DESIGN AND
IMPLEMENTATION OF 89S52 BASED UPS
Perambalur
(expertsyssol@yahoo.com)
ABSTRACT
UPS
control using micro controller is highly reliable less complex and economical
when compared the conventional UPS system. This paper explains about the design
and implementation of UPS using micro controller. The micro controller is
mainly used for control applications. So, micro controller is used for this
proposed work. The main function of the UPS (uninterrupted power supply) is to
provide an uninterrupted power supply and it should function automatically when
the mains supply cutoff. This automatic function in the conventional UPS is
done by control system. It involves certain complex work. So, in this proposed
work, micro controller does the automation of the UPS. Some of the automatic
functions to be done by the micro controller are overload protection, no load
release, deep discharge cutoff and inverter operation.
There
are different types of micro controller families. In this proposed work, the
micro controller-89S52 because of its high on chip ROM capacity, RAM capacity,
serial ports, input ports, etc. The micro controller 89S52 is superior in its
memory capacity. This micro controller is best suited for fast development.
Since flash memory can be erased in few seconds compared to the twenty minutes
or more needed for the 8751. By this, 89S51 is used to eliminate the waiting
time needed to erase the chip and thereby speedup the development time. It is a
40 pin micro controller in which 3 pins are used for serial interfacing, i.e.,
one acts as receiver another acts a transmitter and the third as ground. By
this we can interface any components serially, it has 4 ports, port 0, port
1,port 2 and port 3 and it is used for various functions of UPS such as on load
release, deep discharge cutoff and so on. This micro controller can be operated
at high frequencies and it consumes low power. Thus it is ideal for many
projects.
There
are different types of UPS. They are OFF line UPS and ON line UPS. This paper
focuses on the design of Offline UPS. Because it is mostly prepared than ON
line UPS. For example, it finds its application in the household appliances, a
personal computer, and so on.
The
transistors used in this UPS design are replaced, as MOSFET’S because of its
certain special features are positive temperature coefficient so that it has
high current carrying capability. It has low switching losses and the MOSFET
turn on and turn off can be obtained rapidly. Also it is easily available and
has switching performance.
INTRODUCTION:
-
The conventional UPS system involves
complex control system. In order to reduce the complexity of the control system of conventional UPS embedded
controller are currently being used. This project describes the design and
implementation of 1KVA UPS using micro
controller. The micro controller used here are AT89C51 because of its high
memory capacity. The type of UPS involved in our project is OFF LINE UPS.
An UPS is one, which provides
uninterrupted power to the load. UPS is essential for computers, data
processors, data transmitters, microwave relay station, Nuclear reactor
control, etc., There are two major types of UPS. They are ON LINE UPS and OFF
LINE UPS. The off line-UPS are one that supplies power during the commercial
power failure and the charge over takes place through relay automatically. The
ON LINE UPS is one, which virtually free from dips, fluctuations as it works on
the battery all the time irrespective of the commercial power failure. This
project describes the design of OFF LINE UPS because of its extensive use.

UPS
SPECFICATIONS:-
Output Power :- 1 KVA
Output Voltage :- 230V
Output Frequency :- 50Hz
Battery
input :- 12V, 120AH
Battery used :- Lead acid Battery
Charging Time :- 8 Hours
Discharging Time :- 4 hours
Type of UPS :- OFF LINE UPS
MOSFET IN UPS DESIGN:-
In this project N- Channel MOSFET (IRFZ44)
is used. Banks of MOSFET’s are used and they are connected in parallel fashion.
Also, while connecting in parallel the layout should be symmetrical. During
paralleling the gate of the MOSFET’s should not connected directly and it
should be connected through resistors, which is called ferrite bead resistor.
The drain source resistance of the MOSFET should be equal else it will cause
thermal stabilizing effect. Also the drain source resistance greatly depends
upon the dimension. At low voltages the Rds (on) of MOSFET is low. But it
becomes high when the current is high.
MOSFET SPECIFICATIONS (IRFZ44):-
VDSS :-
55V
Rds (on) :-
17.5mW
ID :-
49A
The
special features of IRFZ44 are,
§ Ultra Low on Resistance
§
Fast switching
Why
MOSFET, why not Power transistor?
— Low switching losses,
— Drive power required is low,
— High current carrying capability,
— Low voltage (4V) is required to turn on the MOSFET and energy
efficient,
— Self commutating, and
— Reliable and can be operated at hazardous condition.
BATTERY:-
Battery is one of the major
components of Battery. There are two major
types of UPS. They are (1) Primary Batteries and (2) Secondary Batteries. The
primary batteries are not chargeable. Some of the major types of primary
batteries are Carbon Zinc, Alkaline, lithium cells and so on., The rechargeable
batteries are most widely used type. Some of the major types of batteries are
Ni-Cd, Lead acid batteries, Ni-Cd, NiMH, Rechargeable alkaline and Lithium ion.
Recharging it can reuse these types of batteries. Of these types Lead acid
batteries are mostly preferred because both the battery product and the
manufacturing process are proven, economical and reliable. The lead acid
batteries are discovered during 1950 and it is the most widely used battery in
the world. Lead acid batteries remain popular because they can produce high and
low currents. The reaction which occur inside the lead acid batteries are
PbO2+Pb+H2So4 ®
2 PbSo4 + 2H2O
When lead acid battery is discharged
beyond certain limits, sulfation will occur and it results in permanent failure
of the battery. Connecting deep discharge cut off circuit can prevent this. The
indication for this sulfation is, the positive plate becomes light brown and
the negative plates will become dull, off white.
BATTERY
CHARGER:-
Battery
has to be charged by a charger through supply mains. A lead acid battery should
have 2.1V per cell when fully charged and while discharging it should be around
1.8V per cell else it will cause permanent damage to the battery. The charging
and discharging of a battery is ideal at 12 hours rate which means that a 120AH
battery is to be charged or discharged at 120/12 =10 amps rate. A 120AH battery
when discharged at 10A rate will take 120/10 =12 hours to be completely
discharged. But in practice it is observed that the battery will get discharged
within about 11 ½ hours. In other words higher is the discharge rate the lower
will be the capacity.
MICROCONTROLLER: -
The micro controller is one of the
major components in this design. It performs various control actions. There are
different families of micro controller. This design uses AT89C51, which belongs
to 8051 families. It is a 40 pin micro controller, which has 4 ports, and each
takes 8 pins. Rest pins are designated for Vcc, GND, XTAL1 and XTAL2. The major
advantages of 89C51 are high memory capacity, on chip ROM in the form of flash
memory. In this design the various control actions to be done by the micro
controller are
(1) Deep discharge cut off
(2) No load Release
(3) Over voltage and under voltage cut
off
(4) Inverter operation
Programming on the ports can do these
functions.
NO LOAD RELEASE: -
When there is no load across the
secondary terminals of inverter transformer T2 (0-230-600V as output tapping),
its voltage shoots up to 290V. A sensing transformer (T1) which is connected
across 0-230V tapping of T2, the output of this transformer is rectified by the
rectifier circuit and filtered by L-C filter to smoothen the output of the
filter is given to a non inverting terminal of the op-amp and the op-amp gives
the logic “1”as output during no load condition. For normal loaded condition,
output of the op-amp will be logic “0”. When the output is 1, switch off signal
is send to the micro controller.
DEEP
DISCHARGE CUT OFF:-
This circuit prevents the battery from
deep discharge. There will be a preset value set by the potentiometer PR1 that
is connected to the inverted terminal of the op-amp 741. When the battery
voltage drops below the preset value output of the op-amp will be logic ”1”
which is indicated by LED glow. When LED glows, then a switch off signal is
send to micro controller.
LOW BATTERY
CUT OUT: -
The circuit is built by op-amp 741. This
circuit operates when low voltage occurs in the battery. The glow of the LED is
the indication of the low voltage of the battery. The circuit is mainly
involved while operating the inverter on the PC. By this indication the
programmer can safely shut down the system safely after saving the programs.
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