development of on-line single phase uninterruptible power supply
International Seminar on the Application of Science & Mathematics 2011
ISASM 2011
Asmarashid Ponniran 1 , Normalyiana Zu lkifly 2 , Ariffuddin Joret 3
1, 2, 3
Faculty of Electrical & Electronic Engineering, Universiti Tun Hussein Onn Malaysia
Uninterruptible Power Supply (UPS) is an electrical apparatus that provides emergency
power to a load when the input power source (fro m main utility) fails to deliver electric
power. The purpose of this paper is to show development of an o n-line mode single
phase UPS that suitable for 240 V (A C), 50 Hz type of electrical appliances, esp ecially
for personal computers or low power electrical appliances. The advantage of the online mode of UPS is there is no transfer time during the transition fro m normal to backup modes. The design consists of battery charger/ rectifier module, inverter module and
battery. One of the important components used is IC NE555 and the function is to
generate pulses and control the frequency of inverter. Proteus 7.1 SP2 software is used
to simulate the designed circuits. The UPS is developed with output specification, 240
V (A C), 50 Hz. The developed UPS has been tested on a personal computer and
successfully provides backup power up to 400 W for about 15 minutes. Therefore, the
developed UPS is able to provide temporary backup electric power for critical
electrical appliances when outage condition occurs.
Keywords: Uninterruptible Po wer Supply, Inverter, Rect ifier, Sing le Phase UPS, On line mode UPS.
Electrical power is one of the sources of energy that is important in daily life. However,
the power disturbances always can be happened which can caused by faults on the
distribution system, the operation of nearby equipment, lightning strikes, normal utility
operations, or any other causes [1]. The resulting disturbances such as electrical noise,
voltage spikes, sags, swells, and complete outages can exceed the electrical tolerances
designed for the electrical equipment in use [2]. This sudden problem will cause big
problems to the user. For instance, user of the sensitive loads like computer will deal
with the problem such as missing the precious documents due to the sudden blackout.
In order to eliminate or reduce the loss of important data or control, it may be
necessary to provide a level of power protection as needs. An Uninterruptible Power
Supply (UPS) is the perfect answer. These devices are designed to provide continuous
power to a load, even with an interruption or loss of utility supply power. While not
limited to safeguarding any particular type of equipments, the UPS is typically used to
protect computers, data centers, telecommunication equipment or other electrical
equipment where an unexpected power disruption could cause injuries, fatalit ies,
serious business disruption or data loss [3-5].
A line-interactive UPS has been proposed by [4] and Improved Single-Phase LineInteractive UPS by [5] have been discussed. These types of UPSs offer the
characteristics of an inverter-preferred UPS. This is based on the combination of two
full-bridge voltage source inverters (VSI) converters: one in series with the input and
the other in parallel with the load [4]. An inverter-preferred UPS, also known as an
online double-conversion UPS, supplies the load through the inverter during either
abnormal or normal input power conditions. A rectifier charges the battery, floating on
the dc link, and also powers the inverter. A static bypass switch may connect the input
line to the load, bypassing the inverter during overload or inverter failure. This UPS is
composed of the pulse width modulation (PWM) rectifier, providing a regulated output
voltage regardless of input power conditions. This topology is usually the most costly.
[6-7] discussed about standby UPS by considering the application of a simple six
SCR Bridge, the inverter of the UPS. However, the topology of the passive standby
UPS itself has disadvantages, including a limited load voltage regulation capability, no
ability to reduce the source voltage harmonics, and a long switching time, resulting in a
system that can not accept certain sensitive loads. Therefore, the development of online UPS is expected to overcome all these deficiencies.
On-line UPS systems consist of a converter as a rectifier/charger, a battery set, an
inverter, and a static bypass switch as shown in Figure 1. The rectifier/charger
continuously supplies the DC bus. Its power rating is required to meet 100% of the
power demanded by the load as well as the power demanded for charging the battery
The batteries are rated in order to supply power during the back up time. The
duration of this time varies in different applications. The inverter is rated at 100% of
the load power since it must supplies the load during the normal mode of operation as
well as during the back up time. It is connected in series with the load; hence, there is
no transfer time associated with the transition from normal mode to stored energy mode
The main advantage of on-line UPS is very wide tolerance to the input voltage
variation. In addition, there is no transfer time during the transition from normal to
stored energy modes. It is also possible to regulate or change the output frequency [9].
Figure 1: On-line UPS Block Diagram
International Seminar on the Application of Science & Mathematics 2011
ISASM 2011
The objectives of this paper is to show the development of online mode single
phase UPS that able to supply temporary electric power to the personal computer or
other low power electrical appliances during sudden outage condition. The output
specifications of the UPS are 240 V (AC), 50 Hz and 400 W.
2.1 Rectifier/Charger Circuit
A bridge rectifier is used as a battery charger as shown in Figure 2 has been considered.
The rectifier/charger circuit is in normal condition when the green and red LEDs are
light up as shown in Figure 3. In the case of power failure, the green LED is OFF and
the red LED is switch ON to indicate that the system is now in backup mode.
Figure 2: Rectifier/Charger Circuit
Red LED is
switch ON
Green LED is
switch ON
Figure 3: Rectifier/Charger circuit when the presence of power supply
2.2 Inverter Circuit
Inverter circuit for this system consists of a step-uptransformer, an IC NE555 to
generate pulses, power transistors for switching, and a relay for by-passed switch as
shown in Figure 4. The ON condition of the inverter is represented by the light up of a
green LED as shown in Figure 5.
Figure 4: Inverter Circu it
Green LED is
switch ON
Figure 5: Inverter circu it in ON condition
International Seminar on the Application of Science & Mathematics 2011
ISASM 2011
3.1 Simulation Result
Figure 7 shows the circuit of rectifier that simulated on Proteus 7.1 SP2 software. The
output of the rectifier circuit is about 15 V (DC).
Figure 7: The rect ifier circuit
The charger circuit is shown in Figure 8. The input voltage is fed from the output
of the rectifier circuit which is 15 V (DC). The voltage regulator L7805CV is used to
regulate voltage from 15 V to 12.6 V to charge the battery.
Figure 8: The charger circu it
The IC555 timer is used in the inverter circuit to generate pulses as shown in
Figure 9. While, Figure 10 shows duty-cycle of the IC555 timer output.
Figure 9: IC555 connection
Figure 10: duty-cycle
3.3 Hardware Result
Figure 11 shows the measured output from rectifier, 15 V (DC). The measured output
shows the agreement with simulation result. The measured output result from IC
NE555 of pulses is shown in Figure 12. The time (period) of the IC NE555 is measured
as 20 ms and equal to 50 Hz with amplitude 18 V.
Figure 11: The rectifier output
Figure 12: The generated pulses
The generated pulses have been amplified through connection of the six transistors
D1047. The amplified waveform is shown in Figure 13(a) whereby peak to peak
International Seminar on the Application of Science & Mathematics 2011
ISASM 2011
voltage is 326 V, 50 Hz. The measured output signal before step-up transformer is 180
V peak to peak, 50 Hz and shown in Figure 13(b).
The final measured output signal is in AC square wave and provides 673 V peak to
peak and frequency is about 50 Hz, Figure 13(c). Therefore, the final output signal in
rms is about 238 V (AC, rms). However, this type of waveform is not suitable for
powering devices with high inductive or capacitive loads, like electric motors and surge
suppression devices. This type of waveform is hard on the DC power supplies in
computers, and should not be used to power that device except for power backup for
few minutes that needed to perform a proper shutdown of the computer.
Figure 13: (a) The amplified signal, (b) The output of inverter circuit before step -up transformer,
(c) The final output of the project
The objective to develop 400 W with 240 V (AC, rms), 50 Hz single phase
Uninterruptible Power Supply (UPS) that provide the uninterrupted power for about 15
minutes has been presented. Unfortunately, the project only generated AC square wave
output and the output waveform can be improved by considering appropriate filter
circuit. However, the system is able to give temporary power for low power of
electrical appliances (up to 400 W).
The authors would like to thank the Universiti Tun Hussein Onn Malaysia for technical
assistance and financial support.
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