Via Appliancedesign.com . Imagine a world where the skyrocketing demand for energy, driven by the increasing scarcity of fossil fuels and the rapid economic development of emerging economies, leads to frequent electrical brownouts and blackouts. Now imagine if local utilities could communicate with appliances in homes such as a water heater, air conditioner, clothes dryer, or dishwasher, and instruct each one to cycle down during high-demand periods. This can help minimize power demand across the grid and avoid blackouts. Or better yet, imagine load-management programs that automatically drive down consumer electrical bills by turning off appliances and lights during high-cost peak periods and reinstating them when electricity rates are lower.
That’s the promise of powerline communications (PLC). By leveraging the vast electrical infrastructure already in place, PLC systems can use existing electrical lines rather than dedicated cabling to transmit data. The technology basically eliminates the high cost of installing network cable by allowing devices to communicate with one another after being plugged into standard electrical outlets. The concept is hardly new. Utilities have used PLC since the early 20th century to remotely control equipment on the grid. Only recently, however, have designers looked to PLC as a suitable low-cost methodology to precisely and efficiently manage electrical usage in home and building automation applications.
Early implementations of powerline-based technology for control applications offered limited performance. Initial derivations of the technology, such as CEBus and X-10, supported data rates of less than 1 kbps. Moreover, utilities using powerline networks had to grapple with extensive interference and a great deal of noise. Fluctuations in powerline conditions, in addition to noise from motors and other sources, frequently disrupted or terminated transmission.
Today’s PLC technologies use different methods to encode the information, including amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK), spread spectrum (SS), or orthogonal frequency division multiplexing (OFDM). Among them, the most efficient solution for cost-sensitive, medium data rate applications is narrowband FSK. With this technique, digital data (0 and 1) are represented by two different frequencies, narrowly shifted from the central carrier frequency.
Such PLC systems operate by impressing this modulated carrier signal on the wiring system. Different types of PLC systems use different frequency bands. Home control systems usually modulate a carrier signal between 20 kHz and 200 kHz. As transmission rates have risen, designers have proposed PLC as a networking scheme for the interconnectivity of a wider array of electronic products via standard Ethernet or USB interfaces.
Today, industry groups are eyeing opportunities for PLC in higher-speed home networks for multimedia or entertainment applications such as high-definition TVs and home theaters. The HomePlug Powerline Alliance, a U.S.-based group of leading network technology, service and content providers, came together in March 2000 to develop and promote a common approach to PLC. The organization’s first act was to define the HomePlug 1.0 specification and outline a certification program to promote interoperability. More recently, the alliance has defined HomePlug AV (HPAV), a higher-speed standard designed to support video distribution with secure connectivity and integrated Quality of Service (QoS).
In the meantime, the rapidly rising cost of energy has refocused attention on a potentially vast market for lower-speed, PLC-based command and control applications. For home networking control of lighting, appliances, climate control appliances, and other basic functions, the HomePlug Powerline Alliance has drafted the HomePlug Command and Control (HPCC) specification as a lower-speed, lower-cost complement to HPAV. Using existing household electrical wiring as a transmission medium, PLC offers a low-cost and highly reliable networking solution for remote control of appliances and lighting systems without requiring the installation of additional wiring. The technology also offers a relatively high level of security. Unauthorized access to the medium is generally difficult when dealing with high voltages, and designers can add encryption with a network key and on-chip security features to further protect information.
Networks of this type not only give utilities and building managers more visibility into the electricity distribution and monitoring system, they also enable the use of completely remote, automated meter reading (AMR) as well as instant reporting of outages and system failures. Rather than a human meter reader visiting every customer’s house to manually log power usage, utilities can now track power usage in real time and use smart meters to manage power consumption. Ideally, this capability will enable utilities to respond more quickly and efficiently to changes in demand across the distribution network. It will also enable customers to use power more efficiently and drive down costs.
In this type of home area network or building automation application, utilities would use a variety of PLC products to intelligently manage lighting, heating and cooling, security, access control, and energy usage. Keypad controllers, for example, would act as standalone transceivers and replace standard switches in the powerline home or building network, and communicate with intelligent PLC-enabled appliances. The PLC system manufacturer would provide software to program the keypad controller and create various control scenarios for the managed network.
PC-based powerline transceivers ensure reliable communication of data across the network, communicating with host computers via Ethernet or USB interfaces. An analog front end performs signal conditioning and couples the modulated signals, generated from a custom modem chip with the powerlines. Using specialized software, the modem chip is capable of implementing custom configurations and more advanced functions such as signal-level measuring and signal repetition. At the networking level, simple plug-in PLC load modules provide remote control of individual appliances or lights via command signals transmitted over the same electrical wires that power the appliance. Each module is programmed by a keypad controller or transceiver to respond to on/off, bright/dim, or ramp up/ramp down commands. Installation is simple. The user plugs each load module into the wall outlet closest to the appliance or light. The appliance or light is then plugged directly into a receptacle on the module. No wiring installation is required.
Each powerline module and transceiver capable of functioning within a powerline network will require a digital modem IC and a controller. Eventually this functionality could be either embedded in an appliance’s motherboard or mounted on a separate daughtercard. The daughtercard approach allows appliance manufacturers to easily modify or update their designs by replacing the card as industry standards evolve. Once industry standards are resolved, most appliance manufacturers will probably opt to embed the modem onto the motherboard to reduce space requirements and minimize cost.
Design flexibility and cost are key considerations when selecting a modem IC for PLC applications. Ideally, a PLC modem must support a wide range of programmable transmission rates as well as communication frequencies. It should also offer a range of on-chip security peripherals. Reliability is also crucial. To reap the benefit of PLC technology, utilities need command and control solutions that are always available. Proven IC manufacturing processes and the integration of extensive on-chip error correction capabilities help ensure data accuracy and system uptime.
To give the PLC network designer maximum flexibility, a modem IC should also support the use of more than one protocol within the same network and the use of more than a single protocol in a given application. Given the stringent cost requirements of the appliance market, the IC must deliver those capabilities in a low-cost, compact, and reliable package compliant with industry-standard, high-volume manufacturing techniques.
While most appliances can be controlled via a hardwire connection, some functions such as gas or water meters or door sensors may not have access to a powerline. In other situations, utilities may need to transport commands from one wireless device to another via wired powerline networks. To cover all potential scenarios and offer complete command and control, utilities in the future will likely expand their home area networks by integrating wireless communications capabilities.
The leading wireless networking technology for sensing and control applications today is called ZigBee. Many utilities and manufacturers are rapidly adopting ZigBee Smart Energy, a new standard for energy management and efficiency built around the ZigBee language. This program is designed to enable wireless communication between utilities and common household devices such as thermostats and appliances. The program improves energy efficiency by allowing consumers to choose interoperable products from different manufacturers, enabling them to manage their energy consumption more precisely using automation and near real-time information. The program also helps utilities implement new advanced metering and demand response programs to improve energy efficiency and meet emerging government requirements.
Recently, the industry took a major step forward when the Homeplug Powerline Alliance, the ZigBee Alliance, and leading utilities announced plans to develop a common application layer for advanced metering applications that will allow devices compliant with the ZigBee Smart Energy initiative and devices compliant with the Homeplug standard to run on the same Home Area Network (HAN). This agreement will give utilities tremendous flexibility to create unified wireless and wired solutions for Advanced Metering Infrastructure (AMI) and other smart metering programs by accelerating the development and certification of plug-and-play interoperable devices such as thermostats, water heaters, pool pumps, and other high-energy devices for use in a HAN. Ultimately, it will encourage the widespread adoption of energy management programs that automatically shift energy loads to help customers conserve energy, reduce energy costs and preserve the environment.
Given today’s focus on the environmental impact and rising cost of energy consumption, demand is already building for more precise and efficient energy-management tools. By combining a reliable, cost-effective technology that can be simply installed without using new wiring, PLC-based command and control networks offer a highly attractive solution for both utilities and energy consumers.
For more information, visit:
Ariane Controls: http://www.arianecontrols.com
NEC Electronics: http://www.am.necel.com
Sidebar: Design Flexibility
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Cost-effective and highly configurable modules are crtical to wide-scale adoption of PLC-based command and control systems. To achieve that goal, designers need highly reliable and affordable components.
One of the first modem ICs for these applications is the PLM-1, designed by Ariane Controls and available in volume from NEC Electronics America. Utilizing licensed intellectual property from Ariane’s PLC technology. The PLM-1 integrated circuit was designed on NEC Electronics’ CMOS-9HD quick-turn, gate-array platform and fabricated on a small, 44-pin, low-profile, quad-flatpack package, allowing for easy integration into the powerline transceivers applications. The PLC modem IP is easily migratable throughout NEC Electronics’ process technologies to provide ASIC customers with a critical PLC building block, as well as added functionality to NEC Electronics’ standard solutions lineup for emerging applications in the smart grid, intelligent lighting control and HAN markets.
The PLM-1 modem implements a half-duplex transmitter/receiver for PLCs using a frequency shift-key modulation technique. The modem also supports programmable transmission rates ranging from 100 baud to 20,000 baud and communication frequencies ranging from 50 kHz to 500 kHz. The protocol-neutral device also features a set of high-level functions designed to simplify the implementation of high-performance PLC networks. To ensure reliable communication, the chip also provides on-chip cyclical redundancy check (CRC), error detection and forward-error detection functions. Operating at 3.3 V, the chip minimizes power consumption by dissipating as little as 24 mW of power.
Designers developing complete PLC solutions can complement the PLM-1 with different devices in NEC Electronics’ line of microcontrollers (MCUs) for different applications. For example, a designer could combine the PLM-1 with a low-cost 8-bit 78K0 MCU for simple appliance control functions. For more sophisticated applications, such as network bridging or combination PLC + Zigbee communications, an efficient solution offering more integrated memory support for NEC Electronics’ Zigbee software protocol stack would fall under the 16-bit 78K0R MCU family. Finally, in complex applications, such as a smart meter to manage signals between multiple appliances and the utility, the designer could select one of NEC Electronics’ higher-performance 32-bit V850 MCUs.
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