Research On Power Quality Disturbances Recognition And Classification

In recent years, with the innovation of the science and technology and the rapid development of the national economy, the demand for power quality is becoming higher and higher. Meanwhile, the power quality is influenced by many factors as a result of the increased interference load in the power system. Nowadays, Power quality problems have been more and more serious; voltage sags and short interruptions have been recognized as the most serious problems affecting the safe operation of many electrical devices normally.For the steady power quality detection, algorithms have been more mature at home and abroad, particularly it can be achieved very high precision by the high-precision FFT algorithm's handling of the steady. However, for the transient power quality problems, both theoretical research and the development of devices are still in the stage of trying to apply. Taking reasonable measures is the guarantee to improve the power quality, and the correct detection and identification of power quality are the first and foremost. For this reason, power quality disturbances (five transient power quality disturbances and harmonics) detection and identification methods are studied in this paper. On the basis of the conclusion of the detection methods, this paper presents a new recognition and classification method of power quality disturbances.Firstly, a more comprehensive introduction to the concept of power quality, power quality classification and the present situation of power quality signals denoising and detection methods is proposed. This paper gives an illustration of the necessity of denoising before the power quality disturbances detection and uses wavelet-denoising method to denoise disturbances signal.Secondly, this paper presents the use of Hilbert-Huang transform (HHT) and wavelet transform to detection analysis of the disturbances signal, with two chapters introducing and simulating the transient power quality disturbances (voltage sags, voltage swells, voltage interruption, transient oscillations and transient impulse) and harmonics signal detection. Simulation results show that wavelet transform can effectively distinguish transient power quality disturbances and harmonics, and can accurately locate the time of the transient power quality disturbances beginning and ending, but it does not distinguish types of transient disturbances, while HHT can not only distinguish types of transient disturbances, but also accurately detect harmonics.Finally, on the basis of the conclusion of the results of power quality disturbances detection on these two methods (wavelet transform method, HHT method), a new detection method based on wavelet transform and HHT is proposed. This paper details the ideas and detection steps of this new method, and gives three simulation examples. Simulation results show the effectiveness and accuracy of this new method.