Designing A Cost-Effective and Versatile Home Area Network Device
The sky-rocketing cost of energy
production has necessitated a more efficientenergy consumption
process. This has brought revolution in electrical equipment
manufacturing and energy metering infrastructure. Home area network
(HAN) is an advanced electrical ecosystem in which a smart utility
meter and HAN devices communicate with each other to control the
energy consumption profile. Armed with the latest technological
advancements in the fieldof energy utilisation, HANs are ready to
supplant the traditional electrical ecosystems at home.
Fig. 1: Application diagram of HAN device |
This low-cost device can be hooked in
the existing electrical infrastructure without the need to replace,
renovate, alter or rework the infrastructure. The power consumption
is very low (in microamperes) when it’s not in use. The following
sections describe certain enhancements to the basic HAN device
architecture which extend its capability and feature-set.
Architecture
The HAN device can be considered as an intelligent power socket, which at one end connects to the normal power socket and on the other end offers pluggable connection interface for home appliances, e.g., microwave and air-conditioner. It can be controlled directly by the utility meter over wireless interfaces like radio frequency (RF) or wired interfaces like power line communication (home plug, etc). Additionally, its firmwarecan be upgraded over the RF/programmable logic controller (PLC) interface by the utility meter. Various energy parameters of the device can be displayed on the LCD. It also supports battery backup option for maintaining the time and date.
Fig. 1 shows the application diagram of
the HAN device. The device consists of a microcontroller, 230V-3.3V
converter, relay, signal conditioning circuitry, infrared (IR)
interface (supporting both transmitter and receiver), LCD panel and
RF/power-line communication physical layer.
Its main operational features are:
- Very low current consumption (10 μA) when it’s not functional
- Very low run current (10 mA); 40 mA at full load
- Fully controlled by the energy meter
- High-voltage cut-off to save the appliances
- Wireless communication over 2.4GHz Zigbee
- Month-wise information storage of the power consumed
- Fully-functional system starting from 90V AC to 300V AC
- Easy to hook on to the network
- Compact in size
Role of various components
Fig. 2 shows the block diagram of the
device components. The role of these components is described below:
Microcontroller. The microcontroller or
system-on-a-chip (SoC) plays a pivotal role in the device operation.
In addition to controlling other components, it stores the
application firware in its internal Flash memory. For supporting
various functionalities of the HAN device, the microcontroller should
be equipped with the following features:
- Low-power processing core with the capability to perform complex arithmetic operations required for energy calculation
- Suitable physical-layer communication interface for RF or power-line communication, if used
- On-chip Flash memory and static random-access memory for storing application firmware and faster operation
- LCD driver for LCD display
- Interfaces like universal asynchronous receiver/transmitter, which can support infrared communication
- High-resolution analogue-to-digital converters (ADCs) with programmable gain amplifierfor voltage and current measurements
- Input/output (I/O) ports for driving relays
- Real-time counter for time keepingThe microcontroller senses the voltage and current through the signal conditioning circuit along with the ADC and programmable gain amplifierto calculate root mean square (RMS) voltage and current values, instantaneous energy consumed and total energy consumed over a period of time (one month or longer). It then sends this data to the utility meter through RF or power line communication and also displays it on the LCD. When a command to turn off the device is received, it drives suitable logic on its I/O ports to operate the relay.
The microcontroller gets its power
supply from the power line through a 230V-3.3V converter. The
converter can be suitably configuredaccording to the operating
voltage of the microcontroller. The on-chip Flash firware can be
updated over the RF or PLC interface by the utility meter. The
protocol and exact details of frmware updation depend on specific
implementations.
Fig: 2: Block diagram of HAN device |
Compared to voltage measurement,
current measurement is less involved. First, the line current is
downsized using a current transformer and then passed through a small
value of high-precision shunt resistor. The voltage drop across this
shunt resistor gives a measure of the line current. As this voltage
drop is very small, it is suitably amplifiedbefore being fed to the
ADC.
The amplifierconsists of programmable
gain stages for amplificationof only the alternating-current (AC)
components, thus preventing the amplifie output from saturation.
Infrared interface. The infrared
interface can be configuredsuitably according to the range and power
consumption. It provides remote configurationsupport for the HAN
device, enabling the user to remotely turn on/off the home appliance
connected to the HAN device. The protocol and exact details of
operation can be flexiblychosen for particular implementations.
LCD panel. The LCD panel displays the
instantaneous energy consumed, total energy consumed last/current
month, date and time of the day, RMS voltage and RMS current. It
inherits some of the utility meter display, thus acting as a
low-accuracy but smart AC energy meter.
In a nutshell, the above architecture
conceptualises a cost-effective and extremely versatile HAN device,
which is replete with all the essential HAN device features along
with the support for advanced features like firmwar upgrade and full
control of appliances over RF/PLC interface. It also doubles as a
low-cost smart AC energy meter, providing round-the-clock energy
consumption details of the home appliance.
Though the device is depicted here as a
standalone intelligent power socket, it can also be implemented
inside home appliances.
No comments:
Post a Comment