DLMS

The COSEM object model, internationally standardised as IEC 62056-61 and 6-62 as well as EN 13757-1, has been developed to model a wide range of utility metering applications, for all energy types and for all application segments from highend metering to residential mass applications.

The COSEM object model specifies a library of interface classes. Each interface class – currently more than 60 of them are specified – provides a set of attributes to characterise all aspects of data units of different complexity, as well as a set of methods that allow performing operations on the attributes.

Obviously, in modern smart meters much more than 60 data units may be necessary. However, many of them – like tariff registers of different energy types, power quality data, gas analysis quantities or device parameters – can be modelled the same way, using different instances of the same interface class, each having a specific name called the OBIS code. While the interface classes are somewhat abstract, the OBIS names are visible, as they appear on the meter display and may appear on the bills as well.

With this, metering application developers have a standardised object library at hand to model the functionality they need. This functionality is seen by data collection systems through the meter interfaces. This message can then be put in the right format, like DLMS protocol data units or files for transportation over various communication media

Years of experience with the COSEM model has shown that it is more than just a standardised language for the meters. It has also become a communication tool between utilities and metering system providers to precisely formulate requirements and to deliver the best solutions.

A good example for this is the development of the Dutch smart meter specification, completed recently. In this project, the interface between the electricity meter and the Central Access Server – the P3 interface – as well as the interface between the electricity meter and other utility meters – the P2 interface – is based on the COSEM model.

Utilities and manufacturers have been working together to develop this speci-fication. First, they represented system requirements with use cases, then went on mapping these use cases to COSEM interface objects. In many cases existing COSEM objects could be used.

To model some novel functionality – like connect-ing/disconnecting the premises, load limitation, setting up the electricity meter as an M-BUS master for data retrieval from other utility meters – new interface classes have been specified, thereby further enhancing the COSEM object model. This modelling process has helped the parties to clarify and formulate requirements, a key to interoperable implementations.

We believe that the Dutch example may be valid for other countries. This project has also shown that DLMS/COSEM is particularly suited to meet country -specific requirements without giving up interoperability.