Research On Synchronized Phasor Measurement Algorithm Under Power System Dynamic Characteristics

In recent years,the smart grid has developed rapidly in China.The formation and expansion of large grid interconnection make the operating environment of power system more complex.Due to the integrity of the power system,sudden failure would lead to a wide range of power outages and cause serious economic losses and inconvenience,if no response were taken in time.In order to meet the new challenges of system security,the monitoring,protection and control performance of power system need a comprehensive upgrade.The wide-area measurement system plays an important role in the smart grid.It acquires dynamic parameters of each node in the power grid and monitors the whole network in real time by using the high-precision timing signal of the GPS system.Synchronized phasor measurement unit is a core part of wide-area measurement system,whose accuracy and real-time performance have a direct impact on the monitoring of power system.Some traditional synchronized phasor measurement algorithms have high precision under the static power system,but the precision degrades seriously when the system is in the dynamic state.In this paper,the research of synchronized phasor measurement algorithm under power system dynamic characteristics is as follows:Firstly,this paper proposes an improved variable forgetting factor recursive least squares frequency tracking algorithm to achieve high accuracy under static condition and fast track under dynamic condition.The algorithm makes the forgetting factor reach its maximum value under the static condition to increase its memory capacity and improve the frequency measurement precision.Under dynamic condition,the algorithm adjust the forgetting factor rapidly to the minimum value to improve the real-time performance of frequency measurement.Better performance of frequency tracking is achieved by adaptive adjustment of forgetting factor.The simulation results show that the algorithm is more accurate and faster than the traditional variable forgetting factor least squares algorithm.Secondly,the cause of the traditional DFT algorithm error under non-synchronous sampling condition is analyzed.According to the error mechanism of the DFT,two phasors ahead and lagging 30° of the measuring point areconstructed and calculated with the traditional DFT algorithm.By rotating the calculation result a new phasor is obtained based on the balance relationship of phasors.The dynamic error of the phasor measurement is reduced by mathematical operation.The phase angle accuracy is further improved by compensating the fixed portion of the phase angle error.As demonstrated by MATLAB simulation,the algorithm has greatly improved the amplitude measurement and phase angle measurement accuracy of phasor.Finally,based on the improved synchronized phasor measurement algorithm,the influence of the attenuated DC component on the measurement results when a failure occurs in the power system is analyzed.Based on the characteristics the attenuated DC component,a novel synchronized phasor measurement algorithm is proposed to filter the attenuated DC component effectively.The real part and imaginary part of the original failure phasor containing attenuated the DC component are obtained with the improved synchronized phasor measurement algorithm and substracted by those of the attenuated DC component respectively to improve the performance of the phasor measurement algorithm.The simulation demonstrates that this algorithm can filter out the influence of attenuated DC component quicklyand improve measurement precision.