A Synchrophasor Measurement Algorithm Considering Out Of Band Interference

The fundamental frequency of power system is fluctuating caused by unbalancing power output,changing load and unexpecting line fault.However,the existing algorithm cannot indicate the dynamic character of frequency,when the frequency deviates from the normal frequency largely.What's more,indispensable protection on the electric generator introduces the out of band interference so that the measurement accuracy is rapidly falling.From what have been mentioned above,how to extract the fundamental phasor accurately under the frequency deviation and how to provide the precise frequency value under the out of band interference would become the research emphasis.Therefore,firstly,this paper offers a frequency tracking method based on the Discrete Fourier Transform(DFT)phasors;secondly,a phasor measurement algorithm based on the multi-frequency model considering frequency deviation is researched and analyzed;finally,the multi-frequency model is enhanced and improved to estimate the out of band interference.As result of the frequency deviation from the normal frequency largely,this paper provides two frequency tracking method based on the DFT phasor.The first one is binary search whose progress is contrasting amplitude,obtaining the spectrum relationship between the amplitude and the frequency,getting the frequency tracking value.The last one is polynomial method,which spreads the higher order information about phase angle and acquires the frequency tracking value.Two methods can give rough frequency values with simple and convenient ways.According to the requirement of IEEE measurement standard on the synchrophasor,the multi-frequency phasor model is employed to reflect the effective information around real frequency,and to establish a phasor model including multi-frequency phasor.The accuracy phasor value can be obtained by estimating rough frequency,looking the matrix table calculated offline,revising the DFT value and shifting phasor.Test results of both simulated signals and PSCAD/EMTDC generated signal show that the proposed estimator can provide accurate phasor estimations under dynamic conditions of frequency ramping and power oscillation at the cost of limited increase of computational burden.According to the requirement of IEEE measurement standard on the out of band interference,firstly,leakage phenomenon is analyzed considering out-of-band interference and fundamental frequency deviation,and a rough out-of-band phasor is obtained by reassigning phasor estimation of DFT.Then,the rough phasor was utilized to calculate rough out-of-band frequency,treated as the reference frequency of the expanding multi-frequency model.Finally,according to the higher-order derivatives of model,accurate frequency estimation could be obtained.Simulations show that the proposed algorithm can accurately yield both fundamental frequency and out-of-band frequency under frequency deviation and noise disturbance.The actual power-system-voltage test illustrates that the proposed algorithm can provide frequency estimations with smaller fluctuation than that of the algorithms in comparison.This paper is proposed to improve the comprehensive performance of synchrophasor phasor measurement algorithm,and the theoretical derivation and simulation result show that multi-frequency model and their modify model bring a new research idea for the dynamic synchrophasor phasor measurement algorithm and the fundamental frequency measurement algorithm.Furthermore,this paper provides the reference information for the out of band interference extraction and filter,supplying the algorithm research on the complex condition.