This paper presents a dual input-port bidirectional DC/DC converter for a Hybrid Energy Storage System (HESS). The converter is non-coupled, non-isolated and it has high-gain. Thus, it does not have transformer or coupling inductances, so voltage spikes or circulating currents are not present which is reflected in its high efficiency. In addition, the DC/DC converter is totally bidirectional, so the sources can transfer the energy between them and to the load. The converter has six switches but only three of them work in each mode, so the control is relatively simple. The main applications of the proposed converter are HESS for DC microgrid applications or small electric vehicles, particularly in which the storage system is small, hence the voltage is low, but the “load” works at a much higher voltage. The article analyses the converter in steady-state and presents the small-signal model, based on that, the control loop is designed. Simulations and experimental results validate the converter.

Energy Storage Systems (ESS) are an attractive solution in environments with a high amount of renewable energy sources, as they can improve the power quality in such places and if required, can extend the integration of more renewable sources of energy. If a large amount of power is needed, then supercapacitors are viable energy storage devices due to their specific power, allowing response times that are in the range of milliseconds to seconds. This paper details the design of an ESS that is based on a modular multilevel converter (MMC) with bidirectional power flow, which reduces the number of cascaded stages and allows the supercapacitors SCs to be connected to the grid to perform high-power transfers. A traditional ESS has four main stages or subsystems: the energy storage device, the balancing system, and the DC/DC and DC/AC converters. The proposed ESS can perform all of those functions in a single circuit by adopting an MMC topology, as each submodule (SM) can self-balance during energy injection or grid absorption. This article analyses the structure in both power flow directions and in the control loops and presents a prototype that is used to validate the design.