Buck and Boost Start-up Operation of a Three-Port Power Supply for Hybrid Vehicle Applications

In future hybrid automotive applications there will be multiple voltage systems in a single vehicle. It is desirable to have bi-directional, isolated power flow between these different voltage levels. The three-port power converter is able to achieve full bi-directional power flow by using a high-frequency transformer, with three windings, connected to a full-bridge converter on each winding or port. The normal control of the power flow between the ports is via phase-shift control of the individual full-bridge converters. However in the automotive application, there may be only a single power source for the initial powering up of the system and in this case, phase-shift control can not be used to start-up the converter system. This paper presents a start-up method for the three-port converter in which the converter is first operated in a buck-mode, followed by an output voltage boosting mode, and is able to finally operate with normal phase-shift control. Detailed analysis of the buck and boost mode during start-up is presented and verified by simulation