A bi-directional DC to DC power converter includes two DC sources, two inductors respectively connected to the two DC sources, a first switch and a second switch respectively connected to the two inductors, two capacitors respectively connected to the two switches, and a third switch connected between the two inductors. The first, second and third switches are respectively connected reversely with a diode in parallel. When the third switch is alternately turned on and off and the first and second switches are always turned off, the power converter operates as a boost power converter and electric energy flows from the two DC sources to the two capacitors. When the third switch is always turned off and the first and second switches are synchronously turned on or off, the power converter operates as a buck power converter and electric energy flows from the two capacitors to the two DC sources.