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1、外文翻译（原文）中文4900字A Comparison of Power Flow by Different Ordering Schemes AbstractNode ordering algorithms, aiming at keeping sparsity as far as possible, are widely used today. In such algorithms, their influence on the accuracy of the solution is neglected because it wont make significant difference
2、 in normal systems. While, along with the development of modern power systems, the problem will become more ill-conditioned and it is necessary to take the accuracy into count during node ordering. In this paper we intend to lay groundwork for the more rationality ordering algorithm which could make
3、 reasonable compromising between memory and accuracy. Three schemes of node ordering for different purpose are proposed to compare the performance of the power flow calculation and an example of simple six-node network is discussed detailed. Keywordspower flow calculation; node ordering; sparsity; a
4、ccuracy; Newton-Raphson method ; linear equationsI. INTRODUCTIONPower flow is the most basic and important concept in power system analysis and power flow calculation is the basis of power system planning, operation, scheduling and control 1.Mathematically speaking, power flow problem is to find a n
5、umerical solution of nonlinear equations. Newton method is the most commonly used to solve the problem and it involves repeated direct solutions of a system of linear equations. The solving efficiency and precision of the linear equations directly influences the performance of Newton-Raphson power f
6、low algorithm. Based on numerical mathematics and physical characteristics of power system in power flow calculation, scholars dedicated to the research to improve the computational efficiency of linear equations by reordering nodes number and received a lot of success which laid a solid foundation
7、for power system analysis.Jacobian matrix in power flow calculation, similar with the admittance matrix, has symmetrical structure and a high degree of sparsity. During the factorization procedure, nonzero entries can be generated in memory positions that correspond to zero entries in the starting J
8、acobian matrix. This action is referred to as fill-in. If the programming terms is used which processed and stores only nonzero terms, the reduction of fill-in reflects a great reduction of memory requirement and the number of operations needed to perform the factorization. So many extensive studies
9、 have been concerned with the minimization of the fill-ins. While it is hard to find efficient algorithm for determining the absolute optimal order, several effective strategies for determining near-optimal orders have been devised for actual applications 2, 3. Each of the strategies is a trade-off
10、between results and speed of execution and they have been adopted by much of industry. The sparsity-programmed ordered elimination mentioned above, which is a breakthrough in power system network computation, dramatically improving the computing speed and storage requirements of Newtons method 4.Aft
11、er sparse matrix methods, sparse vector methods 5, which extend sparsity exploitation to vectors, are useful for solving linear equations when the right-hand-side vector is sparse or a small number of elements in the unknown vector are wanted. To make full use of sparse vector methods advantage, it
12、is necessary to enhance the sparsity of L-1by ordering nodes. This is equivalent to decreasing the length of the paths, but it might cause more fill-ins, greater complexity and expense. Countering this problem, several node ordering algorithms 6, 7 were proposed to enhance sparse vector methods by m
13、inimizing the length of the paths while preserving the sparsity of the matrix.Up to now, on the basis of the assumption that an arbitrary order of nodes does not adversely affect numerical accuracy, most node ordering algorithms take solving linear equations in a single iteration as research subject
14、, aiming at the reduction of memory requirements and computing operations. Many matrices with a strong diagonal in network problems fulfill the above assumption, and ordering to conserve sparsity increased the accuracy of the solution. Nevertheless, if there are junctions of very high and low series
15、 impedances, long EHV lines, series and shunt compensation in the model of power flow problem, diagonal dominance will be weaken 8 and the assumption may not be tenable invariably. Furthermore, along with the development of modern power systems, various new models with parameters under various order
16、s of magnitude appear in the model of power flow. The promotion of distributed generation also encourage us to regard the distribution networks and transmission systems as a whole in power flow calculation, and it will cause more serious numerical problem. All those things mentioned above will turn the problem into ill-condition. So it is necessary to discuss the effect of the node numbering to the accuracy of the solution.Based on the existing node o
