CN102064827B - Rubidium oscillator-based standard frequency and time adjusting method - Google Patents

Abstract

Based on the standard frequency and time adjustment method of the rubidium oscillator, after the rubidium atomic oscillator is selected as the reference frequency source, the FPGA performs frequency multiplication and frequency division on the reference frequency source to obtain the locally generated second pulse signal. The FPGA uses the externally input second pulse signal as a reference to perform phase difference measurement calculations on the intrinsic second signal. The measured phase difference value is assigned to the designated register inside FPAG, and transmitted to ARM through the data bus. ARM calculates the time-varying value of the phase difference between the intrinsic second signal and the external input second signal, and calculates the frequency difference between the rubidium atomic oscillator and the external standard frequency according to the difference. The frequency difference value calculated by the ARM is fed back to the FPGA through the data bus. According to the received frequency difference value, FPGA performs frequency modulation operation on the rubidium atomic oscillator, so that the output frequency of the rubidium atomic oscillator is traceable and synchronized to the superior time and frequency reference. The invention has the beneficial effects of being able to provide high-performance, high-stability and high-precision time signals.

Description

Standard Frequency and Time Adjustment Method Based on Rubidium Oscillator

technical field

The invention relates to the construction technology of high-precision frequency and time sources in the technical fields of synchronous communication, synchronized phasor measurement, traveling wave ranging, wide-area dynamic monitoring and analysis, power grid stability control, and fault wave recording in power systems.

Background technique

At present, high-performance standard frequency sources mainly sample cesium atomic oscillators and rubidium atomic oscillators. Among them, cesium atomic oscillators have the best performance, but are expensive and difficult to purchase, and the performance of rubidium atomic oscillators is lower than that of cesium atomic oscillators. By designing appropriate algorithms and adopting effective and applicable technologies, this product meets the requirements of power system for high-precision frequency and time sources (high accuracy, high long-term stability, and small long-term drift), and obtains close to cesium atomic oscillation device performance. The algorithms and technologies involved in this product include: comprehensive selection technology of multiple frequency sources, taming algorithm of high-precision rubidium atomic clock, UTC time receiving technology, high-precision time signal generation algorithm, self-clock-second phase adjustment algorithm, second signal Phase large jump processing technology, etc.

Contents of the invention

purpose of invention

The purpose of the present invention is to organically combine the high-precision rubidium atomic oscillator with high-precision frequency measurement technology and time synchronization technology, so that the frequency signal and time signal output by the rubidium atomic oscillator can be tamed and synchronized with a higher level of time at the same time Frequency references (China UTC (NTSC) maintained by the National Time Service Center, grid autonomous time center time, Beidou satellite time, GPS satellite time, etc.), improve the long-term stability and accuracy of frequency and time signals, and reduce drift.

Technical solutions

The common frequency standards in the power industry are 10MHz and 2.048MHz frequency signals, and the power rubidium clock equipment receives frequency standards from the superior time center through the frequency input port.

When the frequency selection module has an external frequency input, the external frequency source is preferentially used, so that the time and frequency signal output by the power rubidium clock device is directly synchronized with the superior time center.

When the external frequency input is interrupted, the electric rubidium clock device relies on its own rubidium atomic oscillator to continue to output a stable frequency signal.

After the rubidium atomic oscillator is selected as the reference frequency source, the FPGA performs frequency multiplication and frequency division on the reference frequency source to obtain locally generated second pulse signals. The FPGA uses the externally input second pulse signal as a reference to perform phase difference measurement calculations on the intrinsic second signal.

The measured phase difference value is assigned to the designated register inside FPAG, and transmitted to ARM through the data bus. ARM calculates the time-varying value of the phase difference between the intrinsic second signal and the external input second signal, and calculates the frequency difference between the rubidium atomic oscillator and the external standard frequency according to the difference.

The frequency difference value calculated by the ARM is fed back to the FPGA through the data bus. According to the received frequency difference value, the FPGA performs frequency modulation operation on the rubidium atomic oscillator, so that the output frequency of the rubidium atomic oscillator is traceable and synchronized to the superior time and frequency reference.

The frequency-modulated rubidium atomic clock outputs standard second pulse signals, and one of the second pulse signals is sent to external satellite comparison equipment or traceability equipment to calculate the time difference message value. The FPGA analyzes the time difference message to obtain the phase difference value to be adjusted, and performs phase modulation operation on the output second signal, so that the phase of the intrinsic second signal is synchronized with the standard second signal. The intrinsic second signal after frequency modulation and phase modulation is used to drive the local clock module to generate standard time messages.

The externally input time message is used for the time synchronization operation of the local self-propelled clock, so that the output time message is synchronized with the superior time standard. The time value generated by the clock is assigned to the ARM, and the ARM control panel displays the value of the output time message.

Beneficial effect

The beneficial effect of the present invention is to adopt the principle of preferentially selecting an external input from a higher-level time-frequency reference signal, and distribute the frequency after multiple comparisons (comparison between the external input source and the internal rubidium atomic oscillator) at the timing network layer and time standards, providing high-performance, high-stability and high-precision time signals for power networks.

Description of drawings

Fig. 1 is the design scheme of electric rubidium clock;

Figure 2 is the second signal phase modulation technology;

Fig. 3 is the generation of time message;

Fig. 4 is the embodiment of the dual rubidium clock time central station.

Detailed ways

The design scheme of the electric rubidium clock is shown in Figure 1. According to actual needs, the main functions to be realized are as follows:

Provide a variety of high-precision frequency source input interfaces, access to external standard time sources, and track high-precision time;

Frequency selection unit, the electric rubidium clock has three frequency sources of external 10MHz, 2.048MHz and internal rubidium atomic clock 10MHz, and the external frequency source is preferred;

The frequency modulation unit, according to the frequency stability characteristics of the rubidium atomic oscillator, resonates the local frequency with the higher-level time reference input from the outside;

The time difference message receiving unit receives the phase difference value from the comparison device, adjusts the phase in real time, and synchronizes the output second with the standard second;

A phase measurement unit, which measures the phase difference between the intrinsic second and the second of the externally input time reference;

Phase adjustment unit, receiving phase adjustment from time difference messages, network management and synchronization buttons;

The second signal phase jump processing unit smoothes the second phase jump caused by various abnormalities;

The panel key unit provides a manual trigger mechanism synchronized with the external time reference;

Provide standard time message and second signal input interface to synchronize external standard time signal;

Coordinate the conversion unit from UTC time to Beijing time, and complete the time adjustment function in different time zones;

Time signal output unit, the output is highly accurate and stable. Time signal without jumps;

The management information serial interface unit provides a communication interface for the unified network management system.

The common frequency standards in the power industry are 10MHz and 2.048MHz frequency signals, and the power rubidium clock equipment receives frequency standards from the superior time center through the frequency input port. When the frequency selection module has an external frequency input, the external frequency source is preferentially used, so that the time and frequency signal output by the power rubidium clock device is directly synchronized with the superior time center. When the external frequency input is interrupted, the electric rubidium clock device relies on its own rubidium atomic oscillator to continue to output a stable frequency signal. After the rubidium atomic oscillator is selected as the reference frequency source, the FPGA performs frequency multiplication and frequency division on the reference frequency source to obtain locally generated second pulse signals. The FPGA uses the externally input second pulse signal as a reference to perform phase difference measurement calculations on the intrinsic second signal. The measured phase difference value is assigned to the designated register inside FPAG, and transmitted to ARM through the data bus. ARM calculates the time-varying value of the phase difference between the intrinsic second signal and the external input second signal, and calculates the frequency difference between the rubidium atomic oscillator and the external standard frequency according to the difference. The frequency difference value calculated by the ARM is fed back to the FPGA through the data bus. According to the received frequency difference value, the FPGA performs frequency modulation operation on the rubidium atomic oscillator, so that the output frequency of the rubidium atomic oscillator is traceable and synchronized to the superior time and frequency reference. The frequency-modulated rubidium atomic clock outputs standard second pulse signals, and one of the second pulse signals is sent to external satellite comparison equipment or traceability equipment to calculate the time difference message value. The FPGA analyzes the time difference message to obtain the phase difference value to be adjusted, and performs phase modulation operation on the output second signal, so that the phase of the intrinsic second signal is synchronized with the standard second signal. The intrinsic second signal after frequency modulation and phase modulation is used to drive the local clock module to generate standard time messages. The externally input time message is used for the time synchronization operation of the local self-propelled clock, so that the output time message is synchronized with the superior time standard. The time value generated by the clock is assigned to the ARM, and the ARM control panel displays the value of the output time message.

In view of the functions to be realized by the electric rubidium clock equipment, the invention content of the electric rubidium clock mainly comes down to:

Select the system frequency source according to the priority;

Accurate measurement of the frequency of the rubidium atomic clock, and frequency modulation of the rubidium atomic clock to tame and synchronize its frequency with a higher-level time reference;

Generate self-clock (seconds signal and time telegram) based on frequency source;

Receiving of time difference message and time message;

Adjust the output second phase according to the time difference message value and network management value;

Second signal phase modulation and large phase jump processing;

Manually set the frequency source, time data and phase parameters through the network management;

Provide standard 10MHz frequency, standard second signal and standard time message for the whole time central station.

The functional modules of the system include frequency selection module, phase modulation module, self-clocking module, frequency modulation module, processor interface module, alarm and state quantity collection module, panel display design module and network management design module. The circuit of the system is mainly composed of time signal drive circuit, frequency multiplier, rubidium atomic clock, battery unit, field programmable gate array and microprocessor.

The functions of each module are as follows:

Frequency selection module: select one from the external input 10MHz frequency source or rubidium atomic clock 10MHz frequency source as the working clock of the system. After power-on, the external priority is defaulted. If there is no external, the local rubidium oscillator is selected as the frequency source, and the frequency source can be selected through the network management software;

Phase modulation module: analyze the time difference message from the satellite comparison device to obtain the phase difference value to be adjusted, and perform phase modulation on the output second signal; support the network management program to manually set the phase modulation value, and perform phase modulation on the output second phase; support or Directly press the key to manually synchronize the external input second signal; the phase modulation value is limited in the phase modulation algorithm, and the second phase jump caused by various abnormalities is smoothed. When the phase modulation value exceeds the critical value, the upper limit of the phase modulation value is taken Phase modulation is performed on the second signal to prevent large phase jumps caused by abnormal conditions. See attached Figure 2.

Self-propelled clock module: a clock that runs automatically based on the intrinsic second signal generated by the system clock, which can synchronize externally input time messages, or directly set time data through the network management system; the system outputs time messages externally based on the self-propelled clock time data. See attached figure 3.

Frequency modulation module: When the system clock signal is provided by the rubidium atomic oscillator, the external input second signal is used as a reference to measure the cycle difference between the local second and the external input reference second, and the frequency modulation algorithm based on the stability curve of the rubidium atomic oscillator is calculated. Output frequency modulation value to frequency modulation of rubidium atomic oscillator;

Processor interface module: responsible for transferring data between FPGA and ARM, these data include: frequency modulation value, time data, phase modulation value, state parameters configured by network management;

Alarm and state quantity acquisition module: this module mainly collects various input terminals, rubidium atomic clock, power supply, battery state quantity parameters and sends them to the network management;

Panel display design module: Display device time information through LCD display. The device time is synchronized with the external input reference time through the operation of the panel keys.

Network management design module: The functions of the network management part include: remote control and status monitoring. Status monitoring includes: various external terminal collection data, power battery alarm data, rubidium atomic clock status, current frequency modulation value and current frequency source, etc. Remote control includes: time report setting, phase adjustment, frequency adjustment, frequency source selection setting, etc.

Frequency Modulation Algorithm of Rubidium Atomic Clock

The rubidium atomic clock used in the electric rubidium clock can be reset, FM and other operations through the serial port. When there is no external frequency input, the system clock is provided by the rubidium atomic clock. At this time, the circuit control unit can send a reset command through the network management to lock the output frequency of the rubidium atomic clock at about 10MHz. Based on the external input second signal from the cesium atomic clock of the GPS satellite, the output frequency of the rubidium atomic clock is measured and calculated, and the frequency difference value is calculated by the least square method. The frequency modulation algorithm calculates the frequency modulation value based on the obtained frequency difference value and the frequency stability curve of the rubidium atomic oscillator. The frequency modulation algorithm performs filtering operation on the frequency modulation data, discarding large frequency modulation data caused by abnormalities. According to the frequency modulation value obtained by the frequency modulation algorithm, the frequency modulation command is sent to modulate the frequency of the rubidium atomic clock, which can realize the traceability and synchronization of the output frequency of the rubidium atomic oscillator to a higher-level standard time frequency signal, and finally output a stable 10MHz frequency signal.

The FM command is as follows:

(1) According to the RS232 serial port communication protocol, the FPGA sends the reset command 'RST' in the form of ASICII characters, and ends with the "Enter" key to realize the reset;

(2) The frequency modulation function can be realized by sending the FRExxxxxxxx command + enter; the highest bit of xxxxxxxx is the sign bit: '0' increases, '1' decreases. The last 7 bits of data are the decimal frequency modulation value X, and the unit is millihertz. Its calculation formula is:

X=

表示频差值。 in,

Indicates the frequency difference value.

See Table 1 for the stabilization time required for the rubidium atomic clock to receive the frequency modulation command.

FM range (Hz) Time (s) (reference value) X*10 ^-7 X*5 X*10 ^-8 X*0.5 X*10 ^-9 X*0.05

Table 1. Frequency modulation tracking time of rubidium atomic clock

In the present invention, through the hierarchical selection processing of multiple time sources, the excellent frequency stability of the rubidium atomic oscillator is fully utilized to tame and synchronize to a higher level of time and frequency reference (China UTC (NTSC) maintained by the National Time Service Center, Grid autonomous time center time, Beidou satellite time, GPS satellite time, etc.), providing stable frequency (10MHz) reference, second phase reference and time reporting reference for the master station of the entire time system.

In view of the development needs of the smart grid, the implementation of the power rubidium clock as the time central station is shown in Figure 4, and the design scheme of the dual rubidium clock central station is usually adopted: configure two sets of power rubidium clocks as the frequency reference, the main and standby frequency division clock and Assign amplification devices. The power rubidium clock equipment after frequency calibration can be used as the highest frequency standard of the time central station, and the time service network composed of optical fiber, Ethernet and other transmission media, together with the PTP master clock, clock expansion device and other equipment, form a grid time unified system. The dual rubidium clock devices are mutual backup, which improves the reliability of the time center station, and in this way can also get rid of the transitional dependence on GPS.

Claims (1)

1. based on the standard frequency and time adjustment method of rubidium oscillator, it is characterized in that, comprising the following steps: When the frequency selection module has an external frequency input, the external frequency source is preferentially used, so that the time and frequency signal output by the power rubidium clock device is directly synchronized with the superior time center; When the external frequency input is interrupted, the power rubidium clock device relies on its own rubidium atomic oscillator to continue to output stable frequency signals; After the rubidium atomic oscillator is selected as the reference frequency source, the FPGA performs frequency multiplication and frequency division on the reference frequency source to obtain the locally generated second pulse signal; FPGA uses the external input second pulse signal as a reference to perform phase difference on the intrinsic second signal measurement operation; The measured phase difference value is assigned to the designated register inside FPAG, and transmitted to ARM through the data bus; ARM calculates the change value of the phase difference between the intrinsic second signal and the external input second signal over time, and calculates the rubidium atomic oscillator according to the difference Frequency difference from external standard frequency; The frequency difference value calculated by ARM is fed back to FPGA through the data bus; FPGA performs frequency modulation operation on the rubidium atomic oscillator according to the received frequency difference value, so that the output frequency of the rubidium atomic oscillator is traceable and synchronized to the superior time and frequency reference; After frequency modulation, the rubidium atomic clock outputs standard second pulse signals, one of which is sent to external satellite comparison equipment or traceability equipment to calculate the time difference message value; FPGA analyzes the time difference message to obtain the phase difference value to be adjusted, and The second signal is output for phase modulation operation, so that the phase of the intrinsic second signal is synchronized with the standard second signal; the intrinsic second signal after frequency modulation and phase modulation is used to drive the local clock module to generate a standard time message; the FPGA receives The frequency difference value of the rubidium atomic oscillator is performed on the frequency modulation operation steps, and the frequency modulation value X is calculated according to the following formula: X=

in, Indicates the frequency difference value.

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