Differential and common-mode model-based controller for the double-dual buck transformerless inverter

Abstract This paper studies the double-dual DC-DC buck converter composed by two buck power stages in a double dual connection. This connection has been previously studied with the boost power stage in the well-known double dual boost converter. In contrast to the double dual boost, which can only be used as a dc-dc converter, the double dual buck can be used as an inverter. Furthermore, it has a non-pulsating voltage from the input terminals to the output terminals. This property is exploited to reduce the common-mode current, which is of special interest in transformer-less photovoltaic applications, among others. The study includes a model description of the system in terms of the differential and common-mode variables. A controller based on this model representation is proposed to alleviate the effects of the common-mode component of the inverter output voltage on the leakage ground current. The analysis shows that the double-dual buck based inverter in closed-loop with the proposed controller exhibits a considerably reduced leakage-ground current, i.e., an almost negligible common-mode current flowing through the ground-path. This natural benefit makes it an attractive option for applications such as grid-tied inverters for renewable energy systems and electric vehicles. An efficiency analysis is also provided considering a conventional modulation scheme. Finally, the system performance is evaluated in a 1 kW experimental setup.