Modified transformerless dual buck inverter with improved lifetime for PV applications

Abstract

The Dual Buck Inverter (DBI) possesses no shoot-through concerns and it can improve the efficiency by utilizing power MOSFETs. This is because at accidentally triggered shoot-through states; two inductors are in-parallel with the DC-Side source or capacitor, thus, protecting the DC-Side from short-circuit conditions. Also, the ground leakage current of the conventional DBI is inherently low. Hence, the DBI topology is considered as an attractive option in transformerless Single-Phase grid-connected Photovoltaic (PV) applications. Nevertheless, the inherent 2nd order Single-Phase power ripples may deteriorate the conventional DBIs' reliability. These ripples are normally buffered by utilizing bulky, unreliable and polarized electrolytic capacitors. Therefore, this paper proposes a modified all MOSFET based transformerless DBI topology with an Active Power Decoupling Control (APDC) that relies solely on the Common Mode (CM) operation. The analyses are verified on a 3 kW system. The results indicated that a capacitor of 30 μΚ is adequate to achieve a ripple free DC-Bus voltage for a 3 kW inverter. The size of this capacitor is 50 times smaller compared to the original capacitor required by the system. Also, unlike the non-neutral point clamped topologies that eliminate the ground leakage current (e.g. HERIC and H5), the proposed system can attain grid-codes under non-unity power-factor and low solar irradiance level conditions.