Design and Implementation of a Digital Control and Monitoring System for an AC/DC UPS Andriy Palamar 1 , Mykola Karpinskyy 2 , Valery Vodovozov 1 1 Tallinn University of Technology, Department of Electrical Drives and Power Electronics 2 University of Bielsko-Biala, Department of Electrical Engineering and Automatic andrij777@mail.ru , mkarpinski@ath.bielsko.pl , valery.vodovozov@ttu.ee Abstract - This paper presents the design and implementation of a digital control and monitoring module for an AC/DC uninterruptible power supply (UPS). A hardware and software of the system is developed. Moreover, a friendly graphical-user interface is provided. Management strategy of the UPS in different operation modes is described. The proposed digital control and monitoring system allows to realize the complex algorithms and this way increase the reliability and efficiency of the UPS. I. INTRODUCTION Because of the increasing demand for the devices sensitive to energy quality, such as computers, medical equipment, telecommunication systems, ensuring continuity of power supply is very important. For this purpose, the installation of uninterruptible power supply (UPS) units with energy storage devices is necessary. UPS systems provide continuous, reliable, and high-quality power for important loads in order to prevent expensive hardware failure, data loss or corruption, cessation of the business process in cases of disturbance in the main electrical grid [1]. AC uninterruptible power supply systems are commonly used to provide energy backup to wide ranges of electronic loads. Nevertheless, DC UPS are receiving more and more attention with increasing demand for smaller and cost effective uninterruptible power supplies [2]. Such UPS systems are used in low voltage devices in the telecommunications and computer industry. Uninterruptible power supply systems are still in their research stage. Although UPS has applications in many various fields, it still requires improvement of many technologies for customer needs. Availability of low cost, user friendly and compact control and monitoring system is one of them. Monitoring of input and output electrical parameters of an UPS, digital control of charging and discharging of a battery, and the archiving of events in real time are necessary parts of such control systems. Although numerous interesting applications of intelligent control for AC UPS are available [3] – [5], the digital control system for DC UPS with its peculiarities of topology still needs further research. In response to the requirements above, a digital control and monitoring system for AC/DC UPS is developed and implemented in this work. The purpose of the paper is to design a hardware and software of the system and realize the control algorithms for different operation modes of the UPS. II. OVERALL STRUCTURE OF THE SYSTEM Control block diagram of an AC/DC uninterruptible power supply system based on a microcontroller is shown in Fig. 1. It consists of an AC/DC converter, a lead-acid battery, a control and monitoring module, sensors and switches. The AC/DC converter rectifies the input AC voltage of the main grid into the output DC voltage, provides filtration and stabilization. The value of the output voltage varies depending on the input analog control signal level, which is generated by the control module. The output DC voltage of the converter is used to supply the local loads and to charge the battery storage. The switches are used for disconnection of the battery from the loads in order to avoid deep discharge of the battery storage in case of lack of power provided by the main grid during a long period. The technical specifications of the UPS are listed in Table I. TABLE I TECHNICAL SPECIFICATIONS OF THE DEVELOPED UPS Item Characteristic Input voltage 185 V ÷ 255 V Maximum output power 3.6 kVA Output voltage 42 ÷ 56 V Maximum output current 75 A Back up time 2 hours The control and monitoring module is the core of the management system of the proposed UPS. It comprises a hardware and software. The possibility of computer connection is also present in the system. t Main grid DC loads Non-critical loads Control and monitoring module Computer Battery Sensing signals Control signals Power Lines Fig. 1. The control block diagram of the AC/DC UPS. 978-1-4244-8807-0/11/$26.00 ©2011 IEEE 173