Switched-Midpoint Boost Inverter (SMBI)

Abstract

Conventional three-level inverters such as T-type topology use two series-connected dc-link capacitors to generate three symmetric voltage levels. As their maximum voltage level is limited to only half dc-link voltage, they require a frontend boost converter to extend voltage gain that constitutes a two-stage topology. This paper introduces a single-stage three-phase boost inverter known as the Switched-Midpoint Boost Inverter (SMBI). The proposed topology facilitates control of the dc-link capacitors by incorporating a power switch at their midpoint. By enabling the parallel connection of the dc-link capacitors during charging by a boost inductor, voltage balance is naturally maintained, obviating the need for any voltage balancing controllers or sensors. For a given boost inductor charging duty-cycle, the dc-link voltage of the proposed SMBI is double compared to the conventional two-stage inverter, thus enhancing the voltage gain. In addition, the switched-midpoint circuit that enables single-stage voltage boosting in the proposed SMBI also reduces voltage and current stresses compared to the frontend boost converter in the conventional two-stage inverter. Moreover, the proposed inverter effectively mitigates high-frequency common-mode voltage by establishing a common-ground structure through the direct connection of the ac neutral to the negative terminal of the dc source. The operational principle of the proposed SMBI is thoroughly analyzed and validated through experimental results.