New stability method applied to the stabilization of fuzzy control systems

This paper addresses stability analysis and stabilization for Takagi-Sugeno fuzzy systems via a new stability method previously developed and presented by the authors. The new stability method is here extended to fuzzy systems. In essence, the authors consider the stabilization of a fuzzy control system with parallel distributed compensation. This problem has been considered in detail previously by different authors using fuzzy Lyapunov function theory. However, in this paper the authors show that their new stability method presents a viable alternative to Lyapunov?s method for such control systems. This statement is confirmed by a demonstration that the new stability method always provides necessary and sufficient conditions, the satisfaction of which guarantees that the system in question will be asymptotically stable.     

Multifault calculation method for dynamic stability study of electric power systems

For the fault condition in dynamic stability study, balanced faults have mainly been utilized. Recently, however, with the progress of system protective control technologies such as the multiphase reclosing system for a faulted transmission line, the needs for stability software which would be able to calculate simultaneous faults without any restrictions on fault types, total numbers or location, have been increasing. This report presents the newly developed multifault calculation method based on symmetrical components which is able to calculate simultaneous faults without any restrictions on combination of fault types, and total numbers or location. Fault types consist of balanced/ unbalanced ground fault, short-circuit fault, line-out of transmission lines, and short-circuit of series condenser. The proposed method also allows for calculation of faults at an arbitrary location on the line without any topological changes of each symmetrical network even if the faults include line-end faults with ensuring outages. An example was shown to clarify the validity of the proposed method. Moreover, transient stability limits under the various fault conditions also were discussed.     

提高电力系统大扰动稳定性的最优分岔控制策略

仿真研究了大扰动参数稳定域ΩLDSR和小扰动参数稳定域ΩSSSR的关系,提出了几个合理的假设,据此假设提出了通过收缩相应故障后小扰动参数稳定域ΩSSSR来近似等效大扰动参数稳定域ΩLDSR的方法。结合上述收缩ΩSSSR的方法,提出了基于最优分岔控制策略的电力系统大扰动稳定控制方案。对WSCC 3机9节点系统采用最优Hopf分岔控制策略,通过3个控制步实现了对发电机励磁增益的优化控制,保证了系统大扰动稳定性;对New England 39节点系统采用最优鞍结分岔控制策略,以发电机励磁参考电压为优化变量进行大扰动稳定控制,结果表明,该控制策略可以有效解决此问题。     

提高电力系统小扰动稳定性的最优分岔控制策略

结合小扰动参数稳定域的概念,建议把小扰动稳定控制描述为"保证系统不可控分岔参数μ≥μref,在系统小扰动参数稳定域内寻找最优的可控参数组合以保证系统的控制代价最小"这一最优分岔控制问题;建立了最优鞍结分岔控制和最优Hopf分岔控制的数学模型,考虑了各种不等式约束,从数学上严格保证了电力系统安全性和经济性的最优控制。在New England 39节点系统中研究了一个小扰动最优鞍结分岔控制算例,实现了以励磁参考电压为控制变量的最优分岔控制策略;提出了初值预测和控制变量选择方案,实现了大系统中的最优Hopf分岔控制策略。优化控制结果表明,所提出的控制策略可以有效解决小扰动稳定控制问题。     

Sensitivity analysis by neural networks applied to power systems transient stability

This work presents a procedure for transient stability analysis and preventive control of electric power systems, which is formulated by a multilayer feedforward neural network. The neural network training is realized by using the back-propagation algorithm with fuzzy controller and adaptation of the inclination and translation parameters of the nonlinear function. These procedures provide a faster convergence and more precise results, if compared to the traditional back-propagation algorithm. The adaptation of the training rate is effectuated by using the information of the global error and global error variation. After finishing the training, the neural network is capable of estimating the security margin and the sensitivity analysis. Considering this information, it is possible to develop a method for the realization of the security correction (preventive control) for levels considered appropriate to the system, based on generation reallocation and load shedding. An application for a multimachine power system is presented to illustrate the proposed methodology.     

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.     

一种改善磁光式电流互感器性能的新方法

为改善磁光式电流互感器的性能,将原有磁光式电流互感器的信号处理功能单元进行了虚拟化改造。实验结果表明,虚拟仪器技术的引入,不仅可提高磁光式电流互感器信号处理单元的工作可靠性,且还能使磁光式电流互感器对电流的测量更为简便、更为精确。     

A coherency-based method to increase dynamic security in power systems

Dynamic security analysis is the evaluation of the ability of a system to withstand contingencies by surviving transient conditions to acceptable steady-state operative states. When potential instability due to contingency is detected, preventive action may be desired to improve the system security. This is very important in the on-line operation of a power system, especially when the system is stability-limited. The method proposed in this paper is based on the idea that increasing coherency between generators in the transient behaviour following a system perturbation gives rise to a more stable system. In this paper, we suggest the use of the “input–output feedback-linearization” with a reference trajectory obtained using a system dynamic equivalent based on the centre of inertia. To quantify coherency levels a new coherency indicator has been assumed for the given reference trajectory. The result is an increasing level in coherency, critical clearing time and system stability. The method is tested on the IEEE 30 bus test system.     

A generation rescheduling method to increase the dynamic securityof power systems

In this paper, a new method is proposed for dynamic security dispatch. The idea of coherent behavior of generators is used to find a new generation configuration with better transient stability behavior. Rescheduling the generation in the power system improves system security by increasing the critical clearing time or the transient energy margin without changing total generation. The calculation in the proposed method is simple and direct; the generation rescheduling depends only on the original generation and inertia constants of the machines, and their rotor speeds at the fault clearing time. In this work, the transient energy function (TEF) method is used to check the dynamic security of the system by analyzing all credible three phase faults with single line outages. If the worst energy margin is not acceptable, the proposed rescheduling is done, and the security is checked again. The method has been tested on the Ontario Hydro 55-bus 11-generator system, the IEEE 145-bus 50-generator system and the IEEE 162-bus 17-generator system. Results on several loading levels of the 162-bus 17-generator system are also shown     

电力系统小扰动稳定的直接法分析

对李亚普诺夫直接法用于分析和评价电力系统小扰动稳定性进行研究.介绍了线性定常系统稳定性的直接法判据,剖析了求解李亚普诺夫方程的算法,引入状态偏差量平方积分指标对系统动态性能进行评价.以4个算例系统的低频振荡为对象,具体研究直接法在电力系统小扰动稳定分析中的应用.研究结果表明:直接法可以正确可靠地判断电力系统的小扰动稳定...     

发电机组对电网稳定的适应能力分析

从电源点与电网相互稳定关系出发 ,分析了电网故障时发电机组的自适应能力、发电机组内部故障时的快速恢复供电能力及机组对电网的要求 ,指出各电源点要积极完善适应电网稳定要求的功能 ,同时对提高机组和电网的稳定性提出一些建议     

激波风洞瞬时动导数试验方法研究

为了克服高超声速激波风洞工作时间短,发展并建立了瞬时动导数实验技术。该技术在传统自由振动风洞试验装置基础上,使用新研制了高频动态天平,通过风洞启动时的随机扰动获取模型/天平系统的高频响应数据,最后经瞬时功率谱数据分析方法辨识出动稳定导数。不仅阐述了瞬时动导数实验原理与瞬时功率谱数据分析方法,而且介绍了高频动态天平及其实验装置结构。M=8.0、10°尖锥模型激波风洞试验结果表明,与自由振动方法相比,试验装置结构简单,易于实现,具有较高的精准度,有能力解决在高超声速激波风洞动稳定实验问题。     

Multi-agent systems applied to reliability assessment of power systems

This paper discusses the development of a Multi-Agent Systems (MAS) technology-based platform with potential applications in management and simulation processes in power systems. In order to explore some of the features of MAS, a new methodology is proposed to assess power systems reliability based on Monte Carlo simulation (MCS), exploiting the benefits of the distributed artificial intelligence area and, mainly, the use of the distributed capacity in two ways: building autonomous behaviors to the applications and mitigating computational effort. Through the use of this technology, it was possible to divide the MCS algorithm into distinct tasks and submit them to the agents’ processing. Two different approaches to solve generating capacity reliability problems based on chronological MCS illustrate the potential of MAS in power systems reliability assessment.     

A high‐speed reclosing method to improve the stability in a power system

This paper proposes a high‐speed reclosing operating method to improve the stability in a power system. The proposed method calculates the reclosing time, taking a standard case in which the reclosing is not done using the generator phase angle δ, and the angular velocity ω, and the field system voltage ed′. Also, the execution of reclosing time is calculated, while taking into consideration the acceleration/deceleration energy of the generator during a fault. It can be expected that δ is suppressed by this optimum reclosing operation. Therefore, the system stability can be expected to improve by carrying out high‐speed reclosing when a fault occurs. At present, it has been set at a value which seems to be optimal considering various problems in the reclosing time. However, in those methods, the system stability improvement effect cannot be expected. It was demonstrated that the high‐speed reclosing method serves to depress δ in the computer simulation. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 13–21, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10317     

链式电网动态稳定下多断面耦合特性研究

子系统网架结构及内部潮流对互联系统动态稳定性能有一定影响。针对多断面间呈链式结构的电网,为研究不同断面对系统稳定的影响差异性及断面间耦合特性,提出了动态稳定下链式电网断面相对敏感度与耦合度的计算方法。根据断面潮流与两侧角度差的关系,分析了断面潮流调整下互联系统送受端相对角度与扰动下振荡阻尼比的变化规律。对断面间耦合机理的研究表明,断面敏感度与其等值联系电抗、两侧角度差及送端机群惯量等因素有关。三机系统及实际链式电网算例的分析结果验证了方法的有效性与可行性,能够为实际电网动态稳定运行中断面潮流间的协调控制提供可靠依据。