Utilities set different goals for their AMI systems. Recording monthly energy data over a 12 month period, remote switch control, tamper and supply abnormality reporting are basic functions required by utilities. Load profiles of parameters like current, voltage, frequency and harmonics are also of interest to utilities for the purposes of supply analysis. Sometimes interaction with household appliances is required in order to record and refer to power consumption of each appliance in a chosen period.
In some developing countries, utilities use prepayment energy meters (IC card, keypad) in AMI deployments.
The complexity of the system architecture and network channel capacity must therefore be developed in accordance with the utility initiatives.
The pillars of an AMI system are measurement, transmission, management and application. The measurement part contains meters and modules. Concentrators, collectors, repeaters, GPRS/3G modules or Ethernet network devices fall into the transmission category. The front-end processor, database, application server, router, PC and operator are responsible for management and application.
Power vending and remote top-ups are requested in the management and application part of AMI prepayment systems.
Technology and specifications
As a major technology in an AMI system, communication between meters and concentrators can be PLC, RF, RS485 or M-Bus.
PLC technologies include Prime, G3-PLC, TWACS and GDW-PLC modes. Prime and G3PLC are open and complete technologies developed by many companies, in which interconnection labs are involved for link tests. TWACS, mainly used in the Americas, is a proprietary technology supported only by one company. GDW-PLC, supported by many companies, is mainly applied in China. Interconnection has not been realized for GDW-PLC. Currently, utilities demand a certain module brand and quantity under local deployment circumstances while calling for bids.
RF technology includes Zigbee and GDW-RF. Zigbee, though fully developed, has not been widely applied in developing countries due to its limited communication distance. GDW-RF, supported by many companies, is mainly applied in China. Interconnection is feasible for GDW-PLC.
The concentrator communicates with the front-end processor via GPRS/3G/4G or Ethernet. The power vending part of an AMI prepayment system is mostly implemented in compliance with STS specifications (IEC62055-41). The STS specifications have not provided descriptions for multi-tariff tokens, such as TOU tariff, holiday and weekend. Utilities have to specify related functions.
The author has written about how to realize multiple tariff in compliance with the STS specifications in an article titled Energy meter implements interval multi-tariff function according to IEC 62055-41 published in Smart Energy International, Issue 4, 2010.
Power purchase in prepaid model
The prepaid model allows consumers to pay for electricity before they use it. Convenient power purchase experiences will increase customer satisfaction. A traditional option for power purchase would be going to a utility vending station, which is a good choice as a vending station is fully functional. But consumers often have to travel for a certain distance and then wait in line due to a limited number of vending stations.
Utilities may also partner with banks for power vending. In this way, consumers can purchase power while running errands in a bank. However, this is also subject to limitations. As an example, utilities have to seal a contract with the bank and bear costs of system development. Also, it is not the bank’s responsibility to handle abnormalities like either.
HHU (hand held unit) power purchasing is a complement to existing systems. A full-featured HHU allows power vending to IC card energy meters and keypad energy meters with printed payment slip. HHU power purchase is desirable for remote areas.
In city residential areas, shopping centres and hotel lobbies, self-service terminals are preferred to provide unattended 24/7 power vending services. For keypad energy meters, consumers may use cell phones to purchase power via USSD, SMS and APP.
At least two communication protocols are involved in an AMI system: the protocol between meter and concentrator, as well as the protocol between concentrator and frontend server. Protocols between energy meter and concentrator include DLMS/COSEM (IEC62056-46, 47, 53, 61, 62), IEC62056-21 (replaces IEC61107), ANSIC12.22 and Q/GDW1376.2 Q/GDW1376.1 is a well-developed protocol between concentrator and front-end server.
DLMS/COSEM protocols and the ANSI C12 standards do not specify this part of communication in details, such as login and heartbeat. Therefore, some companies which adopt these protocols have selfdefined some necessary expansions.
System security is also considered with regard to measurement, transmission, management and application.
Measurement security mainly concerns unauthorized switch control, data modification, tamper clearance and even meter reading. The AMI applied with DLMS/COSEM protocols is often encrypted by AES, the authentications of which can be opted from MD5, SHA1 and GMAC. When the Q/GDW protocol is adopted, an ESAM module is installed in the meter. SM2 is utilized for encryption and authentication. During transmission, data tamper and fraud nodes should be prevented. Thus two-way authentication must be conducted between concentrator and meter, as well as between concentrator and front-end server. MD5, SHA1 and GMAC can be used for DLMS/ COSEM protocols. For the Q/GDW protocol, ESAM modules built in meters and concentrator provide authentication for various operations.
The management and application part, besides requiring corresponding security protection at the concentrator, has to consider viruses, hacker attack and disaster recovery. Database backup is the simplest approach to disaster recovery. Real time database backup is more advanced and requires a redundant server. A high-level disaster recovery mechanism offers two data centres with the same equipment although located at different locations. In the event of a disaster like an earthquake or flood, the other data centre will take over immediately.
A sound AMI system evolves with new functional requirements, along with technology and specifications development. The system supports a smooth upgrade to incorporate any newly developed products with the latest industry technology to enhance its performance. The overall system architecture should be designed for scalability from the very beginning.
An AMI prepayment system often supports remote switching between prepaid and postpaid modes. To switch payment mode in batches, an optimized approach would be setting a date and time for an automatic payment switch which would be initiated by a predefined time.
Technical and social development is integrating AMI into the smart city as a part of the IoT. Power consumption data in industrial and commercial applications is recorded separately by device category and time of use. Acquired power consumption data is contributed to the big data for utility analysis. Thus the utility could have a better energy management plan in place and take conservation and environmental protection to the next level. MI