Design of Asymmetric Inductance for Multi-port Active Bridge Converter

The DC-DC converters with multi-port high frequency transformer are promising topology for next generation DC-grid. Among of them, Triple-Active Bridge (TAB) converter is in attention for its flexibility of various DC sources and loads connection that can enhance the functionality of DC grid. To control the power among three DC voltage ports, the leakage inductance of high frequency transformer and phase-shift of terminal voltages are key factors. Small inductance can increase the maximum power transmitted between three DC ports and reduces the system cost and volume. However, the inductor current variation caused by the DC port voltage fluctuation would severely deteriorate and the power variation would be very sensitive with the phase-shift among output voltages. Those might cause the failure of Zero Voltage Switching operation. Therefore, the proper leakage inductance design is important to achieve the stable operation of TAB converter. Meanwhile, when the rated power values of three DC voltage ports are identical, the leakage inductance design is quite simple. However, the inductance design method for the asymmetric three DC ports have not been proposed yet. This paper proposes the design method of leakage inductances in TAB converter of which the nominal power of three DC port is asymmetric. To have desired phase-shift of terminal voltages at nominal power flow, the asymmetric combination of leakage inductance is necessary. The proposed method is verified by simulation and experimental results with TAB converter test setup.