Study On Comprehensive Evaluation Method Of Power Collecting System For Large-scale Wind Power Base

With the continuous development of wind power,many large-scale wind power bases are in planning and construction or have been completed and put into operation.Largescale wind power bases are composed of several wind farm groups,which are gathered from several wind farms.Different topologies of collector system will directly affect the cost of wind power base and the security and stability of grid-connected power systems.However,there are few studies on quantitative comparison and evaluation of large wind power bases,which cannot meet the demand in engineering.Therefore,it is of practical significance to make a comprehensive evaluation and comparison of the power collection system of large-scale wind power base.In this paper,the evaluation index system of collector systems is proposed from three aspects: reliability,economy,technical features.The advantages and disadvantages of three typical power converging topologies including chain topology,radial topology and hybrid topology are analyzed from the perspective of reliability,economy and technical characteristics respectively,and the qualitative analysis results are obtained.The comparative evaluation based on these analyses is investigated subsequently in later chapters.Secondly,three typical topological models are evaluated in reliability and economy.In terms of reliability,the equivalent outage rate,the equivalent outage time and the expected power shortage are proposed to be evaluation indexes of reliability.According to the principle of equal power consumption,the large-scale wind power base is equivalent to electrical sources with equal capacity.Then,the equivalent output power and the corresponding probability of the subsystems composed of several wind farms are calculated by stepwise recursive method,and the sum of product of the output power and the corresponding probability in different states is the expectation of the equivalent power supply.Moreover,the value of reliability index is acquired from above process.In the aspect of economic evaluation,the annual investment cost,the annual operating cost and the cost of power loss are selected as evaluation indexes of economics,and the power loss index is used to calculate the economic losses caused by the expected power shortage in the reliability analysis.Then,the voltage deviation,active power loss,reactive power loss,power flow entropy,capacity credit,node voltage over-limit probability,node voltage variance,shortcircuit capacity and transient voltage drop are selected as technical metrics.The first four indicators could be calculated by analyzing the results of the conventional power flow;voltage over-limit probability and variance indexes can be calculated by the stochastic power flow.In view of the stochastic power flow calculation with large installed capacity of wind farm and the wind speed correlation,this paper adopted the multi-point linearization method and eliminated the linearization error to a great degree.Capacity credit index is based on reliability assessment of the equivalent outages,.The transient voltage drop is the average of the voltage drop of wind farms under different topological modes when the three-phase short circuit occurs at the PCC point.Finally,according to the established evaluation index system,the entropy weight method is adopted to determine the weight of each index,and the gray relational degree analysis method based on area is used to evaluate the different topologies of power bases comprehensively,which deferred the correlation value of different schemes to reference sequences.The larger the value is,the better the overall performance of corresponding schemes are.At last,the planned wind power base in Ningxia power grid is chosen as a practical example----the possible topological schemes are proposed,and the comprehensive evaluation is carried out to acquire the optimal scheme.