Abstract:In this paper, an isolated multi-resonant three-port bidirectional direct current-direct current (DC-DC) converter is proposed, which is composed of three full bridges, two inductor-capacitorinductor-capacitor (LCLC) multi-resonant tanks and a three-winding transformer. The phase shift control method is employed to manage the power transmission among three ports. Relying on the appropriate parameter selection, both of the fundamental and the third order power can be delivered through the multi-element LCLC resonant tanks, and consequently, it contributes to restrained circulating energy and the desirable promoted efficiency. Besides, by adjusting the driving frequency under different load conditions, zero-voltage-switching (ZVS) characteristics of all the switches of three ports are guaranteed. Therefore, lower switching loss and higher efficiency are achieved in full load range. In order to verify the feasibility of the proposed topology, a 1.5 kW prototype is established, of which the maximum efficiencies under forward and reverse operating conditions are 96.7% and 96.9% respectively. In addition, both of the bidirectional efficiencies maintain higher than 95.5% when the power level is above 0.5 kW.

Abstract:In this paper, a two-stage three-port isolated bidirectional DC-DC converter (BDC) for hybrid energy storage system (HESS) applications in DC microgrids is proposed. It has an enlarged zero-voltage-switching (ZVS) region and reduced power circulation loss. A front-end three-phase interleaved BDC is introduced to the supercapacitor (SC) channel to compensate voltage variations of SC. Consequently, wide ZVS range and reduced circulation power loss for SC and DC bus ports are achieved under large-scale fluctuating SC voltage. Furthermore, a novel modified pulse-width-modulation (PWM) and phase-shift (PHS) hybrid control method with two phase-shift angles is proposed for BA port. And it contributes to an increasing number of switches operating in ZVS mode with varying battery (BA) voltage. Phase shift control with fixed driving frequency is applied to manage power flow. The ZVS range as well as the current stress of resonant tanks under varying port voltages is analyzed in detail. Finally, a 1 kW prototype with peak efficiency of 94.9% is built, and the theoretical analysis and control method are verified by experiments.

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Based on the loss distribution and efficiency analysis, a comparative study between a series resonant three-port bidirectional DC-DC converter (SR-TBC) and a multi-resonant three-port bi-directional DC-DC converter (MR-TBC) is reported here. By using the Fourier equivalent analysis method in hand, the resonant current, switching current expressions, zero voltage soft switching (ZVS) conditions of MR-TBC and SR-TBC are deduced. Besides, in consideration of efficiency and soft switching aspects, the loss models of main power components and resonant elements are integrated and optimized for both topologies. Their loss distributions are established, and the different effects derived from the adoption of SiC MOSFET and Si MOSFET on the converter efficiency are discussed. Finally, to verify the theoretical analyses, comparative experiments under diverse load states are conducted based on the prototypes of the MR-TBC and SR-TBC. The obtained results demonstrate that the MR-TBC successfully broadens the ZVS range and thus achieves higher efficiency along the entire load range.