Research On Phasor Measurement And Frequency Estimation Algorithm In Power System

With the continuous development of smart grid and new energy power system,the structure of power system is becoming more and more complex,and the requirement of system perception is also higher and higher.The synchronized phasors obtained by phase measurement unit(PMU)are used for real-time monitoring,diagnosis,protection and control of power system.Phasor measurement algorithm is to accurately estimate the phasor,frequency and rate of change of frequency(ROCOF)in the dynamic process of power system,which is of great significance to the stable operation of the system.This paper first introduces the background and significance of phasor measurement algorithm.Through the analysis of the research status at home and abroad,a phasor measurement and estimation algorithm suitable for power system dynamic conditions is proposed,which improves the measurement accuracy and dynamic performance of phasor estimation algorithm under dynamic conditions.Finally,the inertia of the system is estimated by using the frequency information.The main contents of this paper are as follows:(1)DFT algorithm has some defects,such as asynchronous sampling and frequency domain discretization.When the signal has frequency offset,DFT algorithm will have spectrum leakage in phasor measurement,which makes the calculation result produce error.To solve this problem,the phase angle error equation of DFT algorithm in the case of asynchronous sampling is derived.The phase angle difference is used to track and measure the signal frequency,and the frequency value with higher accuracy is obtained.Then,a synchronous phasor measurement method based on improved DFT is studied.The tracking frequency is used to adjust the data window of DFT algorithm,and the integer and decimal parts of the data window are used to estimate the phasor parameters.(2)For the signal with abrupt change of amplitude and phase angle,firstly,the electrical signal model suitable for dynamic condition is established by Taylor series expansion of the electrical signal with harmonic,noise and other conditions.Then,in order to improve the dynamic performance of the algorithm,Double Suboptimal-scaling Factor Adaptive Strong Tracking Kalman Filter(DSTKF)is used to track and estimate phasors.(3)In order to improve the accuracy of dynamic phasor measurement,this paper improves the signal model under the condition of power system oscillation.Considering the factors of amplitude modulation and phase modulation,the signal is linearized by Taylor expansion.In order to enhance the harmonic suppression ability of the least square method,the weighted least squares algorithm(WLS)is used to estimate the system frequency and frequency change rate.Then,the sampling frequency,data window type and length of the algorithm are analyzed and selected.(4)The inertia of power system is often considered as one of the important bases for synchronous operation of modern power system.According to the energy relation of inertia response,this paper applies a power system inertia evaluation method based on kinetic energy theorem.This method uses the node frequency value and the node active power change before and after the system disturbance to obtain the system equivalent inertia;Finally,in order to analyze the inertia distribution of the system,a kind of inertia distribution index is defined.The inertia distribution of the system is visualized by calculating the inertia index of each node and drawing the system inertia distribution diagram.