A three-leg power converter apparatus including first, second and third input/output ports, a three-leg bridge converter, a filter circuit, a decoupling circuit and a controller is presented. The three-leg bridge converter has three single-leg circuits, two DC terminals connecting to two terminals of the first input/output port, and three mid-terminals with each of them being formed by a middle point of one of the three single-leg circuits. The controller connects to the three-leg bridge converter for controlling an input or output current passing through each DC terminal and mid-terminal. The filter circuit connects between two of the mid-terminals and the second input/output port. The decoupling circuit has two terminals connecting to the second input/output port and another terminal connecting to a terminal of the third input/output port, with the third input/output port having another terminal connecting to the other mid-terminal that dose not connect with the filter circuit.