Raad Z. Homod

1. 2015 IEEE Student Conference on Research and Development (SCOReD)
Smart Plug Prototype for Monitoring Electrical
Appliances in Home Energy Management System
Maytham S. Ahmed¹, a
, Azah Mohamed², a
, Raad Z.
Homod 3,b
a
Department of Electrical, Electronic and Systems
Engineering, Faculty of Engineering and Built Environment,
Universiti Kebangsaan Malaysia, 43600 Bnagi, Selangor,
Malaysia
b
Department of Petroleum and Gas Engineering, Basrah
University, Qarmat Ali Campus, 61004 Basrah, Iraq
¹eng_maitham@yahoo.com, 2
azah@eng.ukm.my,
3
raadahmood@yahoo.com
Hussain Shareef4,c
, Ahmad H. Sabry5,d
, khairuddin bin
khalid6,a
c
Department of Electrical Engineering, United Arab
Emirates University, P.O. Box 155511 Al-Ain,
UAE
d
Control and Automation Engineering
University Putra Malaysia UPM
Serdang, Malaysia
4
hussain_ln@yahoo.com, 5
Ahmed_hsabry@yahoo.com,
6
k4khairuddin@gmail.com
Abstract— Recently, the technology of Home Energy
Management System (HEMS) has expanded for the purpose of
reducing energy consumption. This paper presents the
development of a smart plug with a wireless Zigbee sensor for
measuring power consumption of electrical appliances in the
HEMS. Experiments were carried out to evaluate the power
consumption of a wireless sensor node in a smart plug using only
Zigbee as a microcontroller. Experimental results showed that
the smart plug using Zigbee is capable of processing and
analyzing the analogue sensor signal with lower power
consumption. In addition, the data obtained from the wireless
sensor is more accurate and smoother as compared with the data
obtained from the oscilloscope. The proposed smart plug has the
characteristics of simple design, low cost, low power consumption
and easy to control electrical home appliances by switching on/off
from the HEMS controller.
Keywords—smart plug; power consumption; home energy
management ; zigbee; energy efficiency; home appliance
I. INTRODUCTION
Energy management system considered by both power
utility and customers is developed for the purpose of
increasing energy efficiency, reducing energy costs and
reducing greenhouse gas emissions. In Malaysia the
generation in 2013 was 140.18 GWh, whereas the total
electrical energy consumption was 123.16 GWh [1]. For
efficient utilization of electrical energy, an energy
management system is required. It is noted that residential
buildings have significantly increased the total worldwide
energy in which about one third of energy use is by the
building sector [2]. In Peninsular Malaysia, about 21% of the
total energy consumption in the year 2012 was utilized for
household appliances and cooling systems [3, 4].
Demand response (DR) program can support demand side
management so as to reduce power consumption in residential
and commercial buildings by considering time of use, real
time pricing and critical peak pricing [5, 6]. In the residential
sector, the technology developed for DR strategy is HEMS
that can reduce total electric bill and peak demand by
scheduling the home electrical appliances according to
priority, comfort level and preference setting [7]. A HEMS
involves any device or product that can analyze energy
consumption, control and monitor home electrical appliances
[8].
Many smart devices such as smart meters and smart plugs
have been used to support intelligent buildings so as to assist
homeowners to control the electrical appliances remotely from
their smart phone and make better decisions about energy
consumption [9]. Smart grid technologies are applied to
provide real-time energy consumption to consumer and utility
[10] and it provides two way communication between the grid
and customers. Smart meter is one such monitoring device in a
smart grid system connected at the home entrance to allow
active participation of consumer to manage power delivery
and reduce its cost [11]. A smart plug sits between the wall
outlet and the electrical appliance and it is used to control and
monitor appliances remotely [12]. Furthermore, it allows user
to get data for optimizing the usage of appliance and get
benefit of lower energy consumption by remotely scheduling
or turning on/off the appliance in a room via tablet or
smartphone using Zigbee communication [13]. Non-smart
appliances should also be considered for energy management
systems and therefore it is necessary to find a practical
solution to connect non-smart appliances to a controller. So
the design of smart plugs form a network of distributed
sensing nodes, which provide remotely switch loads (on/off)
and control the electrical appliances in a HEMS. In this paper,
a prototype of smart plug is developed by using a stand-alone
device supported with Zigbee wireless communication for
implementing a HEMS in smart homes. A node is connected
to a home appliances and it is used for sending power
consumption data of each device by means of Zigbee
communication to a data collection device such as personal
computer. This method can record household daily energy
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2. 2015 IEEE Student Conference on Research and Development (SCOReD)
consumption in terms of current, voltage and power for each
device. By implementing a smart plug, it is easy to control the
appliances, low cost and it provides bidirectional
communication channel directly with the central meter of a
house.
II. SMART PLUG PROTOTYPE DEVELOPMENT
A. Overview
The smart plug is designed such that it uses two main
sensors for voltage and current, so as to adopt single supply. A
prototype smart plug is designed similar to plug shape and size
and it provides remote monitoring and switching off/on of the
appliances. Figure.1 shows the smart plug connected between
the electrical appliances and the HEMS controller. The smart
plug implementation steps begin with Zigbee nodes
configuration to initialize the system parameters and to
indicate the maximum and the minimum values of the
measured signal.
Fig.1. Connection of the smart plug between the appliances and HEMS
controller
B. Smart plug hardware implementation
In implementing the proposed smart plug prototype, three
considerations are described accordingly by taking into
account power energy node, data communication and software
design.
i. The Proposed Power Energy Node
A smart plug is an outlet socket that can measure the energy
consumption of an electrical appliance. It measures the
consumed power with the help of current and voltage sensors
and controls it with a relay. The proposed power node includes
three circuits to measure three parameters, current, voltage,
and power factor. These parameters are considered as the main
factors on the management technique of our wireless home
automation system. The hardware design of the slave circuit is
shown in Figure.2
Fig. 2. Simulation design of the proposed power node
The proposed power node shown in Figure.2 represents a
wireless communication transceiver node which is located at
each home appliance. This transceiver node has the essential
elements used for measuring the energy parameters as well as
receiving control signals required for managing energy saving.
The first input channel or the current channel, is connected to
(AD0) or pin 20 of the Zigbee Pro. Current is sensed when the
household current supply passes through the current sensor. A
voltage signal proportional with that current is produced and
delivered to the conditioning circuit. An op-amp circuit is
utilized to convert the AC resultant current signal into average
DC form suitable for Zigbee input to process and to send the
current value by wireless means.
The second input channel or the voltage channel, is
connected to AD1 or pin 19 of Zigbee Pro. Voltage is sensed
when a sample of household supply voltage is taken through a
voltage divider circuit to AD1. The voltage is also processed
and sent by wireless means.
The analog to digital converter (ADC) of the Zigbee
microcontroller has a 10 bit resolution conversion. This means
that the ADC assumes 3.3V is 1023 and anything less than
3.3V will be a ratio between 3.3V and 1023.
𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝐴𝐷𝐶
𝑆𝑦𝑠𝑡𝑒𝑚 𝑉𝑜𝑙𝑡𝑎𝑔𝑒
=
𝐴𝐷𝐶 𝑅𝑒𝑎𝑑𝑖𝑛𝑔
𝐴𝑛𝑎𝑙𝑜𝑔 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑
Analogue to digital conversion depends on the system
voltage. For a 10-bit ADC of the Zigbee on a 3.3V system, the
following equation is derived as,
33

3. 2015 IEEE Student Conference on Research and Development (SCOReD)
1023
3.3
=
𝐴𝐷𝐶 𝑅𝑒𝑎𝑑𝑖𝑛𝑔
𝐴𝑛𝑎𝑙𝑜𝑔 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑
ii. Data Communication Transmit
The energy communication node is designed to perform
data readings, accessing, transmission and parameter
realization through the coordinator node which is connected
directly to a data collector such as a personal computer (PC).
The smart plug transmits the values of voltage and current to
the HEMS via a Zigbee wireless connection. The Zigbee RF
module is line with the IEEE 802.15.4 based specification for
a two-way wireless communication technology with
transmitter and receiver components. The voltage and current
sensors are connected with op-amp conditioning circuits so as
to read the analogue values of data. The op-amp circuit will
generate a signal for voltage or current suitable to the changes
in the sensing side and it provides these signals to the channels
of the analogue input of the Zigbee. The power supply voltage
to the Zigbee module range between 2.8 to 3.7V supplied
through a DC adaptor or from on-board battery. We have used
pins 20 and 19 (analogue input pins) with a reference voltage
equal to the Zigbee biasing voltage (3.3V) and 1mW power
consumption in order to reduce the components and attain the
full range of the input analogue voltage. The collected data is
sent to the HEMS coordinator which is linked directly to the
PC via an appropriate MatLab® program driver which is
developed to manage and access the data.
iii. Software Design
For accessing and configuring the data, a USB interface
card is connected to the data collection device system (PC).
The software X-CTU is used to program the Zigbee to set
parameters directly by connecting the module to the USB
serial port (COM). One Zigbee is connected to the data
collection device system and interfaced with a MATLAB
software so as to configure it as a coordinator. Another Zigbee
is configured to connect with the voltage and current sensors
through the conditioning circuits as an end device. Therefore,
MATLAB program is used as the software to analyse the data
with used appropriate faction to access the energy sensors
data. In order to communicate with the serial of external
device from MATLAB, the specific serial port of the data
collection device system that is connected to the external
device is first identified and created. Subsequent, send a
command signal to the external device and receive the data
from the external device. Finally, disconnect the serial
communication connection from the external device with
release control of the serial port.
III. Experimental Results
The performance of the prototype card is tested in terms of
data transmission rate and accuracy of the received data.
Analytical estimation of energy saving is also made. The
current sensor type ACS712 ±5 A is used and its output is
connected to the Zigbee port. Figure3 shows a prototype of the
developed smart plug. The circuit board sizes are designed
suitable to be placed inside the plug. To test the accuracy of
the received data, an energy analyzer is used to determine
readings for current and voltage. The received signals are
compared with that measured and displayed on the
oscilloscope.
Figure. 4 and 5 show the results of testing the transmitted
data that were measured by using oscilloscope and that
obtained from the wireless Zigbee RF, respectively. In order to
increase the accuracy, the output data signal have been
sampled based-on two different mediums as shown in the
graphs which are obtained from the calibrated oscilloscope
and MATLAB. From both figures, the results show
similarities in the outputs. The accuracy of the proposed
wireless data acquisition circuit, which utilizes the Zigbee RF
Module, is considered satisfactory. In addition, the results of
data obtained from wireless connection are more accurate and
smoother as compared with the data from oscilloscope.
Figure 6 shows an application of the proposed smart plug
by monitoring and measuring the power consumption of home
appliances over a period of 24 hours.
Fig.3 Smart plug hardware
34

4. 2015 IEEE Student Conference on Research and Development (SCOReD)
Fig.4 Test signal from oscilloscope
Fig.5 Test signal from the Zigbee RF module
Fig. 6 Power consumption of home appliances over 24 hours
Sine wave signals with 3.3 V peak-to-peak at two different
frequencies of 50 Hz and 10 Hz were tested. Since the
maximum sampling rate of the Zigbee is one sample per 20ms,
the 50 Hz signal has low accuracy, while the 10 Hz signal
would be more accurate. A comparison of the power
consumed for data processing using the proposed Zigbee and
the conventional Arduino Uno microcontroller is shown in
Table 1.
Table.1 Comparison between the power consumed by the
Zigbee and Arduino Uno
Specifications of
microcontroller
Arduino Uno Zigbee Pro
Data Process Power (mW) 400 64
Transmit Power (mW) 1.9 1.3
Operating Voltage (V) 5 3.3
Length (mm) 96.21 27.61
Width (mm) 77.78 24.38
Weight (gm) 28 5
IV. CONCLUSION
A smart plug prototype has been designed and developed
to measure the power consumption of electrical homes
appliances by using a wireless sensor network interfaced with
a HEM. The proposed smart plug in the HEMS allows end-
users to access power consumption information in real-time.
End-users can easily turn on/off the electrical home appliances
by connecting the appliances to the smart plug with Zigbee
communication. The results showed that proposed smart plug
is efficient and accurate in measuring the power consumption
for signals with less than 20 ms sampling periods. The
proposed smart plug prototype with the Zigbee
microcontroller can be applied for demand response in the
HEMS.
ACKNOWLEDGEMENT
The authors greatly acknowledge University Kebangsaan
Malaysia for funding this project under DIP-2-14-028.
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