Examining an Iranian smart metering programme, along with the challenges of ensuring interoperability across a variety of legacy systems, reveals the importance of having a detailed solution, protocols and international standards, in both meter and control centre levels.
Deploying interoperable infrastructure provides for effective and efficient data exchange as well as stable and standard data portability among the variety of systems in a national smart metering programme. Of particular importance in the Iran Smart Metering Project is the challenge of managing interoperability among the different legacy systems, due to the vast number of systems from a variety of venders. This article is intended to introduce different implementation efforts in terms of interoperability considerations and presentation of technical specifications. The major reference in the Iranian case – considered as the basis of interoperability management among different systems at a control centre level – is IEC 61968-9 and at the meter level is IEC 62056 (DLMS/COSEM protocol).
The interoperability concept
It is a given and common practice that all data collected from smart meters must be transferred to the control centre in order to be properly used. Furthermore, the control centre must be able to send commands to the meters in order to perform changes in meter parameters, clock alignment and enable remote disconnections. Thus, the meter must provide both local and remote communication functions. A very important related topic is the choice of the proper suite of protocols. This greatly influences the way the data is represented, the associated payload and the physical medium used for the exchange of data. The choice of frequency range and bandwidth depends on many factors, related to normative aspects (EMC compatibility in the chosen band), performance on network, requirements for transmission rate and costs. Furthermore, the issue of interoperability must be considered.
There are two main classes of protocols, namely proprietary and standardised. Some protocols, especially the proprietary ones, can be more oriented to reduce payload (data traffic, efficiency and speed) thus increasing the efficiency of data transmission but, because they are not completely standardised, can obstruct adoption by different manufacturers.
In recent years there has been a push by regulatory agencies and international mandates to grow the standardisation of protocols. It may be that an initial proprietary protocol is ‘opened’ to the market by the developer, creating associations and consortiums, trying to increase the number of manufacturers that will adopt it instead of developing a new protocol. This can be a good starting point for the development of a field-proof technology, which can then be proposed to the standardisation bodies. The standardisation process is quite long because it has to generalise and include multiple different technologies and principles. Furthermore, different standardisation bodies are oriented to different protocols.
The adoption of an open standard and of a standardised suite of protocols paves the way to interoperability and even interchangeability of meters coming from different manufacturers. In order to have future-proof functional requirements for meters, the proposed architecture for communication must be open, especially for the integration of new communication devices.
Given the wide acceptance on the meter market of the IEC 62056 and IEC 61968 standards and previous experience of pilot projects around the world, they are considered as the reference guide for this strategy and plan. IEC 62056 and IEC 61968 also offer comprehensive security structures: for access, authentication and encryption.
What is the difference?
The wider definition of interoperability considers the possibility of substitution (removal and replacement) of meters in whatever site of installation – with the guarantee of previous performance of the system. This definition is also referred to as interchangeability. Hence, the term interoperability would apply to the middle layer (e.g. different meters can talk to the same DCU and AHE), whilst interchangeability applies at the physical layer (e.g. exchange of one manufacturer’s meter for another at a customer’s site). The perfect interchangeability of meters from different manufacturers requires a fully defined and agreed set of functionalities and specifications – from the higher levels of the stack defined in the suite of protocols, to the lower levels of communication (and implemented data model).
An example of a consortium of meter manufacturers acting in this direction is represented by the IDIS 2 association, which is also based upon IEC 62056 (smart meter level). The adoption of an open standard (including the suite of protocols and the data modelling) can greatly help interoperability and even interchangeability of meters coming from different manufacturers. It is, however, of vital consideration that even by adopting the same suite of protocols, interoperability can’t be assured. Problems of interoperability can arise even on the same physical medium or even the same type of modulation. Many different types of PLC are using different frequencies and modulation and they are not compatible and hence not interoperable. The interoperability can be achieved at different levels of the AMI architecture. Interoperability should be provided by manufacturers and be tested during the tendering phase. It’s very important to perform a general test before a massive rollout; otherwise the risk is to deploy meters that are not able to communicate with the data concentrator, resulting in additional costs for integration and modification of the devices and firmware. To mitigate the risks, the tender documentation should consider a test in the field before the approval of a final contract and, of course, before a massive rollout.
Layers of interoperability
Complete interoperability can be achieved at meter level. This means that meters of different manufacturers, even operating under the same concentrator, if used, can work without reciprocally affecting the functionalities, including communication.
An even stronger constraint defines interoperability as interchangeability, thus requiring that the replacement of a meter from one manufacturer with another of a second manufacturer will allow for meter interoperability, thus including the services at lower levels, such as the repeater mechanism. This is particularly hard to obtain in residential meters with concentrators.
Defining interoperability at the concentrator level (middle layer) releases some of the constraints at meter level, since the communication between meters and concentrator can be freely defined and adopted, while the concentrators of different manufacturers must adopt a common way of communication with the control centre.
Interoperability at DCU level is recommended at the first stages of implementation, thus avoiding the coexistence of
PLC smart meters produced by different manufacturers on the LV network under the same substation. In terms of interoperability at MDM level, this is the least constrained, since the MDM software will be in charge of requesting information and sending commands according to different standards, thus practically integrating systems, which otherwise are completely incompatible.
Interoperability among products from different manufacturers must, at a minimum, be performed at the concentrator level. This means that, waiting for full standardisation, the meters under the same concentrator will be from the same manufacturer. From the concentrator, the communication medium is IP-based (GPRS, Wi-Fi or fibre optic, when available).
The data concentrator will use the same data model thus being accessed in the same way from the AHE. Meters directly connected to the AHE, via GPRS or LAN, adopting the same data model, objects and OBIS codes, will be interoperable. Interoperability issues will be solved at the front end of the AHE software, which can talk with different types of meters and concentrators using different objects and methods according to COSEM OBIS. ESI
This article is based on a report written by Monenco Iran, under the auspices of the office of the Consulting Engineers Dispatching, Information and Telecommunication Deputy, Smart Grid Department. Monenco Iran is responsible for consultancy services for the implementation, supervision and administration of the advanced electricity metering project in Iran.