—The present work describes the analysis, modeling and control of a transformerless Boost-Buck power inverter used as a DC-AC power conditioning stage for grid-connected photovoltaic (PV) systems. The power conditioning system’s control scheme includes a variable structure controller to assure output unity power factor and a sensorless Maximum Power Point Tracking (MPPT) algorithm to optimize the PV energy extraction. To maximize the steady-state input-output energy transfer ratio a discrete linear controller is designed from a largesignal sampled data model of the system. The achievement of the DC-AC conversion at unity power factor and the efficient PV’s energy extraction are validated with simulation results.