A method for synchronizing intelligent electronic units in a locally limited network.

Abstract

The present invention relates to a method for synchronizing intelligent electronic devices (IEDs) (5) in a locally limited network (1), wherein the locally limited network (1) has at least two timed units (2, 3), and - for a timed unit (2) that has recovered or reconnected to the network, it is checked whether there is another timed unit (3) in the network that is in an active grandmaster role (1); - if another timed unit in a grandmaster role is detected in the locally limited network (1), the first timed unit (2) is forced into a slave state and synchronizes with the timed unit (3) in the grandmaster role; - after synchronization is complete, the forced slave state in the first timed unit (2) is released; - the first timed unit (2) switches to a grandmaster timed unit if it is more suitable for the grandmaster role, or remains in a slave state if another timed unit (3) in the network (1) is more suitable for the grandmaster role.

Description

Technical Field

[0001] For the synchronization of time settings of devices interconnected via a network, the Network Time Protocol, which is called Network Time Protocol in English and hereinafter abbreviated as NTP, was created. Furthermore, a time protocol called Precision Time Protocol in English has been introduced, and this time protocol is hereinafter referred to as PTP. PTP has higher accuracy in obtaining the time of a plurality of devices interconnected via a network compared to NTP.

[0002] A locally limited network is realized, for example, in a power substation for power energy supply. Such a substation is used to lower or raise the dominant system voltage in the supply network using a transformer whose operating method is known. In addition to the transformer, the substation has a switching unit such as a circuit breaker (English: circuit breakers, German: Leistungsschalter), and after receiving a switching signal, the switching unit separates the conductor outgoers (English: conductor outgoers, German: Leiterabgaenge) of the substation from the remaining supply network.

[0003] The above switching signals are generated by protection and automation devices, and these signals are used to monitor the current and voltage changes in the substation's conductors for the presence of fault conditions. If fault conditions are present, a switching signal is generated and transmitted to one or more selected switch units, which then move to their interrupter position. In the interrupted state, the contacts of multiple selected switch units are isolated from each other, preventing the flow of current through the switch units. A conductor run connected to one contact of a switch unit is then disconnected from the rest of the supply network connected to the other contact of the switch unit.

[0004] For protection and automation equipment to monitor the current and voltage changes in substation conductors for the presence of fault conditions, these equipment must be continuously supplied with time-dependent current and voltage values. To provide these current and voltage values, multiple current and voltage converters are provided, which detect the current and voltage in the conductors at measurement points in the substation and provide calibrated measurement signals on the secondary side. These calibrated measurement signals are sampled by acquiring sample values ​​at a specified sampling rate. The sample values ​​are then digitized. Furthermore, a timestamp is fixedly assigned to the sample values. This is done by so-called "merging units" or by using other intelligent electronic units (IEDs) within the substation. In order for the measurements to be comparable to each other, the time acquisition of IEDs connected to each other via a process bus must be synchronized. For this purpose, the aforementioned PTP is used.

[0005] In other words, PTP is used in digital substations for supplying electrical energy to synchronize intelligent electronic units (IEDs), for example, in the so-called IEC 61850 process bus.

[0006] Comparability of measurements from different IEDs is critically important. Loss or insufficient temporal synchronization between these devices can lead to blocking of protective functions within protective and automated devices, or malfunction of switchgear units resulting in unintended interruptions to the power supply.

[0007] Figures 1a and 1b illustrate the procedure for obtaining time using PTP in the process bus communication network 1. In this case, two time-specifying units 2 and 3 are provided, which transmit PTP synchronization messages to IEDs 5, such as protective devices, via the Ethernet switch 4, according to a predetermined configuration of "Announce," "Sync," and "Follow Up." These units are also connected to the process bus communication network 1. In Figures 1a and 1b, dashed arrows correspond to PTP announcement messages, and solid arrows represent synchronization or follow-up messages. The IEDs 5 are in a slave state as defined by the PTP protocol. Therefore, they behave passively with respect to obtaining time values, adopting the time provided by the time-specifying unit, which is in the so-called (Grossmeister-)Grandmaster-Rolle state.

[0008] Time-setting units 2 and 3 can be connected to a primary reference clock source, a so-called primary reference clock (PRC), such as a Global Navigation Satellite System (GNSS). However, such satellite-based global reference clock sources are risky due to the possibility of interference from jamming transmitters or other means (e.g., spoofing), and are often not permitted for use depending on the scope of application. In such cases, an internal oscillator may be used, which is incorporated into one of the time-setting units 2 and 3, in which case they provide a relative time reference in the form of a time value in the process bus communication network 1, independently of external sources.

[0009] The relative time values ​​provided by the local oscillators in the time-specifying units 2 and 3 are sufficient for synchronization when used in the process bus communication network 1 at the substation, because absolute time values ​​are not required.

[0010] The use of two time-specified units is for redundancy, i.e., availability purposes. Under fault-free conditions, a single time-specified unit 2 is selected to become the active grandmaster using the so-called Best Master Clock Algorithm (Best-Master-Clock-Algorithmus). This unit sends a PTP synchronization message via the Ethernet switch 4. The other time-specified unit 3 does not send a PTP synchronization message and remains in a slave state. It receives a PTP synchronization message from the grandmaster time-specified unit 2 and synchronizes its own internal oscillator with the oscillator of time-specified unit 2, so that the internal oscillator of time-specified unit 3 oscillates at approximately the same rate as the internal oscillator of time-specified unit 2. However, time-specified unit 3 is ready to transition to the active role.

[0011] Figure 1b clearly shows the state in which Time Schedule Unit 2 is malfunctioning or disconnected from the network. The absence of Time Schedule Unit 2 is detected by Time Schedule Unit 3 based on the interrupted PTP announcement message from Time Schedule Unit 2. Time Schedule Unit 3 switches to the Grandmaster role.

[0012] IEDs detect the switch of the grandmaster from time-specified unit 2 to time-specified unit 3 based on PTP messages. In this case, the IEDs' time synchronization is not disrupted because the internal oscillator of time-specified unit 3 was synchronized with the oscillator of time-specified unit 2 before the switch. Synchronization of time acquisition between IEDs continues without interruption. There is no time jump (Jump in Time, Zeitsprung) during or after the grandmaster switch.

[0013] If the malfunction of timed unit 2 is resolved, or if the disconnected timed unit 2 is reconnected to the process bus communication network 1, in accordance with prior art, the BMCA immediately decides that timed unit 2 will assume the grandmaster role. As grandmaster timed unit 2, it will resume sending PTP synchronization messages.

[0014] While Timed Unit 2 is absent, the local oscillator of Timed Unit 3 operates at its own speed, moving temporally away from the local oscillator of Timed Unit 2. The time and frequency differences between the local oscillators of Timed Unit 2 and Timed Unit 3 can be considerable at the time of takeover by Timed Unit 2 once it becomes functional or reconnected. The IEDs detect the time jump after the takeover and resynchronize their internal oscillators to the new local oscillator of Timed Unit 2, which is the new grandmaster. This resynchronization process can take up to 20 seconds.

[0015] During this resynchronization process, IEDs disable their protective functions to prevent potential malfunctions of the circuit breakers. This is a significant drawback.

[0016] Figure 2 illustrates the above-mentioned matters using a two-dimensional graph. In this graph, the horizontal axis represents time, and the vertical axis 6 represents the time offset of time-specified unit 3 relative to time-specified unit 2 according to Figure 1, each shown in arbitrary units. The interval 20 between the dashed lines indicates the magnitude of the time offset between time-specified unit 2 and time-specified unit 3 that is permissible for the protection application of IEDs. That is, the solid curve represents the above time offset in a time-dependent manner. If this curve lies between the dashed lines, it is a permissible time offset.

[0017] In the time range referenced by reference numeral 7, time-specified unit 2 is operating without error and is connected to process bus communication network 1. It is operating as grandmaster time-specified unit 2 in this range 7. At time 8, the grandmaster role is taken over by time-specified unit 3 because the PTP announcement messages from time-specified unit 2 are interrupted, which is detected by time-specified unit 3. Subsequently, in time range 9, time-specified unit 3 operates as grandmaster time-specified unit 3. At time 10, the grandmaster role is returned to time-specified unit 2 again. Since the oscillators of time-specified unit 2 and time-specified unit 3 were no longer synchronized in time range 9, the time value of time-specified unit 3 has diverged from the time value of time-specified unit 2. In time range 11, this divergence is greater than the allowable value. The IEDs detect the above time jump and resynchronize their internal oscillators until synchronization with the grandmaster time-specified unit 2, to which the IEDs return at time 12, is complete. This conventional method has the drawback that the IED protection algorithm is blocked in the dashed time range 11. [Overview of the project] [Problems that the invention aims to solve]

[0018] The object of the present invention is to provide the type of method described above in which blocking of IED protection algorithms can be reduced in time or completely avoided. [Means for solving the problem]

[0019] This problem is solved by the features of claim 1 in the present invention.

[0020] Modifications of the present invention are subject to dependent claims.

[0021] Within the framework of this invention, it was recognized that the drawbacks of the prior art described above stem from the fact that a PTP time-setting unit with grandmaster capability assumes the role of grandmaster as soon as it determines, according to the BMCA (Best Master Clock Algorithm), that it is the best PTP time-setting unit in the network. A time-setting unit with grandmaster capability that conforms to PTP can assume the role of grandmaster based on the BMCA, and at the same time, is a time-setting unit that can become the sole synchronization source in the network, i.e., the grandmaster. The problem of missynchronized local oscillators when switching and returning to the grandmaster role, as recognized by the inventors, is not considered in the BMCA and the PTP-Port-State-Machine (PTP-Port-Zustandsmaschine). This leads to the aforementioned time jump and the failure of the protection function (protection algorithm).

[0022] The present invention proposes that, rather than a restored or reconnected, locally synchronized time-specified unit with grandmaster capability immediately assumes the grandmaster role, the following steps are first performed.

[0023] First, it is checked whether an active PTP grandmaster exists in the specific PTP domain defined by its domain number. This check is performed by waiting for the reception of a PTP announcement message. If a time-specified unit with grandmaster capability does not receive a PTP announcement message from another time-specified unit within a predefined time frame, it is assumed that there is no active grandmaster in that domain. If no other grandmaster is detected in the network, the time-specified unit performs a BMCA (Behavioral Management Consultation), and switches to the grandmaster role.

[0024] However, if a grandmaster time-setting unit is detected within the network, that time-setting unit switches to slave mode and begins synchronizing its own internal oscillator with the current grandmaster oscillator.

[0025] After the timed unit synchronizes its internal oscillator with the grandmaster to the required precision, its slave state is released. A BMCA (Behavioral Monitoring Assessment) is performed, and depending on the result of this check, the aforementioned timed unit either switches to the grandmaster role or remains in slave state.

[0026] In other words, the crucial point is that, before a restored or reconnected time-setting unit with grandmaster capability takes over the grandmaster role, if one exists, it must first synchronize its own internal oscillator with the current PTP grandmaster time-setting unit. This method avoids time jumps.

[0027] In English, it is called "local area network" or abbreviated as "LAN" for a locally limited network. In the meaning of the present invention, a spatially limited network is understood. A locally limited network is, for example, a network defined by the IEC standard IEC61850. Advantageously, the locally limited network has structured wiring. According to a preferred variant, this network is a process bus communication network. This spatially limited network includes intelligent electrical devices (IEDs), and the intelligent electronic units are connected to each other via, for example, wired communication lines or wirelessly, such as a 5G wireless network. However, within the framework of the present invention, the use of Ethernet technology is preferred. However, basically, other locally limited networks are also possible within the framework of the present invention.

[0028] The abbreviation IED should be understood to mean an intelligent electronic unit within the framework of the present invention. An IED is, for example, a protection or automation device, a relay, or a field control device, and is used, for example, in the field of protection and control technology in a substation. An IED is often also called a processor-based controller.

[0029] Advantageously, within the framework of the present invention, PTP is used. In this case, the forced slave state is performed by adjusting the priority of the above-mentioned time specifying unit. When the priority of the time specifying unit with grandmaster capabilities is set to, for example, 254 or 255, it remains in its slave state in the check by the BMCA.

[0030] Advantageously, the check as to which time specifying unit is more suitable for the active grandmaster role is performed according to the best master clock algorithm of the IEEE1588 protocol (English: best master clock algorithm, German: Best Master Clock Algorithmus).

[0031] Further advantages arise when each time input unit has its own oscillator. Such an oscillator may be, for example, a quartz crystal, whose vibrations are converted into a time standard (Zeitnormal). Since oscillators are well known to those skilled in the art, there is no need to discuss their precise operating principles further here. However, within the framework of the present invention, oscillators used in time-specifying units can be synchronized with other oscillators.

[0032] In another purposeful variation, a locally limited network is a wireless network. Advantages arise, especially if the wireless network is a 5G wireless network.

[0033] According to a preferred embodiment of the present invention, the locally limited network is a process bus communication network in a substation. In the process bus communication network, Ethernet technology is preferably used.

[0034] Within the framework of this invention, the number of time-specifying units is not limited to two. For example, five or more time-specifying units can communicate with each other within a network.

[0035] In a useful embodiment, at least one time-specifying unit is integrated, or rather, built into, the IED; that is, it is a component of the IED and is located within its housing.

[0036] Further advantages arise when at least one IED is a device for protecting or automating an electrical energy supply network.

[0037] A further modification of the method according to the present invention comprises a time-specified unit with grandmaster capability, which has become available again or reconnected to the network, not immediately assuming the grandmaster role again after synchronizing with the current grandmaster. Instead, it remains in a slave state and continues to synchronize further with the current grandmaster time-specified unit. Only when the absence of the grandmaster time-specified unit is detected does the time-specified unit switch to the grandmaster role based on BMCA. This method reduces the number of grandmaster switchovers in the network, which is advantageous in terms of the stability of PTP synchronization.

[0038] The present invention further relates to a time-scheduling unit for a locally limited network through which intelligent electronic units (IEDs) are connected to one another. According to the present invention, the time-scheduling unit is configured to perform at least one of the methods described above.

[0039] In the sense of the present invention, a time-specifying unit is understood as any unit that is in a state of generating a time standard. This unit may exist as a separate device, or it may be a component or element of another device, for example, a protective device or an automation device.

[0040] The present invention will be described in more detail below with reference to examples, in which the same reference numerals refer to components that function identically. [Brief explanation of the drawing]

[0041] [Figure 1a] Figure 1a illustrates an example of a process bus communication network with two properly functioning time-specified units. [Figure 1b] Figure 1b illustrates an example of a process bus communication network with a time-specified unit that has failed or been isolated from the network. [Figure 2]Figure 2 illustrates a two-dimensional graph illustrating how to follow conventional methods for taking over the role of Grandmaster. [Figure 3] Figure 3 illustrates a two-dimensional graph illustrating a method according to the present invention for assuming the role of Grandmaster. [Figure 4] Figure 4 schematically illustrates an embodiment of the method according to the present invention using a flowchart. [Modes for carrying out the invention]

[0042] Figures 1a, 1b, and 2 have already been mentioned in relation to the evaluation of the prior art.

[0043] Figure 3 illustrates an embodiment of the method according to the present invention. This schematically shows the progress of a time instruction defined within a local network according to Figure 1, and the time instruction to which an IED in network 1 synchronizes, based on a two-dimensional graph in which the horizontal axis represents time and the vertical axis 6 represents the time offset of time instruction unit 3 relative to time instruction unit 2 according to Figure 1, in arbitrary units.

[0044] The distance 20 between the dashed lines is, again, the magnitude of the time offset between time-specified units 2 and 3 that is permissible by the IED protection application. That is, the solid curve shows the progression of the time offset between time-specified units, dependent on time. If the curve lies between the dashed lines, it represents a permissible time offset.

[0045] In the time domain referenced in 13, timed unit 2 is operating without error and is connected to process bus communication network 1. In this domain 13, timed unit 2 is operating as grandmaster timed unit 2. At time 14, the role of grandmaster is taken over by timed unit 3. In time range 15, timed unit 3 then operates as grandmaster timed unit 3. At time 16, timed unit 2 has regained its full functionality. In other embodiments, it is disconnected from the network and reconnected to network 1 at time 16.

[0046] In contrast to conventional technology, it does not immediately assume the grandmaster role again, but instead synchronizes, or in other words, synchronizes its oscillator with the oscillator of the grandmaster time-designated unit 3. This synchronization is achieved at time 17. Using BMCA, it is determined that time-designated unit 2 is more suitable for the grandmaster role. The switchover of the grandmaster role takes place at time 17. In time range 18, time-designated unit 2 once again assumes the grandmaster role.

[0047] Within the framework of this invention, the time offset of IEDs will not exceed any permissible limit at any point in time. Blocking of IED protection algorithms is avoided within the framework of this invention.

[0048] Within the framework of the present invention, in order to avoid an immediate handover of the grandmaster role, that is, to enforce a slave state for each time-specified unit, this embodiment of the invention based on PTP operates using so-called priority. However, it should be noted that the enforcement of the slave state can also be performed by other means without departing from the scope of the present invention.

[0049] Priority is a parameter defined in the IEEE 1588 standard, and these are evaluated by BMCA. According to this, each time-specified unit 2 can basically be assigned priority 1 or priority 2. After a failure of time-specified unit 2, its priority 1 is limited to 255 and 254. The priority value of time-specified unit 3 remains fully adjustable by the user; that is, priority 2 is kept at the initial value set by the network user.

[0050] Under normal, fault-free conditions, the priority parameter set by the user is used. At time 16, the priority value of timed unit 2 is set to the maximum possible value of 255, which corresponds to the lowest priority for assuming the grandmaster role. In the execution of BMCA, timed unit 2 is therefore guaranteed to remain in its slave state.

[0051] At time point 17, the internal oscillator of timed unit 2 is synchronized with the oscillator of the current PTP grandmaster, i.e., timed unit 3, with the required precision. At time point 17, the priority 1 value of timed unit 2 is reset to the value pre-set by the user. Thus, the forced slave state is released. Timed unit 2 re-assumes the grandmaster role through the execution of BMCA.

[0052] Figure 4 illustrates the method according to the present invention using a flowchart. For space reasons, Figure 4 describes a control clock (Leituhr) instead of a time-setting unit in the role of grandmaster.

[0053] When a timed unit, for example, timed unit 2, becomes functional again or is reconnected to the network, the first step is to determine whether a timed unit in the role of grandmaster, i.e., a control clock, exists in the network. If a control clock does not exist, timed unit 2 reverts to its normal operation. BMCA determines that timed unit 2 should assume the grandmaster role. This is then executed.

[0054] However, if it is determined that a control clock exists within the network, the priority 1 of time-specified unit 2 is set to 255. This forces time-specified unit 2 into a slave state. Subsequently, the control clock is searched for within the loop, and time-specified unit 2 synchronizes with the control clock, i.e., time-specified unit 3 in this case. This loop runs as long as the time offset between the control clock and time-specified unit 2 is greater than a predetermined threshold, and the control clock still exists. Then, the priority 1 value is set again to the previously set value. [Explanation of Symbols]

[0055] 1…Network, 2…Time indicator unit (first time indicator unit), 3…Time indicator unit (second time indicator unit), 4…Ethernet switch (switch), 5…Intelligent electronic unit (IED)

Claims

1. A method for synchronizing intelligent electronic devices (IEDs) (5) in a locally limited network (1), wherein the locally limited network (1) has at least two time-specified units (2, 3), - For a time-specified unit (2) that has been restored or reconnected to the network, it is checked whether there is another time-specified unit (3) that is active in the network and has the role of grandmaster (1). - If another time-setting unit with the grandmaster role is detected in the locally limited network (1), the first time-setting unit (2) is forced into a slave state, and the first time-setting unit (2) synchronizes with the time-setting unit (3) with the grandmaster role. - After synchronization is complete, the forced slave state in the first time-specified unit (2) is released. - The first time-setting unit (2) switches to the role of a grandmaster time-setting unit if it is more suitable for the grandmaster role, or remains in the slave state of another time-setting unit (3) of the network (1) if it is more suitable for the grandmaster role. method.

2. The slave state is enforced by adjusting the priority of the aforementioned time-specifying unit (2) while using PTP. The method according to claim 1.

3. The check to determine which time-specified unit (2, 3) is more suitable for the active grandmaster role is performed according to the best master clock algorithm of the IEEE 1588 protocol. The method according to claim 1 or 2.

4. Each time-specified unit (2, 3) within the network (1) is characterized by having an oscillator. The method according to claim 3.

5. The locally limited network (1) is characterized in that it is a single domain. The method according to any one of claims 1 to 4.

6. The locally limited network is characterized in that it is a substation process bus communication network (1), The method according to any one of claims 1 to 5.

7. At least one IED(5) is a protective or automated device, The method according to any one of claims 1 to 6.

8. The IED is characterized by having at least one time-specifying unit incorporated into it. The method according to any one of claims 1 to 7.

9. A time-scheduled unit capable of becoming a grandmaster, which has become available again or has been reconnected to the network, remains in a slave state and continuously synchronizes with the current grandmaster time-scheduled unit, and only switches to the grandmaster role upon the decommissioning of the grandmaster time-scheduled unit. The method according to any one of claims 1 to 8.

10. A time-specified unit (2, 3) for a locally limited network (1) that interconnects intelligent electronic units (IEDs) (5), The method is configured to perform any one of claims 1 to 9, Time-specified units (2, 3).

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