Transformer-less Series-Input-Parallel-Output Dual Active Half-Bridge for MV-LV DC/DC Converter

This paper proposes a transformer-less Series-Input-Parallel-Output Dual active Half-Bridge (SIPO-DAHB) converter. The transformer-less SIPO-DAHB converter is a high power bi-directional converter and it has a high voltage conversion ratio. Each DAHB directly transfers power from high voltage side to low voltage side (or vice-versa) with optimal efficiency. A high voltage capacitor is used for a line capacitor to block MVDC voltage or to form a resonance tank. Because the high voltage insulation transformer is replaced with a capacitor, power density could be much higher than the transformer type SIPO converter. Furthermore, the core loss and copper loss of the transformer are much higher than the capacitor ESR losses, so that high efficiency could be achieved. However, due to the transformer-less structure, in the SIPO-DAHB converter, the current of the higher module flows through the DC-link capacitors of the lower modules and causes ESR losses. To minimize ESR losses, this paper also proposes a control strategy that interleaves adjacent modules and adjusts duties. With the control strategy, the current cancelation occurs between adjacent modules and results in the minimization of the ESR losses of lower modules. The harmonic analysis of the current confirms the advantages and experimental results verifies the effectiveness of the proposed topology and control strategy.