Research On Power Quality Evaluation Of Random Access To Distribution Network

With the rapid development of national economy,the power consumption is increasing progressively,and the scale of the power grid is expanding gradually.Though the power customers of randomness has become the main consumer in the power grid because of its environmental friendliness,reliability and low cost,the problem of power quality will be carried out when a large number of random power customers are connected.Therefore,it is of great practical significance to study the power quality evaluation on stochastic power customers.According to the characteristics of stochastic power and the requirements on power quality evaluation,meanwhile,considering the existing researches on power quality evaluation,the evaluation model combining probability statistics and vector algebra is proposed in this thesis,which can realize the individual evaluation and comprehensive evaluation on power quality respectively.In this thesis,the individual analysis on power quality on the condition that wind turbine and photovoltaic power grid is at grid-connected and off-grid is evaluated through the proposed evaluation model,based on probability statistics and vector algebra.Moreover,the influential index of power quality on the state of grid-connected and off-grid is analyzed respectively,which provides reference value for the quality control of power quality at grid-connected and the self sufficiency of power quality control at off-grid.Weight is one of the key steps in the evaluation of power quality.In this thesis,AHP is introduced to determine the weight,whereas there exists some problems,such as the consistency verification of traditional analytic hierarchy process(AHP)to determine the weight,the inaccuracy of the judgment accuracy and the otherness is not obvious enough.Therefore,the introduction of improved AHP method is proposed subsequently to compensate the traditional shortcomings.The judgment matrix is determined on the basis of the three-scale method,then the optimal matrix is transformed into consistent matrix,which can avoid the consistency of traditional AHP judgment,inaccurate judgment and obsolete difference.Finally,an example is given to verify the validity and feasibility of the proposed evaluation method,accordingly,the proposed comprehensive evaluation on power quality index of random customers can dominate the overall power quality status in the power grid.