Distributed Photovoltaic Generation(DPVG) systems have become more important in recent years because of energy pinch and air pollution. Grid-tied inverters, as the indispensable parts of the DPVG systems, have drawn a lot of research attentions. Among various constructors, the Aalborg inverter was proposed as a candidate for the interface between the PV arrays and the power grid for some potential advantages, such as the wide range of input DC voltages, high efficiency, low cost and no leakage current. For a conventional Aalborg inverter, however, in order to gain a symmetrical gird-injected current, when the input DC voltages generated by the PV arrays are not equal, part of the input DC energy has to be discarded, which will reduce the conversion efficiency of the whole system. In this paper, a modified Aalborg inverter with a single input DC source is proposed to extract the maximum DC energy of PV arrays. The operating principle is illustrated via equivalent circuits. The control strategy is designed to balance the capacitor voltages and smooth the grid-injected current. A 110 V/50 Hz/800 W prototype has been built to verify the validity of the proposed inverter together with the effectiveness of the control strategy.