Research And Implementation Of The System Of Power Quality Analysis

With the development of modern industry, nonlinear loads of power system are greatly increased. The electrical characteristics of these nonlinear loads, including nonlinearity, impulsion and imbalance, result in voltage aberrance. Voltage aberrance makes power quality severely worsen, endangers power system running safely and economically and affects some users’ working normally. The harmonic is the important parameter in power quality. So, harmonic measurement is very important in power system.A survey on the harmonics detection methods especially focusing on new methods and new theories emerged in recent years are given in this paper. The features and limitations of each method are also analyzed.The Fourier Transform cannot be directly used to the harmonic analysis because of its large errors, especially the phase error. A new method is proposed in this paper to reduce the errors, which is based on self-convolution cosine window and interpolation of phase difference correcting. Experimental results in MATLAB show the proposed method has very good performance and is easy to implement. It also really meets the need of on-line applications.The greatest shortcoming of FFT-based method is inaccurate in non-steady harmonics analysis. The paper proposes a method based on the use of the wavelet packet transform for the time-frequency analysis of steady and non-steady harmonics in power systems. The method uses Daubechies Wavelet as wavelet function to analyze steady and non-steady harmonics. Experimental results in MATLAB show the proposed method has very good performance.This paper designs and implements a system of power quality analysis based on dual-core processor OMAPL137. The system consists of a few power quality analyzers, a time system and a server. Each power quality analyzer can be used as a node to monitor and analyze the power system; also it can be available as a single portable instrument. The server analyzes the entire power network data and records the fault data. In this system, power quality analyzers use dual-core processor OMAPL137as cores. Therefore, this system is simple, low cost, extensible, easy to install and debug. Experimental results show the system is stable and accurate.