Single-phase three-level transformer-less inverter for residential distributed generation

Single-phase voltage source inverters are commonly used for interfacing small distributed generation units to the grid. Requirement in terms of THD, reliability and power factor correction is getting tightening day by day, so it is necessary to implement efficient and reliable algorithms that are capable to adapt control parameters to the varying grid operating conditions, in order to assure low current distortion, as well high efficiency and reliability. This paper deals with the investigation of both configuration topology and control algorithm with the purpose of achieving high performance in terms of efficiency as well THD of the output current, despite the non ideal grid characteristics. The proposed inverter uses a second order generalized integrator based phase-locked loop, a single loop current control based on a grid frequency tuned proportional-resonant controller, and a damped output LC filter in cascade with a switching frequency tuned LC-series trap-filter.