OPTIMAL REACTIVE POWER FLOW BY SENSITIVITY METHOD

A new approach based on sensitivity method for the optimal power flow is presented in the paper. This method has the following advantages: it is suitable to solve a 200-node power system on the microcomputer; the convergence is easy to reach and the computation speed is quick; it is possible to reduce 8-14% power loss and to get maximum economic benefit by using this method; in power system dispatch center it can be used as an on-line voltage and reactive power control program to keep good voltage level. The proposed method has been proved successful by IEEE 118-node test system and the several real power systems such as 49-node, 61-node, 99-node and 200-node systems.     

A Reactive Power Optimization of Classic Method Combined with Lincar Programming

A tow-stage VAR optimization model is presented in this paper.First.the optimal solution is quickly solved by VAR classic method,which only considers the limitaryconditions of Reactive Power and reactiue power equation and yet linear increment model based onsensitivity is set up and linear programnung is employed to correct the overlimit varlables,Theoptimal resnlts in the tirst stdge are corrected to be feasible.The proposed method has beensuccessful in the sample systems and reai systems.     

A HIERARCHICAL CONTROL METHOD FOR REACTIVE POWER OPTIMIZATION IN LARGE-SCALED INTERCONNECTED POWER SYSTEMS

This paper presents a new hierarchical and coordinative control method for reactive power optimization in large-scale interconnected power systems. It combines the interconnection forecast method for hierarchical control in large-scale steady state industrial systems with the incremental linear programming method for reactive power optimization in real time. The results of applying the method to power system examples show that the method not only solves the problem of high dimension in order, but also keeps the advantages of the incremental linear programming method. The proposed method is also suitable for the security analysis of reactive power correction in large-scale interconnected power systems.     

Application of Linear Programming in the Steady-State Real Power Security Region

This paper presents a new rnethod for analysis and computation of steady-statereal power security region by linear programming.In this method based on the D.C load flow,theupper and lower bounds of the hyper-cuboid explicit steady-state security region are chosen asunknown variables.The objective function is the total amount of the adjustable generations withweighting factors.The model of the steady-state real power security region is changed in to the proposed linearprogramming methed for ealculation.The numerieal exarnples are tested on IEEE 6-bus and 30-bussample systems.The computational resuIts showed the proposed model a nd algorithm feasible andeffective.     

AN A. C. LOAD FLOW ANALYSIS OF THE RELIABILITY EVALVATION OF COMPOSITE GENERATION AND TRANSMISSION SYSTEMS

An A. C. load flow analysis of the reliability evaluation of composite generation and transmission systems is presented on the basis of a fast outage simulation algorithm and an optimal model of active and reactive power adjustment after outage contingencies. The information of the first -level outage events is utilized for simulating higher -level outage events in the fast outage simulation algorithm ; the optimal model is satisfactory in speed and accuracy with the application of concentric relaxation and linear increment constraint on the comprehensive adjustment of active and reactive power. As an example. the IEEE Reliability Test System is tested and the results show that the method is accurate and well-matched in speed with the method studied by R. Bllinton, et al.     

OPTIMAL ACTIVE POWER ADJUSTMEMT OF LARGE HYBRID AC/DC SYSTEMS AFTER OUTAGE CONTINGENCIES WITH THE APPLICATION IN RELIABILITY EVALUATION

An optimal active power adjustment model is deve in this paper for hybrid AC/DC systems after outage contingencies. The objective of the model is to minimize the rejection of load when some elements are out of service, with adjustment strategy approaching practical system operation. A large number of outage contingencies are simulated when the Monte-Carlo Method is emyloyed to evaluate the system reliability, requiring fast calculation of each simulation. The model and computer method proposed in this paper satisfy such a requirment because of the application of concentric relaxation, recursive branch constraint treatment in linear programming and a direct method for B-1 matrix modification. This paper is concerned with the simplified steady state conditions of the system based on DC load-flow, which implies the reliability indices calculated are the measures about static loss of load. The results for a 14-bus hybrid AC/DC system are given.     

Four-node Membrane Element of Vector Form Intrinsic Finite Element for Large Deformation Analysis of Membrane Structures

Based on fundamental principles of the vector form intrinsic finite element (VFIFE), the basic formulas of 4-node quadrilateral membrane element were first derived in this paper. The procedure for the determination of pure nodal deformation through reverse movement was elaborated, and the method for the calculation of internal nodal forces through deformation coordinate system was presented. Feasible approaches were also proposed for several issues for 4-node membrane element, including the location statuses and the numerical integration for internal forces. A computer program of 4-node membrane element was developed. By the analysis of the numerical example, the correctness and validity of the membrane element theory and the computer program were verified. Then the approach was applied for more analysis of large deformation and large rotation problems of membrane structures, including cushion inflating and cloth draping.     

COMPOSITE SYSTEM RELIABILITY EVALUATION CONSIDERING LOAD MODEL

The study for dealing with the load model in composite system reliability evaluation is almost at a standstill because of the inherent computational complexity. In this paper, an algorithm for composite system reliability evaluation considering load model is proposed. This method is powerful in computation because it can avoid unnecessary state enumeration by means of the relationship among basic reliability informations of load levels. As an example, the IEEE 24-node Reliability Test System is tested on VAX-11/750 computer. The average CPU time to calculate the reliability indices of the system corresponding to a load level is about 5 seconds.     

A Reactive Power OptimlZation Method by Linear Program ming with Secure Correction

This paper presents a reactive power optimization method which combines thelinear programming model with secure correction. In correction. this mOdel presents a new idea inwhich the feasible control region of con trol variables is resolved by over constrained state varlables. This method is quick and reliable and overcomes oscillation of a general linear programming model.     

An Improved Method of the Transient Waveform Analysis in Power Systems

The angular frequency and decaying constant of each copmonect for the transient waveform in power systems were obtained by using the discrete Fourier transform; the amplitude and phase angle were calculated in the linear curve fitting method. And all of the parameters obtained above were treated in an unified optimization by using the curve fitting optimization of the least square method of general nonlinear funcrion so as to get the results of waveform analysis. Two examples are included.     

A preventive control model for static voltage stability considering the power constraints of weak branches

The voltage instability of power system often occurs when the active power on one or more weak branches exceeds its transfer capability. A preventive control model for static voltage stability is proposed using the active power transfer capability of weak branches as static voltage stability constraints. A local line based voltage stability index is used to determine the critical contingencies, weak branches and transfer capability of each weak branch. A static security analysis method, which is based on DC power flow equations, is used to establish the non linear active power flow expressions on weak branches following each critical contingency. The active power constraints on weak branches can be obtained from the active power flow expressions and transfer capabilities of weak branches. A quadratic optimal model for preventive control including the proposed active power constraints on weak branches is presented. The simulation results for IEEEE14 bus system and IEEE118 bus system demonstrate the correctness and effectiveness of the proposed preventive control model.     

THE MONTE-CARLO METHOD FOR RELIABILITY EVALUATION OF LARGE SCALE COMPOSITE GENERETION-TRANSMISSION SYSTEMS

The paper presents a Monte-carlo method for reliability evaluation of large scale composite generation transmission systems. The method, which possesses coputational rapidity and sufficient accuracy,is based on combining the dispersed sampling techique with the analysis approach and the optimization model of power not supplied. Because the amount of calculation increases only linearly with, the number of elements, it is specially sui- table for large scale systems. The Monte-carlo sampling draws more near the real situation than determinate state enumeration in simulating occurrence of power system outages. Also, the method can be easily generalized to involve multi-states of elements, multi-levels and stochastic distribution of loads. The results of IEEE-RTS, as example, are given and compared with ones obtained by using the other two methods.     

A record-based simulation of spatially correlation ground motion

A record based approach has been developed for the simulation of spatially correlated ground motion. This procedure uses autoregressive model to establish a power spectrum, and uses the multivariate linear prediction to simulate the parameter of unknown position. The random factor of earthquake is relected by Gaussian distribution random number, and the known records are subdivided into a sequence of time windows to account for its temporal variation. Compare of the simulated record and the true record show that this procedure is accurate and reasonable, and it is applicable for the design of discretely supported systems.     

Approach for Calculating Short Circuit on Transrmission Lines by Using Piece-wise Method with Structure Network Fault

Based on the properties of linear network,a new generalized diakoptical modeland its algorithm are presented in the paper to calculate short circuit at the arbitrary location on anytransmission line of large-scale power systems,in which the proposed techniques of transferring faultport current,and modifying nodal current sources and column impedence elements, are appliedcomprekensively. The method given here is espocially efficient to calculate short circuit in piece-wisemethod for any mutually coupled cuts between subdivisions in the system with constant or variablestructures. And it is an important improvement for short-circuit current calculation.     

Low frequency oscillation restraint in power systems that include asynchronized turbogenerators

Yangtze River is abundant of water and can provide enough water as cooling and heating source for water source heat pumps (WSHP). A pair of contrast experiments with open loop system and close loop system of WSHP were finished in order to get the heat pump's COP, the system's COP and the distribution of water temperature in the heat exchanger etc. This paper compared the characteristic and the COP of these two kinds of system. The heat pump's COP of the open loop system and close loop System are 3.08 and 3.77 respectively, and the system's COP are 2.83 and 2.80 respectively. At last, applications of open loop system and close loop System of WSHP at Yangtze River were analyzed and the key problem for attention was pointed out in the paper.      

APPLICATION OF DECOMPOSITION COORDINATION METHOD OF LARGE - SCALE SYSTEMS AND METHOD OF NONLINEAR PROGRAMMING TO ECONOMIC SCHEDULING OF POWER SYSTEM

In this paper,we discuss a mathematical mode) for optimization of active power dispatch of large-scale hydro-thermal power systems with cascaded hydropower stations. The following factors are taken into account: the variation of the head in the hydropower stations, water transport delay between cascaded stations etc. Using the decomposition-coordination method of large scale systems, we obtain a three-layer-hierarchical coordination system and a three-layer-hierarchical computational structure. We also discuss the computational methods which are used by each hierarchy. We have taken a test computation and analysing the result of an actual hydrothermal power system. The computational results show that it may obtain a satisfactory economic benefit. The paper provides some research work on the economic scheduling of hydrothermal power systems by the decomposition-coordination method of large-scale systems,multiplier method and a new variable metric method.     

The on line monitoring method of power transmission line fault basednon linear frequency response function

A novel method for power transmission line monitoring and fault diagnosis is proposed based on non linear frequency response analysis. The power line carrier signal has been used for on line monitoring of power transmission line. As the non linear frequency response function describes the system inherent characterization, different frequency response patterns corresponding to different operation states of transmission line can be established. Based on the analysis of transmission line characteristics of fault modes, various fault features can be extracted, thereby achieve online monitoring and fault diagnosis on transmission line. Simulation experiments show the effectiveness of the proposed method.     

PROBABILISTIC STABILITY EVALUATION OF AC/DC POWER SYSTEMS WITH PARALLEL MONTE CARLO METHOD

This paper presents a new method for the probabilistic stability evaluation of AC/DC power systems. The transient stability model is described and the stochastic factors having effects on the stability behaviors are analysed and modeled. A theorem governing the probabilistic relations among the occurences of different types of disturbances is derived. A method of parallel computation is oresented, which is based on Monte Carlo simulation. An illustrative example is also given to show the application of the concepts and method presented in this paper.     

加工番茄产量组合预测模型研究

为了实现加工番茄产量的精准预测,通过采用方差倒数法来确定权重,将一元线性回归模型、灰色预测模型和指数平滑模型加以组合,根据2001—2009年新疆某加工番茄种植及产量数据,建立了加工番茄产量组合预测模型。以预测2010年和2011年番茄产量为例,结果表明此组合预测模型与单一预测模型相比更加准确可靠。该研究为加工番茄产业决策支持系统的建立奠定了理论基础。     

A New Method of Piece-Wise Solution in Faulted Power Systems with Variable Configurations

A new model and its algorithm are presented in this paper to simulate calculating the electric values of short circuit fault in large-scale power systems with variable configurations. The method proposed herein reduces the computer storage requirements compared with the available approaches. And it completely avoids the modification computation of nodal impedance (or admittance) matrices of the original networks and the repeated calculations for each type of faults.