An improved fast decoupled power flow model considering static power–frequency characteristic of power systems with large‐scale wind power

Large‐scale wind power (LSWP) integration may cause significant impact on power system frequency, so it is necessary to take frequency regulation issues into account in power system steady‐state operation analysis. An improved fast decoupled power flow model considering static power–frequency characteristic of power systems with LSWP is proposed in this paper. In this scheme, the active power of generators and loads are presented with their static power–frequency characteristics. The slack bus degenerates to the nodal voltage phase angle reference bus of the system, and all the generators with frequency regulation capability participate in unbalanced power regulation. The power flow calculation results can reveal the impact to the system frequency of operation mode change and load variation, and present the output adjustment of the generators. The proposed model can be solved conveniently by the block solving technology based on the fast decoupled power flow algorithm. The scheme presented in this paper has been tested on the IEEE standard 30‐bus test system by simulating basic operation and primary and secondary frequency regulation of the generators, which demonstrated the validity by the method. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Studies of load flow methods in polar and rectangular coordinates

This paper presents a study on the performance of load flow methods (in polar and rectangular coordinates) with regard to computation speed, convergence reliability and memory requirements. The load flow techniques in polar coordinates that are studied are the Newton-Raphson and the fast decoupled load flow methods; in rectangular coordinates, the load flow methods considered are the second-order load flow and a decoupled load flow. A modification of the standard fast decoupled load flow for systems with high R/X ratio is also presented and compared. Numerical results were obtained on a 16 MHz, 80386-87 personal computer. Simulations were performed on the IEEE 24-bus reliability test system and the IEEE 118-bus test system. These systems were simulated with several different R/X ratios and under various load conditions.     

Real-Time Decoupled Equivalent Models for Static Security Analysis

This paper presents some new decoupled external system equivalent models for use in system security evaluation. Three different models i.e., decoupled Tie-line power flow model, decoupled Boundary bus Impedance model and decoupled Impedance-Admittance model are developed based on P-? and Q-V relations of fast decoupled load-flow formulation. The structure component of the models are then identified by processing real time data using Kalman filtering technique. Then the operating components of the decoupled equivalents are obtained from two new approaches. The performance of the various models with regard to contingency analysis has been presented using simulated data on a 25 bus test system. Persistency analysis of different input-output data is given to determine apriori choice of models. Also the bias conditions are derived to ascertain the accuracy of the models.     

基于坐标旋转变换的配电系统快速解耦潮流计算方法

配电系统中各支路的电阻与其电抗的比值较大,因此,经典的快速解耦潮流计算方法不适用于配电系统潮流计算。提出了一种坐标旋转变换方法,并将这种变换方法与经典的隐式Zbus高斯方法相结合,导出了配电系统的解耦潮流计算方法。以IEEE 33节点、IEEE 69节点和一个实际的145节点配电系统为例,对提出的解耦潮流算法进行了测试。结果表明,所提出的解耦方法不影响经典的隐式Zbus高斯方法的收敛性,因而是一种高效、实用的快速潮流计算方法。     

电力系统预想事故快速分析

鉴于自适应化简等值算法的有效性，本文提出了一个电力系统预想事故快速分析的新算法，该逄法首先构成了包括断开支路在内的局部等值小网，然后利用快速前代和快速回代技术对等值小网进行ＡＣ潮流求解，通过对ＩＥＥＥ－５７节点试验系统和华东１５８节点系统的验算，证明该算法不但有令人满意的精度，而且有较理想的机时节约。     

Improvements in sparse matrix/vector technique applications foronline load flow calculation

Several analytical and computational improvements in sparsity applications are discussed. A novel partial matrix refactorization method and ordering algorithm are presented. The method is very efficient when applied to programs such as online load flow, optimal power flow, and steady-state security analysis. It is applied in a fast decoupled load flow program which includes the treatment of tap violations on underload tap changing transformers and reactive power generation on PV buses. The effects of proposed improvements are tested and documented on a 118-bus IEEE test network and two utility networks with 209 and 519 buses, respectively     

一种新的含UPFC的电力系统潮流算法

提出了一种新的UPFC功率注入模型。基于该模型,推导了含UPFC的电网潮流方程,提出了一种新的算法来求解含UPFC的电网潮流问题。该算法基于快速解偶法(FDLF),包含了两个交替迭代过程,继承了快速解偶法的基本特性,雅可比矩阵在迭代过程中保持对称、定常。此外,采用该潮流计算模型可以直接方便地得到UPFC控制变量的较佳初始条件,有利于算法的收敛。通过实例的计算和比较,最后验证了算法的可靠、快速和准确。     

An operations-oriented formulation and solution to the load flow problem

This paper presents an operations-oriented formulation and solution to the load flow problem. In this approach all the unit real power outputs are assumed specified and the objective is to calculate the bus loads. This fundamental change is useful in some power system problems and is also closer to the actual problem facing a load flow user.Different solution approaches, including a decoupled method, are proposed to solve the above problem. The numerical and analytical properties of this new decoupled load flow approach are similar to those of the conventional decoupled method. The main advantages of this proposed approach are: all the bus generations can be specified, a slack or swing bus need not be defined, and losses are independent of a choice of reference bus.This fundamental change in the load flow formulation has various applications. These include transmission loss evaluation, loss penalty factor calculation, and study applications in energy management systems.     

Fast linear programming state estimation using the dual formulation

The authors present a fast and efficient technique for solving the power system state estimation problem using linear programming (LP). The dual formulation of the original problem is described. This formulation improves the solution time significantly. Four LP state estimators are presented and test results on the IEEE 30, 57, and 118 bus standard systems are included. Both the full and decoupled dual problems were solved. Test results indicate that the dual estimators are superior to the primal estimators     

修正节点接入导纳潮流算法

针对牛顿–拉夫逊法初值选取不当和PQ分解法受网络RX比例影响造成的计算不收敛问题,提出了一种修正节点接入导纳的潮流算法。理论证明该算法是正确的。算例分析表明,该方法收敛可靠、计算速度快,同时不受RX比例与初值选取的影响。     

Linear Var Flow Methods for Security Assessment

ABSTRACT

In this paper, an investigation of various approximations for the solution of reactive power flow equations, suitable for security assessment, is presented. When the loads are assumed to be a combination of constant current and constant impedance types, the power flow equations can be decoupled exactly. The reactive power flow equations become linear with parameters which are functions of phase angles. Hence, once the phase angles are known, voltage magnitudes can be computed exactly without iterations But approximations are required to simplify computations for on-line application. Various approximations and the factors that influence the accuracy of the solutions are investigated.lt is shown that iterative linear power flow (ILPF) and fast decoupled load flow (FDLF) methods (for voltage computations) can be derived from one set of approximations.

Case studies of a 30 bus system is presented to compare the accuracy of various approximations. The results indicate that a major factor influencing the accuracy of the solution is the variability of conductance to susceptance ratio in a system. A new method is presented which gives very accurate results with moderate computing effort.     

基于联络线功率等值约束条件的潮流算法研究

针对互联电网区域间限制联络线传输功率的要求,提出了一种系统扰动后维持联络线功率为设定值的新算法。该算法设定联络线的交换功率,分区域潮流计算,可以实现通过改变受端系统侧的运行方式,维持联络线功率为设定值的目的。该算法物理意义清晰,容易实现,收敛性好,给出的算例验证了提出算法的可行性。     

Unified Fast Decoupled Load Flow in a Parallel Distributed Computation Framework

Abstract

This research proposes a parallel and distributed computation approach for the fast decoupled load flow (FDLF) analysis applicable to both transmission and distribution networks of large electrical power systems. In this approach, the overall repetitive FDLF computations are performed by the respective control centers identified for each sub-system, the sub-systems being formed by partitioning the system through a network tearing procedure splitting the identified buses. The data of each subsystem are stored at their own control centers and hence the subsystems are solved using message passing distributed memory architecture. The computations performed by the control centers in various sub-systems are coordinated from a regional control center. The investigations on IEEE 118 bus standard test system indicate that the proposed approach provides faster solution than the conventional approach, without affecting the solution accuracy. The effectiveness of the proposed technique over the conventional approach become more visible when it is applied for the load flow analysis of large scale systems spread over a wide geographical area.     

计及无功充裕度的电力系统可靠性评估与规划(英文)

结合基于蒙特卡罗抽样技术和解耦最优潮流算法,建立一种电力系统可靠性评估与规划的新算法,该算法在计算过程中计入了无功充裕度与电压静态安全约束对系统可靠性的影响.对RBTS测试系统进行了算例分析,计算结果表明了文中算法的准确性和合理性.通过定量分析可靠性指标随着系统机组容量与无功充裕度的变化而变化的规律,提出了一种寻求特定运行条件下提高系统可靠性水平最优措施的方法,能够为电力系统的规划和运行提供量化决策依据.     

Continuation fast decoupled power flow with secant predictor

The conventional Newton and fast decoupled power flow methods are considered inadequate for obtaining the maximum loading point of power systems due to ill-conditioning problems at and near this critical point. At this point, the Jacobian matrix of the Newton method becomes singular. In addition, it is widely accepted that the P-V and Q-/spl theta/ decoupling assumptions made for the fast decoupled power flow formulation no longer hold. However, in this paper, a new fast decoupled power flow is presented that becomes adequate for the computation of the maximum loading point by simply using the reactive power injection of a selected PV bus as a continuation parameter. Besides, fast decoupled methods using V and /spl theta/ as parameters and a secant predictor are also presented. These new versions are compared to each other with the purpose of pointing out their features, as well as the influence of reactive power and transformer tap limits. The results obtained for the IEEE systems (14 and 118 buses) show that the characteristics of the conventional method are enhanced and the region of convergence around the singular solution is enlarged.     

分布松弛节点法在发电偏离电量研究中的应用

针对电力市场环境下经济补偿分析的需要,采用分布式松弛节点的超解耦潮流算法对某实际电网发电偏离电量的现象进行了模拟分析计算.通过计算并动态调整各个调节电厂和联络线的调节分配因子,得到比单个松弛节点计算时更加实际的潮流变化.以上数值方法经实际运行,证明是切实可行的.     

基于功率注入法的UPFC潮流分析算法研究

基于功率注入法提出了一种舍UPFC的输电系统潮流计算模型,将UPFC引起的附加注入有功和无功功率作为独立的状态变量,避免了由于引入UPFC而引起的振荡或者发散,潮流的收敛速度快。IEEE-9节点系统验证了本算法的有效性。     

Determination of load shedding to provide voltage stability

A computationally simple algorithm is developed for studying the load shedding problem in emergencies where an ac power flow solution cannot be found for the stressed system. The proposed algorithm is divided into two sub-problems: restoring solvability sub-problem and improving voltage stability margin (VSM) sub-problem. Linear optimization (LP)-based optimal power flow (OPF) is applied to solve each sub-problem. In restoring solvability sub-problem, rather than taking restoring power flow solvability as direct objective function, the objective function of maximization of voltage magnitudes of weak buses is employed. In VSM sub-problem, the traditional load shedding objective is extended to incorporate both technical and economic effects of load shedding and the linearized VSM constraint was added into the LP-based OPF. Case studies with a real 682 bus system are presented. The simulation results show that the proposed load shedding algorithm is effective, fast in finding the load shedding scheme to solve the problem of restoring solvability and improving VSM.     

Sparse Reactive Power Scheduling by a Penalty Function - Linear Programming Technique

This work presents a linear programming based algorithm to solve reactive power dispatch problems. A mixed set of variables (generated voltages and reactive power injections) and the reactive power model of the fast decoupled load flow algorithm are used to derive linear sensitivities. A suitable criterion is suggested to form a sparse reactive power sensitivity matrix. The sparse sensitivity matrix is in turn modeled as a bipartite graph which is used to define an efficient constraint relaxation strategy to solve linearized reactive power dispatch problems. The penalty function - linear programming technique method is used in a complete reactive power dispatch solution algorithm, the performance of which is discussed by solving a 256-node, 58 control-variable test system.     

Fast decoupled load flow analysis with SSSC power injection model

This paper presents a facile incorporation of a static synchronous series compensator (SSSC) into the fast decoupled (FD) load flow method. The model is based on power injection formulation. The SSSC is represented by a series impedance and two power injection loads at the terminal nodes. These power injection loads are based on the specified power flow and updated during the iterative process. This developed model of SSSC can be implemented easily in the FD load flow method without changing in the basic computational algorithm. The developed model overcomes the problem of power flow SSSC model which exists when only the SSSC links two subnetworks. The FD load flow with the power injection model of SSSC has been validated using standard IEEE data. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.