An overview of
ZigBee’s Smart Energy Profile 2.0 standard
Srinath Balaraman and Anil Khanna, Mentor Graphics
5/14/2013 7:30 AM EDT
The number of devices defined as part of the “Internet of Things” continues to grow quickly as individuals and industries alike find innovative ways to utilize connected devices and networks.
Enabling machine-to-machine (M2M) communication has endless possibilities, and is one of the more prominent technology areas in the emergence of smart energy.
As home meters, personal devices and appliances begin to connect to each other, a bigger and far more comprehensive picture emerges on how to make smarter energy consumption decisions. Connecting devices in the home and local Internet networks to a smart grid enables two-way communication between homeowner and the power company and is becoming more of a reality with each passing day.
This article provides an overview of the Smart Energy Profile 2.0 (SEP), an emerging standard in the smart energy market, being developed by the ZigBee Alliance.
With the basic understanding of SEP 2.0, software developers will be better prepared to select embedded software suited for the development of smart energy applications.
A new frontier with the Internet of Things
The Internet of Things is a popular buzz phrase and one that conjures up exciting visions of the future – a future where your refrigerator self-checks its contents and emails you a grocery shopping list just as you are about to leave work (not that grocery shopping is a terribly exciting experience), your house gets ready for your arrival by adjusting the temperature to an optimum level, and the oven can pre-heat for dinner.
The rapid proliferation of devices embedded with a combination of powerful microprocessors, sensors, and wireless connectivity has resulted in more functionality and intelligence which leads us towards the vision of a smart networked world.
Figure 1: Energy providers, the development of a nationwide smart grid and energy-conscious consumers will usher in a new era of smart energy use
One of the applications of this set of technologies is to improve energy consumption, also termed smart energy.
The concept behind smart energy is controlling energy use internally, within the home, and externally from the home to outside connected devices, networks, and the smart grid itself—all with the goal of optimizing energy production, distribution, and usage.
Bi-directional communication between home networks and the power grid opens up possibilities for improved reliability and sustainability.
Figure 2: In a typical smart home, devices such as a washing machine, an in-home display, and a power meter all work together in tandem –to make the home and grid smarter
Being smart about smart energy
Smart grids and smart homes (smart appliances, gateways etc.) and smart meters (electricity, gas, water) are key elements of the smart energy ecosystem.
Smart home appliances are typically those devices consumers interact with daily.
By enabling these devices to talk to each other and be controllable by the consumer, a whole new dimension of convenience is added (Figure 2).
There are several products (smart thermostats, smart switches, smart refrigerator, and more), which are available today that offer some level of intelligence and wireless connectivity. Some of the more advanced appliances include built-in Web servers to interact with other devices in the connected home.
Smart meters are the gateways into these homes (and offices) and collect and measure resource usage before sharing some or all of this information with the smart grid.
The grid, in turn, acts upon this information by taking necessary steps such as load adjustment, peak curtailment, and even demand-side management.
Smart energy devices, apart from performing their standard functions, must be able to communicate with other smart energy devices within the local network and be able to send and receive relevant information (pricing, usage, alerts, etc.).
The exchange of data not only improves the overall efficiency and fault tolerance but optimizes the consumption of energy. Smart meters collect and transmit usage data to the energy providers and allow consumers the ability to monitor and manage their own energy consumption. In other words, usage data flows from the consumer to the energy provider and, at the same time, pricing data flows from the energy provider to the consumer.
This bi-directional flow of information allows consumers to make decisions to manage consumption. This two-way, real-time communication enables energy providers to improve planning and improve energy distribution.
Standardizing smart energy design
As multiple manufacturers design smart energy systems, it is becoming increasingly clear that all devices interoperate in a network.
The ZigBee Alliance is working on a specification called the Smart Energy Profile 2.0 (SEP 2.0) to help formalize the requirements for many aspects of the smart energy ecosystem including device communication, connectivity and information sharing requirements.
SEP 2.0 provides the guidelines in which the devices should communicate with one another. It defines various device properties that can be manipulated.
These properties (also known as “resources”) work together in logical groups to implement SEP 2.0 functionalities (called the “function sets”).
A metering system, or pricing system, is an example of an application-specific function set.
Devices like smart meters implement one or more function sets to provide value-added services such as usage statistics and trends.
These pricing statistics and trends can then be used by either the energy provider or the consumer to further manage services or usage, respectively.
Function sets and their resources on a device are accessed through HTTP URLs.
These devices dynamically discover relevant services on the network using technologies like mDNS and DNS-SD and register themselves to further access resources to implement SEP 2.0 functionality.
To provide for a truly interoperable ecosystem of interconnected smart energy devices, use of TCP/UDP and IP-based networking is necessary.
Support for security features within a device is critical because of vulnerabilities from exposure to a broader network, and more importantly, the access a device provides to the energy grid.
Since many smart devices serve up continuous, reliable, and real-time data, they must be "Always-ON" and "Connected" which necessitates that all smart energy devices be power efficient themselves. Lastly, they must also support both wired and wireless networking capabilities.
The hardware for connected devices
A majority of existing home appliance devices are not built to support the advanced features of the emerging M2M wave, so incorporating many different capabilities into a single device means significant and expensive hardware upgrades, resulting in an increased bill of materials and cost.
Manufacturers must balance the benefits of delivering smart energy-enabled appliances with the additional cost.
Moving forward, appliance manufacturers have more options to find cost effective solutions to design home appliances that are smart energy enabled. The choice of SoC hardware for these home appliance devices should be made by striking the right balance between functionality, form factor, software support, and cost. 32-bit microcontrollers (MCUs) provide a unique blend of processing power, memory, and connectivity to make them a strong candidate. The current generation of microcontrollers, such as Freescale Kinetis, STMicroelectronics STM32, or the TI Stellaris (ARM Cortex-M core), offer tremendous amounts of features and capabilities at a very compelling price point. Selecting the right hardware is only the beginning. The differentiator in this equation is the software choice.
Figure 3: An example of a hardware design that can support a wide range of peripherals, powered by a real-time operating system such as Nucleus RTOS, which offers all the services required by SEP 2.0
Click on image to enlarge
Selecting the right software
The software technology requirements laid out by the SEP 2.0 specifications include:
a rich TCP/IP stack with UDP support; IPv6 services with dynamic service discovery capabilities like mDNS and DNS-SD;
and a HTTP implementation with support for primitives like GET, PUT, POST, and DELETE. SEP 2.0 also mandates support for security implementations like SSL/TLS
and several modern day Internet technologies like the RESTful architecture, XML, and EXI encoding schemes etc.
Such extensive support for software technologies is readily available in Linux, but unfortunately, the use of microcontrollers with RAM sizes in the range of 96K to 128K eliminates Linux as an option. Developing such technologies in-house is expensive and time consuming, which leads to the possible implementation of a real-time operating system (RTOS) for these devices.
RTOSes are not only fast, efficient and robust, they typically include an extensive networking stack, a solid support for security using SSL or TLS, and most certainly meet the heavily constrained footprint and other memory requirements these devices require.
The Nucleus RTOS provided by Mentor Graphics is an example of one such solution (Figure 3). Nucleus is a widely deployed and scalable RTOS that meets all smart grid device requirements. It has both hard, real-time performance and integrated power management services.
Such an RTOS can fit in a memory-constrained MCU, yet still provide the large set of functionality required by a connected, smart grid device.
With the projected rapid growth in the adoption of smart grid technologies, designing fully compliant devices that keep the bill of materials minimized will become a major challenge for manufacturers.
To create a device compliant with the SEP 2.0 specification, a homegrown software design is likely not an option due to the high number of functional requirements and the expensive in-house development efforts.
On the other extreme, using a general purpose operating system will result in unacceptable cost increases because of the need for significantly upgraded hardware resources.
Device manufacturers need to find the right balance when choosing both the software design and hardware platform.
The use of a scalable, power-efficient, real-time operating system with extensive networking support (wired and wireless) — along with one of the 32-bit MCUs now available in the market—is the closest to meeting all of these requirements. Following this design paradigm, designers will significantly reduce their time-to-market and still realize all of their smart grid application goals.
About the authors
Srinath Balaraman is a software development engineer in the Embedded Software Division of Mentor Graphics, also known as Mentor Embedded. In his eight years at Mentor, his main area of focus has been the design and development of networking and security products for Nucleus RTOS. Srinath holds an MS degree in Computer and Information Sciences from the University of South Alabama.
Anil Khanna has over 15 years of technical and product marketing experience with a background in both design automation tools (EDA) as well as programmable logic hardware design. Anil is currently senior product marketing manager of Mentor Embedded Sourcery Tools. Prior to moving into Mentor Embedded, Anil was responsible for worldwide market development for Mentor’s ASIC/FPGA synthesis solutions including Catapult and Precision Synthesis. Anil holds a Masters in Electrical and Computer engineering from Portland State University in Portland, Oregon.
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