Research On Waveform Capture And Data Compression Of Complex Transient Power Quality Disturbances

In recent years, under the background of the smart grid development, more and more people begin to pay close attention to how to provide convenient and high quality power, which serves better for the information society. At the same time, contradictions in economic and social development make the power quality problems present new characteristics, On the one hand, with the improvement of power quality monitoring system, power grid structure is increasingly complex, more and more various non-linear devices are connected to power grid, and complex disturbance occurred is increasingly diverse. Therefore, how to capture complex transient power quality disturbance timely and effectively by using monitoring terminal becomes increasingly important. On the other hand, along with the gradual increase of monitoring points and constant increase of monitoring indicators, the consequent huge amounts of data need to be timely processed and analysed, the role data compression technology plays in the improvement of power quality problems becomes more important. On this basis, this paper studies and analyzes mainly focused on both complex transient power quality disturbance waveform capture and data compression.Firstly, in order to facilitate capture research, the complex transient disturbance is divided into three types, coverage, overlap and connection. Detailed analyses of the complex disturbance signal characteristics presented during waveform capture, aiming at different disturbance characteristics of disturbance events, four types of disturbance capture criteria are given.Complex transient disturbance waveform is captured using the constructed lifting complex wavelet scheme, capture algorithm also applies to the single disturbance.Secondly, in terms of complex transient power quality data compression, this paper expounds the basic principle of lifting wavelet packet transform and lossless compression method. According to the nature of the data compression and the characteristics of the electric power data, the compression algorithm which is based on the combination of both lifting wavelet packet transform and LZW lossless coding is designed. Signal is decomposed by using lifting wavelet packet transform, the best wavelet packet basis is searched and thresholding is processed, further lossless data compress is generated by reusing the LZW encoding, so good compression effect of power data is obtained.Finally, under the environment of Matlab, the mathematical model of transient disturbance signal is built and simulations for the above-mentioned two aspects are respectively made. The simulation results show that the capture algorithm can not only accurately capture single disturbance, complex disturbance and complex transient disturbance which contains background signal, such as harmonic and noise, but it also won’t capture small disturbance signal by mistake. Compression algorithm generates effective compression of the complex transient power quality data, the compression ratio of which is better and the reconstruction precision of which is high.