In this article, an isolated zero-voltage switching three-port dc–dc converter (TPC) using a planer transformer is proposed and operated for the frequency of 1 MHz. The proposed converter has a bidirectional operation. In the proposed converter, the main transformer is used to isolate low dc voltage ports from the high dc voltage port and to increase the voltage conversion ratio of the secondary side port, which supplies the load. The proposed converter is partially isolated TPC and has the advantage of galvanically isolation between one of the ports which are interfaced to the main load and the other two ports (input and storage-side ports) are nonisolated and common-grounded. The proposed converter is compared with other recent converters of the same type, and it is concluded that the proposed converter has achieved the capabilities of having an isolated structure with lower volume, interfacing three different dc voltages in the three dc ports, having the bidirectional operation, high-voltage gain, zero-voltage switching operation of all four switches, simple switching pattern, achieving simple controlling way for all ranges of duty cycles both step-up and step-down operations, utilizing a nonlinear digital controlling system, smaller size, higher operating frequency, higher efficiency, and high power density.