A practical method for simplifying the dynamic stability analysis of interconnected power systems

In this paper a practical method for simplifying the analysis of large interconnected power systems is described. The approach is based upon a decomposition scheme which directly exploits the system structure. By analysing and quantifying the strength of connection among generating units, a large power system is decomposed into weakly connected subsystems, each consisting of a group of tightly coupled machines, a common situation in practice. Then the overall system stability is established from the analysis of each decoupled individual subsystem.The method, which can be carried out systematically, saves a considerable amount of storage space and computation time and provides sufficiently accurate results. The procedure is illustrated using a five-machine fifteen-bus system.     

交直流互联电网动态等值的实用化方法

针对同调等值法等值过程中各个环节存在的若干问题,提出了相应的实用化解决方法:通过母线电压波动曲线的相关性分析,基于母线电压同调辨识出外网保留节点;针对网络化简过程中出现的不符合物理规律的参数,采用人工删除高阻抗支路并适当微调附近节点上的负荷参数,或将负电阻参数调整为0使负电阻提供的有功功率分配到线路两端节点上,并调整两端节点有功负荷进行修正,从而提高动态等值精度。针对等值后动态响应效果,提出了分时段量化评估方法。以南方电网为实例,分析验证了所提方法的有效性。     

Security for space power systems

An initial system security monitor (SSM) developed for the power system of a proposed NASA permanently manned space station is presented. Four types of ranked disturbances or faults to the transmission system are successively corrected by remedial action of the SSM. After each corrective action, the SSM verifies the system change that has been implemented, then proceeds to examine lower-priority disturbances if they persist. The SSM authority is limited by the operating state of the system, and only one correction is permitted for each scan cycle. The disturbance signals are verified by the use of a state estimator. The small network size permits use of connectivity searches of the network topology for possible corrective actions and a load flow to predict the effect of corrective actions. The data scan rate is higher than for earth-based systems. Line switching actions are implemented within line cycles because thyristors are used as circuit breakers. The work presents examples of disturbance identification and remedial action that could also apply to earth-based power systems     

Security for space power systems

An initial system security monitor (SSM) developed for the power system of a proposed US National Aeronautics and Space Administration (NASA) permanently manned space station is presented. Four types of ranked disturbances or faults to the transmission system are successively corrected by remedial action of the SSM. After each corrective action, the SSM verifies that the system change has been implemented, and then proceeds to examine lower-priority disturbances if they persist. The SSM authority is limited by the operating state of the system, and only one correction is permitted for each scan cycle. The disturbance signals are verified by the use of a state estimator. The small network size permits use of connectivity searches of the network topology for possible corrective actions and a load flow to predict the effect of corrective actions. The data scan rate is higher than that of earth-based systems. Line switching actions are implemented within line cycles because thyristors are used as circuit breakers. Examples of disturbance identification and remedial action that could apply to earth-based power systems are presented     

Damping representation for power system stability studies

The paper includes a review and summary of the actual damping in electric power systems and the methods for modeling such damping in the various computer programs used to study power system stability. It is concluded that great care is required in both software development and program application to avoid serious errors in the study of power system stability. Judgment is often required for reasonable modeling of damping. Recommendations are provided to guide the power system stability practitioner, and research activities are recommended     

Digital controller design for enhancing steady-state stability of interconnected power systems

This paper presents a microprocessor based digital controller design for static phase-shifters used with other stability enhancement tools to damp inter-area electromechanical modes of oscillations and stabilize AC interties. The digital controller's robustness under different contingency conditions such as system parameter changes, disturbances, control loop and sensor failures are assessed.     

Stabilizing interconnected power systems using static phase shifters

This paper presents a digital simulation study of proposed thyristor controlled static phase shifter applications in steady state stability enhancement of interconnected power systems. Incorporation of a detailed linearized model of a static phase shifter into the dynamics of the interconnected power system facilitates the investigation of different control strategies for static phase shifters to damp the electromechanical and torsional oscillations.     

Stability analysis of interconnected power systems coupled withmarket dynamics

The use of market mechanisms to determine generation dispatch, and the natural tendency to seek improved economic efficiency through rapid market updates, raises a critical issue. As the frequency of market-based dispatch updates increases, there will inevitably be interaction between the dynamics of markets determining the generator dispatch commands, and the physical response of generators and network interconnections. This paper examines questions of stability in such coupled systems by means of numeric tests using various market update models, (including detailed generator/turbine/governor dynamics) for the New England 39 bus test system. The results highlight the nature of potential instabilities and show the interaction modes between physical and market quantities through eigen-analysis. Understanding of potential modes of instability in such coupled systems is crucial both for designing suitable rules for power markets, and for designing physical generator controls that are compatible with market-based dispatch     

基于强化学习的互联电网CPS自校正控制

AGC是一个动态多级决策问题--马尔可夫决策过程(MDP),应用强化学习算法可有效地实现控制策略的在线学习和动态优化决策.引入Q学习算法作为强化学习核心算法,将CPS值看作包含AGC的电力系统"环境"所给的"奖励",依靠奖励值Q函数与CPS控制动作形成的闭环控制结构实现在线学习.学习目标是使CPS控制动作从环境获得的长期积累奖励值最大,从而快速自动地在线优化CPS控制系统的输出.仿真研究显示,引入强化学习自校正控制后显著增强了整个AGC系统的鲁棒性和适应性,有效提高了CPS考核合格率.     

互联电网动态稳定安控策略优化方法

电网输送断面部分线路断开后,可能引发互联电网的低频振荡问题。紧急降低送端发电机组出力是抑制振荡的有效措施,不同机组控制的效果存在一定差异。发电机的控制系统阻尼及其接入点与受端网络之间的电气距离是影响切机效果的两个重要因素,分别用阻尼贡献和节点电压的相角差对其进行量化,加权后进行切机优先度排序。其中,阻尼贡献指标将电磁力矩中的同步力矩和阻尼力矩解耦,对阻尼力矩的作用进行了分段累加。利用华北电网实际系统进行仿真验证,将所提方法的计算结果与现有安控策略进行对比,证明了所提方法能够优化控制效果,减少控制代价,有一定的实用价值。     

电力市场下的互联系统自动发电控制改进模式

自动发电控制（AGC）作为能量管理系统（EMS）中最重要的控制功能之一,能有效地提高电网互联系统频率质量,提高经济效益和管理水平。但随着我国电力系统市场化体制改革的不断深入和完善,互联系统原先以联络线和频率偏差控制（TBC）模式为主的频率控制方式就成了电力市场环境下互联系统区域间交易的壁垒。为了适应现代电力市场环境的要求,提出一种新的以TBC为基础、满足二次辅助服务市场开放要求的区域间AGC改进模式。     

Decomposition-coordination strategy to improve power transfer capability of interconnected systems

The maximum power transfer across critical corridors or interfaces is limited by various system constraints such as thermal, voltage, and stability limits. In an open transmission access environment, these constraints would be deeply influenced by the interactions among the path flows in different control areas. In particular, small signal stability, commonly in the form of low frequency oscillations, is considered a crucial factor since it limits the power transfer capability of transmission paths in interconnected multi-area systems. Based on such considerations, the focal point of this paper will be a new approach to coordinating the path transfers across multiple control areas, giving exclusive attention to the small signal stability. The differential eigenvalue method is used to derive the damping ratio constraints for satisfying the small signal stability criteria which are linear inequality constraints expressed in terms of the control parameter. Using Bender’s decomposition, the proposed methodology is formulated as a master problem and a set of sub-problems, each associated with one area motivated by the improvement of the overall computational efficiency via parallel processing. The performance of the decomposition-coordination method is illustrated with a 68-bus system from which it might be deduced that inter-area transfer margin could be improved by reasonable rescheduling of the neighboring tie-line flows.     

Delay-independent decentralized stabilizer design for large interconnected power systems based on WAMS

Recent stabilizer design using wide-area measurement systems (WAMS) signals has been suggested to enhance the dynamic performance of large interconnected power systems. However, there is an unavoidable delay involved before these signals are received at the stabilizer site. Long time-delay may be detrimental to system stability and may degrade system performance. Therefore, the delay-independent robust control problem of large interconnected power systems based on WAMS is studied via H_∞ fuzzy control method. First, a set of equivalent Takagi–Sugeno (T–S) fuzzy model is employed to represent the large interconnected power systems. A wide-area state feedback decentralized control scheme is developed to stabilize the T–S fuzzy systems without any wide-area signals delay information such that the H_∞ performance is achieved. The H_∞ fuzzy robust control design problem is parameterized in terms of a linear matrix inequality (LMI) problem, and the LMI problem can be solved very efficiently using the convex optimization techniques. Finally, the performance of the robust control is studied using a fourteen-machine interconnected power system example.     

A decentralized solution to the DC-OPF of interconnected power systems

This paper presents a new method for the decentralized solution of the DC optimal power flow (OPF) problem in large interconnected power systems. The method decomposes the overall OPF problem of a multiarea system into independent OPF subproblems, one for each area. The solutions of the OPF subproblems of the different areas are coordinated through a pricing mechanism until they converge to the global OPF solution. The prices used for the coordination of the subproblem solutions are the prices of electricity exchanges between adjacent areas. Test results from the application of the method to the three-area RTS-96 and the Balkan power system are reported.     

基于最优动态闭环控制的水火电互联大电网自动发电控制策略

研究了含有水电和再热式火电机组的大电网自动发电控制问题。建立了两区域互联的大电网自动发电控制状态空间数学模型。引入新的动态性能指标,基于最优化控制理论,提出了最优动态闭环自动发电控制策略。与全状态反馈控制相比较,该方法既降低了互联系统内部的耦合性,又能及时了解系统内部的关键状态,具有更好的实用性和可操作性;与传统的PI控制策略相比,提出的方法从全动态的角度出发,对复杂的互联大电网具有更好的动态适应性。仿真分析验证了理论分析的正确性。     

A new optimal approach for coordination of overcurrent relays in interconnected power systems

In this paper, a new method for optimum coordination of overcurrent relays is proposed. The proposed method is based on only constraints. Minimization is inherently included by setting the time dials to minimum and increasing their values gradually. Configuration changes of the network are taken into account. The method does not need any initial solution. It can consider both linear and nonlinear relay characteristics models. The optimal settings of overcurrent relays for 8-Bus and England Norweb networks are obtained and comparison between the new method and existing methods is made.     

Optimal variable structure controller for the load-frequency control of interconnected hydrothermal power systems

A new approach is presented for the load-frequency control of interconnected power systems using the theory of variable-structure systems and linear optimal control theory. A systematic procedure for the selection of the switching hyperplane, which is of vital importance in the design of variable-structure controllers, is developed by minimizing a performance index in the sliding mode operation. The proposed control scheme is illustrated by digital simulation of an interconnected power system consisting of a hydro power plant and a steam power plant.