Improvement of large-scale power systems decomposition-aggregation approach

An N-machine power system with uniform damping and with transfer conductances is decomposed in this work into (N−1)/2 interconnected subsystems, instead of the usual decomposition into (N−1) subsystems. Each subsystem consists of three machines, one of which is the comparison machine, and is described as a fourth-order multi-nonlinear Lurie-Postnikov system. Six nonlinearities are assumed to be contained in each free (disconnected) subsystem. A vector Lyapunov function is used for aggregating the system, and an aggregation matrix of order (N − 1)/2 is obtained. Two power systems (with five and seven machines) are used as examples. An estimate of the asymptotic stability domain is determined for the seven-machine system. It is shown that the decomposition scheme presented can lead to a considerable reduction of the conservativeness of the decomposition-aggregation method.     

Semi-implicit Runge—Kutta methods for power system transient stability studies

Some semi-implicit numerical integration algorithms for solving a set of differential equations are developed and applied for power system transient stability studies. These methods possess the desirable properties of explicit methods (no iteration) as well as those of implicit methods (numerically A-stable). Much larger time steps can be used without encountering any numerical instability problems, even for systems characterized by stiff differential equations. The algorithms have been tested on a number of sample systems.     

Multimachine stability analysis using vector Lyapunov functions with inertial-centre decomposition

Multimachine power system stability is investigated by means of a new decomposition technique. The power system is decomposed into subsystems using the inertial-centre concept. Individual Lyapunov functions are then obtained for each subsystem. Stability conditions for the overall system are established, taking into account the interconnection characteristics. The least restrictive overall system Lyapunov function is obtained by weighting each subsystem instability is then used to determine the critical clearing time.     

Probabilistic determination of the margin of transient stability

The sensitivity values of the critical clearing angle and the operating angle of a generator connected to an infinite bus through a double-circuit transmission line, with respect to the system parameters and operating variables are evaluated. The limiting values of the parameters and variables within which the system can remain stable are identified. The sensitivities of the margin of transient stability with respect to the various parameters and variables are also determined. Finally a probabilistic evaluation of the transient stability margin has been carried out from the deterministic sensitivity values of the transient stability margin. The results show that probabilistic evaluation of the transient stability margin should be carried out because deterministic studies give conservative results.     

基于李雅普诺夫函数的带锁相环的VSC大扰动稳定性判据

对于带锁相环的并网VSC大扰动稳定性问题,首先依据VSC的内环电流控制和外环功率控制响应速度差异得到简化二阶非线性模型,然后分别定义了两个李雅普诺夫函数。第一个李雅普诺夫函数具有清晰的动能和势能概念,但推导的稳定域较小,第二个李雅普诺夫函数推导的稳定域较大但缺乏清晰的物理概念。最后结合这两个李雅普诺夫函数,得到实用的稳定性判据,兼具明确的物理意义和较宽的稳定域。如果在系统最后一次动作时已知锁相环状态量,则可以预测系统稳定性。仿真结果验证了该判据的正确性。     

Dynamic equivalents for transient stability studies of electrical power systems

Along with the growth in size of electrical power systems, attention is increasingly being given to various reduction techniques of dynamic system models for transient stability studies. One of these is the topological reduction that includes coherency-based aggregation. A theorem from the nonlinear vibrations theory is applied to derive analytical coherency-criteria for a classical model of the system. A simplified algorithm of coherency recognition is given and results for a sample system are shown. Important properties of topological equivalents are proved and a relationship to modal reduction is pointed out.     

Virtual synchronous generator model control of PV for improving transient stability and damping in a large‐scale power system

Because of the significant changes in environmental policies and electric power deregulation in the last decade, a lot of photovoltaic generations (PV) have been and will be installed into the power system in Japan and the ratio of PVs to other synchronous generators will be increased. As a countermeasure against the decrease in the rotational inertia in the whole power system, a virtual synchronous generator (VSG) model control of the PV has so far been proposed. However, the system stabilization effect of the VSG in large‐scale power systems has been unclear. In this paper, a virtual step‐out blocking method of VSG for improving the transient stability is proposed. In addition, the necessity of governor control of VSG in a large‐scale power system is discussed. Finally, the rated kw and kwh capacities of the battery required for realizing the VSG‐model control are evaluated.     

虚拟同步机孤岛并联系统暂态同步稳定性分析

针对虚拟同步机孤岛并联系统暂态失稳机理不明且传统等面积法则定量计算保守性强的问题,提出了一种考虑阻尼缩放的改进等面积法则。该方法运用等面积法则,将阻尼项抵消的不平衡功率缩放为对功角可积项,可定量计算虚拟同步机控制参数对并联供电系统极限切除角和极限切除时间的影响。研究结果表明,虚拟同步机的虚拟阻尼对暂态稳定性影响较大。虚拟阻尼与极限切除角和极限切除时间呈正相关;虚拟惯量与极限切除角呈负相关,与极限切除时间呈正相关,在系统容量充足的情况下应优先考虑提升虚拟阻尼。另外,初步探索了计及虚拟同步发电机过流保护的多机并联系统暂态同步稳定性研究思路,并分析了所提方法在多机系统中的适用性。最后,基于PSCAD/EMTDC仿真平台验证了理论分析和所提方法的正确性。     

Transient analysis of load switches of self‐excited induction generators based on Lyapunov stability theory

Load connection and disconnection are important factors for a comprehensive investigation on the performance of induction generators, providing theoretical foundation and technical support for the optimization of system configurations and safeguard measures. Based on the transient equivalent circuits of self‐excited induction generators under the two‐phase stationary reference frame, steady‐state motion equations are derived through the steady‐state operation analysis. The analytical computation of the motion equations successively gives the necessary condition for the loaded operation, the sufficient condition for the transient operation under a given speed, and the necessary and sufficient condition for the buildup arrival to steady states. Using the holistic analysis approach based on Lyapunov stability theory, this study presents a theoretical analysis approach for transient processes and analytically solves the load ranges under the specified performance indices. Good agreement between experimental and theoretical results verifies the correctness and validity of the theoretical analysis approach and its analytical conditions with better practicability and referenced values in engineering. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Coherency identification by the method of weak coupling

A computationally efficient method for identifying groups of slowly coherent machines in an interconnected power system is presented. The method is based on the concept of weak coupling and uses a linearized representation of the total system. An algorithm is developed that rearranges the synchronous machines of the power system in order of their relative coupling. The machines are grouped into slowly coherent areas corresponding to the point of least coupling using a ‘coupling graph’. The method is illustrated by a case study on an 18-machine system. The results are validated by comparison with swing curves obtained from a transient stability simulation of the total system. It is shown that the proposed method identifies coherent groups that are independent of fault location.     

Improvements of numerical stability of electromagnetic transient simulation by use of phase‐domain synchronous machine models

The present paper proposes the use of a phase‐domain (abc frame) generator model in electromagnetic transient analysis instead of the conventional dq0‐domain generator model in order to improve numerical stability. The drawback of the conventional dq0‐domain machine model is that the prediction of a number of electrical variables as well as machine speed is needed in order to interface the circuit of a machine model with the rest of the power system network, and the prediction of these variables leads to numerical instability. In contrast, prediction of electrical variables is not needed in the proposed phase‐domain model. In this paper, the phase‐domain machine model is developed. The proposed model is validated by comparisons with an existing EMTP type‐59 machine model. The paper makes it clear that numerically stable solutions are obtained by using the proposed model even in cases where numerical instabilities occur when the existing type‐59 model is used. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 53–62, 1999     

辛几何算法在电力系统暂态稳定性分析中的应用

将辛几何算法引入电力系统暂态稳定性数值计算.以一个简单的电力系统为例,通过数值实验将新方法与电力系统分析中常用的隐式梯形积分法及传统的Runge-Kutta方法进行了对比分析.初步的数值实验结果表明,辛几何算法与传统算法相比,在计算精度和数值稳定性方面具有较为明显的优势,因而更适合于电力系统暂态稳定性及相似问题的数值计算.     

基于PEBS法的交直流输电系统暂态稳定分析

计及直流系统的动态构建了交直流输电系统的暂态能量函数,直流换流站交流母线电压和发电机转速功角一样作为显式变量出现在暂态能量函数中,暂态能量函数的变量从平衡点到势能边界面出口点的积分路径不作线性假设.视为慢动态的发电机转速和功角,沿着持续故障轨迹或受扰轨迹积分,而视为快动态的直流系统变量的积分路径通过修正后得到,并讨论了应用势能边界面法求取临界能量和临界切除时间的问题.分别利用所提方法和逐步积分的时域仿真法求取了4机和10机交直流输电系统的临界切除时间,通过比较验证了所提方法的有效性.     

考虑暂态稳定约束的串联电抗器优化配置

基于暂态能量函数法,提出考虑暂态稳定约束的串联电抗器优化配置新算法.该算法利用基于稳定域边界的主导不稳定平衡点法(BCU法)计算系统暂态稳定裕度,并将暂态稳定裕度作为约束条件加入到优化配置模型中,从而将串联电抗器配置问题转化为非线性规划问题,使得在求解的过程中能够充分考虑串联电抗器对系统稳定性的影响.同时根据串联电抗器...     

正规形理论在电力系统稳定性研究中的应用(三)--电力系统运动方程泰勒展开的特点及矩阵表示

应用正规形理论求电力系统在主导不稳定平衡点处的局部稳定和不稳定流形，首先要将电力系统的运动方程的泰勒展开用矩阵表示。研究了电力系统运动方程泰勒展开式的特点，正是这些特点使得电力系统运动方程的泰勒展开式得以用矩阵表示，具体推导了四阶泰勒展开式中各矩阵元素的表达式。     

正规形理论在电力系统稳定性研究中的应用(四)--复杂电力系统的稳定边界研究

正规形理论应用于电力系统的暂态稳定性分析中，可以依据所采用的非线性变换的阶数对电力系统故障后的主导不稳定平衡点上的稳定流形作几阶近似，从而得到某阶近似的电力系统稳定边界的解析式。更进一步地，可以得到系统的极限切除时间。以新英格兰系统为例，推导了四阶近似的局部稳定边界的解析表达，计算了几种故障情况下的极限切除时间，与逐步积分法的比较结果表明采用四阶近似的稳定边界是较精确的。     

Global exponential stability of a class of impulsive cellular neural networks with supremums

In this paper, we study the problem of global exponential stability for impulsive cellular neural networks with time‐varying delays and supremums. Using Young's inequality and Lyapunov‐like functions, new stability criteria are proved. Because supremums and impulses are relevant in various contexts, including problems in the theory of automatic control, our results can be applied in the qualitative investigations of many practical problems of diverse interest. Copyright © 2013 John Wiley & Sons, Ltd.     

含非同步机电源交流电网暂态稳定性的电磁暂态仿真研究

随着非化石能源占一次能源比重和电能占终端能源比重的大幅度提升,大量非同步机电源通过电力电子换流器并网,导致同步机电源在电网中的主导地位被打破,使原本复杂的电力系统稳定性问题变得更加复杂。针对包含非同步机电源的交流电网的暂态稳定性问题,基于电磁暂态仿真软件PSCAD/EMTDC,在2区域4机系统中,通过逐步等容量替换同步机电源,仿真研究分析了交流系统临界清除时间随非同步机电源比例、非同步机电源同步机制、非同步机电源并网位置、故障类型和故障位置5个影响因素的变化趋势。仿真结果表明,随着系统中非同步机电源占比的增加,系统的暂态稳定性逐渐增强。当系统中非同步机电源占比相同时,非同步机电源分散并网可以同时增强所在区域的暂态稳定性;在非同步机电源占主导的交流电网遭受故障时,暂态响应快,故障恢复时间短,不会表现出同步机电源的功角特性。     

Small‐signal stability based on a synchronous generator model with field mutual‐leakage reactance

Power system small‐signal stability studies have been carried out using a synchronous machine model with a field mutual‐leakage reactance called the Canay reactance in the d‐axis equivalent circuit. The influence of the Canay reactance on the effectiveness of a power system stabilizer (PSS) was evaluated by the eigenvalue calculation method. The values of the Canay reactance reported in the literature were also investigated statistically, and an approximate expression applicable to power system stability studies was proposed. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(2): 19–29, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20163