Elimination of the Transfer-Time Effects in Line-Interactive and Passive Standby UPSs by Means of a Small-Size Inverter

• Published in: IEEE transactions on power electronics Vol. 27; no. 3; pp. 1468 - 1478
• Main Authors: Arias, M., Hernando, M. M., Lamar, D. G., Sebastián, J., Fernández, A.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.03.2012; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Batteries; Capacitors; Controllers; Convertors; Direct energy conversion and energy accumulation; Electric power; Electrical engineering. Electrical power engineering; Electrical machines; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Equations; Exact sciences and technology; Hysteretic controller; Inductors; Inverters; line-interactive uninterruptible power supplies (UPSs); Mathematical model; Power electronics, power supplies; Surge protectors; transfer time in UPSs; Uninterruptible power supply; Uninterruptible power systems; Voltage control; Performance evaluation; Costs; Load distribution; Hysteretic controller; Power system economics; Standby power supply; Power supply; Hysteresis loop; Output voltage; Power markets; Bridge convertor; Inverter; Control system; Secondary cell; Power electronics; Topology; Experimental study; Failures; Standards; Transfer processing; Interactive system; Uninterruptible power supply; Critical load; line-interactive uninterruptible power supplies (UPSs); Open market; transfer time in UPSs
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2011.2163421

The main drawback of line-interactive and passive standby uninterruptible power supplies (UPS) is the transfer time when changing from normal mode of operation to battery mode of operation. During this time, the critical loads protected by the UPS are under the influence of the grid disturbance that forced the mode change. On the other hand, equipment protected by a double-conversion UPS is never affected by disturbance in the mains. Unfortunately, the efficiency of this topology is lower and its size and cost are considerably higher. Hence, the elimination of the transfer process between modes in line-interactive and passive standby UPSs would make them more competitive than double-conversion UPSs in many situations. In this paper, a method for eliminating the transfer time is proposed. It is based on a half-bridge inverter with a hysteretic controller whose output voltage is only applied to the load during the transfer time. Considering the random nature of the grid failures and the short duration of the transfer time, the design and selection of the components are nothing but standard. This also leads to a nonstandard hysteretic controller that needs to be fully analyzed. Experimental results are provided for a 750-W line-interactive UPS whose transfer time of 4 ms was eliminated by the proposed system.