Auto-connected electronic phase-shifting transformer concept for reducing harmonic generated by nonlinear loads in electric power distribution system

In this paper, the concept of applying an autoconnected electronic phase-shifting transformer to reduce harmonics generated by nonlinear loads is presented. The concept is an extension of the conventional line frequency, phase-shifting transformer. With the addition of power electronic AC-AC converters, magnetic components are operated at higher frequency to yield small size and weight. With the adaptation of four-step switching strategy, snubberless operation of the electronic transformer with no input and output filters is achieved. With the proposed approach, 5th and 7th harmonic currents generated by two sets of nonlinear loads are subtracted within the electronic transformer, thereby reducing the current THD at the utility input. The approach is robust and the VA rating of the converter and magnetic is 0.18 pu due to auto-connection.