Single-phase three-wire transformerless inverter

A single-phase inverter providing three wire two-voltage (generally 110/220 V) power is designed and implemented. Instead of using a full-bridge inverter and an output transformer with centre-tapped winding, a three-leg inverter is used to yield a single-phase three-wire circuit. In performing the switching control, the proposed inverter system is decoupled into differential-mode and common-mode subsystems. The controllers of the differential mode are designed mainly to shape and regulate the main output voltage (220 V). As to the common-mode subsystem, its controllers are arranged to compensate the imbalance between two suboutputs (110 V). Each subsystem has an inner current loop as well as an outer voltage loop. In addition, the feedforward control is augmented 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 ratio of the two suboutputs can be programmable. The effectiveness of the proposed method is confirmed by simulation and experimental results