Study On Voltage Sags Detection Method And Its Application Based On Generalized S-transform Algorithm

With the rapid promotion of new energy and microgrid,more and more nonlinear,impact and asymmetric power loads are connected to the power system,which causes the problem of power quality to become increasingly prominent,which has become an important factor that hinders the development of smart grid and threatens the safe operation of the power grid.Voltage sag is one of the typical power quality problems with high destructiveness,high frequency and wide range of influence.It has attracted more and more attention in recent years.Accurate and rapid detection of voltage sag is a prerequisite for monitoring power quality problems and ensuring clean,safe and efficient operation of power grids.Therefore,it is of great theoretical significance and application value to study the detection method of voltage sag,to explore the time frequency analysis algorithm with high accuracy and real-time,and to implement it on the practical engineering application platform.First,the basic concept of voltage sag is introduced,and its causes and hazards are analyzed.The current research status of common power quality analysis algorithm and detection device is introduced,and the key point of this thesis is the adaptive detection method of voltage sag based on generalized S-transform.Then,in view of the problem of poor noise resistance and large amount of calculation,the fast Fourier transform is used to obtain the spectrum,and the fundamental frequency amplitude is compared with the threshold to determine whether the sampling signal has a sudden drop of voltage.This method can quickly and accurately identify the voltage sag and can be used in the generalized S-transform algorithm when the voltage sags occur,thus reducing the computational complexity of the generalized S-transform.Then,aiming at the problem that the voltage sag of the sudden drop time is different to the time-frequency resolution of the generalized S-transform,a adjusting factor is introduced in the Gauss window to construct the Gauss optimization window,and the simplified operation of the S-transform is carried out only at the fundamental frequency point to improve the real-time performance of the algorithm.Through the quantitative analysis of the relationship between the adjustment factor,the drop time and the detection error of the voltage sag characteristic value,the optimization method of the adjustment factor is given.On this basis,the adaptive extraction mechanism of eigenvalue of voltage sag is proposed,that is to initialize the regulating factor as a constant value first,calculate the sudden drop time and phase jump by the generalized S-transform,and then adjust the adjustment factor based on the polynomial fitting function of the regulating factor and the sudden drop time,and calculate the sudden drop amplitude by t he generalized S-transform.At this point,we can extract the eigenvalues of voltage sag automatically.Secondly,a voltage sag detection and fault recording function is implemented on an embedded hardware platform based on ADC+DSP structure.The hardware schematic diagram and software program implementation steps of voltage signal conditioning,data acquisition and data processing are introd uced in detail.The voltage sag estimation and eigenvalue extraction method are explained in detail.Finally,the voltage sag detection device is tested in the sta ndard source,and the error sources are analyzed.The experimental results show that the volt age sag detection method proposed in this thesis can be accurate,fast and reliable on the embedded platform,and provides a good reference for the pr oblem of voltage sag detection.