A 15 kVA, Three-Phase Triport - A New Approach to UPS

A 15 kVA, three-phase triport is being developed for minicomputer applications requiring three-phase protected ac power where the source of standby power is a 48 volt battery. The chief advantage of this approach over a conventional UPS is much higher overall efficiency under normal operating conditions when commercial ac is available. An efficiency of 90 percent is achieved under conditions of nominal inputs and balanced, full load outputs. Three-phase commercial ac is processed in parallel with the outputs of three square wave inverters through three ferroresonant transformers. The basic configuration of the three-phase triport is presented and the various control concepts employed to regulate the magnitude and phase of the output voltages under steady state and transient conditions are discussed.