Controlled islanding of power systems using label propagation

This paper presents a label propagation controlled islanding (LPCI) algorithm for large interconnected power systems. The proposed algorithm is suitable for finding an islanding solution quickly when a power system with large disturbances need to avoid uncontrolled system separation and to prevent wide‐area blackouts. By referring to the graph theory for the power system, a similar graph is first introduced according to the branch power flows the power system. Then, the buses of coherent generators are viewed as labeled data, while the left buses are viewed as unlabeled data. As a result, the controlled islanding problem is converted into a semi‐supervised learning problem. At last, a classical semi‐supervised learning algorithm, i.e. label propagation, is applied to solve the controlled islanding problem. In addition, a small‐scale strategy space for power system splitting is provided according to the proposed entropy criterion. Characteristics of the proposed algorithm are presented, as well as feasibility to the active splitting control of power systems. The results on four test cases show its correctness and computationally efficient. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Loading margin calculation with line switching: A decomposition method

This paper presents a model for loading margin calculation integrated with transmission line switching. A mixed-integer nonlinear optimization model is developed which maximizes the loading margin of the system subject to various operational system constraints. An iterative algorithm, based on the Benders decomposition method, is used to solve the problem. The proposed method is tested on medium and large scale test systems and optimization results are compared with that of a non-decomposed method to show the efficacy of the proposed approach.     

Optimal load shedding study of naval-ship power system using the Everett optimization technique

This paper reports an application of the Everett optimization technique for value-based load shedding in naval-ship power system with network constraints and application of reliability constraints. A new congestion analysis index—expected contingency margin (ECM), which considers the probability of disturbance, and reliability indices loss of load probability (LOLP) and expected unserved energy (EUE) are presented to filter the critical outage and congestion cases. The optimal load shedding scheme carried out using the Everett optimization technique uses a utility function, which addresses the cost of allocating pay-off while satisfying the network and reliability constraints and generation capacity limits. The algorithm search for the optimal λ to form a fair pricing mechanism, which produces maximum pay-off and minimum load shedding while, satisfying system constraints. The proposed approach is examined on naval-ship power system and detailed results are shown.     

Application of fuzzy-analytic hierarchy process algorithm and fuzzy load profile for load shedding in power systems

In an electrical competitive market, load shedding decision support systems are needed to find the ways to process load shedding to satisfy both economic and technical conditions. This paper proposed the Fuzzy Analytic Hierarchy Process algorithm (Fuzzy-AHP) and fuzzy logic for load profile approach to determine the weight of the load nodes of the system and select the control strategy when the system operates at various load levels. Weights of the load nodes were calculated by triangular fuzzy numbers in the pair comparison. These results combined with the fuzzy logic for load profile to draw out the suitable control strategies for various load levels in case of emergency. The effectiveness of the algorithm was demonstrated through the experiment of load shedding of IEEE 37 bus compared with traditional AHP algorithm.     

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.     

输电系统风险评估中的分层分级负荷削减模型

负荷削减计算是输电系统风险评估中的关键步骤.为解决目前负荷削减模型还存在的没有考虑无功潮流和节点电压约束、无法考虑负荷类型削减优先级对风险指标的影响等不足,提出了一种分层分级最优负荷削减模型.按负荷类型重要度从高到低依次分层削减负荷,兼顾就近和最优原则,将参与负荷削减的节点限制在一定分级范围内,减小计算规模.IEEE-...     

Adaptive load shedding and regional protection

The requirement for improved efficiency whilst maintaining system security necessitates the development of improved system analysis approaches and the development of advanced emergency control technologies. Load shedding is a type of emergency control that is designed to ensure system stability by curtailing system load to match generation supply.This paper presents a new adaptive load shedding scheme that provides emergency protection against excess frequency decline, whilst minimizing the risk of line overloading. The proposed load shedding scheme uses the local frequency rate information to adapt the load shedding behaviour to suit the size and location of the experienced disturbance. The proposed scheme is tested in simulation on a 3-region, 10-generator sample system and shows good performance.     

Optimal corrective actions for power systems using multi-objective genetic algorithms

In this paper, optimal corrective control actions are presented to restore the secure operation of power system for different operating conditions. Genetic algorithm (GA) is one of the modern optimization techniques, which has been successfully applied in various areas in power systems. Most of the corrective control actions involve simultaneous optimization of several objective functions, which are competing and conflicting each other. The multi-objective genetic algorithm (MOGA) is used to optimize the corrective control actions. Three different procedures based on GA and MOGA are proposed to alleviate the violations of the overloaded lines and minimize the transmission line losses for different operation conditions. The first procedure is based on corrective switching of the transmission lines and generation re-dispatch. The second procedure is carried out to determine the optimal siting and sizing of distributed generation (DG). While, the third procedure is concerned into solving the generation-load imbalance problem using load shedding. Numerical simulations are carried out on two test systems in order to examine the validity of the proposed procedures.     

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.     

高渗透率光伏接入电网暂态电压失配风险及切负荷方法

高渗透率光伏接入电网后严重影响了故障后的电压恢复,使得传统以断面功率作为稳控门槛值的切负荷方法存在失配风险。针对此问题,提出了计及光伏接入效果的切负荷方法。该方法首先分析了光伏对外等效导纳动态变化特性,指出光伏恶化系统暂态电压稳定的机理。然后,根据故障后光伏汇集站吸收无功功率的变化,形成电压失稳主导因素判别方法。当失稳主导因素为光伏时,利用光伏等效导纳变化指导切负荷量。而当失稳主导因素为断面时,切负荷量表达为断面功率的近似线性关系。最后,在实际系统中进行仿真验证。结果表明,所提方法能够对不同失稳主导因素进行精准负荷控制,从而验证了该方法的有效性。     

Performance and suitability assessment of controlled islanding methods for online WAMPAC application

Controlled islanding can be used as an efficient action to prevent catastrophic blackouts. It splits a power system into a group of stable islands, according to an islanding solution that has been generated using an islanding method. A detailed understanding of these methods is a sound basis for the development of feasible controlled islanding methods for future networks. In this paper three methods (a) Ordered Binary Decision Diagram, (b) Weak Connection and (c) Spectral Clustering, are selected as typical islanding methods. The paper presents an analysis of their essential differences and their potential suitability for use as part of a practical implementation of controlled islanding. They are critically assessed and contrasted in terms of the objective function, graph model, solving algorithm and time complexity. The key difference between these methods is the nature of the objective function used: minimal power imbalance, minimal dynamic coupling or minimal power-flow disruption. A different objective function may require a different graph model and a different solution algorithm, which may result in the islanding methods having different time complexities and produce different islanding boundaries for the same network. Each method is applied to the IEEE 118-bus system to explore their strengths and weaknesses. Criteria for the selection of a suitable, practical method are discussed, as is the feasibility of Controlled Islanding as a WAMPAC application.     

A new optimal unified power flow controller placement and load shedding coordination approach using the Hybrid Imperialist Competitive Algorithm-Pattern Search method for voltage collapse prevention in power system

As power systems become more complex and heavily loaded, voltage collapse has become one of the most destructive events in modern power systems leading to blackouts in electric utilities worldwide. Voltage collapse is mainly caused by operating power systems at lower stability margins due to a surge in electric power demand. This paper presents an optimal unified power flow controller (UPFC) placement and load shedding coordination approach for voltage collapse prevention in N − K (K = 1, 2 and 3) contingency condition using Hybrid Imperialist Competitive Algorithm-Pattern Search (HICA-PS). ICA is the main optimizer of the proposed algorithm while pattern search is applied to further fine tune the results of the ICA. To show the effectiveness of the proposed approach in preventing voltage collapse in complex power systems, we implemented it on the New-England 39 bus power system. Its performance was also compared to that of some classical optimization techniques. Decrease in load shedding amounts, continuity of energy supply and voltage collapse prevention is the main positive features of the proposed approach.     

Emergency transmission line switching to suppress power system inter-area oscillation

Electromechanical oscillation is an inherent property of ac power systems which can occur in the forms of local and inter-area oscillations. The inter-area oscillations may impose a serious threat on the system if they are not controlled properly. Over the past two decades, many methods have been introduced to control and suppress electromechanical oscillations. This paper proposes a new supplementary emergency damping control (SEDC) to suppress inter-area oscillations. In the proposed approach, a system brittleness index (SBI) is introduced which can show system risk for splitting into uncontrolled islands. Following a sever fault, the value and sign of SBI is used as an indicator for activation of SEDC. By using sensitivity analysis of the inter-area mode with respect to line switching, the most effective transmission line switching (TLS) is utilized as an emergency damping control for suppressing inter-area oscillations. For this purpose, by offline studies, a priority list of the effective lines switching is prepared. Then, in the real time operational environment, by using an optimization algorithm, the most effective line switching is implemented as SEDC activation. The optimization algorithm guarantees system operation against any potential violation due to line switching. The proposed SEDC has been demonstrated on IEEE 39-buses system with promising results.     

Self-healing in power systems: an approach using islanding and rate of frequency decline-based load shedding

This paper provides a self-healing strategy to deal with catastrophic events when power system vulnerability analysis indicates that the system is approaching an extreme emergency state. In the authors' approach, the system is adaptively divided into smaller islands with consideration of quick restoration. Then, a load shedding scheme based on the rate of frequency decline is applied. The proposed scheme is tested on a 179-bus, 20-generator sample system and shows very good performance.     

电力系统低频减载分析软件包的开发和应用

低频减载是控制电力系统一般故障及大面积复杂故障重要而有效的手段。合理而快速地切除负荷或解列,可以使整个电网在最短的时间内恢复至稳定运行状态,切负荷的整定计算必须合理精确,以最小的切负荷量在最短的时间内使系统频率恢复正常。文中的切负荷软件包由系统数据库建立、数据转换和导入、频率计算和分析以及切负荷方案优化等模块组成,能根据系统的参数特性和运行要求给出最优方案,且具有友好的人机界面和便于维护更新的系统数据库,在上海电网的应用及仿真表明了上述优点。     

Hierarchical under frequency load shedding scheme for inter-connected power systems

Severe disturbances in a power network can cause the system frequency to exceed the safe operating range. As the last defensive line for system emergency control, under frequency load shedding (UFLS) is an important method for preventing a wide range of frequency excursions. This paper proposes a hierarchical UFLS scheme of “centralized real-time decision-making and decentralized real-time control” for inter-connected systems. The centralized decisionlayer of the scheme takes into account the importance of the load based on the equivalent transformation of kinetic energy (KE) and potential energy (PE) in the transient energy function (TEF), while the load PE is used to determine the load shedding amount (LSA) allocation in diferent loads after faults in real-time. At the same time, the infuence of inertia loss is considered in the calculation of unbalanced power, and the decentralized control center is used to implement the one-stage UFLS process to compensate for the unbalanced power. Simulations are carried out on the modifed New England 10-generator 39-bus system and 197-bus system in China to verify the performance of the proposed scheme. The results show that, compared with other LSA allocation indicators, the proposed allocation indicators can achieve better fnadir and td. At the same time, compared with other multi-stage UFLS schemes, the proposed scheme can obtain the maximum fnadir with a smaller LSA in scenarios with high renewable energy sources (RES) penetration.     

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.     

光伏发电系统并网点谐波电压波动特征孤岛检测法

光伏发电系统并网点处的谐波电压由系统扰动、本地负荷和光伏发电系统共同确定,基于波动量法提出一种以并网点谐波电压波动量为特征的光伏发电系统孤岛检测方法。测量公共联结点谐波电压,用小波变换法提取测量电压中包含的高次谐波分量,以高次谐波电压波动量变化规律作为孤岛识别和检测指标,无需外加扰动,可消除检测盲区。基于IEEE.Std 1547标准,对理想光伏发电并网系统进行的仿真证明,利用并网点测量电压中包含的谐波电压波动量进行孤岛检测,当测量点处的电压和频率在正常范围内时,不仅可快速、准确地检测孤岛,还能准确识别电网故障引起的电压暂降、投切负荷等干扰,避免伪孤岛引起的检测错误。     

Electrical load detection for SSPC regardless of power source switching status

The existing solid state power controller (SSPC) can output several statuses of loads and power sources, but the output statuses are not enough to detect load connection status, especially when the power source is switched off. In this paper, a detection circuit is designed in SSPC to judge the load connection status effectively, regardless of whether the power source is switch on or off. The circuit is constructed by three modules of which mechanism and logic state truth table are presented. Moreover, the delay characteristic of resistor–capacitor (RC) circuit is analyzed and formulated by a theoretical way. Experiment results show that the presented method can detect the load status accurately whether the electric power source system is powered on or off, which is more effective than existing SSPC. Additionally, it is verified that the theoretically calculated voltage in RC delay circuit is much closer to the actual measured voltage than the conventional approach.     

A dynamic model for coordination of generation and transmission expansion planning in power systems

This paper presents a new dynamic approach on the expansion planning problem in power systems. First, the coordination between generation system expansion and transmission system expansion has been formulated as a mixed integer nonlinear programming (MINLP) problem. Then, it has been shown that this MINLP model cannot be efficiently solved by the traditional MINLP solvers. Since the nonlinear term comes from the multiplication of a binary variable by a continuous one, a Benders decomposition approach has been employed to convert the MINLP formulation into a mixed integer linear programming (MILP) master problem, and a linear programming (LP) sub-problem. Besides, different times of construction have been considered for different transmission and generation facilities. In addition, a clustering based algorithm has been proposed to evaluate the reliability of the system at hierarchical level II (HLII). Since this dynamic planning method is an upgraded version of a recent developed static model, the result from both methods have been also compared. A simple 6-bus test system and IEEE 30-bus system have been selected to confirm the effectiveness of the introduced method.