Modelling and Controlling of the DC-UPS using Micro controller PIC16F877

Abstract

The uninterruptible power supply (UPS) is used in applications for which a loss of supply could have severe consequence. Out of the two types of UPS, the DC-UPS offers several advantages like efficiency, reliability, power quality and economy as compared to the AC-UPS. The DC-UPS is an internal part of the AC-UPS (DC- UPS + Inverter= AC UPS).If it is considered from the Inverter usage point of view, the DC-UPS is considered as a O -line UPS. The DC-UPS can be used in applications like radio base stations and repeaters, SCADA systems, tower and obstruction lightening, remote telemetry, video cameras, gate openers, security systems, roadway caution signs, LED traffic controls, WiFi/WiMax back-up power, grid-tie solar systems, low voltage lighting, Railway coach battery charger etc. Due to the so many advantages offered, the DC-UPS is developed which has specifications: 3Ø ‑, 50 Hz, 415 V AC input; 405 V DC, 25 A Output. The DC-UPS consists of a six pulse fully-controlled rectifier , a choke, a capacitor and a battery bank containing 34 batteries, fuse, MCCB, thyristor ring circuit, feedback control circuit, power supply etc. For the easy controlling of the system parameters like voltage and current, a microcontroller PIC16F877 is used. This microcontroller is a 40-pin IC having 20 MHz clock input, 200 ns instruction cycle and many more features. The tasks like generation of the gating signals for thyristos, zero crossing detection of the input line-to-line voltage, conversion of analog signal to digital form and many more are taken care by the microcontroller.