Control and Operation of Medium-voltage High-power Bi-directional Resonant DC-DC Converters in Shipboard DC Distribution Systems

Shipboard power system is moving towards more insertion of medium voltage (MV) dc sub-system in the existing MVAC power system. Isolated bidirectional dc-dc converter, analogous to a dc energy router, is one of the key enabling components in such a MVDC system to inter-tie different dc buses with the capability of power flow control as well as fault isolation. Control of such converters in medium voltage and high power scale is always a challenge to ensure fast power flow dynamic response and high efficient operation. In this paper, a variable frequency and phase-shift control solution is presented to regulate the bi-directional power flow in a 1kV to 5kV MW-class LLC resonant converter. The proposed method achieves soft-switching on all power devices across the entire power range as well as seamless power direction change. In addition, a system level control is implemented to fulfill the multifunctional operations in the shipboard applications. Both the hardware-in-loop (HIL) test and the hardware test results are presented.