부산대학교 도서관

This paper presents a single-phase to single-phase three-wire converter, which comprises a conventional two-level(2L) four-leg converter in series with H-bridge. The H-bridges are supplied from the main converter by means of a DC-DC converter with a high-frequency transformer. The proposed converter: (i) can supply three loads, wherein two are phase voltages 180 degrees-lagged, and a third load with twice the amplitude of the phase voltage, (ii) has the output voltages with constant frequency and amplitude even under unbalanced loads, and (iii) has sinusoidal grid current and high-power factor even supplying nonlinear loads. In this way, the proposed system is suitable for uninterruptible power supply. Furthermore, the pulsewidth modulation (PWM) technique is proposed to generate the pole voltages of the converters, so that the output voltages have better power quality. The proposed converter is compared with a conventional 2L in terms of harmonic distortion. Simulated results are provided to verify the operation of the proposed system.