Optimized Modulation and Dynamic Control of a Three-Phase Dual Active Bridge Converter With Variable Duty Cycles

The three-phase dual active bridge (3p-DAB) converter is a promising topology for high power dc-dc conversion due to advantages of bidirectional power flow, inherent soft-switching capability, and reduced filter volume. This paper presents comprehensive analysis of the duty cycle control (DCC) for optimizing the performance of the 3p-DAB. Based on DCC, an optimized modulation strategy is proposed to minimize the conduction losses of the 3p-DAB in the whole load range. The proposed modulation strategy extends the soft-switching range of the 3p-DAB with large voltage variations simultaneously. It is established through loss analysis that the proposed modulation strategy boosts the efficiency of the 3p-DAB, especially at low loads. When the duty cycles change fast as a result of the abruptly changed transmission power, the transformer currents can become unbalanced, leading to the magnetic bias and oscillations in dc currents. This paper further proposes a fast transient current control (FTCC) method for the 3p-DAB with variable duty cycles. The FTCC enables the converter to transfer from one steady state to another within about one-third switching period, hence balancing the transformer currents rapidly and avoiding oscillations in dc currents. Finally, experimental results verify the outstanding performance of the proposed modulation strategy and FTCC method.