Distributed energy generation systems with energy storage and microgrids have attracted increasing research interest in recent years. Therefore, multi-ports dc-dc converters have gained more interest. However, when integrating into multiple port converters, the power flow control and ports regulation increase in complexity. In this paper, an isolated multi-port bidirectional converter based on an LLC converter is presented. The converter operates as a dc transformer at a fixed switching frequency and duty cycle without any control loop. The resonant tanks are designed to ensure soft-switching for the whole power range and minimize the voltage variation of the unregulated ports. In order to verify the converter operation, a 1 kW prototype with a 600 V maximum voltage has been implemented.

Abstract-Developing bidirectional dc-dc converters has become a critical research topic and gains more and more attention in recent years due to the extensive applications of smart grids with energy storages, hybrid and electrical vehicles and dc microgrids. In this paper, a Partial Parallel Dual Active Bridge (P 2 DAB) converter, i.e. low-voltage (LV) side parallel and high-voltage (HV) side series, is proposed to achieve high voltage gain and low current stress over switching devices and transformer windings. Given the unmodified P 2 DAB power stage, by regulating the phase-shift angle between the paralleled active bridges, the power equations and voltage gain are then modified, and therefore the operation range can be extended effectively. The operating principles of the proposed converter and its power characteristics under various operation modes are studied, and the design constraints are discussed. Finally, a laboratory prototype is constructed and tested. Both simulation and experimental results have verified the proposed topology's operation and design.

Abstract-This paper presents a nonisolated Three Port Converter (TPC) with a unidirectional port for photovoltaic (PV) panels and a bidirectional port for energy storage. With the proposed topology single power conversion is performed between each port, so high efficiencies are obtained. A theoretical analysis is carried out to analyze all operating modes and design considerations with the main equations are given. A 4kW laboratory prototype is developed and tested under all operating conditions. Results obtained feature on efficiencies higher than 97% for all operating modes and all power levels from light load to full load.

Abstract-Regenerative fuel cells (RFC) have become an attractive technology for energy storage systems due to their high energy density and lower end-of-life disposal concerns. However, high efficiency design of power conditioning unit (PCU) for RFC becomes challenging due to their asymmetrical currentpower characteristics that are dependent on the operation mode (energy storage / energy supply). This paper proposes a new PCU architecture for grid-tie RFC with which the RFC's asymmetrical characteristic becomes less critical and thus a much more symmetrical power rating of the dc-dc converter for both operating modes is possible. This paper discusses the design considerations for this novel PCU, and verifies its operation principle with Matlab/Simulink simulations. Experimental results on a tailored dc-dc converter confirm the design simplifications for high efficiency operation along the entire power operating range of the RFC as well as the utilization of the same control strategy design for the two RFC operating modes.

DC nanogrids have become a subject of interest in recent years due to the increase of renewable energy sources with energy storage systems. Hybrid AC/DC systems with different DC buses are an interesting solution to efficiently supply different AC and DC loads. In this paper, a high efficiency bidirectional converter to interlink a 400 V DC bus with a 48 V DC bus is presented. The proposed converter is based on a LLC resonant converter operating as a DC transformer at a fixed frequency and duty cycle without any complex control strategy. A clear and simplified design procedure for high efficiency operation and optimal self-load regulation is presented. To verify the converter operation, a 1 kW prototype has been implemented, featuring on maximum efficiency of 96.7 % and a self-regulated output voltage with 3 % of maximum offset from the nominal voltage.