A Single Stage Transformer-less Micro Inverter with Integrated Battery Storage System for Residential Applications

This paper proposes a single stage transformer-less (SSTL) microinverter with integrated battery storage system (BSS). This topology is envisioned as a high switching frequency power semiconductor unit with compact size passive elements that realizes 120/240V/50-60Hz AC output. The proposed system establishes a common ground between solar PV and battery storage. Both MPPT function for PV along with charge/discharge controller function for storage battery is enabled by the power sharing stage. The power-sharing unit is followed by a two-stage twin DC-DC interleaved modular multilevel converter (IMMC) units to boost the PV/battery output to 400VDC. Due to 180 degrees phase shift control and symmetry of upper and lower DC-DC IMMC units voltage ripple is cancelled. The DC-AC inverter stage has a built-in active decoupling stage to eliminate twice the line frequency ripple in the dc-link capacitor. This function along with the 180-degree phase shift control of the DC-DC IMMC stage drastically reduces the size of the dc-link capacitor value. Various Modes of operation are simulated to show the performance of the proposed system under different insolation conditions demonstrating battery charge/discharge functions. Preliminary experimental results from a prototype laboratory converter is presented in the paper.