The first story in this series described how smart meters and HEMS (Home Energy Management System) devices save energy. Additionally, it, introduced electricity metering development solutions that apply advanced Renesas MCUs. This Part 2 story continues the technology discussion, focusing on the communication functions that form the core of smart grids. It provides useful tips for designing smart-grid products that handle communication methods used in different countries and regions, and offers suggestions for accelerating system development projects.
Renesas' smart-grid communication solutions increase the efficiency of the product development. They also facilitate mass-production because they consume very small amounts of power and incorporate system scalability features. These traits and more make them ideal for controlling the consumption, generation and storage of energy in BEMS products for buildings, FEMS equipment for factories, and the CEMS installations that serve communities. Besides smart electricity meters and energy-management systems, the many diverse applications for smart-grid communication solutions include gas meters, sensor networks, streetlights, and building automation systems.
Addressing the challenges of implementing smart grid communication
Smart meters and HEMS devices are largely defined by their communication functions. Consider smart meters, for example. They usually have two communication routes（Refer to Figure 1 in Part 1). Route A implements communications with energy suppliers (electric utility companies, etc.), while Route B is used to exchange control commands and data with consumer products (household HEMS devices, etc.). However, the communication methods employed in both routes vary in different countries and regions.
In Route A, it's essential that electric companies comply with a basic set of standard communication specifications. Still, they might incorporate extensions to those specifications to meet specific needs. By contrast, in Route B the primary focus of the standardized communication specifications is on interoperability and connectivity. Originality must be sacrificed to ensure that smart meters can link seamlessly with diverse HEMS devices.
Looking globally, different communication methods are being used or considered for both Route A and Route B. They include the Wi-SUN, PLC (Power Line Communication) and ZigBee® approaches, the wireless multihop method, and 2G/3G mobile communications, as well as meter manufacturers' own unique communication techniques.
In Japan, the Wi-SUN wireless communications standard has been adopted as a main communication method for Route B links. This is supplemented by PLC, which is used if wireless communications are not possible. On the other hand, for Route A networks, the wireless multihop method, wireless 1:N method, and PLC are under consideration.
Route B links are usually connected to household devices such as HEMS (or BEMS) servers. The servers are the key digital electronic elements in smart homes and buildings, responsible for maintaining optimum levels of energy consumption.
Focusing on the leading smart grid communication methods: Wi-SUN and PLC
Typically, the Wi-SUN and PLC approaches play important roles in connecting the different HEMS (BEMS) facilities within structures. Therefore, the discussion that follows describes these two communication methods in detail. Currently they are the communication key enablers for the rapid expansion of products and markets for energy saving embedded control techniques.
(1) Wi-SUN: A key sub-GHz wireless communication standard
Wi-SUN is a newly created communication standard that allows seamless interconnections between smart-grid devices produced by different manufacturers. The wireless interconnectivity it ensures makes it possible to create a HAN (Home Area Network) that connects multiple home appliances to implement efficient HEMS installations. This capability facilitates embedded system applications in the area of the IoT (Internet of Things) beyond just smart meters—especially devices for M2M (Machine-to-Machine) applications and networks of remotely located sensors.
Wi-SUN based wireless equipment operates in frequency bands below 1GHz. In this region of the frequency spectrum, regulations typically allow unlicensed, low-power radios that achieve good communication performance, even in the presence of interference and some types of obstacles. The bands used vary slightly in different countries, but are usually around 900 MHz. Examples are 920 MHz in Japan, 915 MHz in the United States and 863 MHz in Europe.
A big advantage of Sub-GHz wireless communications is that it can be implemented with extremely low levels of power consumption compared with other wireless communications, such as WLAN, which operates on the 2.4 GHz and 5 GHz bands. The energy efficiency of Sub-GHz technology recommends it for difficult applications like remote sensor networks that have to operate for years without battery replacements.
From a technical standpoint, the Wi-SUN wireless approach is related to, but distinct from, the familiar Wi-Fi technology. It's a low-speed communication scheme that adopts the IEEE802.15.4g standard for physical layers, and can maintain communications even in environments that have over 1000 nodes. Its MAC layer conforms to IEEE802.15.4e. Although IEEE802.15.4e and IEEE802.15.4g establish transmitter/receiver performance requirements, Wi-SUN compliant networking equipment must meet additional requirements on actual communication operations.
Wi-SUN technology achieves improvements in throughput and security compared to wireless networks based just on IEEE802.15.4. From the outset, Renesas has been a core member of the group that developed the Wi-SUN specifications.
(2) PLC: Version for smart meters differs from PLC for data communications
PLC technology achieves communications by inserting a signal frequency higher than the 50/60Hz alternating current into wiring that distributes AC power (see Figure 6). This technology requires no additional work to install because it uses the existing power lines to carry digital messages and data. Importantly, this communication method performs well in places where metal or thick reinforced concrete walls block wireless signal transmissions.
PLC provides robust connectivity not only in smart meter applications, but also in other huge markets such as building automation systems and streetlight control and monitoring equipment.
Smart meters apply a type of PLC that is quite different from the PLC used for data communications via PCs. One is NB (Narrow Band)-PLC and another one is WB (Wide Band)-PLC. NB-PLC uses 10 to 500 kHz frequencies; WB-PLC uses 2 to 30 MHz to obtain faster data rates.
Multiple PLC protocols exist for smart meters. They include G3 and PRIME, which are predominantly used in Europe; IEEE1901.2, which is used in the United States, and Meters & More, the PLC version used in Italy. In Japan, the G3-protocol PLC (G3-PLC) has been adopted. Renesas is involved in the standardization activities for all these methods, participating in all working groups for G3 and PRIME, in particular.
(3) ECHONET Lite: Communication standard for connecting different devices
It isn't possible to control home appliances, a smart meter and a solar power generation system merely by connecting them together using Wi-SUN or PLC links. Information cannot be sent mutually when the data formats and sequences used for transmissions vary, depending on which company manufactured the device or system. One solution for this problem is ECHONET Lite, a communication protocol developed by the ECHONET CONSORTIUM in Japan that standardizes data formats and sequences.
ECHONET Lite mainly regulates the application layers (OSI layers) of the communication process. It implements control compatibility on the common access interface in upper layers of the Wi-SUN and PLC protocols. Products that implement this standard can control over 80 types of HEMS devices.
The capabilities of ECHONET Lite can be applied to produce substantial energy savings. The technology enables HEMS equipment to control and track the operating status and power consumption of home appliances, for instance.
As more home appliances and storage batteries become compatible with ECHONET Lite, smart meters and other HEMS devices will be able to reduce or limit a household's overall power consumption. Additionally, they will also be able to control the power consumed by individual devices and optimize the generation, sales and storage of power.
Testing to ensuring communication performance and interoperability
As previously mentioned, communication technology is key to smart grids. Whether the method used is wireless or wired, it must adhere to a precise set of specifications and achieve minimum or greater levels of defined performance to suffice for smart meter markets. This requires more than just developing a written communication standard and meeting its stated requirements in products that will be networked together.
The problem is that, by necessity, written technical standards are comprehensive and extremely voluminous. It's not an easy task to read and understand everything described therein. Besides, some issues are not covered in the specification and therefore are open to interpretation.
A considerable amount of engineering effort and cost can be expended to produce a design that is believed to be capable of meeting the requirements of the communication standard. However, it then must be put through a certification test by the appropriate standardizing body. Unless it passes that test, a product cannot be called "standard compliant".
Unfortunately, passing a standard's certification test does not necessarily guarantee a product's connectivity. Successful implementations must adequately and correctly address factors other than those covered in the standards—software routines, for example.
Obviously, a targeted networked device must be able to understand the control signals and data it receives. Otherwise, the communication is meaningless. For this reason, standardizing bodies also conduct interconnectivity tests to ensure a product's interoperability and connectivity.
A level of engineering expertise must be acquired in order to produce communication functions that pass certification and interconnectivity tests. Achieving success requires more than just implementing technologies according to what is written in the standards. Considerable engineering experience applying technology is necessary to avoid hidden pitfalls.
Fortunately, there is a fast, easy way to ensure that smart grid products can pass the requisite compliance tests. System developers can incorporate into their designs communication modules and protocol stacks that have already been certified.
Minimizing the work and delays associated with communication compliance testing ―Communication Functions―
The task of creating smart grid products poses many engineering challenges. As previously discussed, a major one is that designs for communication functions often seem to be in strict accordance with standards, yet they tend to experience variances in connectivity depending on how they are implemented.
Pre-certified solutions by Renesas address this issue directly, however. They eliminate compliance problems while also drastically reducing the man-hours needed to implement robust networking capabilities. Their use allows more system engineering resources to be used for giving competitive advantages to smart meters and HEMS devices.
To further enhance and accelerate the R&D work for producing smart-grid products, Renesas offers support tools that can boost system development productivity. These helpful, timesaving tools are described below.
(1) Kits for reducing power consumption or adding features
Providing certified test bed units in two Wi-SUN platforms
Renesas now offers its customers two Wi-SUN-based smart meter development kits. One is the Wi-SUN Basic Platform for Sub-GHz band development kit, which is based on an RL78/G13 MCU (see Figure 7). A key feature of the design of this kit's communication unit is extremely low power consumption.
The other communication unit design tool is the RX63N-equipped Wi-SUN Advanced Platform for Sub-GHz band development kit (see Figure 8). Its high scalability makes it possible to design smart grid devices that accommodate various types of operational functions.
Accredited by the Wi-SUN Alliance, the wireless unit (including protocol stack) that is used in both of these kits is certified as an official test head unit (CTBU: Certified Test Bed Unit). Thus, Renesas' protocol stack will be the basis on which other vendors' products will be tested for connectivity. So all products that have passed the connectivity test will be guaranteed connectivity with Renesas' protocol stack. As a result, these kits greatly ease the task of successfully passing connectivity tests.
(2) A development solution that implements compatibility with different PLC methods via software changes
Delivering high developmental efficiency and aiding mass production
The Renesas kit solution for PLC applications (see Figure 9) consists of a PLC evaluation board mounted with a global PLC modem (the µPD809508) and a software document. The µPD809508 chip is compatible with both G3-PLC and PRIME PLC methods, and Renesas has acquired certification with its protocol stack.
Simply by changing a software library, the PLC modem can be made compatible with the G3-PLC standards used in different regions (Europe, the US and Japan) and the PRIME standard. Because this communication functions solution is based on software, the algorithms used in its protocols can be modified as required to overcome common PLC issues such as noise and signal attenuation.
This hardware/software approach allows the same modem LSI to be used for different countries. That design advantage improves R&D efficiency. It also reduces BOM costs by making it possible to produce large quantities of a basic design that can programmed to address the different needs of diverse markets.
The Renesas R&D staff continues to develop modems and software for smart-grid related devices and systems. Progress is being made on a single model to comply with G3-PLC and PRIME, and IEEE1901.2 in the U.S. and the latest PRIME version, V.1.4.
The solution kit's evaluation board has received a certificate of conformance to Japanese regulation. Simply by purchasing two kit solutions and connecting them to a power line, engineers can instantly conduct connectivity tests. This eliminates the need for the special test environment that would otherwise be required to prevent the PLC signal from leaking out onto a utility's power lines.
Opening more opportunities for developing global smart grid products, offering cost-saving solutions that shorten development cycles
This two-part series of EDGE stories has introduced Renesas' solutions for smart grid-related devices. Our advanced semiconductors, application software and development tools give customers important benefits. Key examples include a metering function that consumes extremely small amounts of power, and certified connectivity solutions that drastically reduce design-engineering man-hours.
Low power consumption, scalability and high developmental efficiency are the primary hallmarks of Renesas' smart grid solutions. Their feature sets, combined with the support services we offer, facilitate the creation of systems designed to control energy consumption, generation and storage for HEMS, BEMS, FEMS and CEMS equipment. Beyond those systems and smart electricity meters, the expanding number of applications for our smart-grid related innovations includes gas meters, sensor networks and streetlights.
The discussions in the Part 1 and Part 2 stories underscore Renesas' strong goal of helping customers produce profitable smart grid products that enhance their business successes. Please contact us to learn more about the extensive benefits that our capabilities deliver.
※Wi-SUN is a registered trademark of Wi-SUN Alliance, Inc., Renesas is licensed to use this trademark.
※ZigBee is a registered trademark of ZigBee Alliance.