Investigation of three-phase capacitor-tapped multi-module voltage source converter with selective harmonic elimination

Abstract

In conventional Two-Level Voltage Source Converters (2L-VSCs), connecting between high/medium dc voltage and medium/low ac voltage requires semiconductor devices rated at the high/medium dc-voltage, which negatively affects the converter cost. Alternatively, the Capacitor-Tapped Multi-module VSC (CT-MC) can be used, where it has a good bucking capability. The CT-MC consists of three (or multiple of three) Half-Bridge Inverter (HBI) modules, where the dc terminals of these modules are connected in series across the high/medium dc-link voltage, i.e. semiconductor devices with a lower voltage rating can be employed. The ac outputs of the involved HBIs are integrated to the ac gird through proper transformer(s). In this paper, the performance of the CT-MC is investigated, when Selective Harmonic Elimination (SHE) method is employed for dc-ac conversion to reduce the converter switching losses, while keeping the Total Harmonic Distortion (THD) of the ac currents within the recommended range. Simulation results are Prasented to show the performance of CT-MC when SHE is applied.