Research On Optimal Allocation Of Voltage Sag Monitoring Point And Voltage Sag Data Compression

With the increasing proportion of the sensitive load in the modern power grid,the power quality problem is paid more and more attention.In all complaints of power quality problems,the proportion of voltage sags is the largest.The unpredictability of the short-circuit fault in the system causes the randomness of the voltage sag,and then affect the normal working state of the sensitive equipment in the system,resulting in the economic loss of the power users.So observing the voltage sags for the actual distribution network with multiple voltage levels has important practical significance,which can reduce the economic loss of the power users and improve the power supply quality.Considering the cost input of power quality monitoring equipment,under the premise of ensuring the voltage sag can be observed,the monitoring point is chosen to be the least.How to effectively solve the problem of the large amount of data and the difficulty of storage and transmission caused by voltage sag detection is an important research direction.In view of the above two problems,this paper proposes a method to optimize the allocation of voltage sag monitoring points and compress voltage sag data.Based on the improved MRA method,the optimal allocation method of voltage sag monitoring points is proposed.The bus in the system is classified according to the voltage level,and the zero sequence impedance matrix is determined according to the relative position between the monitored bus and the monitored line.At the same time,according to the connection mode of the transformer and whether the system is effectively grounded,the voltage sag value is corrected.The simulation results of traditional MRA method are mainly for the standard node test system.In this paper,the actual distribution network with four voltage levels is simulated and analyzed.By comparing the results of this paper with the traditional MRA method,the method proposed in this paper can overcome the shortcomings of monitoring blind spot existing in the traditional MRA method,and effectively optimize the voltage sag monitoring points allocation of the actual distribution network with multiple voltage levels.According to allocation of voltage sag monitors,the concentric relaxation vulnerability whose center is the fault point is proposed.The proposed definition can effectively reduce the workload involved in traditional voltage sag vulnerability areas and provide us a judgment reference of the attribution of liabilities between power supply department and power users.Based on the optimal allocation,for the problem of huge amount of data,which is difficult to store and transmit.This paper applies the compressive sensing theory to the acquisition and transmission of the voltage sag signal,and the reconstruction algorithm of the sag signal is orthogonal matching tracking algorithm.By comparing the recovery effect of the voltage sags signal under different compression sampling ratio,it is concluded that the higher the number of sampling points,the better the reconstruction effect.Under the condition of using FFT as sparse base,the voltage sags signal is reconstructed by selecting different measurement matrices.After simulation experiments,it is found that some-hadama matrices have the best reconstruction effect.In order to further explore the effect of the sparse degree K of the signal on the reconstruction effect of the voltage signal,this paper compares the reconstructed effect of the algorithm by setting different sparse degrees K in the orthogonal matching tracking algorithm.It is found that the choice of sparse degree K has a great effect on the effect of reconstruction.Through the simulation analysis,the validity of the voltage sag data compression method based on the compression perceptual theory is proved.