Importance of PLC Modems in Smart Meters

In recent years, driven by the awareness of green energy conservation, smart grid with smart meters as the core has become a key area of ​​development for many countries such as Europe, the United States, Japan and China. Grid technology is facing an important revolution, not just a simple technological evolution.

Table 1: Simple comparison between traditional power grid and new smart grid.

In smart grids, smart meters play a key role in enabling interaction between users and the power system. For example, on the one hand, they help power agencies accurately understand the user's electricity consumption patterns and set differentiated electricity prices for peak or off-peak electricity consumption; on the other hand, users can also reasonably adjust their electricity consumption plans to optimize electricity bill expenditures. From the perspective of functional modules, in addition to power supply and metering modules, smart meters also involve data storage functions, which require the use of safe and reliable storage; in addition, two-way real-time communication is an important feature of smart grids, so the communication module is crucial, and it is necessary to select a suitable communication method and the corresponding optimal solution.

In fact, the smart grid is a huge system involving multiple levels such as power, communication and application, as well as different network types such as local area network (LAN) and wide area network (WAN). Among them, LAN connects different types of smart meters in homes or buildings to data concentrators. As far as this section of network connection is concerned, they usually do not require high communication speeds. The most important consideration is to reduce costs. Common communication methods include wireless radio frequency networks, wired power line carriers (PLC) or power line broadband (BPL). The specific communication method to be adopted needs to consider factors such as the actual conditions of the power grids in various countries. At the same time, the practices of countries that have taken the lead will also provide reference significance.

Figure 1: A simplified diagram of the Linky project of ERDF, a subsidiary of EDF, France.

For example, Electricité de France (EDF), which has a significant influence in the European energy market, launched Linky, the world's largest smart meter project, in mid-2009, planning to deploy 35 million smart meters in France by 2017. This project selected PLC technology for communication between smart meters and data concentrators, and then used General Packet Radio Service (GPRS) technology to transmit data to the company's data center. Considering that China's smart grid is still in the pilot stage, the choice of ERDF in France is also of reference significance to China and other countries.

Selection of PLC modulation technology

Although PLC technology provides a low-cost option, power lines were not originally intended for communication, so there are some challenges when applying PLC communication. In particular, designers need to pay close attention to the signal attenuation and noise issues that will occur, which in turn requires complex transceiver technology.

In order to suppress signal attenuation caused by noise, reduce bit error rate, and improve frequency efficiency, it is necessary to use appropriate signal modulation technology. In fact, when power agencies deploy smart meter reading systems, there are many different modulation methods, but there are three main ones, namely orthogonal frequency division multiplexing (OFDM), phase shift keying (PSK) and spread spectrum frequency shift keying (S-FSK).

OFDM has a high theoretical bandwidth, but in practice a large portion of the bandwidth is lost under noisy conditions in low-voltage networks, and OFDM is expensive to apply and consumes considerable power when operating. PSK modulation technology is very cheap to apply, but it is not particularly reliable, performance is affected by phase noise, and it cannot fully cover longer distances. In comparison, although S-FSK has a lower data rate than OFDM, it is more suitable for smart meter applications. This modulation technology can achieve reliable communication, while being cheaper to apply and consuming less power. Therefore, for current smart grid PLC applications, S-FSK modulation technology is undoubtedly a more suitable choice due to its low complexity, greater commercial potential and reliable field application record.

In fact, in the Linky project specifications of the French ERDF, the physical layer reference specification is IEC61334-5-1/EN50065, in which the modulation technology specified is S-FSK, the communication frequency is the mark frequency (Fm) 63.3kHz and the space frequency (Fs) 74kHz, the transmission rate is 2.4Kbps, and it is physically synchronized with the 50Hz electrical network frequency.

Application Advantages of ON Semiconductor PLC Modems

ON Semiconductor has a long history of developing PLC modems. The 1.2 kb AMIS-30585 was launched earlier and was originally developed to comply with the IEC 61334 standard (SFSK specification). It has been tested in field applications for 8 years. The newly launched AMIS-49587 is a highly integrated, standard-compliant low-power PLC solution that supports 4 different modes required for PLC field deployment, such as NO_CONFIG, MASTER (concentrator), SLAVE (meter) and SPY (raw data for testers). It is very suitable for smart meters, smart street lights and smart sockets. Compared with the AMIS-30585, the AMIS-49587 supports a higher half-duplex adjustable communication rate of 2.4 kb, which meets new market requirements such as the ERDF specification. It has been pre-used by French original equipment manufacturers (OEMs) and has been selected by several leading meter customers in China. The two devices are pin-to-pin compatible, providing customers with greater design convenience.

The AMIS-49587 complies with the IEC61334-5-1 standard and offers numerous application advantages to customers. For example, the device is based on the ARM7TDMI processor core and includes both the physical interface transceiver (PHY) and media access controller (MAC) layers, making it a single-chip solution that combines analog modem front-end and digital post-processing functions, while most competing solutions require complex embedded software to perform the same functions as the AMIS-49587. Using the AMIS-49587 modem, designers can simplify their designs and develop a complete interoperable PLC solution in less than a quarter, while also reducing development and application costs. In fact, the AMIS-49587-based modem solution uses only two ICs (the other is the NCS5650 2 A PLC line driver), plus 16 resistors, 17 capacitors, two diodes, a crystal, and a pulse transformer, for a total of only 39 components, providing a low bill of materials (BOM) cost.

In addition, AMIS-49587 uses S-FSK modulation technology, combined with high-resolution filtering algorithms, and automatic trust value/repeater functions to provide high-reliability data communication based on long-distance power lines. Communication errors are lower than other optional and existing solutions. This device synchronizes with the AC mains signal through an onboard low-jitter phase-locked loop (PLL). Due to the inclusion of a 16-bit resolution analog front end, the device has excellent noise immunity and extremely high receiving sensitivity.

AMIS-49587 is also easy to use. With built-in protocol processing, designers do not need to deal with the details of PHY and MAC protocol transmission, saving up to 50% of software development costs, thereby accelerating time to market and reducing total costs. The device is directly connected to the user's main microcontroller (MCU) via a serial interface.

AMIS-49587 is compatible with both single-phase and multi-phase meters to meet different customer needs. In addition, its energy consumption is lower than that of digital signal processor (DSP)-based solutions, making it very suitable for PLC communication applications from smart meters to concentrators. In order to help designers speed up the development process, ON Semiconductor also provides an evaluation kit AMIS49587EVK to facilitate user development. This kit contains 2 PLC modems for configuring communication between the client and server; it also contains an open source graphical user interface for configuring end-to-end communication.

ON Semiconductor provides complete solutions for smart meter applications

Compared with ordinary meters, smart meters are undoubtedly more complex systems. ON Semiconductor provides complete solutions for smart meter applications. In addition to the above-mentioned PLC modem and line driver solutions for communication applications, it also provides solutions for key functions such as power management, measurement and storage. For example, in the power management module, ON Semiconductor's NCP1014, NCP1015 and other AC-DC converters, LM2596, NCP3063 and CS51411 and other DC/DC converters, MC78L05, MC7805, CAT6217 and CAT6219 and other low-dropout (LDO) regulators, as well as NTMFS4823 and other medium-voltage and high-voltage FETs can be applied. In addition, in smart meter applications, ON Semiconductor's series of EEPROM, SDRM and other memories, as well as ESD/TVS, SIM card interface, logic, USB protection, monitoring, I/O expansion, clock and temperature sensors can also be used.

Figure 2: ON Semiconductor’s solution for smart meters.

Conclusion

Smart meters play a key role in the emerging smart grid applications. Designers need to choose a suitable communication method for the communication between smart meters and data concentrators, and PLC has become the choice of leading companies and early test projects in the industry, which is quite demonstrative and referenceable. Designers need to choose a modem solution for PLC communication. ON Semiconductor's modem products for PLC meet standards and customer specifications, and provide many application advantages, such as simplifying design, reducing costs, reducing power consumption, providing reliable communication and accelerating the process of listing. ON Semiconductor also provides complete solutions for smart meter applications, including key functions such as power/power management and protection, communication, measurement and storage, which facilitates customers' choices, helps them reduce procurement costs and accelerate product listing.