Masatoshi Uno

Equalization technique utilizing series-parallel connected supercapacitors for energy storage system

Series connection of supercapacitors (SCs) leads to cell voltage imbalance due to individual differences in cell properties. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energies of SCs. In this paper, an equalization technique utilizing series-parallel connected SCs, which is considered to be suitable for energy storage systems using SCs instead of secondary batteries as main energy sources, is proposed. The proposed equalization circuit, which requires only SCs and switches as its main elements, utilizes SCs not only for energy storage but also for charge shuttling between adjacent SCs for equalization. The operating principle and experimental charge/discharge performance of the SCs using the proposed equalization technique are presented.

Supercapacitor-based energy storage system with voltage equalizers and selective taps

A supercapacitor-based energy storage system, with which high efficiency and high energy utilization ratio of supercapacitors (SCs) can be realized, is proposed. This system consists of voltage equalizers and selective intermediate taps. Output voltage variation is limited to a particular range by the selective intermediate taps, while voltage imbalance of SCs due to charging/discharging through these taps is minimized by the equalizers. This paper presents operating principles and experimental performance of the proposed energy storage system.

Energy storage system based on supercapacitors with an unregulated dc-dc converter and selective intermediate taps

A novel supercapacitor (SC)-based energy storage system comprising a combination of an unregulated dc-dc converter and selective intermediate taps, with which SCs can discharge efficiently and deeply, has been designed, assembled, and tested. The output voltage to the load is roughly regulated by the selective intermediate taps while a high utilization ratio of SCs is achieved by the combination. The operational principles and experimental discharge/charge cycle performance are presented in this paper.

Reactant Recirculation Technique Utilizing Pressure Swing for Proton Exchange Membrane Fuel Cell System

Fuel cell systems aiming for high energy utilization require a reactant recirculation system in which unreacted reactants discharged from the outlet of the fuel cell are recirculated back to the inlet to minimize wastage of the reactants. Conventional recirculation systems using mechanical pumps have major drawbacks in terms of efficiency, vibration, and reliability. This paper proposes a novel reactant recirculation technique that utilizes pressure swings produced by the reactant supplies and consumptions. The pressure swing recirculation system requires only two check valves and a fluid control device. It, therefore, offers a simple, efficient, and highly reliable system. The pressure swing recirculation was applied for both anode and cathode systems. Experimental performance tests demonstrated that the fuel cell could operate for long hours with the pressure swing recirculation, whereas the cell voltage declined rapidly in dead-end mode operation.