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Boundary Clock over multiple Ordinary Clocks

IP.com Disclosure Number: IPCOM000249167D
Publication Date: 2017-Feb-08
Document File: 6 page(s) / 484K

Publishing Venue

The IP.com Prior Art Database

Related People

Ioannis Sotiropoulos: INVENTOR [+4]

Abstract

The invention described below allows multiple Ordinary Clocks to share the same time information and to act transparently to the external system as one Boundary Clock. Such BC is connected to multiple subnetworks but its clock can only be synchronized to one side at the time. The gap that this patent fills is how to combine multiple independent OCs which are connected to different subnetworks so that they can act to the external system as one BC (Merged BC).

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ABB Switzerland Ltd Invention Disclosure5 Version: -Date: 1 2017-02-06 Department resp.: Authors:: Title: Distribution: Language: Page: PGGA-PT2 Ioannis Sotiropoulos, Sven

Meier, Andreas Roland, Thomas Schaub

Boundary Clock over multiple Ordinary Clocks

- EN 1/6

Effective for: Derived from: Replaces: Classification: ABB File:CH-1603501

PGGA-PT2 - - confidential CH-1603501_IPCOM.docx

We reserve all rights in this document and in the information contained therein. Reproduction, use or disclosure to third parties without express authority is strictly forbidden. © Copyright 2013 ABB

(2013-05-31) Form: 1KHL000228-0101 / E

1 Background of the Invention

Communication networks in digital substation automation systems are divided in subnetworks, the buses. The buses typically separate the functionalities in the digital substation, therefore, different types of traffic are transferred in each bus. Information can be transferred horizontally (between nodes of the same bus) or vertically (between different buses). Communication between subnetworks is often not necessary or not allowed, which creates islands of information in the system. Devices, such as IEDs (Intelligent Electronic Devices), can be connected to multiple subnetworks at the same time. Apart from receiving and processing the messages from the subnetworks that are connected to, they can either act like bridges (they forward traffic between the subnetworks) or act as end-nodes (they don’t forward traffic between the subnetworks, and serve the subnetworks independently).

In digital substation automation systems time synchronization of the nodes is a basic requirement. It is typically achieved over Ethernet by applying EEE1588 (PTP). Time synchronization over PTP is based on a Master-Slave relationship. Each nodethat needs to be synchronized has an Ordinary Clock (OC) which can either receive the time information (Slave state) or is the so-called Grand Master, which generates the time information and synchronizes other nodes (Master state). All the devices that participate in the time- synchronization system are able to reach a consensus about who the current Grand Master should be. This is achieved by the Best Master Clock (BMC) algorithm, which is executed by the OCs. Afterwards, the Grand Master distributes its time information and the other nodes (typically) become Slave-Clocks and synchronize their OCs. Depending on how the digital substation allows the information to flow in the system, the time information of one Grand Master will be distributed to the whole system (so different subnetworks will be in-sync), or various synchronization islands will exist in the system (every island will have its own Grand Master). A Boundary Clock (BC) is a device that acts like a time-bridge between two subnetworks by transferring the time information of a Grand Master from one subnetwork to the other. Therefore, depending on the requirements of the system, two (or more) subnetworks can share timing info...