System and method for power transfer between the two DC voltage sources comprises a first and a second DC voltage source and a DC-DC converter. The DC-DC converter includes a first bidirectional converter, an isolating transformer and a second bidirectional converter. The first bidirectional converter has a bridge circuit of variable configuration to increase the control range of the DC converter, the second pair of input/output pins being connected to the first winding of the isolating transformer via a series connected capacitor. According to the method, the voltage difference between the first and second DC voltage sources is determined, and according to the voltage difference value, the bridge configuration of the first bidirectional converter is changed between full-bridge and half-bridge.