The technical feasibility of automatic meter reading (AMR) within the residential sector has already been demonstrated in various trials. By the end of 2005, 30 million households had been equipped with advanced meters connected via powerline carrier (PLC) to the automatic meter management (AMM) system of ENEL, the leading Italian electricity provider and network operator.
In the Netherlands, the grid operating company Continuon carried out a successful trial which involved the remote reading of energy meters in several hundred homes. Furthermore, promotion of AMR systems is supported by legislation. “EU Member States shall ensure that: Billing reflects actual consumption in understandable terms, and is carried out frequently enough to enable customers to regulate their own energy consumption.” (Excerpt from “Proposal for a Directive of the European Parliament and of the Council on energy end-use efficiency and energy services”. COM(2003) 739, Article 13). Sweden is the only country in Europe so far that has transformed the idea of accurate monthly billing into a national law. By 2009, 5 million Swedish electricity customers must be billed monthly according to their actual consumption. Monthly billing, based on measured consumption data, creates energy consumption awareness by giving the customer immediate feedback on his saving measures.
Nevertheless, in order to be a cost-effective solution in the residential market, the metering systems should go far beyond the ‘classical AMR’ (ie just remote reading) applications. The system should launch new services for the customer (such as security services and home automation) and provide valueadded services for utility companies (such as online contact to any meter in the grid at any time and easier fraud detection). These services should also include multi-metering (automatic reading of electricity, gas, water and heat meters) as well as remote contract management, by offering contracts based on flexible time-of-use tariffs, maximum demand limitation (enforced by price penalty or by disconnection) or prepaymentbased contracts.
Of course, all these different services have to be integrated into one system and share the same medium. PLC is an interesting technology for AMR in the residential market. On the one hand powerline communication competes with communication via dedicated wires like field buses, telephone lines with voice-band-modems, and LAN systems; and on the other hand with radio-based systems like DECT, GSM/GPRS, ISM-band modems or wireless LAN. All these technologies have been available for a long time, are successfully employed in their respective fields and, due to their production on a large scale, can be offered at low prices.
However, radio-based systems require an infrastructure, such as GSM, which makes operation of the system expensive. A profitable application for PLC would have to be a system where the wiring imposes the main expense, because the distribution line already exists and a radio-based system would not be feasible or cost-effective. Low voltage networks in densely populated residential sectors meet these prerequisites for PLC systems. A major benefit to utilities is that they own the infrastructure, and so do not incur an additional per message cost.
An operational cost comparison between the different communication systems can be found in “Materialienband zur VWEW-Fachtagung: Smart Grids – der Beitrag virtueller Kraftwerke zur nachhaltigen Energieversorgung” of 7th and 8th June in Fulda, Germany. In this study a huge German electronic company states that the application of PLC, especially the DLC system of iAd (see below) is the most economic system when compared with other technologies like radio-based systems.
AFFECTING COMMUNICATION PERFORMANCE
Since the power lines were not built for communication, they are a rather harsh environment for data transmission. Varying impedance, considerable noise, high signal attenuation and distortion are the main factors that affect communication performance. Furthermore, the powerline channel is a frequency-selective channel, and in addition to background noise it shows impulsive noise and narrowband interference. The best solution to withstand narrowband interference and notches in the transmission channel is to spread the information among several carriers to increase robustness: multi-carrier modulation is the natural result. Multiple carriers are realised efficiently in digital signal processing using fast Fourier transformation. These methods are often called OFDM – Orthogonal Frequency Division Multiplexing. In combination with Forward Error Correction (FEC), OFDM is able to achieve reliable and bandwidth-efficient communication, even with the impairments of a hostile powerline channel.
ADDRESSING THE NEEDS OF RESIDENTIAL AMM
Taking all this into account, iAd GmbH (Germany) and ELGAMA-ELEKTRONIKA (Lithuania) joined forces a few years ago to address the needs of residential AMM systems. The iAd GmbH invested its expertise in PLC communication systems, and ELGAMA-ELEKTRONIKA shared its skills in metering. Since the public powerline network is publicly accessible – and therefore must be regarded intrinsically as not to be trusted – special security measures had to be undertaken to ensure integrity, authentication and confidentiality of the transmitted messages and information stored inside the system.
The appropriate security measures, based on smart card technology, are integrated in the network management protocol, where the main challenges were found in the peculiarities of the PLC system – restricted bandwidth and packet size, different services, and time synchronisation. Furthermore, WELMEC (the Western European Legal Metrology Co-operation) recommendations for compliance with the software-related requirements contained in the European Measuring Instruments Directive (MID) are taken into account. Issues like software download and protection from unauthorised access or attack are considered.
NETWORK MANAGEMENT SYSTEM
The ad hoc network management system is based on the EU-founded project REMPLI (www.rempli.org). This allows a soft real-time, secure and reliable communication via MV and LV distribution lines for a large number of participants. The flooding master-slave concept, based on the single frequency network technology of iAd, guarantees reaction times over several repeater levels, even during abrupt changing topologies or load scenarios. In combination with the multi-master concept, the TDMA scheme allows real redundant communication, which is automatically managed by a specialised transport layer. QoS parameters and optimisation of throughput and reaction time ensure real-time features on 100% load on the communication network. This allows an integrated communication infrastructure for SCADA systems and AMM.
The integrated security layer in the communication system ensures maximum security with minimal overhead, and enables multi-cast communication. Even in large networks the applications see only a virtual star and can directly address all meters. A link status table provides the line state and the communication cost for every participant in the network.
An automatic parameter and frequency scan allows meter installation and communication set-up without parameterisation. Parameters like tariffs can be downloaded and verified from a centralised database, which allows installation of the meter without specialised technicians or access to security-critical configurations in the field. Only the configuration of the meter number is required to get a correlation between meter and customer in a service centre. Excellent results have been achieved in several field tests of the system, which confirmed the feasibility of cost-effective multi-service PLC-based AMM solution for residential markets. For further face-to-face discussions or questions please visit ELGAMA-ELEKTRONIKA Ltd. stand 5.07 at the Metering, Billing/CRM Europe 2006 exhibition, taking place in Copenhagen, Denmark, 10-12 October, 2006.