Characteristic Analysis And Detection Method Of Power Grid Voltage Sags

With the continuous construction of smart grid,a large number of sensitive large-scale power electronic devices are widely used in power systems.Duo to voltage sag will seriously affect the normal work of these devices,the fault should be eliminated from the power system as soon as possible to ensure the power grid to resume normal operation.On the other hand,the realization of low voltage ride through of wind turbine generator also need to accurately obtain the information of voltage sag characteristics.Therefore,it is great practical significance to realize fast and accurate detection of voltage sag characteristics.In this paper,power grid voltage sag detection methods are taken as the research object.Based on the Matlab/Simulink software platform,different voltage sag models are built.The simulation results show that the effect of grid voltage is caused by load changes of the user terminal and different short circuit faults occur in power grid or transmission line.At the same time,the commonly used method of voltage sag feature detection is studied,the advantages and disadvantages of each method are summarized.At last,the improved method is proposed,it establish simulation model to simulate and verify the feasibility and accuracy of the improved method.Firstly,the technical route and the overall scheme of characteristic analysis and detection method of power grid voltage sags are analyzed.Due to the different degree of voltage sag,various fault types are classified according to ABC classification method,it lists the mathematical models of voltage sag for each fault type.At the same time,the principle of commonly used method of the amplitude of positive and negative component fundamental voltages detection and voltage phase angle and frequency detection are analyzed briefly,and the advantages and disadvantages of these detection methods are also given.Secondly,the analysis of voltage sag is mainly focused on,it introduces classification,characteristics,causes and harms of voltage sag.At the same time,the fault model of transmission line,the fault model of transmission line and the large load on-off model of user terminal are built by using Matlab / Simulink,the simulation results and analysis of grid voltage sag are given,and it analyze the harmonics.Thirdly,in order to solve the problem of poor harmonic interference and slow detection,the basic principle of the traditional symmetrical component method is deeply studied,it presents an instantaneous symmetry component method based on adaptive notch filter.At last,the simulation results show that the improved algorithm can detect the amplitude of voltage positive and negative sequence components quickly and precisely,and accurately track the change of grid frequency.Finally,the phase detection of the voltage phase of the power grid is usually based on the phase-locked loop method.When the three-phase voltage is unbalanced and contains higher harmonics,output phase waveforms of the traditional phase-locked loop appeare serious shock,and test results deviate from the true value.To solve this problem,an improved synchronous coordinate system(PLL)based on multivariable filter is proposed.From the simulation results can be seen that the proposed improved algorithm can accurately lock the voltage phase and detect the grid frequency offset with good accuracy and effectiveness.