A device for controlling a single-phase power conditioner for a renewable energy system is disclosed. The device comprises: a power system, providing alternating current (AC) utility power; a renewable energy system, using a natural resource so as to generate direct current (DC) power; a DC-to-DC converter, accepting the DC power generated by the renewable energy system so as to convert an input DC voltage of the DC power to an output DC voltage at a voltage level different from the DC input voltage; a grid-tied power conditioner, transforming voltage levels of the AC power and DC power; a controller, issuing a control signal for controlling the grid-tied power conditioner; and a load, consuming electricity by way of the grid-tied power conditioner.