Design and Construction of an Intelligent Uninterruptible Power Supply (IUPS), 500VA, 220V, 50Hz

Power Electronics

An Uninterruptible Power Supply is a system connected between the electric grid and the consumer, comprising electric hardware and rechargeable batteries. The fundamental purpose/aim of this project - Design and Construction of an Intelligent Uninterruptible Power Supply (IUPS) - is to provide an uninterruptible (continuous, steady, non-stop) and clean (qualitative) source of power supply of 500VA, 220V, 50Hz for domestic equipment it supplies and protects. This is achieved by basically designing and constructing a battery charging circuit and an inverter circuit. An inverter is a power electronics device which converts DC (in this case, from a 12V DC battery) power to AC power (500VA) at the required output voltage (220V) and frequency level (50Hz). The salient features are: Firstly, upon power outage (from the mains power supply) a square wave is generated through the means of an AT89C51 microcontroller. The program controlled microchip device (AT89C51) forms the basis of realization of this project. Bipolar Junction Transistors are applied as switching system connected to the oscillating output pins of the chip. An inverter drive MOSFETs pairs are incorporated with a 12V~220V, center tapped transformer working to transform the oscillating signal to pure AC signal. This project takes its power from two power sources which automatically switch between each other: the utility mains and a DC lead acid battery. The experimental results conformed to the desired design analysis with acceptable and negligible errors. The results of this project research show that the AT89C51 microcontroller (an intelligent device) can be used as a square wave generator (oscillator) as well as to control the working conditions of the system in which it is used.

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