Isolated Medium-Voltage AC-DC Converter Using Level-Shifted PWM Control

Abstract

The authors have proposed an isolated medium-voltage AC-DC converter using a Modular Matrix Converter (MMxC). The proposed circuit directly converts medium three-phase AC voltage to DC voltage because the MMxC has a high breakdown voltage capability. Therefore, the proposed circuit can be downsized because it does not need a commercial transformer to convert the medium voltage to the low voltage. This paper presents a level-shifted PWM control in the proposed circuit's MMxC to generate the multi-level output voltage. When the MMxC output voltage frequency is equal to the switching frequency, the level-shifted PWM control is more suitable than phase-shifted PWM control for generating the MMxC multi-level output voltage. Level-shifted PWM control can reduce the source current harmonics and the MMxC switching loss. The total-power-factor of the high-frequency transformer can be improved by level-shifted PWM control. The theoretical waveforms of applying level-shifted PWM control to the proposed circuit can be experimentally obtained using a 6-kW small power system. In addition, this control method's effectiveness is verified, compared with the conventional control method which generates the three-level PWM waveform in the MMxC.