Armed with the latest technological advancements in the field of energy utilization, Home Area Networks (HAN) are ready to supplant the traditional electrical ecosystems at home. This paper introduces a HAN device architecture which not only integrates seamlessly with a Home Area Network; but also keeps a tab on the energy consumption and operation of electrical equipments while acting as a low cost energy meter.
The sky-rocketing cost of energy production has necessitated making the energy consumption process more efficient. This has brought revolution in electrical equipment manufacturing and energy metering infrastructure. A Home Area Network (HAN) is an advanced electrical ecosystem in which a smart utility meter and HAN devices communicates with each other to control the energy consumption profile. A basic HAN device has a two-way communication link with a utility meter and optionally, with other HAN devices, in a HAN ecosystem; sharing energy consumption data of the equipment it is connected to, and also receiving commands to turn-off or hibernate that equipment when unused. The following sections describe in detail, certain enhancements to the basic HAN device architecture; thus extending its capability and feature-set.
Brief Architecture Overview
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 the home appliances e.g., Microwave, AC etc. It can be controlled directly by the utility meter over wireless interfaces like RF or wired interfaces like power line communication (HomePlug etc.). Additionally its firmware can be upgraded over the RF/PLC interface by the utility meter. On the LCD, it can display various energy parameters of the device. It also supports battery backup option for maintaining time and date. Figure 1 shows the application diagram of the HAN device.
Figure 1: HAN device application diagram
The HAN device consists of the following components.
1. A Microcontroller
2. 230V to 3.3V converter
4. Signal conditioning circuitry
5. IR interface (Supporting both TX and RX)
6. LCD panel
7. RF/Power line communication PHY
Figure 2 shows the block diagram representation of the above components.
The various important components of the HAN device and their role are described below.
The microcontroller/System-on-a-chip plays a pivotal role in the device operation. In addition to controlling other components, it stores the application firmware in its internal flash memory. For supporting various functionality of the HAN device, the microcontroller should be equipped with the following features.
1. Low power processing core having the capability to perform complex arithmetic operations required for energy calculation.
2. Communication interface with RF PHY or suitable interface for Power line communication PHY, if used.
3. On-chip flash memory and SRAM for storing application firmware and faster operation.
4. LCD driver for LCD display.
5. Interfaces like UART which can support Infra Red communication.
6. High resolution ADCs with Programmable Gain Amplifier (PGA) for voltage and current measurements.
7. IO ports for driving relays.
8. Real time counter for time keeping.
The microcontroller senses the voltage and current through signal conditioning circuit along with ADC and PGA to calculate RMS voltage and current values, instantaneous energy consumed, total energy consumed over a period of time (can be for one month or more). It then sends these data to the utility meter through Rf or Power line communication PHY and also displays them on the LCD. When it receives a command to turn-off the device it drives suitable logic on its IO ports to operate the relay. The microcontroller gets its power supply from the power line through 230V to 3.3V converter. This converter can be suitably configured according to the operating voltage of the microcontroller. The on-chip flash firmware can be updated over the Rf or PLC interface by the utility meter. The protocol and exact details of firmware updating will depend on specific implementation.
The signal conditioning unit consists of analog front end for voltage and current measurement. The line voltage ismeasured by first downsizing it with resistor ladder, thereafter DC filtering and DC biasing the same. Compared to voltage measurement, current measurement is little involved. First the line current is downsized using a current transformer and then it is 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 has to be suitably
amplified before it can be fed to the ADC. The amplifier consists of programmable gain stages for amplification of only the AC components; thus preventing the amplifier output from saturation.
The Infra-red interface can be configured suitably according to range and power consumption. This interface provides remote configuration support for the HAN device. It enables the user to remotely turn on/off the home appliance connected to the HAN device. The protocol and exact details of operation can be flexibly chosen for particular implementations.
The LCD panel displays the following parameters.
1. Instantaneous Energy consumed
2. Total Energy consumed last/current month
3. Date and Time of the day
4. RMS voltage
5. RMS current
The LCD panel inherits some of the utility meter display; thus acting as a low accuracy smart AC energy meter.
In a nutshell, the above architecture conceptualizes 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 firmware upgrade and full control of appliance over RF/PLC interface; while also doubling as a low cost smart AC energy meter, providing round the clock energy consumption details of the home appliance. Though this paper depicts it as a stand-alone intelligent power socket, it can also be implemented inside home appliances.
1. Smart grid article on Wikipedia
2. Article on Smart Energy initiative by HomePlug
3. Article on Smart Plug
4. AVR465: Single Phase Power/Energy Meter with Tamper Detection (Application Note)
About the authors:
Manish Jindgar, Senior Automotive Application Engineer, Biswaprakash Navajeevan, Senior Design Engineer and Manish Sharma, Application and Reference Design Manager, are with Freescale Semiconductor India Pvt. Ltd. in Noida.