SINGLE-PHASE 3-WIRE TRANSFORMERLESS INVERTER

A single-phase inverter providing three-wire two-voltage (generally 11 0/220 V) power is designed and implemented. Instead of using a full-br idge inverter and an output transformer with centre-tapped winding, a three-leg inverter is used to yield single-phase three-wire circuit. I n performing the switching control, the proposed inverter system is de coupled into differential-mode and common-mode subsystems. The control lers of the differential mode are designed mainly to shape and regulat e the main output voltage (220 V). As to the common-mode subsystem, it s controllers are arranged to compensate the imbalance between two sub outputs (110 V). Each subsystem has an inner current loop as well as a n outer voltage loop. In addition, the feedforward control is augmente d to the feedback control to yield sinusoidal output voltage with good regulating control performance. Furthermore, the output impedance of the proposed inverter can be significantly reduced and the voltage rat io of the two suboutputs can be programmable. Effectiveness of the pro posed method is confirmed by some simulation and experimental results.