Research On Low-cost Synchronous Phasor Measurement Device For Large-scale Deployments In Distribution Networks

With the continuous access of distributed power sources and electric vehicles to the distribution networks,the structure of the distribution networks becomes more diversified,and its dynamic process becomes more complex and changeable,so it is particularly urgent to implement more comprehensive monitoring of its various parts.As the current mainstream PMU devices are expensive,when deploying PMU in distribution networks containing a large amount of new energy,the rationality of technology and economy and the actual demand form a contradiction.Therefore,in order to meet the monitoring requirements of the distribution networks and realize the large-scale deployments of PMU devices in the distribution networks,it is very necessary and practical to develop low-cost,miniaturized,and high-precision PMU devices.Therefore,this article aims to study a low-cost and high-precision PMU device suitable for large-scale deployments in the distribution networks,and to provide a solution for realizing synchronous monitoring of the distribution networks.First of all,this article analyzes the actual situation and practical application requirements of the current distribution networks,and discusses the necessity and practical significance of developing low-cost and high-precision PMU devices.The sub-station,master station and communication system that constitute the WAMS system are introduced.Furthermore,a distribution networks PMU arrangement scheme based on the mixed deployment of low-cost PMU devices and high-performance multi-function PMU devices is proposed.The proposed scheme can meet the monitoring requirements while achieving good overall economic benefits.Secondly,this article studies the high-precision time synchronization technology for synchronous phasor measurement,and designs a low-cost time synchronization device that can correctly decode the externally input IRIG-B(DC)code,and provide each PMU device with correct time information and a high-precision synchronization second pulse 1PPS signal.This article describes the IRIG-B(DC)code decoding method and its specific steps in detail,expounds the method of achieving high-precision time synchronization between the time synchronization device and the PMU devices,and experimentally verifies the time synchronization device.Finally,this article introduces a software frequency measurement method,expounds the basic principle of the discrete Fourier transform method(DFT)and the improved DFT method that divides the DFT calculation into integer part and decimal part based on real-time frequency to correct the measurement error under asynchronous sampling,and carries out simulation verification.Combining the software frequency measurement method with the DFT method can also realize the development of low-cost and high-precision PMU devices.In this article,a low-cost and high-precision PMU device based on the non-DFT method is developed.It uses a shaping circuit and a zero-crossing detection method to measure the frequency and phase of the phasor,and uses a rectifier circuit to measure the amplitude of the phasor.The specific circuit design of each part is given,the measurement errors are analyzed and the software compensation methods are given.The low-cost PMU device based on the non-DFT method can still ensure the high-precision measurement of the fundamental phasor when the frequency is shifted.