Robust design principles for home smart grid metering

A worldwide trend toward more efficient energy utilization is extending so-called Smart Grid technology into the home. This is creating a demand for new energy meters that can serve as a two-way communication hub between the home and the utility, and have the ability to measure, verify, dispatch, and enable demand response for power usage within the home.

To meet this demand, developers must address key design goals such as small size, low cost, and integration of metrology, control, and communications. As the cost of energy keeps rising, the need to manage energy more efficiently is becoming more evident. Utilities, for instance, must find a way to address growing demand by building new generation capacity or better utilizing the capacity they already have.

Energy generation capacity is typically sized to meet peak demand, which results in much of that capacity remaining unneeded much of the time. In Pennsylvania, New Jersey, and Maryland utility (PJM) area studies, it has been shown that generation needs to run at only 85% of full capacity 98% of the time.

If the utilities had a way to moderate that peak demand, they could reduce their need for capital investment. According to the California Energy Commission, implementing a demand response system to reduce peak energy demands is one-sixth the cost of adding new capacity

Governments are also interested in curtailing demand by managing energy consumption more efficiently. Reduced energy demand improves both national security and trade balances by lowering dependence on an uninterrupted supply of imported fossil fuels.

Implementing a smart grid to manage energy can also improve national security by providing more effective ways to prevent or mitigate attacks on a nation’s energy infrastructure. Increasingly, governments are also interested in reducing energy demand to lower carbon emissions that may be contributing to climate change.

Consumers, too, will benefit from the development of a smart utility grid for energy management. At the very least, they would see more accurate billing. More importantly, however, a smart grid will give consumers the tools to lower their energy costs.

One such tool is time-of-use pricing, which charges consumers less for the energy they use outside of peak demand periods. The cost differential encourages consumers to change their energy use patterns to make capacity utilization more uniform, as trials by Puget Sound Energy have demonstrated. The implementation of time-related pricing yielded a 6% reduction in peak demand and a 5% reduction in energy use overall.

Smart Grid Needs Smarter Meters

But to make time-of-use pricing possible, as well as provide other energy management tools to create the smart grid, there need to be smart energy meters. The traditional energy meter has remained essentially unchanged for more than a century.

It only measures accumulated power usage, providing a single point of information without any inherent time history. To learn what energy has been used over a time period requires reading of the meter at the beginning and the end of the period.

Further, these readings have to be made by a human being. This creates several problems. One is the labor costs involved in making repeated readings in order to determine billing. Another is that such manual readings are prone to errors, which can affect cash flow or create customer dissatisfaction depending on the error type.

In addition, residential energy meters can often become inaccessible for reading without customer involvement due to the construction of fences or other barriers, aggravating both cost and error concerns.

Utilities began addressing these problems by introducing automated meter reading (AMR) in the 1990s. AMR utilized energy meters that had an ability to communicate unidirectionally with a handheld reader unit, vehicle-mounted unit, or to a central office using powerline or wireless communications.

This one-way link allowed reading of the meter electronically, eliminating the need for visual inspection. Although not eliminating human involvement completely, AMR yielded significant reductions in billing cost and improvements in accuracy.

In some cases, AMR also supports time-of-use metering, with the meter recording energy usage over preset time intervals. This additional information allows the utility to engage in time-of-use pricing, but only in a static fashion. Time intervals are pre-set with limited or no flexibility and the consumer has no access to the information to help guide their energy use in real time.

Utilities are now engaged in deploying the Advanced Metering Infrastructure (AMI) to allow full automation of the billing process and add flexibility to time-of-use billing. AMI meters maintain continual two-way communications with the utility, eliminating even the need for drive-by readings. Instead, the utility’s billing system can automatically read any AMI meter remotely, either on a schedule or on demand.

This automated remote reading capability not only streamlines billing, it provides an opportunity for the utility to perform real-time system analysis and gather feedback on power utilization.

Such analysis can help utilities apply their resources more efficiently. A block-by-block analysis, for instance, can help a utility choose transformers of the optimum size for a given area, preventing the expense of too large and the reliability issues of too small a transformer.

The AMI meters also support dynamic time-of-use metering. The meters record power usage based on time intervals and they can change the definition of those intervals. The communications link is bidirectional, so the utility simply downloads new timetables to the meter as needed.

While the AMI meters are a major step forward for utilities, a new generation of advanced smart meter designs will be needed for the smart grid to achieve its full potential. These advanced smart meters (ASM) will provide two additional capabilities that AMI meters lack.

One is to give consumers real-time billing information that can help guide them to moderate peak demand as well as reduce their overall energy usage. The other is to give utilities access into home networking systems for more direct control of consumer energy usage.

The key to both of these capabilities is giving the meter access to home area networking (HAN). Such networks have already begun to appear in new residential and commercial construction in appliances, heating and air conditioning (HAC) systems, and lighting.

The network provides intelligent monitoring and control for these elements, allowing a PC or other central controller to turn nodes on and off, adjust settings, and gather status information. The network links may use building wiring, such as powerline signaling, or may be wireless as with the ZigBee protocol.

The advanced smart meter links the utility to the HAN through the smart grid. The meter serves as a communications hub, providing bidirectional communications between the utility and the building. This allows the utility to monitor individual systems within the building, such as reading thermostat settings, and offers an avenue for control, as well.

The value of this link between the utility and the HAN is a significant increase in the flexibility of demand response systems. The meter can, for instance, provide the HAN with real-time energy usage and cost information for display to the residents. Armed with such information, consumers can make real-time choices on what systems to use or turn off, adjust HAC settings to optimize cost and comfort, and track down “vampire” appliances such as printers, computers, and entertainment systems that are in standby mode rather than being completely shut down.

The link can also allow the utility to take control of some home systems as the need arises. During a heat wave when air conditioning usage skyrockets, for instance, the utility could change thermostat settings through the HANs to keep power demand from triggering a brownout or blackout condition. Under more typical conditions the utility could similarly take action to help reduce residential energy consumption during periods of peak demand.

Advanced Smart Meter Requirements

The design of such an advanced smart meter must meet many functional requirements. The prime function, of course, is to provide energy metrology. This metrology requires that the meter know the time (for billing) as well as current power utilization. Further, the implementation must be flexible to accommodate differences between the ways utility service providers measure and track such utilization. The energy meter may also offer the ability to integrate with other utilities such as gas and water to eliminate multiple meters (Figure 1 below ).


Figure 1 .  The advanced smart meter will do more than measure energy; it will link the utility to the consumer for detailed monitoring and control of energy consumption and coordination with energy generation.

In addition to measuring current power utilization, the meter must be able to record cumulative power utilization. For time-of-use billing, this requires that the meter offer multiple “bins” for tracking power consumed at the different rates. These bins must be configurable in order to provide the utility with a mechanism for making changes to times and rates.

A second design requirement for the advanced smart meter is an ability to communicate with both the smart grid and the home network. There is little consensus, however, on what those communications channels are to be.

Depending on the provider, communications with the utility network may use mesh RF, powerline signaling, WiMAX, or even the cellular network. Similarly, regional and individual preferences may call for the HAN to use ZigBee, powerline, WiFi, or some other protocol. Ideally, then, the meter design would be flexible enough to accommodate easy configuration of its communications channels to meet specific installation requirements.

The meter must provide hub functionality in order to be effective, including address translation for the utility to be able to control appliances on the home network. But the meter is not simply a translation device between the two networks. It must be able to provide security in order to prevent malicious intrusion as well as drive the user interface within the residence.

Security functions are essential safeguards for both the consumer and the smart grid with three key components: authentication, validation, and authorization. Authentication is needed in order to ensure that messages to the utility or the meter have the proper origin.

This prevents a system errors and third parties from introducing false messages that can interfere with billing or hijack control through the network. Validation ensures that a received message has the right form and content, helping prevent errors from causing unexpected or undesirable results.

This may include making certain that a command does not violate safety restrictions, such as turning a water heater up beyond a pre-set limit. Authorization ensures that the message sender has the right to issue commands in the first place.

The user interface is key toward making the consumer an active element in demand response systems. Without some way of seeing in real-time the effects of their energy usage decisions, and some way of implementing their decisions, consumers cannot respond effectively. Thus the meter needs to provide a means of controlling energy usage at the unit level as well as monitoring energy consumption of the house as a whole.

One effective way to provide these monitoring and control capabilities is for the meter to include a link to a control and display panel mounted inside the structure for convenient user access. The panel would show energy usage and cost in real-time to prompt action from the consumer as well as indicate the outcome of that action.

Ideally, the panel would also be the user interface for taking action through the HAN such as disabling energy consumers or adjusting settings, to make the process more convenient for the consumer and thus more likely to occur. For the same reason, the interface must be easy to understand and use.

In addition to meeting all these functional requirements, an advanced smart meter design must address several practical concerns. For example, the meter needs a compact form factor in order to maximize the opportunities for placement during field installation. The design should also provide for easy integration with a variety of home and utility networks to maximize the applicability of a meter design to multiple markets.

To be economically feasible, the design needs to utilize components that help keep development and production costs as low as possible by being optimized for metering needs. Yet the design must also be flexible to accommodate evolution in networking and smart grid standards and changing regulatory requirements with little or no modification to the base design or rework of installed units.

These design requirements, in turn, impose requirements on the semiconductor solutions that meter developers will seek out. One of the first requirements on a suitable semiconductor solution is a high level of integration.

This addresses several meter design requirements, including compact form factor resulting from small board size and low design and production cost. The low production cost comes from the minimal BOM needed to implement the design. Having most system elements on the same IC already interconnected and proven to work together helps keep design costs down.

Integration taken too far, however, will compromise another key element of a semiconductor solution: flexibility. The market for advanced smart meters is still highly fragmented in its requirements for utility and HAN interfaces.

Integrating those interfaces completely would narrow a semiconductor solution, and corresponding meter design, to a narrow market. Instead, the solution should include a variety of standard interfaces for attachment of various network-specific components.

In addition to offering a variety of network interface options the semiconductor solution needs to support customization of various functions.

The way in which utilities measure power usage, for instance, is still part of their “secret sauce” in providing services, so the meter design must support customization of metrology. Similarly, the user interface needs to be customizable in order to support a variety of display choices as well as to allow the utility to “brand” the consumer’s experience.

A flexible semiconductor solution can also help “future proof” the basic meter hardware design, as well. A device that is programmable and offers multiple interface choices will make design evolution easier, reducing the effort needed to adapt as industry-wide standards for advanced smart meters emerge. That flexibility also supports the adaptation of meter design to address regional preferences.

An often overlooked requirement on the semiconductor solution is the support a low-power implementation. Meters are typically installed in small, unventilated housings, so the lower the power dissipation the less likely those thermal issues will arise in the field. Further, low power can represent a significant cost savings over the meter’s operating life. Multiplied by millions of installations even a fractional watt less power consumption per meter saves megawatts of power.

Software Support Required

A highly-integrated, flexible, low-power semiconductor is still not a solution to advanced smart meter design needs, however, without adequate software support. That support should include both design tools and reference libraries of readily-adaptable software for most metering tasks.

In addition, the software support should leverage existing standards for communications, networking, security, and the like. This support will greatly simplify the meter design effort, allowing developers to concentrate their energies on their unique requirements and features. Further, by leveraging standards the software will simplify integration of the meter with the smart grid and the HAN.

Such semiconductor solutions for advanced smart meter design have already begun to emerge. One example is the AppliedMicro APM801xx family and the product evolution roadmap behind it. The APM801xx integrates numerous I/O and system interfaces (Figure 2 below ).

These include mass storage interfaces for Flash and SATA storage systems; serial communications interfaces such as USB and 1G Ethernet with hardware TCP/IP support; system interfaces such as PCI express, SPI, TDM, and I2 C; an LCD controller, and a 10-bit ADC. JTAG and Trace connections are available for debugging and maintenance access and both security and encryption acceleration engines are available options.


Figure 2. The AppliedMicro APM801xx family addresses the many needs of advanced smart meter design by offering high functional integration with multiple connectivity options for easy customization to specific installation requirements. (Click here to see an expanded image)

This combination meets all the functional needs of smart meter applications while offering considerable flexibility in connectivity and operational behavior. The entire package consumes <1W operating at 600 MHz while providing all the processing power and I/O needed to implement a smart meter design with minimal additional hardware.

An example of such a design (Figure 3 below ) shows how minimal that addition can be. Along with system DRAM, program EPROM, and a Flash module for non-volatile storage, all the meter design needs is Ethernet and ZigBee PHYs to provide utility and HAN connectivity. This gives the design a footprint of only 3 x 3 inches, including the ZigBee module, thus addressing both BOM cost and size considerations.


Figure 3 . A smart meter reference design shows that only a few external components are needed for full operational configuration when using the APM801xx.

The creation of such advanced smart meters is of growing importance. The smart grid is already on its way, with expansion stimulated both by the economics of energy and the dictates of governments.

To achieve its full potential, that grid needs advanced smart meters that can link the energy consumer with the energy provider for the close coordination needed to maximize efficiency and minimize costs.

Design of such meters must meet many demanding system requirements, including low cost, small footprint, low power, and high functionality, while addressing a market that is still emerging with few standards and much diversity.

Now, however, semiconductor solutions that address these concerns have started to emerge. Devices like the AppliedMicro APM801xx family will help make the promise of the smart grid into a reality.

Vamshi Kandalla is senior director for the Consumer and SMB Business Unit for AppliedMicro, where he is responsible for building the multi-media consumer electronics business in embedded processors for home networking in digital entertainment, wired and wireless networking. Prior to joining AppliedMicro, Kandalla held executive level marketing positions at Moschip Semiconductor and SMSC as well as several other companies. He holds both a master’s in marketing and a bachelor’s in engineering.

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