JP6907684B2 - Time synchronization device, time synchronization method and time synchronization program - Google Patents

Description

The present invention relates to a network time synchronization technique.

IEEE1588 PTP (Precision Time Protocol) is a protocol for synchronizing the time information of each device belonging to the network based on the reference time information. In the time synchronization method based on this protocol, the time difference between the reference time and the time of each device in the network can be obtained by the calculation of the time synchronization process, so the speed at which the internal clock of each device advances is adjusted to synchronize with the reference time. be able to. The time difference obtained at this time includes an error in the fluctuation of the transmission delay and is not accurate, so servo control is often applied (for example, Patent Document 1).

International Publication No. 2011/077558

The IEEE1588 PTP can calculate the time difference between the reference clock and the clock (internal clock) of each device on the network by accurately obtaining the round-trip time of the PTP packet. It will be accurate if the network is composed only of PTP-compatible devices.

However, in a network that does not support IEEE1588PTP, since the transmission time fluctuates and includes an error, servo control is applied in the adjustment of the internal clock of the device.

For example, when a PTP packet arrives via the L2 switch, it waits for the completion of transmission while the PTP packet is transmitted from one port to another port. The waiting time varies depending on the packet size and the number of packets. Therefore, a time difference occurs by 1/2 of the waiting time. Although the PTP packet makes a round trip, the waiting time differs between the going and returning, and a time error occurs in the delay direction and the advance direction.

Generally, the servo control is adjusted so as to approach the target time by PID control based on the difference between the current measured value and the target value as a measure against disturbance.

On the other hand, since the PTP clock can be adjusted accurately and does not cause disturbance, servo control becomes unnecessary. However, due to fluctuations in the transmission delay time, it may not be possible to make accurate adjustments because the measured values include errors, so servo control is required after all.

Servo control has the following problems. It takes a long time to complete the time synchronization (for example, about 1 to 20 minutes). If the transmission time of the PTP packet continues to be uneven on a round trip, it may not be possible to synchronize at the correct time.

Servo control is adopted when there is a device that does not support PTP, but there is no reason to use servo control if it is a system composed of PTP-compatible devices or a system directly connected to a network.

In view of the above circumstances, it is an object of the present invention to improve and shorten the responsiveness of time synchronization without requiring servo control.

Therefore, one aspect of the present invention is a time synchronization device that synchronizes the internal clock of the device belonging to the network with the reference clock of the network, and the time change of the internal clock is based on the time change of the internal clock and the reference clock. The adjustment amount calculation unit that calculates the adjustment amount for correcting the inclination of the internal clock, and the inclination correction that corrects the inclination of the internal clock based on the adjustment amount to match the inclination of the time change of the internal clock and the reference clock. A unit and a time correction unit that further corrects the inclination to match the time value of the internal clock with the time value of the reference clock and then matches the inclination with the inclination of the time change of the reference clock.

One aspect of the adjustment amount calculation unit is based on the difference between the time values of the reference clock and the internal clock at the time of the previous time synchronization and the difference between the time values of the reference clock and the internal clock at the time of the current time synchronization. Calculate the adjustment amount.

One aspect of the adjustment amount calculation unit corrects the inclination of the time change of the internal clock in one second of the internal clock after the time synchronization of this time.

One aspect of the present invention is a time synchronization method executed by a time synchronization device that synchronizes an internal clock of a device belonging to a network with a reference clock of the network, and the internal clock is based on a time change between the internal clock and the reference clock. The process of calculating the adjustment amount for correcting the inclination of the time change of the clock and the process of matching the inclination of the time change of the internal clock and the reference clock by correcting the inclination of the internal clock based on the adjustment amount. The process includes a process of further correcting the inclination to match the time value of the internal clock with the time value of the reference clock, and then matching the inclination with the inclination of the time change of the reference clock.

The present invention can also be an aspect of a time synchronization program that causes the computer to function as the time synchronization device described above.

According to the above invention, it is possible to improve and shorten the responsiveness of time synchronization without requiring servo control.

The block block diagram of the time synchronization system in embodiment of this invention. The block block diagram of the time synchronization apparatus in the said embodiment. A graph showing the time values of the reference clock of the network and the internal clock of the device belonging to the network over time. The graph explaining the process of correcting the inclination of the time change of the internal clock. The graph explaining the process of correcting the inclination within a predetermined time. The graph explaining the process of synchronizing the internal clock with the reference clock after the correction.

An embodiment of the present invention will be described below with reference to the drawings.

[Outline and configuration of this embodiment]
The time synchronization system 1 of the present embodiment shown in FIG. 1 is an example of a time synchronization system based on the IEEE1588 PTP (hereinafter, PTP) of the network 2.

The network 2 includes a local network 3 to which the management server 30 belongs, a local network 4 to which a plurality of devices 6 belong, and a wide area network 5 connecting the local networks 3 and 4. Then, each device 6 includes a time synchronization device 10 which is one aspect of the present invention.

In the graph illustrated in FIG. 3, the vertical axis represents the time value of the reference clock 31 of the network 2 of this embodiment and the internal clock 61 of the device 6 belonging to the network 2, and the horizontal axis represents the time. As shown in the figure, the time value increases as time elapses. The reference clock 31 and the internal clock 61 advance based on the frequency of a crystal device such as a crystal oscillator, but since an error occurs in the frequency, the inclination of the passage of time value is different, and the difference between the time values of the two. Increases over time.

Here, when the first PTP process (time synchronization based on PTP) is executed, the time difference Diff_A between the reference clock 31 and the internal clock 61 can be obtained. Then, when the second PTP process is executed, the time difference Diff_B between the reference clock 31 and the internal clock 61 can be further obtained. The timings T2_A and T2_B of the first and second PTP processing are the timings at which the reference clock 31 transmits the PTP packet, and the processing cannot be executed at arbitrary timings in the individual devices 6.

Therefore, if the difference between the two obtained time differences is divided by the elapsed time of the first time and the second time as shown in the following equation (1), the difference in the slope of the time change between the reference clock 31 and the internal clock 61 can be obtained. .. The value of this difference is an adjustment amount per unit time for matching the inclinations of the internal clock 61 and the reference clock 31.

(Adjustment amount per unit time) = (Diff_B-Diff_A) / (T2_B-T2_A) ... (1)
Examples of applying this adjustment amount are shown in FIGS. 4 and 5. The method of changing the advancing speed of the time value of the internal clock 61 is that if the number of counts when counting the frequency of the crystal device is reduced, the clock advances faster, and if it is increased, the clock advances slower. The adjustment differs depending on the mechanism of the internal clock 61, and examples thereof include a method of adjusting at an arbitrary timing shown in FIG. 4 and a method of adjusting the internal clock shown in FIG. 5 at 1-second intervals. Be done.

In the adjustment methods of FIGS. 4 and 5, the current speed of the internal clock 61 is set to a value obtained by adding the adjustment amount per unit time in order to match the slope of the time change of the reference clock 31.

Further, in the method of FIG. 5, there is a waiting time of up to 1.0 second until the correction is made. The timing of transmitting the PTP packet is based on the reference time, but has nothing to do with the timing of 1 second of the clock. If the time synchronization has already been adjusted once, the inclinations of the reference clock 31 and the internal clock 61 are substantially the same, and the influence is small. If it is desired to reduce the fluctuation of the time synchronization, the time difference can be eliminated by the adjustment shown in FIG.

According to FIG. 4, the slope of the time value of the internal clock 61 can be made to match the reference clock 31, but at that time, the time difference of Diff_B remains, and as shown in FIG. 5, the reference clock 31 and the internal clock 61 The time value follows parallel lines.

Therefore, the time of the internal clock 61 illustrated in FIG. 6 is corrected. That is, the slope of the time change of the internal clock 61 (Equation (2)) is adjusted so that the time difference between the reference clock 31 and the internal clock 61 becomes 0 in the time zone of 1 second next to the internal clock 61. Further, when this inclination is matched with the inclination of the time change of the reference clock 31, the internal clock 61 becomes the time synchronized with the reference clock 31. If the hardware of the time synchronization device 10 can accurately adjust the internal clock 61 in an arbitrary period, it is not necessary to limit the time to 1 second.

(Inclination for 1 second) = (Current inclination)-(Diff_B / 1 second) ... (2)
As described above, there is a period of measurement by two PTP treatments and a period of adjusting the internal clock 61 from the result. It is possible to carry out these two periods at the same time, but it is complicated and the responsiveness is slightly improved.

A configuration example of the time synchronization device 10 of the present embodiment illustrated in FIG. 2 will be described.

The time synchronization device 10 implements the adjustment amount calculation unit 11, the tilt correction unit 12, and the time correction unit 13 in collaboration with the hardware resources and software resources of the computer.

The adjustment amount calculation unit 11 calculates an adjustment amount for correcting the inclination of the time change of the internal clock 61 based on the time change of the internal clock 61 and the reference clock 31. Specifically, the adjustment amount is calculated based on the difference between the time values of the reference clock 31 and the internal clock 61 at the time of the previous time synchronization and the difference between the time values of the reference clock 31 and the internal clock 61 at the time of the current time synchronization. More specifically, the adjustment amount when the period from the previous time to the present time is 1 second can be mentioned.

The inclination correction unit 12 corrects the inclination of the internal clock 61 based on the adjustment amount to match the inclinations of the time changes of the internal clock 61 and the reference clock 31. For example, by correcting the inclination of the internal clock 61 based on the adjustment amount when the period from the previous time to the present time is 1 second, the inclinations of the time changes of the internal clock 61 and the reference clock 31 are matched.

The time correction unit 13 further corrects the inclination to match the time value of the internal clock 61 with the time value of the reference clock 31, and then matches the inclination with the inclination of the time change of the reference clock 31.

[Operation example of this embodiment]
A specific operation example of the time synchronization device 10 of the embodiment will be described below.

When the time difference obtained by the PTP processing is larger than a predetermined value, for example, 1 second, the time synchronization device 10 adjusts the unit of the year, month, day, minute, and second of the internal clock 61. At this time, there is a difference in the advancing speed of the time value due to the time difference of less than 1 second and the accuracy of the crystal device of the internal clock 61. Initially, the time is generated at the standard frequency of the crystal device, and the adjustment of the internal clock 61 is not executed. Therefore, the slope of the time change of the internal clock 61 is recorded as 0.

The reference clock 31 transmits a Sync packet based on PTP at an arbitrary timing. When the time synchronization device 10 on the device 6 side receives the Sync packet, it returns the Delay_Req packet to the reference clock 31. After that, when the time synchronization device 10 receives the reply of the Delay_Resp packet from the reference clock 31, the time synchronization device 10 calculates the time difference between the reference clock 31 and the internal clock 61 by the PTP calculation. This time difference is recorded in the storage unit of the time synchronization device 10 as the first time difference Diff_A, and the time T2_A of the internal clock 61 is recorded in the storage unit. After that, when the time synchronization device 10 receives the next Sync packet from the reference clock 31, the time synchronization device 10 records the second time difference Diff_B and the time T2_B at this time in the storage unit.

Then, the time synchronization device 10 synchronizes the internal clock 61 with the reference clock 31 by executing the following processes of S1 (calculation of adjustment amount), S2 (correction of inclination), and S3 (correction of time).

S1: The adjustment amount calculation unit 11 calculates the adjustment amount for matching the slopes of the time changes of the reference clock 31 and the internal clock 61 by the calculation of the equation (1).

S2: The inclination correction unit 12 corrects the inclination of the time change of the internal clock 61 based on the adjustment amount in order to adjust the internal clock 61 to the advancing speed of the reference clock 31, so that the time of the internal clock 61 and the reference clock 31 is adjusted. Match the slopes of change.

Specifically, the inclination is corrected by the calculation according to the following equation (3).

Tilt (after correction)
= Slope (previous value)-(Adjustment amount per unit time)
= Slope (previous value)-((Diff_B-Diff_A) / (T2_B-T2_A)) ... (3)
When the time of the internal clock 61 is advanced, the adjustment amount per unit time is a positive value, so it is subtracted from the slope of the time change of the internal clock 61 before correction. In this embodiment, the elapsed speed of the internal clock 61 is adjusted to be slow by increasing the frequency counter value of the crystal device of the internal clock 61. The adjustment of the frequency counter value is executed by the calculation of the following equation (4).

Frequency counter value (after correction)
= Frequency counter value (previous value) + (adjustment amount per second)
= Frequency counter value (previous value) + (standard counter value) x ((Diff_B-Diff_A) / (T2_B-T2_A)) ... (4)
When the frequency counter value after the adjustment is applied in the time adjustment of the internal clock 61, the slope of the time change of the internal clock 61 is corrected to the same slope as the time change of the reference clock 31 as shown in FIGS. NS.

S3: The time correction unit 13 applies the frequency counter value obtained by the following calculation in the time zone of the next 1 second of the internal clock 61 as shown in FIG. 6 in order to eliminate the time difference of Diff_B. ..

That is, the inclination of the time change of the internal clock 61 is adjusted by the following calculation so that the time difference between the reference clock 31 and the internal clock 61 becomes 0 in the time zone of 1 second next to the internal clock 61. After that, this inclination is made to match the inclination of the time change of the reference clock 31 corrected in S2.

1 second tilt = (current tilt)-(Diff_B / 1 second)
Frequency counter value (after adjustment)
= Frequency counter value (previous value) + (adjustment amount per second)
= Frequency counter value (previous value) + (standard counter value) x (Diff_B / 1 second)
When correcting the time to wait until the next 1 second, it is as follows.

Frequency counter value (after adjustment)
= Frequency counter value (previous value) + (standard counter value) x ((Diff_B x (1 + waiting time [seconds])) / 1 second)
If the frequency counter value (adjusted) is applied for only one second and then returned to the original frequency counter value (previous value), it can be synchronized with the reference clock 31 as shown in FIG.

Since the above series of processes is completed in 2 to 3 seconds, the responsiveness is higher than that of the servo control.

Quartz devices fluctuate due to temperature and voltage in the long term, and fluctuate around a certain frequency in the short term. Long-term fluctuations can be followed sufficiently, but if the frequency fluctuates in a short period of about several seconds, it will be affected.

As described above, according to the time synchronization device 10 of the present embodiment, the inclination of the time change of the internal clock 61 of the device 6 is corrected based on the time change of the internal clock 61 and the reference clock 31. Then, the time value of the internal clock 61 whose inclination is corrected is corrected so as to match the time value of the reference clock 31.

According to this aspect, the time adjustment of the internal clock 61 is completed in a short time. For example, servo control requires 1 to 20 minutes for time synchronization, but according to the time synchronization method of this embodiment, synchronization can be performed within 1 μsec in 3 to 30 seconds.

In particular, by applying the slope of the time change of the corrected reference clock 31 to the time correction of the internal clock 61, the responsiveness of the time synchronization of the time synchronization device is improved. For example, the response time is 2-3 seconds.

Further, since the internal clock 61 synchronizes with the reference clock 31 in a state where the time change of the internal clock 61 matches the time change of the reference clock 31, the error between the internal clock 61 and the reference clock 31 can be grasped, so that the system design can be performed. It will be easy.

On the other hand, servo control, which is a conventional technique, has slow responsiveness and the included error is not clear, which makes system design difficult.

Further, since the continuation of the PTP processing at regular time intervals and the time correction of the internal clock 61 for a predetermined period are exclusively executed, the calculation becomes simpler than the case where the PTP processing and the time correction are executed at the same time. Further, it is not necessary to set the PID control parameter of the servo control.

Further, it is possible to correct the time change of the internal clock 61 based on the difference between the time values of the reference clock 31 and the internal clock 61 of the previous PTP processing and the difference of the time values one second after the previous time. Therefore, by applying this synchronization method to electric power equipment such as a protective relay that does not require high-precision synchronization, it is not necessary to provide a high-precision reference clock, so that the equipment cost is reduced. As a result, low-cost redundancy of electric power equipment is realized, and the availability of the electric power network system is improved.

Another aspect of the present invention can be realized by configuring a program that causes a computer to function as a part or all of the time synchronization device 10 and causing the computer to execute the program. Alternatively, it can be realized by configuring a program that causes a computer to execute a part or all of the processes of S1 to S3 of the time synchronization method executed by the time synchronization device 10, and causing the computer to execute the program. Then, this program (time synchronization program) can be stored and provided in a well-known recording medium that can be read by the computer. Alternatively, the program can be provided via a network via the Internet, e-mail, or the like.

The present invention is not limited to the above embodiments, and can be implemented in various embodiments within the scope of the claims of the present invention.

1 ... Time synchronization system 2 ... Network, 31 ... Reference clock 6 ... Device, 61 ... Internal clock 10 ... Time synchronization device 11 ... Adjustment amount calculation unit, 12 ... Tilt correction unit, 13 ... Time correction unit

Claims (3)

A time synchronization device that synchronizes the internal clock of a device belonging to a network with the reference clock of the network.
Time variation of the previous time the internal clock based on the difference of the synchronization time of the reference clock and the difference between the time value of the current time synchronization when the reference clock and the internal clock of the time value of the internal clock and the reference clock The adjustment amount calculation unit that calculates the adjustment amount to match the inclination of
After the current time synchronization, the inclination of the time change of the internal clock is corrected based on the adjustment amount in the time zone of 1 second of the internal clock so that the inclination of the time change of the internal clock and the reference clock are matched. Tilt correction unit and
After further correcting the inclination in the time zone of the next 1 second of the internal clock to match the time value of the internal clock with the time value of the reference clock, the inclination is referred to as the inclination of the time change of the reference clock. With the time correction unit to match
A time synchronization device characterized by being equipped with. A time synchronization method executed by a time synchronization device that synchronizes the internal clock of a device belonging to a network with the reference clock of the network.
Time variation of the previous time the internal clock based on the difference of the synchronization time of the reference clock and the difference between the time value of the current time synchronization when the reference clock and the internal clock of the time value of the internal clock and the reference clock The adjustment amount calculation process for calculating the adjustment amount for matching the slopes of
After the current time synchronization, the inclination of the time change of the internal clock is corrected based on the adjustment amount in the time zone of 1 second of the internal clock so that the inclination of the time change of the internal clock and the reference clock are matched. Tilt correction process and
After further correcting the inclination in the time zone of the next 1 second of the internal clock to match the time value of the internal clock with the time value of the reference clock, the inclination is referred to as the inclination of the time change of the reference clock. With the time correction process to match
A time synchronization method characterized by having. A time synchronization program, characterized in that the computer functions as the time synchronization device according to claim 1.

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