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Content for  TR 22.867  Word version:  18.2.0

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5.22  Use Case of ensuring uninterrupted MTC service availability during emergenciesp. 80

5.22.1  Descriptionp. 80

During emergencies, public mobile land networks (PLMNs) may restrict network access, which may lead to a lack of service reliability for machine-type communication (MTC) in critical applications, such as power systems and in particular in microgrids. Microgrids are separate parts of a power grid, which can be controlled and operated individually in a so-called island mode or together as a whole. Existing features of a mobile network can be used to differentiate MTC of devices in a microgrid from other MTC or human-to-human (H2H) communication and ensure that these microgrid devices have service during emergencies, which enables use of mobile communication to co-ordinate the use of Distributed Energy Resources (DER) in microgrids, so that they can autarkically perform blackout recovery of an islanded microgrid. The idea is to ensure reliable communications for selected MTC devices during emergency conditions, without giving these devices additional priority over other network users during normal conditions or adversely affecting the service to prioritised users during emergencies. It was shown that this method allows the blackout recovery 100 times faster than with a conventional black start [58].
Figure 5.22.1-1 shows an example of power grid restoration after a large-scale blackout using conventional and autarkic microgrid blackout recovery methods.
Copy of original 3GPP image for 3GPP TS 22.867, Fig. 5.22.1-1: (a) Conventional grid restoration (hierarchical top-down blackout recovery) and (b) autarkic microgrid restoration (each islanded microgrid autonomously recovers from blackout) Figure taken from [58]
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Grid restoration after a large-scale blackout is conventionally done by first starting power stations with black start capability, then expanding the re-energised grid to include more large synchronous power stations and expanding the re-energised grid. In this way, medium voltage and low voltage levels are re-energised hierarchically and top-down, i.e., from the transmission level.
The autarkic microgrid blackout recovery method presented in [53] assumes that the MV/LV grid is divided into a set of microgrids (Figure 5.22.1-1 (b)), which can be operated in island mode and are assumed to be autarkic, meaning that they have sufficient local energy generation and storage to be self-sufficient, and autonomous, meaning that they can manage themselves, although in normal operation they may be managed by distribution grid (DG) management systems external to the microgrid.
In the context of a microgrid, having reliable communications during a blackout means that the microgrid can continue to manage itself during blackout, i.e., even when the distributed energy resources (DER) in the microgrid are connected to a de-energised grid, the distributed controllers at the DER sites can continue to communicate with each other.
If communications from the microgrid to external management systems are working, the microgrid can perform autarkic blackout recovery under their direction. If, however, there is a loss of communication from the microgrid to external management systems, the microgrid can autonomously perform the autarkic blackout recovery. In any case, the autarkic blackout recovery relies on having communications which continue to function locally in the microgrid during blackout to allow the agents to act together to perform a black start using local DERs.
In the autarkic microgrid blackout recovery method, the medium/low voltage grid is assumed to be divided into a set of autarkic microgrids, as shown in Figure 5.22.1-1 (b), which are islanded in case of blackout. The DERs remain connected to the grid and continue to use their Multi-Agent System (MAS) MTC devices to communicate with each other and with the distribution grid control centre during the blackout [53]. In this scenario, each microgrid has its own gNB equipped with an emergency power supply. In case the emergency power supply for a gNB is not available, only this specific microgrid covered by the affected gNB cannot perform autarkic blackout recovery. However, other microgrids which are not affected by the malfunctioning gNB can still perform blackout recovery.
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5.22.2  Pre-conditionsp. 81

The MAS's within one microgrid must be covered by a large-scale, wide-area communications network, and the communications network must continue to operate during blackouts.
The network must support MTC and the MAS's can communicate within the microgrid using MTC.

5.22.3  Service flowsp. 81

Blackout recovery using autarkic microgrids:
  • Identify which nodes in the MAS are working
  • Identify the current microgrid topology and DER capacity
  • Re-energise the microgrid and the loads.

5.22.4  Post-conditionsp. 82

The microgrids have recovered from the blackout and operate normally again.

5.22.5  Existing feature partly or fully covering use case functionalityp. 82

None.

5.22.6  Potential New Requirements needed to support the use casep. 82

Characteristic parameter (KPI) Influence quantity
Communication service availability Communication service reliability: mean time between failures Max Allowed End-to-end latency (notes 1, 2) Service bit rate: user-experienced data rate (note 2) Message size [byte] Survival time UE speed # of UEs Service Area
99.9999 %100 ms< 1 Kbit/s per DERStationary
NOTE 1:
Unless otherwise specified, all communication includes 1 wireless link (UE to network node or network node to UE) rather than two wireless links (UE to UE).
NOTE 2:
It applies to both UL and DL unless stated otherwise.
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