A FAST ALGORITHM FOR DIGITAL SIMULATTON OF HVDC SYSTEMS

After considering the features of the differential equations which have described the dynamic behaviours of HVDC systems, a fast algori -thm is presented for these equations. Compared with the fourth Runge-Kutta Method,this method has less amount of calculation with the same precision, numerical stability and other properties. Therefore, the use of the method has greatly increased the speed of the digital simulation of HVDC systems.In this paper an example of calculation is given, and the results obtained hv using this example are compared with the results obtained by calculating with the fourth Runge-Kutta Method. The speed of simulation by using this method is about 1.8 timss as fast as that by using the fourth Runge-Kutta Method.     

求解粮食调运问题的两阶段优化算法

粮食调运优化问题过去已有研究,但是当问题较为复杂时,传统算法就要花费大量时间而且准确性也难以保证.针对这一缺陷,本文对已有的粮食调运模型进行改进,并基于该改进模型提出了一个解决粮食调运优化问题的两阶段求解方法,在第一阶段,由图搜索算法产生所有可行的运输路线,并根据约束条件对搜索树进行剪枝;在第二阶段,采用蚁群算法从第一阶段产生的可行路线集合中选取最佳路线,使总的运输成本最低.经过实例测试,该算法在粮食调运过程中具有较好的效果.     

A NEW ON LINE AND REAL TIME METHOD FOR DETERMINING HARMONIC AND REACTIVE CURRENTS

According to the basic idea of phasar analysis and by applying a special multiplier, a new on line and real time method is derived for determining harmonic current and reactive current of an electric network. This method has a good dynamic response characteristic and solves for the first time the determining problem for the compensation system in single phase system,which is also appliable to the three-phase system.     

A contour extraction algorithm for digital images based on water balloons snake model

Due to weak edges and low contrast areas in digital images, such as a left ventricle in Magnetic Resonance Imaging (MRI) images, a deformation curve may leak from the outer boundary when images are segmented using the traditional snake model. An improved algorithm based on the water balloons snake model is introduced to solve this problem. Firstly, the barycenter and the boundary shape area of the left ventricle in a digital MRI image are obtained through mathematical morphology. The left ventricular watershed line is obtained next using a watershed transform algorithm, which is taken as the initial deformation curve in a balloon snake model to capture the contour. Different snake models are tested to digitally tagged MRI images of left ventricles of small pigs. Contrast results indicate that the water balloons snake model can solve the leakage problem in traditional snake and balloon snake models. In addition, the processing speed is improved significantly.     

A STUDY OF THE OPTIMIZATION OF CIRCULAR ARC TOOTH PROFILE TRANSMISSION

For the first time, we point out the new idea that we can approximate the involute tooth profile transmission to circular arc tooth profile transmission. Looking upon it as a fourbar linkage we try to minimax the error of the velocity ratio and evaluate the strong-weak point of circular arc tooth profile transmission.     

A NONLINEAR PROGRAMMING MODEL AND ITS ALGORITHM FOR TRANSMISSION NETWORK PLANNING

The problem of transmission network planning is studied thoroughly by applying the mathmatical optimal tecqhniue in this paper. A novel approach is put forward for computer aided transmission network planning, which is quite different from what is based on D.C. load flow equations. A nonlinear transmission planning model is set up by regarding A.C. load flow equations as the system model. A practical model which can be solved more easily, and an united algorithm are obtained by applying the SUMT to the nonlinear model. The results of some practical examples indicate that this method can not only make the planning results more accurate, but also provide the voltage qualities and produce planning plans autometically and seek the plans optimally and fast.     

A NEW METHOD FOR DETERMINING THE INITIAL CONDITIONS OF NETWORKS WITH DEGENERATE CUT-SETS

This paper suggests a new method for determing theinitial condittons of networks with degenerate cut-sets,which is strictlybased on the physical relationship between currents and magnetic fieldcorresponding witth them.This method first sets up a reasonable magne-tic network for solution,and then finds out the transfer linkages byexciting sources in this network,so that the initial conditions can befinally determined.Consequently,this method is simple,normalizable,having clear and correct physical concept,and advantageous to solvingcomplex networks.     

A NEW COMPENSATIVE SNUBBER FOR ELIMINATING THE SURGE AND NOISE IN PWM CONVERTERS

A new compensative snubber is presented for eliminating the surge current and high frequency parasitic oscillation in rectified circuit of the PWM DC-DC converters. The output surge and noise voltages are de-creased over 4/5. The working principle of the sunbber is analyesd in detail, the designing formulas are derived. The theoretic analysis is consistent with the experimental results.     

A NEW METHOD FOR THE STATIC MEASUREMENT AND CALCULATION OF PARAMETERS OF SYNCHRONOUS MACHINES

This paper presents and improved static measurement method for the parameter measurement and calculation of synchronous. By four static-tests of this method all the parameters in the d-axis equivalent circuits of synchronous machines can be determined, and transient and subtransient parameters are calculated. Testing results proves that this method is available in indusirail testing.     

PARALLEL ALGORITHMS FOR A LARGE SPARSE SYSTEM OF LINEAR EQUATIONS

ABS algorithms new agorithm is introduced with the discussions of the sparse structuere of the projection matrixes and the reorder methods of equations. To apply ABS algorithm on qarallel computer, the parallel ABSalgorithu is also discussed with numerical examples and the time need for the computation.     

A NEW METHOD BY USE OF MASS AND ACCELARATION PARAMETERS FOR BALANCING THE SHAKING MOMENT OF ARTICULATED MULTI-BAR LINKAGES

In this paper,a new method with general purpose ispresented for balancing the shaking moment of articulated multi-barlinkage.The concept of this method is clear.The moment equation oflinkages is easy to establish and solve.Furthermore its pattern structuremakes it convenient to be programmed.     

高效低毒新型杀虫剂——杀虫磺防治水稻害虫的试验研究

杀虫磺田间亩用量50克防治水稻二化螟、三化螟,其效果与杀虫双、杀虫单在同一水平上,残效期可维持7-14天,田间施药1-2次可控制螟害,它不仅具有内吸和触杀作用,还兼有胃毒作用.杀虫磺属神经毒剂,对螟害具有特殊的中毒症状及毒杀机制,对高等动物属低毒,无致癌、致突变作用,也不会引起畸胎的形成,根据杀虫磺的理化特性、代谢、转化等分析,它积累在环境中或食物链上的可能性不大,可以取代有机氯农药,其特殊的毒杀机制在克服害虫的抗药性方面,可能作为一个取代的新品种,是一个很有希望的杀虫剂.