A transformerless single phase on-line UPS with 110 V/220 V input output voltage

In this paper, it is proposed a new nonisolated UPS system configuration that allows the bypass circuit operation even if the input voltage is different from the output voltage. The UPS system is composed by an AC-DC/DC-DC three level boost rectifier/converter combined with a double half bridge inverter. This topology allows the reduction of some parameters that are commonly discussed in the nonisolated UPS systems such as size and cost, compared with others isolated UPS configurations for the same purpose. Also, the efficiency are improved due to reduced number of switches and batteries, as well as no low frequency isolation transformer is required to realize bypass operation because of the common neutral connection. Both stages of the proposed circuit operate in high frequency, using a passive nondissipative snubber circuit in the boost converter and IGBTs switches in the double half bridge inverter, with low conduction losses, low tail current and low switching losses. A simple and well-known control strategy is used. Principle of operation and experimental results for a 2.6 kVA laboratory prototype are presented to demonstrate UPS performance.