A novel high temperature superconducting (HTS) flux pump device was built to charge second-generation (2G) HTS double pancake coils (DPC). This device generates a controllable ac travelling magnetic wave based on similar mechanism as a short-stator linear motor, while the wave has been dc-biased by dc windings on the magnetic circuit. A section of YBCO tape (superconducting stator) is placed transversely to the travelling direction of the wave, which output a neat dc voltage. The superconducting stator short-circuited an HTS DPC, with its output dc-voltage charges the DPC to the desired current. This paper describes the construction and operation of this novel HTS flux pump device, which will drastically decrease the cost of the superconducting dc power supply, and has a wide application prospect in HTS magnets and superconducting electric machines.