Research On Analysis And Detection Method Of The Power Quality Disturbances

In power system, mass use of power electronic devices, the increase of impact and nonlinear load and distributed power grid have resulted in increasingly serious power quality problems, which are severely influenced on power system and socio-economic. In order to take appropriate measures to improve power quality signals must be detected, analyzed and processed quickly and effectively. Combined with teager energy operator (TEO) demodulation method, this paper used the local mean decomposition (LMD) and intrinsic time-scale decomposition (ITD)to detect characteristic extraction and locate disturbance start and end time position of the power system disturbance signals.The causes of the deficiencies of the LMD in the disturbance detection at the time location capability was analyzed.An energy operator demodulating approach based on LMD was applied to power quality disturbance signal detection and analysis. The method was consisted of LMD and Teager operator. Firstly, voltage signal was decomposed into a number of product function(PF) component by LMD, then Teager energy operator demodulated PF to get instantaneous amplitude and instantaneous frequency of the signal. According to frequency mutation point of the time-frequency diagram, the starting and ending time of the disturbance occurring can be effectively located. The simulation results of the single disturbance signal and mixed disturbance signals of power quality showed that the method can detect amplitude and frequency precisely as well as effectively locate disturbances begin-end time.Improved ITD method is used for detection and analysis of power quality disturbance. According to the linear transformation of ITD which is easy to distortion, it uses the cubic spline and cubic polynomial interpolation in proportion. For mode mixing of local characteristic-scale decomposition, a new method of differential and integral local characteristic-scale decomposition was proposed.Voltage sag, voltage swells, harmonics,inter-harmonic and damped oscillation and other single and composite disturbance signals were decomposed by improved ITD to obtain several intrinsic scale components, and then ISC was demodulated by TEO to obtain instantaneous frequency and amplitude and locate the starting and ending time of the disturbance occurence. The method has the advantages of higher frequency precision, smaller amplitude fluctuations, better end distortion and more accurate time positioning. The simulations prove the feasibility and effectiveness of the method.