Smart Grid Technology - Smart Meter
By today's technological standards, the common electromechanical energy meter is a relic of the past –
incapable of anything but flat-rate pricing and infrequent meter readings.
Smart meters go well beyond the rudimentary functions of a basic electrical meter. Above all, the
distinguishing quality of a smart meter is to support 2-way communication with utility providers. This is
the key that opens the door to all other "smart" functions and the benefits thereof. Smart meters can
provide support for remote diagnostics, dynamic pricing, tamper notification, consumption analysis, and
more.
What does this mean for utility customers? For one, it creates something that has not existed since the
grid's creation: an informed consumer base. People can analyze their own energy usage in as much detail
as desired and then adjust the amount, manner, and time in which high load devices are used. Even today,
most consumers are unaware that for utility providers, the cost of a kWh is greater during times of peak
demand – after all, electricity is traditionally billed at a flat rate. By offering dynamic pricing
based on real-time energy demand, electric companies create opportunities for customers to significantly
lower their energy bill with simple changes, such as using the clothes dryer at off-peak hours. Also,
these kinds of changes have the effect of reducing or "shaving" the demand peaks over the course of a
day, which can further reduce energy costs.
In a two-chip solution, the essential metrology functions of the device are implemented as a separate
functional unit, i.e. an energy meter IC. There are many possible reasons for choosing this
architecture; for instance, the metrology firmware may require isolation and specific qualifications.
Active power is sensed with a current transformer, commonly a Rogowski coil, which then provides the
energy meter IC with analog power measurements. Typically, delta-sigma ADCs (analog-to-digital
converters) within the energy meter chip perform the A/D conversion. The chip also tracks energy
consumption, transmitting the data to the application processor, and possibly provides additional
functions such as pre-amplification and tamper detection.
The application processor provides the substantial amount of non-volatile memory, processing power, and
connectivity options needed to implement most of the smart meter's "smart" functions, such as
consumption analysis, dynamic pricing, and other demand response features. All smart meters are capable
of 2-way communication with a utility company, whether it is via power line communication (PLC), Zigbee
wireless mesh networks, RS-485, or some combination of communications technologies. Choice of
communications channel(s) and meter reading method are often dictated by cost, which depends largely on
pre-existing infrastructure and the local regulations of a given region.
Major subsystems include:
- Application Processor
- Sensing and metrology: current and voltage sensors, energy meter IC
- Power management: offline AC/DC converter, voltage regulator, battery management system
- AMR-enabled communications: PLC modem, Zigbee, RS-485, etc.
VREG
RTC
Supervisory
Battery
ISM RF
LCD Display
AFE
a
Smart Meter Block Diagram
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This design is for reference only. The design, as well as the products suggested, has not been tested
for compatibility or interoperability.
AC/DC Converters for Smart Grid
An AC/DC adapter is a
type of external power supply, often enclosed in what looks like an over-sized AC wall-plug.
Other names include power adapter, power converter, plug-in adapter, adapter block, domestic
mains adapter, line power adapter, or simply AC adapter. AC adapters are used with electrical
devices that require DC power but do not have the internal circuitry to accomplish the
conversion of AC to DC.
Voltage Regulators for Smart Grid
A voltage regulator produces a
constant level of voltage over time regardless of load, changes in power supply, or temperature.
Voltage regulators are used in power supplies, analog-to-digital converters, digital-to-analog
converters, and many other applications where voltage levels must be maintained at a steady
level. Without a voltage regulator, precision is greatly affected and may render the device
inoperable. Voltage regulators can vary greatly in performance. A voltage regulator for a power
supply might hold its output to within only a few percentage points off of its nominal or stated
value; however, a voltage regulator to instrumentation-level standards are measured in parts per
million regarding stability and precision to the nominal or specified value.
Energy Meter ICs for Smart Grid
An energy meter IC is a
specialized type of microcontroller used for measuring the amount of electric energy consumed by
a household or business. These chips are distinct from generalized microcontrollers in a number
of ways; for example, energy meter ICs will often have extensive analog measurement circuitry,
including precision amplifiers and delta-sigma ADCs (analog-to-digital converters), as well as
sensor configuration options and digital signal processing capabilities tailored to suit energy
metering applications.
Real Time Clocks for Smart Grid
Real Time Clocks (RTCs) are IC
devices that keep track of time. A typical RTC can provide the time of day as well as the date
via a serial bus such as I2C or SPI. Although similar in many ways, RTCs should not be confused
with clock generators, which are used to synchronize various parts of a circuit.
PLC Modems for Smart Grid
A power line communications
(PLC) modem is a device which facilitates data transmission over the power grid. Some
electronics manufacturers offer complete PLC modules that include modem, analog front-end (AFE),
line drivers, and other components necessary for a “plug-in” solution. However, many PLC modems
are simply a communications IC, and require the addition of a line driver and AFE to operate as
a PLC transceiver.
Supervisory Circuits for Smart Grid
Supervisory circuits are
used to monitor the power status of electrical systems and protect the processor or MCU from
faulty operation due to system power up sequence, brown-outs, and other power related faults.
Many supervisory devices include extra functions such as watchdog timers, battery monitors,
over-temperature protection, and more.
Batteries for Smart Grid
Batteries are a portable,
wireless means of storing energy via the use of self-contained chemical cells. They can be for
one-time use and discarded, or recharged and reused. In essence, a battery is an energy storage
device, but can only store and release electricity as direct current. Direct current is a flat
line at a given amplitude (until it declines as it is exhausted), versus alternating current,
which is a sinusoidal wave.
Battery Chargers for Smart Grid
Battery charging
circuits are used to recharge batteries and are available in linear or switching topologies.
They can be completely autonomous in operation or used with a microcontroller. Generally
speaking, integrated chip charging technology can produce charge currents in a range from around
625 nA, up to around 4.5A. Battery charger ICs often do more than just charge; they can protect
from overcharging, regulate voltage, and manage charging from irregular sources such as energy
harvesters or very low voltage sources. In portable technology, battery chargers are
indispensable.
Application Processors for Smart Grid
The term
"processor" refers to an electronic device that performs computational functions and carries out
the instructions of a stored program. Other terms for processor are microprocessor, central
processing unit, and digital signal processor. Essentially, the processor refers to "the brains
of a computer."
ZigBee Modules for Smart Grid
Zigbee is built upon the
IEEE 802.15.4 standard. Zigbee adds both routing and multi-hop functionality. Star networks as
well as peer-to-peer and mesh networks are supported, making Zigbee networks dynamic, scalable,
and decentralized. These qualities and more make Zigbee an excellent technology for applications
like home/industrial automation, medical monitoring, and HVAC control. WiMax is built to a
standard designed to provide 30 to 40 megabit-per-second data rates. With the latest updates
WiMax can deliver up to 1 Gbit/s for fixed stations. WiMax goes beyond the 100 feet wireless
range of a conventional Wi-Fi local area network that can acommidate a cities wide area networks
needs with a signal radius of about 30 miles.
ISM RF for Smart Grid
The ISM (industrial, scientific
and medical) bands are a part of the radio spectrum originally reserved for devices that fall
under those categories. Today these bands are used for short-range low-bandwidth wireless
communications. Its unlicensed nature has made the ISM bands a popular choice for many wireless
technologies such as Bluetooth, Zigbee, and Wi-Fi (IEEE 802.11), and cordless phones.
Smart Card Interface ICs for Smart Grid
A smart card is a
pocket-sized device with embedded integrated circuits containing a microprocessor and
non-volatile memory. Smart cards are used in a variety of applications such as banking,
identification, and security. Designed to be portable, smart cards forgo any form of power
supply, instead relying on the card reader for power. Energy metering applications may use smart
cards as a type of household utility pre-payment card. A smart card interface IC allows a
processor or MCU to communicate with a smart card.
RS-485 Transceivers for Smart Grid
In contrast to complete
interface standards which define physical, functional, and electrical specifications, RS-485 is
an electrical-only standard. RS-485 signaling can be used with many protocols such as Profibus,
Interbus, Modbus, or BACnet, depending on the requirements of the end user. Sometimes controller
area network (CAN) or EtherNet are preferred for network requirements. RS-485 has a 10 Mbps
maximum data rate (@ 40 feet) and a 4000 foot maximum cable length (@100 kbps.) RS-485 is robust
and well suited for long distance networking in noisy environment.
USB Transceivers for Smart Grid
USB is a standard
connection interface between computers and digital devices. A USB transceiver is a physical
layer device that prepares data for transmission and then sends to, and receives data from,
another transceiver. The transceiver detects connection and provides the low level USB protocol
and signaling. The term "transceiver" indicates an implementation of both transmit and receive
functions. It transmits and receives, encodes and decodes data, provides error indication,
implements buffers to stage data until it can be managed, and adjusts for the clock rate from
the serial stream on the USB SuperSpeed bus to match that of the “link layer” higher up on the
communication stack.
Ethernet Transceivers for Smart Grid
Ethernet is the
most commonly used technology for non-wireless local area networks (LANs). Ethernet controllers
perform the function of interfacing computers and other electronic devices in a network.
Ethernet itself only defines the physical (PHY) and datalink (MAC) layers of the OSI Model;
however, processors with integrated Ethernet controllers can provide additional functions such
as a TCP/IP protocol stack.
LCD Displays for Smart Grid
LCD means "liquid crystal
display." It is an electronically driven flat panel screen that orients liquid crystals within
the panel in a direction that blocks or transmits light coming from behind the panel. LCDs are a
low cost, energy efficient visual display that can be controlled in segments or as individual
pixels, in shades of black and gray or in full color. LCDs have most commonly replaced bulky
cathode ray tubes in televisions and computers and are available in all sizes. Liquid crystals
were first discovered in 1888, but were first put into common use in the early 1970s as
electronic digital-display watches.
Smart Card Connectors for Smart Grid
A smart card is a
pocket-sized device with embedded integrated circuits containing a microprocessor and
non-volatile memory. Smart cards are used in a variety of applications such as banking,
identification, and security. Designed to be portable, smart cards forgo any form of power
supply, instead relying on the card reader for power. Energy metering applications may use smart
cards as a type of household utility pre-payment card. A smart card connector safely houses a
smart card and physically inferfaces the smart card’s 8 contact pads with a smart card interface
IC.
D-Sub Connector for Smart Grid
A D-sub or "D-Subminiature
Connector"contains two or more parallel rows of pins or sockets, usually surrounded by a
D-shaped metal shield that provides mechanical support, ensures correct orientation, and may
screen against electromagnetic interference. The part containing pin contacts is called the male
connector or plug, while that containing socket contacts is called the female connector or
socket.
USB Receptacles for Smart Grid
USB plugs and
receptacles are designed to reduce human error by their unique shape; they fit together in only
one way. USB plugs and receptacles are Type A (connecting to hosts or hubs) or Type B
(connecting to devices) and are available 3 sizes: standard, mini, and micro. Type A plugs
always face upstream, Type B faces downstream. USB is used in many applications covering all
areas of electronics that require communication, but more commonly with devices that need fast
or easy connections for interaction with computers. Since USB provides a small charging current
as well, it is becoming a de facto standard for charging portable devices.
RJ-45 Connectors for Smart Grid
RJ-45 connectors are a
type of electrical connector commonly used for Ethernet jacks. The term "RJ-45" is something of
a misnomer, but it almost always refers to an 8P8C (eight position, eight contact) modular
connector with wiring pin-outs compatible with standard Ethernet.
Analog Front Ends for Smart Grid
Line drivers and analog front-ends
(AFEs) are needed to enable power line communications (PLC) modems to both transmit and receive
data over a power line. They are commonly available as separate devices, but many electronics
manufacturers offer PLC-specialized IC’s which integrate the two. Line drivers increase the
strength or power of the output signal to the power line to allow for transmission over
sufficient distances. Using integrated high-precision analog-to-digital converters (ADCs) and
programmable gain amplifiers (PGAs), the AFE receives and processes incoming data for use by a
PLC modem.
Application Notes and Resources
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