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  1. 1. EXPERT SYSTEMS AND SOLUTIONS48, North Street, Aranarai, Perambalur, Tamil Nadu, India. Email ID: expertsyssol@yahoo.com, Phone: 9345276362, 9865129743, DESIGN AND IMPLEMENTATION OF 89S52 BASED UPS Perambalur (expertsyssol@yahoo.com) ABSTRACT UPS control using micro controller is highly reliable less complex andeconomical when compared the conventional UPS system. This paper explains aboutthe design and implementation of UPS using micro controller. The micro controller ismainly used for control applications. So, micro controller is used for this proposedwork. The main function of the UPS (uninterrupted power supply) is to provide anuninterrupted power supply and it should function automatically when the mainssupply cutoff. This automatic function in the conventional UPS is done by controlsystem. It involves certain complex work. So, in this proposed work, micro controllerdoes the automation of the UPS. Some of the automatic functions to be done by themicro controller are overload protection, no load release, deep discharge cutoff andinverter operation. There are different types of micro controller families. In this proposed work, themicro controller-89S52 because of its high on chip ROM capacity, RAM capacity, serialports, 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 beerased in few seconds compared to the twenty minutes or more needed for the 8751. Bythis, 89S51 is used to eliminate the waiting time needed to erase the chip and therebyspeedup the development time. It is a 40 pin micro controller in which 3 pins are usedfor serial interfacing, i.e., one acts as receiver another acts a transmitter and the thirdas ground. By this we can interface any components serially, it has 4 ports, port 0, port1,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 highfrequencies 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. Thispaper focuses on the design of Offline UPS. Because it is mostly prepared than ON line
  2. 2. UPS. For example, it finds its application in the household appliances, a personalcomputer, and so on. The transistors used in this UPS design are replaced, as MOSFET’S because ofits certain special features are positive temperature coefficient so that it has highcurrent carrying capability. It has low switching losses and the MOSFET turn on andturn off can be obtained rapidly. Also it is easily available and has switchingperformance.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.
  3. 3. 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.
  4. 4. MOSFET SPECIFICATIONS (IRFZ44):- VDSS :- 55V Rds (on) :- 17.5mΩ ID :- 49A The special features of IRFZ44 are,  Ultra Low on Resistance  Fast switchingWhy 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
  5. 5. 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-
  6. 6. amp will be logic ”1” which is indicated by LED glow. When LED glows, then a switchoff 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 inthe 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 thisindication the programmer can safely shut down the system safely after saving theprograms.