Transfer Time Suppressor with Series-Parallel Connection

A line-interactive UPS has a higher efficiency than double conversion topology. It also has lower cost and size. Nevertheless, the transfer time between modes is an important drawback which makes impossible for line-interactive UPS to be implemented in certain applications. During this transfer time, which the UPS needs to detect the grid disturbance and to establish the stored-energy mode of operation, the load is still connected to the grid and, hence, under the influence of the mentioned disturbance. As a consequence, eliminating this transfer time without incrementing the cost or size of the UPS would represent an important advantage and would widen the fields of application in which this topology could be used. This paper proposes a system which can eliminate the voltage transient which affects the load during the transfer time. It is based on the typical topology of Dynamic Voltage Restorers (DVRs), but it has been deeply modified in order to be suitable for this application. The amount of energy to be delivered by the system and the duration of the disturbance in a UPS output are conditions completely different from those a DVR has. A prototype has been built and experimental results have been obtained in order to validate the proposed system.