Study On Power Quality Supervisory Method

With the high development of the industrial technology and information technology, power quality (PQ) has become a problem, which attracts the concern in many fields. The basic concept and national standard of power quality are described in chapter 1. Several commonly used digital signal processing methods are introduced. To the actuality of PQ supervisory study and its problems, a systematic and deep study in the PQ monitoring is carried out in this dissertation. This paper mainly studies the algorithms of measuring harmonics, interharmonics, flicker and dynamic power quality disturbances (DPQDs).To monitor the interharmonics, this paper makes analysis and comparison among many modern methods. In order to simplify the calculation and consolidate with the harmonics measurement, we decide to adopt the FFT method. In this paper, a technique based on a double-stage signal processing procedure is used: In the first stage, the harmonic components are accurately estimated via phase-lock loop and filtered away from the original signal so that in the second stage, interharmonics can be evaluated via Hanning-weighted interpolating FFT.In chapter 3, the IEC proposed standard to quantify flicker level is discussed and various digital implementations are analyzed. Both the digital filtering method and the voltage spectral method present some problems. The method proposed in this paper is based on the forward and inverse fast Fourier transform (FFT), and on filtering in the frequency domain, for the implementation of the weighting filter of block 3 of the IEC functional diagram. This method is flexible and simple in calculation.As to DPQDs, a method for detecting and classifying DPQDs based on Mathematical Morphology (MM) is proposed in chapter 4. In this method, the magnitude characteristic of the denoised signal is extracted via dilation operation with a long morphologic structure element. The instant of the disturbances can be located accurately through analyzing the morphologic gradient of the differential signal.Finally, based on the magnitude characteristic of the signal and the morphologic gradient of the differential signal, the main five types of DPQDs can be classified.In the fifth part, simulations 'results are given showing that those new supervisory algorithms derived from this thesis are effective, simple and fast ways which can meet our requirement. Their performances are better than those commonly used detecting algorithms.To enhance the power quality, it is the first thing to detect and classify the power quality disturbances and then take measures. In this paper, algorithms for measuring major PQ index were discussed in length. Through simulations and comparison, extensive research was made on several algorithms applicable for Real-time PQ measurement, which laid the solid theory ground for the design of Real-Time PQ Instrument. At last, a conclusion is made and some further research problems are pointed.