Analysis On Power Flow Calculation And Probabilistic Characteristic Of Distribution System With Considering Distributed Generators

The problem of energy and environment make the power generation way change,and it turn into the combination of conventional power generation and distributed generators.Distributed generators supply in the constant enlargement of the proportion of power distribution system,and it is imperative to study the effect of distributed generators on the system steady state operation.At the same time,the distributed power generation technology have a great influence on the power distribution system,such as change distribution system structure,complex on control and management of the distribution system.Probabilistic load flow calculation can analyze the effects of distributed generators uncertainty on the power distribution network,thus analysis on power flow calculation of distribution system with considering distributed generators is very important.In this paper,it mainly analysis on power flow calculation and probabilistic characteristic of distribution system with considering distributed generators.First of all,the probability theory knowledge is analyzed,and the theory is relevant of probabilistic load flow calculation(including probability density function(PDF),cumulative distribution function(CDF),distribution type and function of random variable,origin moment,central moment,cumulant and Gram-Charlier expansion).The commonly algorithm of probabilistic power flow calculation are studied,and the basic principle of three kinds of probabilistic power flow calculation methods are analyzed and compared.It is established,respectively,the distributed generators probability model and load probability model.There are three nodes processing models for distribution network with distributed generators,and it is analyzed and compared.In the process of probabilistic load flow calculation,this paper adopted the simplified PQ nodes model,which provides a convenient for probabilistic load flow calculation.Secondly,according to the characteristics of cumulant method,such as simple in principle,less calculation steps,fast calculation speed,but the cumulant of input variables of complex and unknown distribution function is difficult to calculate,therefore,the method of Latin hypercube sampling and cumulant is proposed to calculate power flow.The principle of proposed method: a linear model is established to describe the behaviors of probabilistic load flow.Each cumulant of input random variables is evaluated in the linear model using Latin hypercube sampling and the conventional numerical method.Then the cumulants of output random variables are found using a Gram-Charlier expansion,according to which the cumulative distribution functions of the output random variables are obtained.The outperformance of this proposed method over a conventional counterpart is demonstrated in IEEE34 nodes system.This proposal shows a good performance agreement with the counterpart,while provides a higher accuracy,and can be viewed as a reliable means for electrical dispatch analysis.At last,according to the probabilistic model of the random disturbance,the distribution network probability characteristics of distribution network with random disturbance are analyzed by the proposed method.The dates of node voltage probabilistic characteristic under three different conditions are calculated,and draw the CDF curves of some nodes voltage.The influence of random disturbance on the distribution network node voltage is analyzed and compared.The results show that the random load reduces the mean value of the magnitude of the node voltage,and the distributed generators increase the mean value and standard deviation of the magnitude of the node voltage,and random disturbance make smaller influence for the mean value of the magnitude of the node voltage and voltage quality.It keeps a better voltage quality for distribution network.This works can provide a theoretical basis for the planning of the dispatching department.