A PV power system with a flexible grid interface is studied in this paper. The flexible grid interface comprises two power conversion stages, a two-mode buck-boost converter (TMBBC) and a variable-level inverter (VLI). The operation of VLI is flexible according to the output DC voltage of the PV array, and it generates an AC voltage with three levels, five levels or seven levels and outputs a sinusoidal current to the grid. Partial power from the PV array is directly converted to AC power via only one power conversion such that the power efficiency for the PV power system is improved. Besides, the operating voltage range for the PV array can be extended because of the high boost gain of TMMBC. A hardware prototype is implemented to demonstrate the performance of the proposed flexible grid interface. (C) 2017 Elsevier Ltd. All rights reserved.