GPS-based precision clock online frequency calibration and time service

To improve the wide-area timing accuracy and stability of global position system (GPS) clock, the generalized regression model of complementary clock was established according to the different characteristics of GPS clock and crystal oscillator clock, and the crystal oscillator frequency was estimated in real time using generalized least squares method, which fixed the error of the regression model caused by frequency change of measured value, then accurate frequency estimation was achieved in the large crystal frequency drift and long time interval measurements. On this basis, timing pulse per second (PPS) synchronizing with coordinated universal time (UTC) was generated, which realized the precise online time service by using phase correction algorithm to eliminate the phase difference between timing PPS and UTC PPS. The experiment shows that the timing error of the algorithm is less than ±25 ns during long time operation using the SBR-LS receiver module and ordinary active crystal, which validates that the timing stability and accuracy are greatly improved. Therefore, the proposed algorithm accomplishes the precise online time service for wide area measurement, locating faults and other applications, and meets the online wide-area timing requirements of power grid monitoring system.