Research On Duration Detection And Disturbance Source Identification Of Voltage Sag

With the development of science and technology and a great quantity use of nonlinear power electronic devices, power quality has been concerned by more and more users. Voltage sag is one of the most frequent and serious power quality problems. Voltage sag duration which detection accuracy is premise and guarantee for DVR and other compensation devices working is the most important indicator to describe voltage sag. Voltage sag can be aroused by short circuit fault and induction motor starting and commissioning of transformer. Determining the voltage sag disturbance source is of significance to make definite responsibility and stable operation of power grid.Firstly, the thesis presents that the starting and ending times of the voltage sag are detected and located by use of information-entropy theory, and then the voltage sag duration can be calculated. Adaptability of the method is analyzed in conditions of different dropping amplitudes and harmonic waves and noise, the mathematical morphology filter is introduced to preprocess the voltage sag signal with containing noise. Using the Matlab software environment to prove the feasibility of the method proposed, the simulation result shows that this method is not only simple in principle but also has higher accuracy in detection, and this method has strong adaptability.Secondly, empirical mode decomposition energy-entropy is proposed to indentify the voltage sag disturbance source, which is the combination with empirical mode decomposition and information-entropy. Making empirical mode decomposition for voltage sag signals so that getting several stable intrinsic mode functions and calculates the energy-entropy each of them. Then, calculating the standard deviation of energy-entropy in every phase of ABC and getting the feature vector which could identify the different voltage sag disturbance source. The Matlab simulation results demonstrates that this method could identify the voltage sag disturbance source accurately and reliable, and calculations are simple.