| With the continuous development of electric power system, more and more nonlinear loads, such as rectifier loads and impulse loads, added increasing to the modern electric power systems. The existence of these nonlinear loads in power systems will results in bad power quality, such as voltage distortion, voltage fluctuation, voltage flicker and three phase unbalance. As a result, the power supply quality and the operation condition of the power system are exacerbated. In recent years, the disputes and faults induced by power supply quality trend to ascent. It is increasing important to manage power supply quality and treat the electric pollutions.This thesis focus on the subject of power quality. First, the basic contents of electric power quality, individual indexes describing power quality, and definitions of power quality are investigated in detail; Then, the main causes and harms influencing power quality indexes are presented; And then, the standards of power quality are discussed, based on the analysis of the power quality standards adopted in and outside our country; Based on the analysis of the concepts and methods of fuzzy logic, the feasibility and merits of applying the fuzzy logic theory to power quality complex appraising are revealed. A new power quality complex appraising method is proposed, which consists of the first-grade appraising, the second-grade appraising and the final appraising. The appraising method fuses all indexes describing the electric power quality. Weights corresponding to each power quality indexes are introduced to consider the impacts of individual power quality indexes on the final unique power quality index.The field data are adopted to illustrate the proposed method. The analysis procedure and the calculation of complex power quality index are given. The theoretical and simulation results show that the proposed method is reasonable and effective. The proposed method is meaningful for appraising electric power quality in electricity markets.
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