Research On The Phasor Estimation Algorithm Of ?PMU In The Distribution Network

In recent years,the research and application of distributed generation have experienced rapid development.This trend has brought profound changes to the traditional analysis,planning and control strategies of distribution networks.In summary,the grid connection of various distributed energy sources has brought great challenges to the operating conditions of the distribution grid,such as bidirectional power flow,voltage rise,power loss reduction,harmonic and stability.The development of the synchronous phasor measurement provides a solution to the above problems.But the Phasor Measurement Unit(PMU)is mainly applied to the transmission grid.And the research and development of the synchronous phasor measurement technology of the distribution network is insufficient,and there is no suitable measuring algorithm and devices.Thus,the emergence of high-precision real-time monitoring systems is needed urgently.In the past two years,our country began to design the miniature synchronous phasor measurement unit(?PMU)according to the requirements of the distribution network.Due to the particularity of the distribution network,the phasor measurement algorithm of the transmission network cannot meet the accuracy requirements of the distribution network.Thus,the research on the synchronous phasor measurement algorithm of distribution network which plays an important role in the synchronous measurement system of distribution network is a problem that needs to be solved urgently.Firstly,this paper makes a deep study on the accuracy of the synchronous phasor measurement algorithm for the distribution network based on the characteristics of three-phase unbalanced outburst of the distribution network.Then,a conditional maximum likelihood estimation(CML)method suitable for phasor measurement of distribution network ?PMU is proposed on the basis of the established power signal model of three-phase unbalanced power distribution system,and this method was used to estimate the phasor magnitude and phase angle of three-phase three-wire and three-phase four-wire systems in distribution networks.Finally,the benchmark phase of the CML method is optimized,and a maximum likelihood estimation method(ML)for solving the reference phase and system frequency is proposed.The performance analysis and the example simulation of the benchmark phase optimized CML method are carried out through Matlab.In the experiment,the voltage and frequency estimations values of the algorithm are compared with the measured values of the previously studied ?PMU.The three-phase phasor values of the 33 node distribution system are compared with the three-phase voltage estimation values of this algorithm.Thus the steady-state and dynamic performance of the algorithm are verified,and the accuracy of phasor and frequency measurement is improved.It solves the problem that the data measurement accuracy of the traditional measurement algorithm cannot meet the requirements of the distribution network,and is of great significance to the improvement of the next ?PMU device.