Power System Power Quality Analysis Method

With the rapid development of new technology, the sudden increase of loads, especially the incessant increase of nonlinear, impulsive and fluctuating loads, power quality problems often occur, such as harmonic, voltage sag, voltage fluctuation and flicker, unsymmetrical voltage, etc..This paper firstly introduces the definition, classification, harms, and compensating strategies of power quality problems. In various power quality problems, voltage sags are the worst dynamic power quality problems. With high-power impulsive and fluctuating loads accessing electrical network, voltage fluctuations can't be tolerated in some power supply networks. This indicates dynamic power quality problems have become primary disturbances influencing supply reliability now. But the research in those aspects such as harmonic, voltage deviation, frequency deviation and etc. of power quality is more than in voltage sag, voltage fluctuation and flicker. The research about voltage sag, voltage fluctuation and flicker started so late and still has many problems. So this paper mostly studies the algorithm of detecting voltage sag, voltage fluctuation and flicker in power quality problems.In order to detect voltage sags, this paper makes analysis and comparison among the methods of detecting voltage sags in every relative literature, points out their advantages and shortcomings. And then this paper proposes a new discrete method that is used to detect fundamental positive-sequence voltage based on park transformation. With complex integral algorithm replacing filter, the accuracy of detecting direct current component can be improved. This method can't be influenced by voltage distortion, and can be apply on the case of unsymmetrical loads. Its dynamic response time is half of fundamental period. The result of this method detecting voltage sags is stable, and possesses very high calculation accuracy. This method can be realized easily. Matlab is adopted to simulate the algorithm fordetecting voltage sags. The simulation result indicates that this method can accurately detect the magnitude, duration and phase jump information of voltage sags.In order to detect voltage fluctuation and flicker, this paper firstly summarizes methods of detecting voltage fluctuation and flicker in every relative literature. Then, the Hilbert transform (HT) are introduced in this paper as an effective and real-time approach for detecting the voltage flicker levels in distribution systems. Compared with the commonly used algorithms in the literature, the proposed technique is simpler in math, and is implemented easier. Moreover, the HT is capable of detecting the variations of the voltage flicker and supply frequency in distribution systems with high precision. Such accurate detecting facilitates the implementation of the control of flicker mitigation devices. Many different voltage flicker signals are adopted to validate the approach. Matlab simulations of the proposed approach for detecting voltage flicker that profile the different factors affecting tracking accuracy are presented. The simulation results are provided to verify the detecting capabilities of the HT and indicate the superior performance of the HT in detecting voltage flicker.According to IEC standards involved, short-time flicker Pst is primary indexscaling voltage fluctuation and flicker. This paper studies the analogue and digital realization of IEC flickermeter. Detecting methods in flickermeters are introduced. Then the principle of IEC flickermeter and both the analogue and digital realization methods are expounded as emphases. At the same time, all parts of flickermeter are designed. Linear interpolation method is adopted to calculate Pst. Matlab simulationand calculation results indicate that this flickermeter meets IEC's accuracy standards. Finally, this paper is summarized, and prospect of this topic is viewed.