A Hybrid Decoupled Power Flow Method for Balanced Power Distribution Systems

This paper proposes a hybrid decoupled power flow method for balanced power distribution systems with distributed generation sources. The method formulates the power flow equations in active power and reactive power decoupled form with polar coordinates. Second-order terms are included in the active power mismatch iteration, and constant Jacobian and Hessian matrices are used. A hybrid direct and indirect solution technique is used to achieve efficiency and robustness of the algorithm. Active power correction is solved by means of a sparse lower triangular and upper triangular （LU） decomposition algorithm with partial pivoting, and the reactive power correction is solved by means of restarted generalized minimal residual algorithm with an incomplete LU pre-conditioner. Typical distribution generation models and distribution load models are included. The impact of zero-impedance branches is explicitly modeled through reconfiguring of the adjacent branches with impedances. Numerical examples on a sample distribution system with widespread photovoltaic installations are given to demonstrate the effectiveness of the proposed method.

Optimization Design of the Grate Cooler Based on the Power Flow Method and Genetic Algorithms

As an important process during the cement production,grate cooler plays significance roles on clinker cooling and waste heat recovery.In this paper,we measured experimentally the heat balance of the grate cooler,which provided initial operating parameters for optimization.Then,the grate cooler was simplified into a series-connected heat exchanger network by power flow method.Constructing the equivalent thermal resistance network provided the global constraints by Kirchhoff’s law.On this basis,with the objectives of the minimum entropy generation numbers caused by heat transfer and viscous dissipation,solving a multi-objective optimization model achieved the Pareto Front by genetic algorithm.Then selecting the scheme of the lowest fan power consumption obtained the optimal operating parameters of the grate cooler.The results showed that the total mass flow of the optimized scheme did not change significantly compared with the original scheme,but the fan power consumption was 25.44%lower,and the heat recovery efficiency was 88.43%,which was improved by 11.35%.Furthermore,the analysis showed that the optimal operating parameters were affected by the local heat load.After optimizing the diameter of clinker particles within the allowable industrial range,the clinker with particle diameter of 0.02 m had the optimal performance.

Equivalent Method of Integrated Power Generation System of Wind, Photovoltaic and Energy Storage in Power Flow Calculation and Transient Simulation

针对工程实际开展风光储联合发电系统在潮流计算和机电暂态仿真中的等值方法研究，旨在为大容量风光储联合发电系统的并网仿真分析奠定基础。将潮流计算的等值分为单元机组和集电系统2部分来研究。单元机组等值采用根据不同控制模式选取不同节点类型的方法，针对集电系统等值提出基于损耗不变原则的方法。等值模型和详细模型的算例结果表明，潮流计算等值方法具有较好的精度。在机电暂态仿真动态等值中，基于实际工程计算的最严重工况分析原则，提出运行在满出力点的单机“倍乘”等值模型，为工程计算中的风光储联合发电系统动态等值提供了一种解决方案。

Power Flow Calculation Method of Large Shipboard Power System

The effect of line voltage drop is considered larger on loads, especially on asynchronous motor, transformers and other non-linear load parameters in power system of large ships. A novel power flow method based on improved node voltage method is proposed, and a typical ship power system, which has 2 power stations and 10 nodes, with closed-loop design but open-loop operation, is taken as an example. Simulation results show that the improved power flow calculation method has achieved higher accuracy and better convergence.

Analysis and management strategies for the low voltage problems of rural power grid based on the distribution network flow calculation method

For a long time, because of the lack of investment capital and enough attentions, the overall constructions of rural power grid were far behind than the urban power grid in Chongqing Jiangbei Power Company. The low voltage problems were highlighted in the rural power grid due to the characteristics of rural power grid. Using the distribution network flow calculation method, we evaluated the low voltage problems of the rural power grid which belongs to Chongqing Jiangbei Power Company. In addition, we collected the data of distribution transformers in electricity consumption peak period. Some practical management strategies were proposed by the analysis and evaluation of potential and appeared low voltage problems.

A probabilistic power flow calculation method considering the uncertainty of the static frequency characteristic

In a power system, power generation and load have frequency response characteristics, which randomly fluctuate with changes in operating status. This study investigates a probabilistic power flow method that considers the unit and load uncertainty of the static frequency characteristic. Firstly, a calculation model is established on the basis of the characteristics of the frequency modulation performance of the unit and load. Then a calculation method is developed using the concept of dynamic power flow in order to determine the probability distribution of the active power flow of each line under the occurrence of a fault in the system. In the method, Monte Carlo sampling with the semi-invariant method is applied for analysis and calculation. The IEEE-30-buses system is taken as an example to analyze the impact of different responses of units on the power flow distribution of various branches. The method discussed herein is compared with the Monte Carlo simulation method to verify its effectiveness.

A NEW MODELING METHOD FOR MACHINE-FOUNDATION COUPLING SYSTEM AND ITS APPLICATION TO THE CONTROL OF POWER FLOW

A new concept, namely, the equivalent mobility matrix of coupling subsystem is proposed, and the corresponding threesubsystem coupling progressive approach is explored. With the new efficient approach presented, the complexity in dealing with a more complicated dynamic coupling system is greatly reduced. The new modeling method is then combined with the theory of power flow to investigate the dynamics of the overall non rigid isolation system from the viewpoint of energy. The interaction between the resilient machine of its main modes and the resonant behavior of the flexible foundation on power flow transmission is studied. Taking a machine tool mounted on a multi story working plant as an example, the dynamic characteristics of the machine foundation coupling system are analyzed, and their effects on power flow transmission are revealed under various service frequency bands. Some advisable control strategies and the design principle for machinery mounted on flexible structure are proposed.

Solving Load Flow Problems of Power System by Explicit Pseudo-Transient Continuation (E-ψtc) Method

This paper is a further study of two papers [1] and [2], which were related to Ill-Conditioned Load Flow Problems and were published by IEEE Trans. PAS. The authors of this paper have some different opinions, for example, the 11-bus system is not an ill-conditioned system. In addition, a new approach to solve Load Flow Problems, E-ψtc, is introduced. It is an explicit method;solving linear equations is not needed. It can handle very tough and very large systems. The advantage of this method has been fully proved by two examples. The authors give this new method a detailed description of how to use it to solve Load Flow Problems and successfully apply it to the 43-bus and the 11-bus systems. The authors also propose a strategy to test the reliability, and by solving gradient equations, this new method can answer if the solution exists or not.

Explicit Analytical Solutions of Radial Permeable Power Rate Flow

The research of different kinds of permeable non-Newtonian fluid flow is increasing day by day owing to the development of science,technology and production modes.It is most common to use power rate equation to describe such flows.However,this equation is nonlinear and very difficult to derive explicit exact analytical solutions.Generally,people can only derive approximate solutions with numerical methods.Recently,an advanced separating variables method which can derive exact analytical solutions easier is developed by Academician CAI Ruixian（the method of separating variables with addition）.It is assumed that the unknown variable may be indicated as the sum of one-dimensional functions rather than the product in the common method of separating variables.Such method is used to solve the radial permeable power rate flow unsteady nonlinear equations on account of making the process simple.Four concise（no special functions and infinite series） exact analytical solutions is derived with the new method about this flow to develop the theory of non-Newtonian permeable fluid,which are exponential solution,two-dimensional function with time and radius,logarithmic solution,and double logarithmic solution,respectively.In addition,the method of separating variables with addition is developed and applied instead of the conventional multiplication one.It is proven to be promising and encouraging by the deducing.The solutions yielded will be valuable to the theory of the permeable power rate flow and can be used as standard solutions to check numerical methods and their differencing schemes,grid generation ways,etc.They also can be used to verify the accuracy,convergency and stability of the numerical solutions and to develop the numerical computational approaches.

Optimal Power Flow in Electrical Microgrids

This paper presents in the first place, the state of art relating to the methods to solve optimal power flows (OPF) and its application in electrical microgrids. Afterwards, a mathematical algorithm based on the gradient method is proposed for the application of OPF in a low power microgrid, in order to improve the voltages profiles and consequently reduce the active power losses. Finally, the proposed algorithm is implemented in a low power microgrid to demonstrate the effectiveness of the method.

Mixture flow of particles and power-law fluid in round peristaltic tube

The erythrocyte and blood flowing in the blood vessel can be treated as the two-phase flow of the mixture of particles and a power-law fluid in a peristaltic tube.In the present work, the peristaltic transport of a power-law fluid and the suspension of particles in a tube is investigated by a perturbation method using the long wavelength approximation. The influence of different parameters on the velocity profile and streamlines is explored. Results show that there is a deflection of the flow field when the power-law index n = 0.5 or 1.5 compared with the Newtonian fluid where the trapping zone is symmetric to a certain cross section. The flux rate and reflux of the material are identified,and the conditions under which the reflux appears are determined. Moreover, a reflux phenomenon occurs near the wall. The trapping zone is related to not only the tube geometry and the flow flux but also the fluid properties. Both the length and width of the trapping zone increase with an increase in θ or φ. The trapping zone is more difficult to produce in the shear-thinning fluid than the shear-thickening fluid.

Design and Power Flow Analysis of Electrical System Using Electrical Transient and Program Software

Power flow analysis is a numerical way of study of behavior of flow of electric power in an interconnected system. In order to meet the growing demands of electrical energy in an optimum way, there is a need to upgrade existing systems or to install new systems. Therefore, planning of new installations and determination of best operating conditions of existing systems need power flow analysis. In this way, cost/benefit ratio for both suppliers and customers is maintained. This research involves the design and power flow analysis of IEEE-14 bus system. Newton Raphson method is applied for better efficiency and reduced computational time. Simulation analysis is conducted in ETAP software because of its excessive used in real life systems.

A Critical Eigenvalues Tracing Method for the Small Signal Stability Analysis of Power Systems

The continuation power flow method combined with the Jacobi-Davidson method is presented to trace the critical eigenvalues for power system small signal stability analysis. The continuation power flow based on a predictor- corrector technique is applied to evaluate a continuum of steady state power flow solutions as system parameters change;meanwhile, the critical eigenvalues are found by the Jacobi-Davidson method, and thereby the trajectories of the critical eigenvalues, Hopf bifurcation and saddle node bifurcation points can also be found by the proposed method. The numerical simulations are studied in the IEEE 30-bus test system.

基于逐步倒推法结合MATPOWER潮流计算的地市级电网网架规划方法

文章介绍了一种基于逐步倒推法结合MATPOWER潮流计算的地市级电网网架规划方法,并利用该方法对2015年荆门市电网220kV主网架进行规划分析,实践证明该方法具可行性。

Risk Control of Transmission Line Overload for Wind-Integrated Power Systems

With the rapid development of the wind generation,uncertainties of random wind and load bring some inevitable impacts on the security of power system. Once the uncertainty causes line power to exceed its limit, line overload will occur. The paper presents the risk control of transmission line overload for windintegrated power systems. Firstly, a risk control model of line overload is proposed considering the uncertainties of loads,generator outputs and wind powers. The generation cost and security level of system associated with overload can be optimally controlled. Then path following interior point method is employed to carry out the optimal control. Finally the simulation is made on the modified IEEE-30 bus system. Results show that the risk of line overload is effectively reduced through the optimization of control variables.

基于功率流有限元法的涡旋压缩机振动特性研究

针对涡旋压缩机内部振动传递路径复杂,采用传统的传递函数法往往不能真实地描述振动产生与传递的本质问题,引入功率流有限元法从能量角度分析振动传递特性,进行涡旋压缩机内部振动产生、传递与空间分布的可视化研究。在分析涡旋压缩机的动力拓扑关系基础上建立激励源,提取与振动响应模型并进行仿真分析;利用实体试验和响应分析结果对比进行模型有效性分析;在验证后的模型上定义8个能量输出面,分析谐波与激励作用下上支撑和下支撑的振动能量传递特性,并且计算节点的功率流矢量确定振源的空间分布。结果表明,涡旋压缩机曲轴在运转到280°时,振动频率在1 000 Hz与1 890 Hz时振动能量传递率较高,上支撑能量分布均匀并集于自身,下支撑能量集中于支脚并向外传递。研究方法和研究成果对于涡旋压缩机振动分布及传递、振动控制和优化设计等方面具有一定借鉴意义。

主动配电网潮流的全纯嵌入计算方法

配电网潮流计算是进行配电网规划和运行的重要基础。目前,配电网潮流求解方法主要有牛拉(Newton Raphson,NR)法和前推回代(forward backward substitution,FBS)法两大类,但NR法和FBS法在潮流收敛性和计算效率等方面均存在一定的不足。全纯嵌入法(holomorphic embedding method,HEM)是一种求解非线性潮流方程的新方法,它可以有效避免NR法和FBS法在配电网潮流求解过程中出现的上述问题,但现有HEM未充分考虑配电网中各类型分布式电源(distributed generation,DG)和智能软开关(soft open point,SOP)控制方式的多样性,且未构建计及负荷电压特性和频率特性的潮流模型,难以适用于不同运行模式下配电网潮流计算。针对上述问题,提出一种可求解含多类型DG和SOP且可运行在并网/孤岛模式的主动配电网统一全纯嵌入潮流计算方法。首先,根据负荷静态电压和频率特性,构建计及配电网频率和节点电压影响的负荷节点全纯嵌入潮流模型;其次,根据DG不同的控制方式以及配电网不同的运行模式,将DG所连节点等效为不同节点类型,构建各类DG的全纯嵌入潮流模型;再次,考虑SOP不同控制方式,构建SOP全纯嵌入潮流模型;从次,依据全纯嵌入潮流模型等式左右两侧同次幂级数系数相等原则,推导配电网各全纯函数幂级数系数的求解递推关系式,进而计算各全纯函数的各项幂级数系数,借助解析延拓理论求取电压和频率逼近值,实现配电网潮流的准确求解;最后,通过修改的IEEE-33节点测试系统和IEEE-123节点测试系统验证所提方法准确性和有效性。

Numerical Simulation of the Churning Power Losses in the Automotive Hypoid Gear Reducer

Improving vehicle transmission efficiency and reducing vehicle fuel consumption is currently one of the main objectives in the automotive field. Reducing gear churning power losses has significant influence on the decreasing vehicle fuel consumption. Based on the two phase flow theory, a 2D two-phase model of the simplified hypoid gear is established to predict the churning losses in different conditions, the VOF method is introduced to track the volume fraction of the free surface, a standard k-ε model is also built to calculate complex turbulence. The oil distributions at the different rotational speed, the different immersion depth and the different viscosity as well as the churning losses of the hypoid gear are obtained and discussed in detail. In general, the churning power losses increase with the increase of the speed, the immersion depth and the viscosity, while the rotational speed shows the greatest influence on the churning losses. It is hoped that this investigation will be helpful in automotive industry applications.

电力系统全纯嵌入潮流的并行计算

潮流计算是电力系统规划和运行的基础,全纯嵌入潮流计算方法(HELM)因无需初值且具有全局收敛性,因而在电力系统潮流计算中受到极大关注。然而,采用HELM求解大规模电力系统潮流时,高维幂级数系数线性方程组求解和节点电压的幂级数有理的逼近计算量大、耗时久,是制约HELM计算效率提升的关键。为此,该文提出一种基于稳定双正交共轭梯度(BICGSTAB)和Aitken差分的电力系统全纯嵌入潮流并行计算方法,该方法首先采用近似逆预处理的BICGSTAB法并行迭代求解HELM的高维幂级数系数线性方程组,以快速计算节点电压的各阶幂级数系数;其次,借助Aitken差分法实现所有节点电压幂级数有理逼近值的并行计算;然后,基于CPU-GPU异构平台设计所提算法的并行流程,以实现大规模电力系统潮流的快速求解;最后,通过节点在1 354~13 802的不同规模测试系统对所提方法进行分析、验证。结果表明,所提电力系统潮流全纯嵌入并行计算方法可实现电力系统潮流的准确、快速求解。

基于全纯嵌入法的三相潮流通用算法

随着高比例新能源接入,电网三相不平衡问题日益突出,迫切需要工程适用的三相潮流算法进行分析。传统三相潮流算法存在初值依赖性强、模型复杂、计算效率较低和适用场景受限等问题。全纯嵌入法是一种解析求解非线性潮流方程的新方法,具有不依赖初值、求解过程中矩阵定常的优势。因此,该文首先基于电网三相元件模型特性,运用相序变换矩阵,构建三相潮流的全纯嵌入模型;其次,基于幂级数系数相等原则,推导模型系数的递推关系,并运用矩阵范型技术简化计算模型;然后,对零序约束方程进行解析重构,运用矩阵行列替换技术,实现不同接地方式下电网三相潮流的高效求解;最后,在IEEE 33、改造的IEEE 123及我国某区域电网系统上,验证所提方法效率高、收敛可靠且不依赖于计算初值的优势。