A Transformerless Solar PV Inverter with Battery Energy Support for Residential Buildings

Abstract

This paper deals with a battery supported grid interfaced transformerless bidirectional power conversion unit (PCU) for roof top solar photovoltaics (PV) system. In order to equalize voltage gain between grid and low voltage solar PV panel, standard solar PV PCU employs low frequency or high frequency transformer, which in turn, increases the mass and energy loss of entire PCU. In light of this, this study explores a transformerless solar PV PCU supported with battery energy storage (BES) for use in residential rooftop installations. In the presented PCU, a full bridge active bridge rectifier is employed at the front-end to interface PCU with grid and home loads. Further, an extended gain bidirectional DC-DC converter with transformerless high gain characteristics, is employed at the back end of the PCU, to maintain desired voltage gain between low voltage sources (i.e., solar PV arrays and BES) and high voltage sink (i.e., front end inverter's DC link) while ensuring effective power transfer between solar PV arrays or BES to grid or home loads. In order to utilize solar PV power maximally, the maximum power point of the solar PV is tracked through a boost DC-DC converter and the generated power is fed to the BES. Whereas, the BES takes care the power imbalance within the entire PCU and decide its operating mode (i.e., charging or discharging mode) accordingly. Notably, with constant power mode control of the front-end inverter, the presented PCU acts as a constant power source/sink at grid end, and thus eliminates the negative impact of the solar intermittency on the grid. The design, control, and operation of presented PCU are verified through MATLAB Simulink, and the relevant results are put forward to provide supporting evidence for the PCU's claimed performance