不确定性超过了负荷需求的不确定性,电力系统概率潮流加大了运行部门的管理难度。针对这一问题,提出了一种基于新能源出力保证率轨迹灵敏度分析的储能配置方法。首先根据新能源出力的不确定性,建立了受考核元件的概率潮流越限方程。其次,以新能源出力保证率作为参数改变量,建立概率潮流的轨迹灵敏度分析模型。然后,提出了使得概率潮流不发生越限储能容量配置策略,针对轨迹灵敏度较小的元件相关节点,计算储能功率需求和储能能量需求。最后,在中国南方某地区实际电力系统进行了算例仿真,验证了所提方法的有效性。     

基于可变减载率超速控制的双馈异步风机参与微电网调频研究

为了使双馈异步风机(DFIG)能够更好地参与微电网频率调节并减少有功控制成本,综合考虑风机向微电网输送有功功率和提供备用容量参与系统调频两方面因素,提出了变减载率超速控制法。计及风速出现概率,采用概率加权求和法,考虑减载成本、调频效益和调频恢复成本求解超速控制成本(COC),得到变减载率曲线。通过对一个含DFIG的微电网系统进行仿真分析,验证所提方法可有效改善微电网频率动态特性,减少风机有功控制成本,有利于微电网的稳定运行。     

电力系统低频减载的单调控制特性

新能源占比的不断提高使得频率稳定问题日渐突出,因此迫切需要研究系统的频率稳定量化评估分析方法,也需对频率安全控制的最后一道防线低频减载进行更深入的分析。将单调控制系统理论运用到低频减载分析过程中,根据单调控制系统的输入-输出判定条件,推导单机和多机系统低频减载时频率分别需要满足的保序特性量化关系。此外,分析时采用全状态模型,在保证电网规律性和解析性的同时获得更高的可扩展性,综合频率与功角、电压以及相关参数间的耦合关系。并结合灵敏度分析了电网内部变量之间的相关关系,以指导电网故障时的参数设置。最后,分析目前光伏参与调频的3种常见情况,分别说明单调控制理论的适用性,并通过算例进行验证。     

Adaptive under-voltage load shedding scheme using model predictive control

Recent system wide disturbances have demonstrated the need for automatic system protection schemes to prevent such cascading disturbances. In this paper, an adaptive under-voltage load shedding scheme using model predictive control is proposed to protect power system against voltage instability. The proposed scheme calculates the criticality of the system based on the measurements of voltage magnitudes and reactive power generations and then in case of voltage instability a model predictive based step-sized load shedding scheme will be triggered. The speed and amount of load shedding steps are adapted to the severity of contingency in the affected region. By devising the grid into the separate regions the proposed scheme acts as a distributed controller without having a central dispatching center. The performance of the proposed model predictive based scheme is verified over a 10-bus dynamic test case. The proposed model predictive control will be solved using sequential quadratic programming technique.