Uncertainty Analysis in Time Distribution Mechanisms for OMS Smart Meters: The Last-Mile Time Synchronization Issue

An efficient energy management requires an exchange of information among different energy grids, such as electricity, gas, and heating. This paper analyzes the open metering system (OMS), a set of protocols used to provide the communication in a multiutility grid, with special focus on its capability of distributing the time information over the infrastructure. Currently, synchronization accuracy on the order of seconds is more than enough for the traditional metering applications, while more advanced power quality and monitoring systems may require synchronization on the order of hundreds of microsecond or less (as stated by the national and international normative for dynamically controlling loads or renewable power generator on the local microgrid). In this paper, advantages and limits of the current standard, when wireless M-bus (wM-bus) is used as a physical layer, are highlighted by means of the analysis of the synchronization uncertainty sources, and by the experimental evaluation. Next, a custom synchronization method is applied for the first time, since the current OMS standard does not propose any solutions. The analysis and the experimental characterization indicate that the synchronization limit on the last-mile segment of wM-bus, using off-the-shelf components, is on the order of 1.8 mu s. The proposed methodology can easily be extended to other communication protocols adopting similar architectures.