The High Precision Synchronous AC Acquisition System Based On GPS

The safety and stability of power system determine whether the construction ofcountry and life of people can be carried out smoothly, so the power grid must takessteps to protect and monitor power system. PMU makes efficient monitor to powersystem and makes sure it can be carried out smoothly. Because of the importance ofPMU, power sectors should take comprehensive detections according to theinspection standard of country before using it to make sure the PMU is accurate andefficient. Designing acquisition system of calibration instrument is the main task ofthis project.The calibration instrument consists of signal source and the high precisionsynchronous AC acquisition system based on GPS which is designed in this project.The system finish sampling of AC signal with asynchronous sampling, signalparameters are calculated with four-term fifth derivative Nuttall window andinterpolation algorithm, system feeds parameters back to signal source and make it tobe a closed-loop system. Acquisition system and PMU sample the signal source withpulse per second of GPS, then transmit data to computer, the system can achievescalibration of PMU with calculation and analysis of software on computer.PMU use asynchronous sapmling to finish the sampling of AC signal, in order toachieve calibration of PMU, acquisition system need to use asynchronous samplingand Nuttall window is used to process the signal, so it can restrains spectrum leakageand fence effect which are caused by asynchronous sampling, finally the calculationsare corrected with four-term fifth derivative Nuttall window and interpolationalgorithm, so it can gets high precision parameters of signal, the precision ofacquisition system is0.05%. System feeds parameters back to signal source incalibration instrument and to be closed-loop system, signal source adjusts outputsignal and makes it reach higher precision and stability.DSP processor TMS320F2812is the core of system, it achieves acquisition ofAC signal and data processing. High accuracy and fast A/D chip ADS8556and highaccuracy and stability OCXO guarantees the system achieve high precision sampling.The GPS receiver provides high precision synchronous pulse per second for system,and it guarantees the calibration instrument and PMU start sampling at same time andachieves the calibration of PMU. Firstly, paper makes a brief introduction to research significance and status ofproject, then expounds the realization process of calibration instrument. it makes aresearch about measuring algorithm of power system, and mainly introduces thefour-term fifth derivative Nuttall window and interpolation algorithm. The paperanalyses the hardware circuit in detail and makes illustration to the theory of circuitwith schematics. The section of software provides flow diagram of program,especially the important modules. Finally, accuracy of acquisition system is verifiedand shortcomings are found through experiments, then more steps are taken toimprove and perfect system.