Steady State Power Quality Comprehensive Evaluation Method And Its Application

With the constant expansion of the power system, a large number of non-linearloads and power electronic components are widely used in practice. As a result, powerquality issues become increasingly conspicuous. The contradictions caused by powerquality issues have also become increasingly prominent. Therefore, an effective powerquality assessment method will be an important reference for power qualityimprovement and for sensitive users to choose the electricity provider.Current Chinese national standards make necessary provisions on the limitvalues of individual power quality indicators, but whether individual indicators isqualified or not could not reflect the overall power quality. Therefore, it is verynecessary to establish certain comprehensive assessment method on the basis ofmultiple indicators of power quality. The main point of this paper is to establish acomplete power quality evaluation system. It introduces the comprehensive powerquality evaluation system from four aspects: the establishment of the index system,the measurement of the index data, the index weight calculation and the selection ofthe evaluation algorithm and so on.The establishment of the index system and the measurement of the index datamainly depend on the relevant requirements in Chinese national standards. Takingthese standards as the starting point, this paper chooses the voltage deviation,frequency deviation, three phase voltage unbalance, voltage harmonic,voltage fluctuation and flicker as the index system of the power quality evaluationsystem. At the same time, the index data are collected by using the data acquisitionequipment to monitor the data of target node.The determination of the weight is of great importance in the process of powerquality evaluation. This paper discusses the subjective weighting method whichdepends on the subjective judgment of the decision maker and the objective weightingmethod which depends on the measured data. On the basis of the full consideration ofthe advantages and disadvantages of the two methods, this paper discusses thecombination of the two weighting methods and finally acquires the combined weightvector by solving the coefficient of the combined weight on the basis of the principleof maximizing deviations. The choice of evaluation algorithm relates to the result of the power qualityevaluation. This paper discusses successively five methods: the probabilistic method,the grey correlation ideal solution, the matter element analysis method, radar chartmethod and the principal components project method and so on. This paper choosesthe principal components project method as its evaluation algorithm, measures powerquality data of the node of Grid-connected PV systems and finally analyzes the powerquality of the node to be evaluated.